5.7 to 383 tuning question
03-18-2015, 10:46 PM
#41
TECH Addict
03-18-2015, 11:05 PM
#42
TECH Resident
Have a read of this....it should help.
http://injectordynamics.com/articles...racterization/
The first picture shows the flow(in red) without the injector offset. The second picture shows the flow with the injector offset applied. Notice that it affected the entire graph.
In the third picture, they zoom in on the lower end of the graph. Notice up to 2mS the lines don't match. This is the non-linear flow area of an injector. The short pulse adders are used in this section to compensate for the flow being erratic in this region. Hence, the non-linear reference.
GM adds a time value(via short pulse adders) to the theoretical linear flow(straight line) to "build" a profile of the red line. Thus you get how the injector actually flows and accurate fuel delivery.
Without proper injector characterization data, accurate fuel flow in the non-linear region is guess work(or at best trial and error).
This may help(or hurt,
) as well....
http://www.camaroz28.com/forums/comp...ts-lt1-770192/
http://injectordynamics.com/articles...racterization/
The first picture shows the flow(in red) without the injector offset. The second picture shows the flow with the injector offset applied. Notice that it affected the entire graph.
In the third picture, they zoom in on the lower end of the graph. Notice up to 2mS the lines don't match. This is the non-linear flow area of an injector. The short pulse adders are used in this section to compensate for the flow being erratic in this region. Hence, the non-linear reference.
GM adds a time value(via short pulse adders) to the theoretical linear flow(straight line) to "build" a profile of the red line. Thus you get how the injector actually flows and accurate fuel delivery.
Without proper injector characterization data, accurate fuel flow in the non-linear region is guess work(or at best trial and error).
This may help(or hurt,
) as well....http://www.camaroz28.com/forums/comp...ts-lt1-770192/
Last edited by ACE1252; 03-18-2015 at 11:27 PM.
03-18-2015, 11:26 PM
#43
TECH Addict
Have a read of this....it should help.
http://injectordynamics.com/articles...racterization/
The first picture shows the flow(in red) without the injector offset. The second picture shows the flow with the injector offset applied. Notice that it affected the entire graph.
In the third picture, they zoom in on the lower end of the graph. Notice up to 2mS the lines don't match. This is the non-linear flow area of an injector. The short pulse adders are used in this section to compensate for the flow being erratic in this region. Hence, the non-linear reference.
GM adds a time value(via short pulse adders) to the theoretical linear flow(straight line) to "build" a profile of the red line. Thus you get how the injector actually flows and accurate fuel delivery.
This may help(or hurt,) as well....
http://www.camaroz28.com/forums/comp...ts-lt1-770192/
http://injectordynamics.com/articles...racterization/
The first picture shows the flow(in red) without the injector offset. The second picture shows the flow with the injector offset applied. Notice that it affected the entire graph.
In the third picture, they zoom in on the lower end of the graph. Notice up to 2mS the lines don't match. This is the non-linear flow area of an injector. The short pulse adders are used in this section to compensate for the flow being erratic in this region. Hence, the non-linear reference.
GM adds a time value(via short pulse adders) to the theoretical linear flow(straight line) to "build" a profile of the red line. Thus you get how the injector actually flows and accurate fuel delivery.
This may help(or hurt,
) as well....http://www.camaroz28.com/forums/comp...ts-lt1-770192/
Last edited by hrcslam; 03-18-2015 at 11:32 PM.
03-19-2015, 11:28 AM
#44
The needed voltage offset is related to how fast the injectors open, that is type (pintle or ball) the taper on the pintle and the windings. Lucus injectors go full flow faster than most others, thus use less offset.
Tip-in lag, like a carb needing accel more pump squirt, is usually a wall wetting issue.
Tip-in lag, like a carb needing accel more pump squirt, is usually a wall wetting issue.
03-19-2015, 04:33 PM
#45
TECH Resident
There is truth to the speed issue and the voltage settings, but I'm not sure it's good to think of it like that. You want the injector opening to be consistent and repeatable across all voltage ranges. Voltage offsets are not really used as a "speed control" tool in that sense(like in a variable motor drive). As such, I think it's better to think of them as either a 1 or 0, open or shut, with a time delay before the opening(and closing) that varies with voltage.
