79 RX7 LS 5.3 Turbo. (8.93 @ 153mph)
06-08-2018, 09:48 AM
#541
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Nice, yes we always like video. I need to put up some Youtube videos of my creation.
While I have a Hi Ram I will say friends have also done well with the Edelbrock Pro Flo. I need to check where they are shifting those and report back.
My hero car (the build I'm mostly emulating) runs 28s and a 3.70 gear and is shifted at 8k. I plan something similar, and am tracking a used 40 spline center section to get so I can rebuild whatever is in this car.
While I have a Hi Ram I will say friends have also done well with the Edelbrock Pro Flo. I need to check where they are shifting those and report back.
My hero car (the build I'm mostly emulating) runs 28s and a 3.70 gear and is shifted at 8k. I plan something similar, and am tracking a used 40 spline center section to get so I can rebuild whatever is in this car.
06-11-2018, 08:27 AM
#542
First time back since fixing the trans and HG. Trans worked perfect, car was so-so. Seems WAY down on power, not sure why.
Boost kept wanting to run away on me. Hit boost cut my first 3 passes. Had to make a ton of changes to the boost control, but got that ironed out I think. Back pressure is right around 1:1 till 17lbs and creeps up slightly 1.2:1. The low back pressure on this small engine and big S480 makes boost harder to control I’m thinking.
All seems well in the tune/logs. 11.5-11.0 AFR, 12* of timing. Was only trapping 142 or so at 20lbs. . Nearest I can tell I’m down about 10-12 mph from where it should be. Still falls on its *** around 6300 as well. That isn’t helping matters, but I don’t think it’s my main issue since it’s always done this. I’ll be swapping my 3.25 out with a 3.60 gear soon.
Noticed the IAT temps seem a little off for the boost level. Only 122* @ 20lbs. Starting out around 100* pre-pass. Need to verify the MAP sensor is correct. Hopefully the MAP is wrong and I’m at less boost than I think I am. I did degree the cam when I put it in. But the engine is only spitting out about 160psi warm cranking compression. That seems super low for a small 216/222 cam @ 10:1 base compression.
Boost kept wanting to run away on me. Hit boost cut my first 3 passes. Had to make a ton of changes to the boost control, but got that ironed out I think. Back pressure is right around 1:1 till 17lbs and creeps up slightly 1.2:1. The low back pressure on this small engine and big S480 makes boost harder to control I’m thinking.
All seems well in the tune/logs. 11.5-11.0 AFR, 12* of timing. Was only trapping 142 or so at 20lbs. . Nearest I can tell I’m down about 10-12 mph from where it should be. Still falls on its *** around 6300 as well. That isn’t helping matters, but I don’t think it’s my main issue since it’s always done this. I’ll be swapping my 3.25 out with a 3.60 gear soon.
Noticed the IAT temps seem a little off for the boost level. Only 122* @ 20lbs. Starting out around 100* pre-pass. Need to verify the MAP sensor is correct. Hopefully the MAP is wrong and I’m at less boost than I think I am. I did degree the cam when I put it in. But the engine is only spitting out about 160psi warm cranking compression. That seems super low for a small 216/222 cam @ 10:1 base compression.
06-11-2018, 09:12 AM
#544
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Shouldn't back pressure ratio be high if there was a boost leak, and probably also IATs on the high side?
Forecefed, this is very interesting! Have you tried adding a degree of timing to see if it wants a bit more?
Forecefed, this is very interesting! Have you tried adding a degree of timing to see if it wants a bit more?
06-11-2018, 10:25 AM
#546
Could be, I’ll pressure test it. That is usually accompanied with high backpressure and inlet temps. 120* is pretty low for 100* ambient at 20lbs+. I’d see 150-160 on the old motor, same boost. But that was with the S476. I can’t see the VSR 80mm unit being much better than the “real” S476 FI unit I had on it. Only swapped because my old turbo went with the old motor
If the MAP and the IAT sensors are correct... I’m stumped.
Dusty at PTC thinks it’s the converter/gearing. But I don’t really understand that. If it were only in 2nd gear maybe... but it does the same in 1st gear. Tried to rev it out to 7k in first to carry the shift and it was crap. Dropping to a 28” tire made it worse as well as I just hit “the wall” faster. I’m betting a shorter gear will do the same.
Everybody screams valve springs... But I’ve got the .660 BTR dual springs in this one. Can’t see that being an issue. Also measured my spring rates in the old motor and had plenty of spring pressure for 7k.
Intake manifold is still the LS6. I know that’s not ideal above 6k but It shouldn’t hit a wall at 6300.
I’m stuck on the lowish compression thing. Still has the OEM pushrods in it... They might be doing funky things. Need to double check lengths and order a decent set to rule it out. Might ditch the cam this winter as well if nothing “fixes” it.
MS3 might also have issues. I keep meaning to try the “batch fire” fuel and spark just to rule it out. Currently on sequential fuel/spark.