On the pump shot, I don't think there is any kind of control like that in the LT1 PCM. I wished there was.....that would make my day.
My slight tip in issue, just off idle, is a lean stumble for sure. I can cure it in SD mode with a 12.5:1 AFR off idle, but in MAF mode I have not been able to fix it(due to the constant 14.7:1 AFR). However, I have not properly tuned either my MAF or VE tables either. When I get the spare cash, I'm going to take a trip to Tick Performance just a few miles up the road to dial that stuff in on their dyno.
I've been talking with other CC503 owners who have stock injectors. Since there is no need for injector setting changes and they generally have the same tip in issue I don't think it's an injector issue per se.
I "think" it's due to overlap confusing the O2s along with a little bit of fuel short circuiting....going straight out the exhaust valve before it closes. The way this can be helped in LS1 PCMs is with the EOI table.
I've learned a lot trying to do my own tune(and still have much to learn...), but it has been much, much, more involved than I thought it was going to be when I started down this path.
On the pump shot, I don't think there is any kind of control like that in the LT1 PCM. I wished there was.....that would make my day.
My slight tip in issue, just off idle, is a lean stumble for sure. I can cure it in SD mode with a 12.5:1 AFR off idle, but in MAF mode I have not been able to fix it(due to the constant 14.7:1 AFR). However, I have not properly tuned either my MAF or VE tables either. When I get the spare cash, I'm going to take a trip to Tick Performance just a few miles up the road to dial that stuff in on their dyno.
I've been talking with other CC503 owners who have stock injectors. Since there is no need for injector setting changes and they generally have the same tip in issue I don't think it's an injector issue per se.
I "think" it's due to overlap confusing the O2s along with a little bit of fuel short circuiting....going straight out the exhaust valve before it closes. The way this can be helped in LS1 PCMs is with the EOI table.
I've learned a lot trying to do my own tune(and still have much to learn...), but it has been much, much, more involved than I thought it was going to be when I started down this path.
Last edited by ACE1252; 03-19-2015 at 04:56 PM.
03-19-2015, 04:53 PM
#46
There is truth to the speed issue and the voltage settings, but I'm not sure it's wise to think of it like that. You want the injector opening to be consistent and repeatable across all voltage ranges. Voltage offsets are not really used as a "speed control" tool in that sense(like in a variable motor drive). As such, I think it's better to think of them as either a 1 or 0, open or shut, with a time delay before the opening(and closing) that varies with voltage.
To my knowledge, I don't think there is any kind of control like that in the LT1 PCM(a table for pump shot). I wished there was.....that would make my day.
My slight tip in issue, just off idle, is a lean stumble for sure. I can cure it in SD mode with a 12.5:1 AFR off idle, but in MAF mode I have not been able to fix it(due to the constant 14.7:1 AFR). However, I have not properly tuned either my MAF or VE tables either. When I get the spare cash, I'm going to take a trip to Tick Performance just a few miles up the road to dial that stuff in on their dyno.
I've been talking with other CC503 owners who have stock injectors. Since there is no need for injector settings and they generally have the same tip in issue I don't think it's an injector issue per se.
I "think" it's due to overlap confusing the O2s along with a little bit of fuel short circuiting....going straight out the exhaust valve before it closes. The way this can be helped in LS1 PCMs is with the EOI table.
I've learned a lot trying to do my own tune(and still have much to learn...), but it has been much, much, more involved than I thought it was going to be when I started down this path.
To my knowledge, I don't think there is any kind of control like that in the LT1 PCM(a table for pump shot). I wished there was.....that would make my day.
My slight tip in issue, just off idle, is a lean stumble for sure. I can cure it in SD mode with a 12.5:1 AFR off idle, but in MAF mode I have not been able to fix it(due to the constant 14.7:1 AFR). However, I have not properly tuned either my MAF or VE tables either. When I get the spare cash, I'm going to take a trip to Tick Performance just a few miles up the road to dial that stuff in on their dyno.
I've been talking with other CC503 owners who have stock injectors. Since there is no need for injector settings and they generally have the same tip in issue I don't think it's an injector issue per se.
I "think" it's due to overlap confusing the O2s along with a little bit of fuel short circuiting....going straight out the exhaust valve before it closes. The way this can be helped in LS1 PCMs is with the EOI table.
I've learned a lot trying to do my own tune(and still have much to learn...), but it has been much, much, more involved than I thought it was going to be when I started down this path.
I am not aware of a lag or flat spot needing addressed with a cam that mild. You may have a tuning issue elsewhere. I get stuff through here all the time to redo, that the last guy tried to cure the rich idle caused by the cam, by fudging the injector flow rate up. That is a hack that simply causes issues elsewhere.
There is a place in the LT1 PCM calibrations for "pump shot", if you know where to look. May not be in your tuning software. I have never had to alter that with that little "CC 305" cam.
03-19-2015, 05:04 PM
#47
TECH Resident
I agree with you. I think it's a combo of MAF, VE, and spark not quite right.
I'm confidant in the calculated injector data from Ford SVO. The LTFT's have went from 13%/25% to -10%/10% at idle with the correct data. There is only a 3% split between them on highway.
I'll post up my results when I do the dyno testing(be it good or bad).
I'm confidant in the calculated injector data from Ford SVO. The LTFT's have went from 13%/25% to -10%/10% at idle with the correct data. There is only a 3% split between them on highway.
I'll post up my results when I do the dyno testing(be it good or bad).
03-20-2015, 11:15 AM
#48
OK back to my original question 
Just picked up the 383 engine (bought the complete car so I could hear it run). Engine has a scat forged 383 kit with H beam rods and Mahle pistons. PO had the engine built and the paperwork from the shop unfortunately did not have part numbers, so here is what I am told by the PO
31 cc pistons ( has to be 31cc dish)
comp 503 cam
stated the engine has 11:1 compression, however this doesn't make sense with the 31cc dish, should be 9:1 with a 58cc chamber. I asked if the heads were decked and was told "yes, a lot"...not sure what to take from that. Machine shop info does say adjustable guide plates were installed to correct the pushrod geometry, not sure if that was needed because of the heads being milled?
So I am going to have to pull the heads to see just what pistons are in there and what the heads look like. If the PO is right just how much would the heads have to be cut to make 11:1 and is it even possible? I am hoping he is wrong and as long as the dished pistons are installed I will be at 9:1 and be ok for the supercharger.
I would use my 355 intake/injectors/TB and can even use the heads if needed to get at close as possible to my present tune. This cam has a slight lope at idle but does not sound a lot different than my original, is the 503 ok to use with the supercharger?
I plan on changing the chamber volume settings and then getting this running and then datalogging to see how far off it is. This 383 currently has a 24X system on it with an LS computer so I do not have the ability to look at its tune, I will have to swap it back over to the LT1 setup with the opti to use my PCM. With your guys guidance I just may be able to tune it myself!
Just picked up the 383 engine (bought the complete car so I could hear it run). Engine has a scat forged 383 kit with H beam rods and Mahle pistons. PO had the engine built and the paperwork from the shop unfortunately did not have part numbers, so here is what I am told by the PO
31 cc pistons ( has to be 31cc dish)
comp 503 cam
stated the engine has 11:1 compression, however this doesn't make sense with the 31cc dish, should be 9:1 with a 58cc chamber. I asked if the heads were decked and was told "yes, a lot"...not sure what to take from that. Machine shop info does say adjustable guide plates were installed to correct the pushrod geometry, not sure if that was needed because of the heads being milled?
So I am going to have to pull the heads to see just what pistons are in there and what the heads look like. If the PO is right just how much would the heads have to be cut to make 11:1 and is it even possible? I am hoping he is wrong and as long as the dished pistons are installed I will be at 9:1 and be ok for the supercharger.
I would use my 355 intake/injectors/TB and can even use the heads if needed to get at close as possible to my present tune. This cam has a slight lope at idle but does not sound a lot different than my original, is the 503 ok to use with the supercharger?