If the MAP and the IAT sensors are correct... I’m stumped.
Dusty at PTC thinks it’s the converter/gearing. But I don’t really understand that. If it were only in 2nd gear maybe... but it does the same in 1st gear. Tried to rev it out to 7k in first to carry the shift and it was crap. Dropping to a 28” tire made it worse as well as I just hit “the wall” faster. I’m betting a shorter gear will do the same.
Everybody screams valve springs... But I’ve got the .660 BTR dual springs in this one. Can’t see that being an issue. Also measured my spring rates in the old motor and had plenty of spring pressure for 7k.
Intake manifold is still the LS6. I know that’s not ideal above 6k but It shouldn’t hit a wall at 6300.
I’m stuck on the lowish compression thing. Still has the OEM pushrods in it... They might be doing funky things. Need to double check lengths and order a decent set to rule it out. Might ditch the cam this winter as well if nothing “fixes” it.
MS3 might also have issues. I keep meaning to try the “batch fire” fuel and spark just to rule it out. Currently on sequential fuel/spark.
06-11-2018, 11:48 AM
#547
Is the hotside still 2" OD tubing?
I have been doing tons of searching regarding power falling off up top trying to wrap my head around it (turbo car mainly). Most people point to valvesprings or the turbo's turbine...but there has to be more to it as I see it frequently even with well set-up systems.
You seem to have done a lot of systematic testing/changing of components so I am really curious to see what resolves the issue. Have a "terrible" roudy NA cam you can throw in there? I will paypal you some Corona money if you have the time to do the swap
I have been doing tons of searching regarding power falling off up top trying to wrap my head around it (turbo car mainly). Most people point to valvesprings or the turbo's turbine...but there has to be more to it as I see it frequently even with well set-up systems.
You seem to have done a lot of systematic testing/changing of components so I am really curious to see what resolves the issue. Have a "terrible" roudy NA cam you can throw in there? I will paypal you some Corona money if you have the time to do the swap
06-11-2018, 12:14 PM
#548
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What are you thinking in terms of this? I have a very underperforming car currently that I suspect to be just super cam limited, but I have it on MS3+MS3X that I built, running on full sequential. Everything appears good in the logs, but I have to admit I'm beginning to grasp at straws a bit.. I'm not above taking a crack at batch firing the injectors and/or using wasted spark if you think there might be something to it.
06-11-2018, 02:04 PM
#549
Yup same 2” hotside. If it flowed well enough to trap 160 on the 370” motor, should do it on a 4.8 too. The “spool” time is really pretty good considering the super tight 14 stator 9.5 converter spec'd for the 370. (was even on the tight side there)
Not sure if a really rowdy cam is the thing for a mild 4.8 with a medium sized single. I still plan to run the boost up a ways more once it’s ironed out. So back pressure will be up quite a bit more. Curts 4.8 did REALLY well with LJMS stage 2 cam. May go that route. His small t4 S475 was taking him to 157ish I believe. My 212/212 @ 112 cam 4.8 went 151 on 19lbs with the T4 S476 as well. This cam’s a little bigger and on a 111 LSA. So should be a little snappier and more “NA like”.
Pointing fingers at the MS3 because my mustang and the previous motor in the RX-7 did the exact same thing. I have a th400 in the mustang (with BTR duals springs) Even with the super low TH400 first gear it acts the same. So I can’t see it being converter or valve train. Changing over to wasted speak/fuel deal should just be a couple clicks in general settings. Easy enough to test anyway.
So far all my engines with low cranking compression have been dogs. All healthy cranking compression engines have run extremely well. My last alum 5.3 was spitting out almost 190-195 psi cold cranking and was a total beast with the triple 12 cam in it. Trapped right at 159 at 25-26lbs.
Not sure if a really rowdy cam is the thing for a mild 4.8 with a medium sized single. I still plan to run the boost up a ways more once it’s ironed out. So back pressure will be up quite a bit more. Curts 4.8 did REALLY well with LJMS stage 2 cam. May go that route. His small t4 S475 was taking him to 157ish I believe. My 212/212 @ 112 cam 4.8 went 151 on 19lbs with the T4 S476 as well. This cam’s a little bigger and on a 111 LSA. So should be a little snappier and more “NA like”.
Pointing fingers at the MS3 because my mustang and the previous motor in the RX-7 did the exact same thing. I have a th400 in the mustang (with BTR duals springs) Even with the super low TH400 first gear it acts the same. So I can’t see it being converter or valve train. Changing over to wasted speak/fuel deal should just be a couple clicks in general settings. Easy enough to test anyway.
So far all my engines with low cranking compression have been dogs. All healthy cranking compression engines have run extremely well. My last alum 5.3 was spitting out almost 190-195 psi cold cranking and was a total beast with the triple 12 cam in it. Trapped right at 159 at 25-26lbs.
08-07-2018, 03:40 PM
#551
RX-7 is still alive and kick’n. Took it out this past Saturday night.