I plan on changing the chamber volume settings and then getting this running and then datalogging to see how far off it is. This 383 currently has a 24X system on it with an LS computer so I do not have the ability to look at its tune, I will have to swap it back over to the LT1 setup with the opti to use my PCM. With your guys guidance I just may be able to tune it myself!
Last edited by drptop70ss; 03-20-2015 at 11:34 AM.
03-20-2015, 03:41 PM
#49
TECH Resident
I'm going to refer you back to my first post in this thread.
You'll need to get several things tweaked in the program to get this running right and given my experience on an NA setup, I'm not sure that tuning a supercharged setup, on your own, with no experience tuning is a good idea as a first try.
Banish's Advanced DVD deals with turbo and supercharged engines. How to scale the tune(if your sensors are limited in range) and things of that nature.....but it builds off the first one.
Who tuned your current setup?
I'm not trying to talk you out of learning how to tune, but you need to understand that there is more to it than you may think. It certainly was in my case.
You'll need to get several things tweaked in the program to get this running right and given my experience on an NA setup, I'm not sure that tuning a supercharged setup, on your own, with no experience tuning is a good idea as a first try.
Banish's Advanced DVD deals with turbo and supercharged engines. How to scale the tune(if your sensors are limited in range) and things of that nature.....but it builds off the first one.
Who tuned your current setup?
I'm not trying to talk you out of learning how to tune, but you need to understand that there is more to it than you may think. It certainly was in my case.
03-20-2015, 04:12 PM
#51
Well the thought was since the 355 supercharged engine was already tuned it would not be too far off if I only changed the displacement, at least that was the original plan until the cam was found to be in bad shape. I do not know who tuned it but it ran well, supposedly put out 540HP to the wheels. It still ran well when I pulled it but was not drivable because the block cracked and was putting coolant into the pan.
So I would be running with my 355 tune on the 383, everything was going to be the same other than displacement, but now I have to make a cam change as well.
What kind of info would be needed in order to have someone adjust the current tune for the new cam and increased displacement? And who would be a good source to send the PCM to for tuning? There is no local dyno tuner that I know of here in NY. Without a dyno do you just use the BLMs as you reference, so if you can get them all to 128 you then consider it tuned?
So I would be running with my 355 tune on the 383, everything was going to be the same other than displacement, but now I have to make a cam change as well.
What kind of info would be needed in order to have someone adjust the current tune for the new cam and increased displacement? And who would be a good source to send the PCM to for tuning? There is no local dyno tuner that I know of here in NY. Without a dyno do you just use the BLMs as you reference, so if you can get them all to 128 you then consider it tuned?
Last edited by drptop70ss; 03-20-2015 at 06:27 PM.
03-21-2015, 03:29 AM
#52
TECH Addict
Well the thought was since the 355 supercharged engine was already tuned it would not be too far off if I only changed the displacement, at least that was the original plan until the cam was found to be in bad shape. I do not know who tuned it but it ran well, supposedly put out 540HP to the wheels. It still ran well when I pulled it but was not drivable because the block cracked and was putting coolant into the pan.
So I would be running with my 355 tune on the 383, everything was going to be the same other than displacement, but now I have to make a cam change as well.
What kind of info would be needed in order to have someone adjust the current tune for the new cam and increased displacement? And who would be a good source to send the PCM to for tuning? There is no local dyno tuner that I know of here in NY. Without a dyno do you just use the BLMs as you reference, so if you can get them all to 128 you then consider it tuned?
So I would be running with my 355 tune on the 383, everything was going to be the same other than displacement, but now I have to make a cam change as well.
What kind of info would be needed in order to have someone adjust the current tune for the new cam and increased displacement? And who would be a good source to send the PCM to for tuning? There is no local dyno tuner that I know of here in NY. Without a dyno do you just use the BLMs as you reference, so if you can get them all to 128 you then consider it tuned?
If you went with 58cc head chambers and .050" head gasket you'll be at 9.97:1 SCR with all other things being the same from the list above. If you use the stock deck height you'll be at about 9.4:1 SCR. The problem here is your quench is not optimal at about 0.074" (you'll want something under 0.040" how much under is debatable, and many consider that too big). You'll also have to deal with un-machined deck and head surfaces (not optimal for reliability and power).
As far as the 383 putting down 540rwhp with the CC503 (NA??) I don't believe it. Maybe at the flywheel (sending 540 to the wheels), but not at the wheels (that'd be closer to 620-640 flywheel HP) I've never seen an NA LTx push out that much power on a cam remotely close to a CC503. So grain of salt there. On the flip side, shaving the heads, deck, obvious RR install, plus cam will require new pushrods to correct valve train geometry. Sounds like they went with NSA which is good.
You need to realize that you are compressing a lot more air when you stroke it. The heads combustion chamber don't really change their volume, but the piston volume of the cylinder does grow by about 8% (355-383).
That being said, you have a 24X? Keep it, use it, run it! It's much much much better than any LT1 PCM. And finding a tuner will be leaps and bounds easier.
Here's my suggestion. Get a good LT1 block and have bored, decked (not zero decked, but just enough for a flat deck), and clearanced for the 383 rotating assembly. Get a custom cam for your build, it's well worth the $400 or what ever. You'll also want to get valve springs to match the cam. Lloyd Elliot or AI can help you here.Don't use the heads from the 383 as their CC are too small for your combo. But I bet you could sell them for a bit of coin if they are still in good shape (there's the money for your cam and springs). Then have it tuned by a professional (dyno time!). A mail order tune can get you in the ball park to get it to the dyno I'd imagine.
Wait a minute, so you have 2 cracked LT1 blocks now?
Last edited by hrcslam; 03-21-2015 at 03:34 AM.
03-21-2015, 07:02 AM
#53
OK let me start from the beginning to try and clear it up some.
Here is the basics of what I started with
1995 Z28 LT1
.030 over, dished forged JE pistons, 9:1 compression
stock head castings mild port work
custom ground comp blower cam 270/276 (215/220@.050) 114CL
1.6 roller rockers
42 lb injectors
vortech V1 s trim supercharger with water to air intercooler, MSD box with boost referenced timing retard, secondary t-rex inline fuel pump
custom tuned, 540RWHP
20K miles on engine build
Bought the car running but coolant getting in the pan. Ran very well but I didnt push it with the coolant problem. Engine block assumed cracked, heads checked out ok at the machine shop. Block will be pressure tested shortly, lets just assume it is NG for the moment.
So the plan was to bore another 350 block .030 and transfer all the engine parts over to the new block. No tuning changes would be needed.
First problem. During the 355 teardown found the cam to have a lot of pitted lobes, none going flat but I do not want to reuse the cam. So changing cams may require tuning changes depending on the cam.
While going over my options I found a 1995 LT1 383 with the following work done
forged scat stroker crank, H beam rods, Mahle 31cc dish pistons (need to confirm) Compression would be 9:1 with stock 58cc chamber heads
comp 503 cam
24x system
heads may be milled to raise compression, machine shop work lists adjustable push rod guides to correct the geometry
there are more external mods but not relevant.
So now the plan would be to use the 383 short block.. I can use my original heads if needed to get the compression to 9:1 (you have me listed at 10:1, but mahle website shows 9:1 with 58cc chambers?), original intake, TB and injectors, etc. Hoping 42lb injectors would still be ok for the 383.
New variables would be the increased displacement from 355 to 383 and the cam change from my custom blower cam to the CC503. I would take off the 24x system and install my original 355 PCM, opti, etc..
I could always buy another cam closer to the original to eliminate that variable, but with the larger displacement the larger 503 cam should have close to the same characteristics as the smaller cam in the 355, correct? So going back to an original style cam may not be needed.
I am hoping that my original tune would be close enough to run the 383, do some data logging, and have the tune tweaked. I wouldn't think it would be the same as starting from scratch since I already have the 355 tune on the PCM.
Any questions fire away, I can answer what I can answer but I did not build either engine so I do not have every detail yet.
Your suggestion is sound, the only reason I bought the 383 (whole car) is a matter of cash..once the car is parted out I will have the engine for basically nothing, so it made sense to go for it. If the static compression will be too high for the blower then I will just save this engine for another project and go back to the original plan of another 355.