Haven’t been to the track much, but I’ve been fighting traction all year with this 4.8. I thought this had to do with lowering the car since it puts a poor angle on the ladder bars and hits the tire much softer. So I removed my drop links and jacked the chassis way up in the rear like it was. Same shock settings, springs, and 150lbs of rear ballast. Looks goofy, but I’m tired of spinning! I raised the rear strut perch until the ladder bar was barely level with the frame. Should be at an upward angle to hit the tires hard, but this chassis won’t allow that with the current FWD bar mounts. (need to change that I guess) Also guessing the Drag radials are past their prime.
Got 8 runs in and blew the tires off on 5 of them. Tried form 3400 to 4400 RPM on 2 step. Anything below 4200 and it bogs pretty bad regardless of boost. I think the baby engine needs a little RPM. Above 7 lbs it spins, below it bogs. Best passes I went up to 4400 and 10lbs then pulled it down to 4* of timing for the first 2.5 seconds. This stuck a 1.5X bogging shortly after the launch. Netted me a 9.6 @ 146 on 17lbs and a 9.4 @ 149 on 19-20lbs. Both at 11* of timing. When it bogs it takes over a second to recover. If I had the chassis to stick this thing hard, It’d be quick! (for a mild 4.8 anyway). I think it has another 5-6mph in the tune easy. I could turn it up, but I’d like to get the launch down before risking the engine.
Haven’t been to the track much, but I’ve been fighting traction all year with this 4.8. I thought this had to do with lowering the car since it puts a poor angle on the ladder bars and hits the tire much softer. So I removed my drop links and jacked the chassis way up in the rear like it was. Same shock settings, springs, and 150lbs of rear ballast. Looks goofy, but I’m tired of spinning! I raised the rear strut perch until the ladder bar was barely level with the frame. Should be at an upward angle to hit the tires hard, but this chassis won’t allow that with the current FWD bar mounts. (need to change that I guess) Also guessing the Drag radials are past their prime.
Got 8 runs in and blew the tires off on 5 of them. Tried form 3400 to 4400 RPM on 2 step. Anything below 4200 and it bogs pretty bad regardless of boost. I think the baby engine needs a little RPM. Above 7 lbs it spins, below it bogs. Best passes I went up to 4400 and 10lbs then pulled it down to 4* of timing for the first 2.5 seconds. This stuck a 1.5X bogging shortly after the launch. Netted me a 9.6 @ 146 on 17lbs and a 9.4 @ 149 on 19-20lbs. Both at 11* of timing. When it bogs it takes over a second to recover. If I had the chassis to stick this thing hard, It’d be quick! (for a mild 4.8 anyway). I think it has another 5-6mph in the tune easy. I could turn it up, but I’d like to get the launch down before risking the engine.
08-28-2018, 11:57 AM
#553
30” tires this year, with a 3.25 gear. My radials were really worn though. Might have been most of the issue with traction. The 14 stator PTC 9.5” isn’t helping!
Just pulled the 3.25’s and put in a set of 3.64’s and dropped to a 28” tire. Going to try it again this weekend I hope.
Just pulled the 3.25’s and put in a set of 3.64’s and dropped to a 28” tire. Going to try it again this weekend I hope.
09-04-2018, 12:33 PM
#558
Well the gear change didn’t do much. Sitting at 6600ish according to the logs and hanging both gears. Resulted in a couple 9.3X @ 147ish passes, but mostly spun. I lost MPH due to the shorter gear and tire. Stopped pulling well before the traps. Guess a re-stall is in order. No telling when I can get that done.
Saw about 1100 rpm drop on the shift. Indicating about 3% slip by trap VS rpm VS VSS
Noted it makes 7-10lbs on the 2 step and is at 20 1.2 seconds in. Most passes I spun right at the 1 second mark.
If all I have is 6600 to work with the 30” tire will put it in a happier place anyway. Going to try that next time. 6600 with a 30” tire and 3% would put it at 157ish.
Baby 275’s
buddy has some good footage of the launch, but still working on uploading it.
Saw about 1100 rpm drop on the shift. Indicating about 3% slip by trap VS rpm VS VSS
Noted it makes 7-10lbs on the 2 step and is at 20 1.2 seconds in. Most passes I spun right at the 1 second mark.
If all I have is 6600 to work with the 30” tire will put it in a happier place anyway. Going to try that next time. 6600 with a 30” tire and 3% would put it at 157ish.
Baby 275’s
buddy has some good footage of the launch, but still working on uploading it.
09-04-2018, 01:41 PM
#559
Have you logged voltage and fuel pressure? I noticed my car would lay over past 5500rpm. Saw a voltage drop so went to a larger alt pully. Then also say fuel drop which was I needed bigger wires to my 2 in tank pumps. Now pulls clean all the way to 6800. Would have never seen the issues unless I watched my volts and fuel pressure logged against rpm