Also the reason I would want to keep my PCM is for being able to do some changes with tunercat (speedometer changes as needed for example) because this engine is no longer in a 95 z28, it will be in a 1951 ford F1 pickup. I have also changed the trans tables so I can run a 4l80e behind the LT1, the 383 has a t56 and I do not know if the harness is setup to run an automatic or not..plus the LS PCM is setup for the T56.
Here is the basics of what I started with
1995 Z28 LT1
.030 over, dished forged JE pistons, 9:1 compression
stock head castings mild port work
custom ground comp blower cam 270/276 (215/220@.050) 114CL
1.6 roller rockers
42 lb injectors
vortech V1 s trim supercharger with water to air intercooler, MSD box with boost referenced timing retard, secondary t-rex inline fuel pump
custom tuned, 540RWHP
20K miles on engine build
Bought the car running but coolant getting in the pan. Ran very well but I didnt push it with the coolant problem. Engine block assumed cracked, heads checked out ok at the machine shop. Block will be pressure tested shortly, lets just assume it is NG for the moment.
So the plan was to bore another 350 block .030 and transfer all the engine parts over to the new block. No tuning changes would be needed.
First problem. During the 355 teardown found the cam to have a lot of pitted lobes, none going flat but I do not want to reuse the cam. So changing cams may require tuning changes depending on the cam.
While going over my options I found a 1995 LT1 383 with the following work done
forged scat stroker crank, H beam rods, Mahle 31cc dish pistons (need to confirm) Compression would be 9:1 with stock 58cc chamber heads
comp 503 cam
24x system
heads may be milled to raise compression, machine shop work lists adjustable push rod guides to correct the geometry
there are more external mods but not relevant.
So now the plan would be to use the 383 short block.. I can use my original heads if needed to get the compression to 9:1 (you have me listed at 10:1, but mahle website shows 9:1 with 58cc chambers?), original intake, TB and injectors, etc. Hoping 42lb injectors would still be ok for the 383.
New variables would be the increased displacement from 355 to 383 and the cam change from my custom blower cam to the CC503. I would take off the 24x system and install my original 355 PCM, opti, etc..
I could always buy another cam closer to the original to eliminate that variable, but with the larger displacement the larger 503 cam should have close to the same characteristics as the smaller cam in the 355, correct? So going back to an original style cam may not be needed.
I am hoping that my original tune would be close enough to run the 383, do some data logging, and have the tune tweaked. I wouldn't think it would be the same as starting from scratch since I already have the 355 tune on the PCM.
Any questions fire away, I can answer what I can answer but I did not build either engine so I do not have every detail yet.
Your suggestion is sound, the only reason I bought the 383 (whole car) is a matter of cash..once the car is parted out I will have the engine for basically nothing, so it made sense to go for it. If the static compression will be too high for the blower then I will just save this engine for another project and go back to the original plan of another 355.
Also the reason I would want to keep my PCM is for being able to do some changes with tunercat (speedometer changes as needed for example) because this engine is no longer in a 95 z28, it will be in a 1951 ford F1 pickup. I have also changed the trans tables so I can run a 4l80e behind the LT1, the 383 has a t56 and I do not know if the harness is setup to run an automatic or not..plus the LS PCM is setup for the T56.
Last edited by drptop70ss; 03-21-2015 at 07:31 AM.
03-21-2015, 07:30 AM
#54
TECH Addict
OK let me start from the beginning to try and clear it up some.
Here is the basics of what I started with
1995 Z28 LT1
.030 over, dished forged JE pistons, 9:1 compression
stock head castings mild port work
custom ground comp blower cam 270/276 (215/220@.050) 114CL
1.6 roller rockers
42 lb injectors
vortech V1 s trim supercharger with water to air intercooler, MSD box with boost referenced timing retard, secondary t-rex inline fuel pump
custom tuned, 540RWHP
20K miles on engine build
Bought the car running but coolant getting in the pan. Ran very well but I didnt push it with the coolant problem. Engine block assumed cracked, heads checked out ok at the machine shop. Block will be pressure tested shortly, lets just assume it is NG for the moment.
So the plan was to bore another 350 block .030 and transfer all the engine parts over to the new block. No tuning changes would be needed.
First problem. During the 355 teardown found the cam to have a lot of pitted lobes, none going flat but I do not want to reuse the cam. So changing cams may require tuning changes depending on the cam.
While going over my options I found a 1995 LT1 383 with the following work done
forged scat stroker crank, H beam rods, Mahle 31cc dish pistons (need to confirm) Compression would be 9:1 with stock 58cc chamber heads
comp 503 cam
24x system
heads may be milled to raise compression
there are more external mods but not relevant.
So now the plan would be to use the 383 short block.. I can use my original heads if needed to get the compression to 9:1 (you have me listed at 10:1, but mahle website shows 9:1 with 58cc chambers?), original intake, TB and injectors, etc. Hoping 42lb injectors would still be ok for the 383.
New variables would be the increased displacement from 355 to 383 and the cam change from my custom blower cam to the CC503. I would take off the 24x system and install my original 355 PCM, opti, etc..
I could always buy another cam closer to the original to eliminate that variable, but with the larger displacement the larger 503 cam should have close to the same characteristics as the smaller cam in the 355, correct? So going back to an original style cam may not be needed.
I am hoping that my original tune would be close enough to run the 383, do some data logging, and have the tune tweaked. I wouldn't think it would be the same as starting from scratch since I already have the 355 tune on the PCM.
Any questions fire away, I can answer what I can answer but I did not build either engine so I do not have every detail yet.
Here is the basics of what I started with
1995 Z28 LT1
.030 over, dished forged JE pistons, 9:1 compression
stock head castings mild port work
custom ground comp blower cam 270/276 (215/220@.050) 114CL
1.6 roller rockers
42 lb injectors
vortech V1 s trim supercharger with water to air intercooler, MSD box with boost referenced timing retard, secondary t-rex inline fuel pump
custom tuned, 540RWHP
20K miles on engine build
Bought the car running but coolant getting in the pan. Ran very well but I didnt push it with the coolant problem. Engine block assumed cracked, heads checked out ok at the machine shop. Block will be pressure tested shortly, lets just assume it is NG for the moment.
So the plan was to bore another 350 block .030 and transfer all the engine parts over to the new block. No tuning changes would be needed.
First problem. During the 355 teardown found the cam to have a lot of pitted lobes, none going flat but I do not want to reuse the cam. So changing cams may require tuning changes depending on the cam.
While going over my options I found a 1995 LT1 383 with the following work done
forged scat stroker crank, H beam rods, Mahle 31cc dish pistons (need to confirm) Compression would be 9:1 with stock 58cc chamber heads
comp 503 cam
24x system
heads may be milled to raise compression
there are more external mods but not relevant.
So now the plan would be to use the 383 short block.. I can use my original heads if needed to get the compression to 9:1 (you have me listed at 10:1, but mahle website shows 9:1 with 58cc chambers?), original intake, TB and injectors, etc. Hoping 42lb injectors would still be ok for the 383.
New variables would be the increased displacement from 355 to 383 and the cam change from my custom blower cam to the CC503. I would take off the 24x system and install my original 355 PCM, opti, etc..
I could always buy another cam closer to the original to eliminate that variable, but with the larger displacement the larger 503 cam should have close to the same characteristics as the smaller cam in the 355, correct? So going back to an original style cam may not be needed.
I am hoping that my original tune would be close enough to run the 383, do some data logging, and have the tune tweaked. I wouldn't think it would be the same as starting from scratch since I already have the 355 tune on the PCM.
Any questions fire away, I can answer what I can answer but I did not build either engine so I do not have every detail yet.
When spec'ing out a cam you want to spec it based on valve timing events dependent on how the engine is built and for what purpose. A CC503 isn't a blower cam, it may work on a blower but it isn't optimal. If you noticed, blower cams have less valve overlap (higher LSA in relation to duration).
You can't judge one cam to another by only looking at the typically advertised numbers. Especially when going from a blown 355 to a NA 383. The CC503 is a popular cam, proven. I still vote for selling it off (assuming it's still good) and getting a custom grind for the 383.
If you plan on using the 383 short block, be sure to measure piston to deck clearance. It was very likely machined down (to get to 11:1 SCR), make sure you account for that in your build.
And if you decide to ditch the 24X, how much do you want for it? I'll take it if the price is right. Honestly, it may be simpler to keep the LT1 PCM, but the 24x is far superior. You already have everything you need to run it and you will need a tune anyway.
Here's the scenario's I see:
383 shortblock, CC503 cam, 355 top end swapped, Complete tune needed.
383 Shortblock, custom cam, 355 top end swapped, Complete tune needed.
383 Shortblock, 355 cam (replica replacement) and top end swapped, Complete tune needed.
In all scenario's you'll need a retune.
Not sure on Injector size, what was your injector duty cycle on the 355? 540rwhp on 42lbs injectors with boost was probably pushing it on those injectors???
03-21-2015, 07:50 AM
#55
Understood on the valve event timing, and understood on the overlap, no sense pushing the boost right out the exhaust. I would never choose a 503, or any cam ground on a 112 lobe separation for boost, it just happens to be in the engine. If I dont use it I will put it in another engine.
I dont have any injector or scan data from the 355, I ran it very little because of the coolant getting in the oil, and never ran it other than moving it around the yard a few times before tear down.
I would pay for dyno tuning if I knew where to go, but finding an LT1 dyno tuner is not easy.
If I were to use the 383 short block, my original heads and top end, custom cam, what are the chances of a mail order tune getting it right? Do you try it, data log it, and send back for adjustments?
I have to think this one over, it may just be easier to put this engine on the shelf, build another 355 and order a similar cam to what I had and avoid the
problems.
I dont have any injector or scan data from the 355, I ran it very little because of the coolant getting in the oil, and never ran it other than moving it around the yard a few times before tear down.
I would pay for dyno tuning if I knew where to go, but finding an LT1 dyno tuner is not easy.
If I were to use the 383 short block, my original heads and top end, custom cam, what are the chances of a mail order tune getting it right? Do you try it, data log it, and send back for adjustments?
I have to think this one over, it may just be easier to put this engine on the shelf, build another 355 and order a similar cam to what I had and avoid the
problems.
03-21-2015, 08:04 AM
#57
My fuel pressure is also boost referenced (kit came with an FMU) so the FP goes up with boost allowing the injectors to flow more than normal..correct or no?
I believe this was all part of the SC kit including the T-rex secondary fuel pump.
I believe this was all part of the SC kit including the T-rex secondary fuel pump.
Last edited by drptop70ss; 03-21-2015 at 08:14 AM.
03-21-2015, 08:51 AM
#60
TECH Addict
Understood on the valve event timing, and understood on the overlap, no sense pushing the boost right out the exhaust. I would never choose a 503, or any cam ground on a 112 lobe separation for boost, it just happens to be in the engine. If I dont use it I will put it in another engine.
I dont have any injector or scan data from the 355, I ran it very little because of the coolant getting in the oil, and never ran it other than moving it around the yard a few times before tear down.
I would pay for dyno tuning if I knew where to go, but finding an LT1 dyno tuner is not easy.
If I were to use the 383 short block, my original heads and top end, custom cam, what are the chances of a mail order tune getting it right? Do you try it, data log it, and send back for adjustments?
I have to think this one over, it may just be easier to put this engine on the shelf, build another 355 and order a similar cam to what I had and avoid the
problems.
I dont have any injector or scan data from the 355, I ran it very little because of the coolant getting in the oil, and never ran it other than moving it around the yard a few times before tear down.
I would pay for dyno tuning if I knew where to go, but finding an LT1 dyno tuner is not easy.
If I were to use the 383 short block, my original heads and top end, custom cam, what are the chances of a mail order tune getting it right? Do you try it, data log it, and send back for adjustments?
I have to think this one over, it may just be easier to put this engine on the shelf, build another 355 and order a similar cam to what I had and avoid the
problems.