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I’m really just looking for some ideas on why power is so low. I have some thoughts, but I’m curious what some others think. The plot below was on the stock GTO plugs, but I got the same results later with the BR7EF plugs.
I do believe the dyno curve as I post-processed it from several 3rd gear pulls on the street – so this is based off the real thrust required to generate the measured g’s.
There are 2 ‘knees’ in the torque curve. The first at 5200 RPM keeps power from rising (i.e. peak power is extremely low at 5200 RPM). The second, at 6200 RPM has the tq really nose dive. I’m somewhat inclined to think I have two separate phenomenon occurring.
Details:
Car is an 05 GTO with a manual 4l80e and 3.73 gears.
L33 bored to 5.7L with F1A Procharger
Ported 243 heads with larger stainless valves
9.5 CR
Cam: Custom FTI - 214/228 .600/.600 with 113 LSA
PAC 1218 valvesprings w/15,000 miles
1-7/8 Kooks headers w/ 3” dual exhaust
Stock LS2 intake
Tune Details:
Fuel: 93 octane at 11.0 average AFR
Timing: 20* start falling to 14* at peak boost
Air Temp: 85*F – 110*F during the pull
I have some upgrade plans this year, but I'd like to get some thoughts on this first and sort out any potential issues and/or help guide my future decisions based on any discussion here.
I think it is hard to compare a dyno chart generated from a street pull, to like a dynojet, or a mustang dyno pull. I've seen 50-100 hp variances in dynos on power levels similar to yours.
I'd say you need a little more boost though, and you need it sooner. Ever consider using a waste gate on your setup? I see some people are over gearing their prochargers to produce more midrange boost, then bleeding it off at higher RPM with a wastegate to basically create a controlled boost leak once they hit a certain boost level. This seems weird to use a waste gate on a cold side, but I've seen a few setups using it now. Either way, I'd put more squeeze to it. I'm pushing more boost on my aluminum SBE than that. Kind of a waste going to a forged setup like you have if your not pushing it anymore than that. I would also say you need to run E85 or have meth injection to get the most out of your combination.
Looks like Valve float, or pulling ALL timing up top.
With 1k miles on those springs, I'll go with valve float. PAC will even tell you their spring will not last nearly as long as an OE spring, especially with any aggressive cams. Many drag race guys change them every season no matter what as part of their general maintenance program.
Low compression/small motor/small cam. I made 830rwhp on a 9.5:1 347 motor with a similar size blower at 23psi. I also made 850rwhp on a little T trim blower with a 402 with 10.8:1 compression, my custom 232/244-118+4 cam that idled like stock on 13 psi. I think there is about 100hp missing from your combo though.
You're running a spring that is rated for a maximum of .600 lift on a cam with .600 lift. If those lobes are even slightly aggressive, its going to float them.
I think it is hard to compare a dyno chart generated from a street pull, to like a dynojet, or a mustang dyno pull. I've seen 50-100 hp variances in dynos on power levels similar to yours.
I'd say you need a little more boost though, and you need it sooner. Ever consider using a waste gate on your setup? … I would also say you need to run E85 or have meth injection to get the most out of your combination.
Well, fair point on dyno variation. This is why I take the street pulls myself and post-process them. I don’t want to digress, but Torque/power numbers are only useful to me if I can put them back into my tractive effort simulation tools and get the exact same speed vs. time plot. It also helps that it’s free! For what it’s worth, of the dyno’s I’ve tried, the Superflow chassis dyno came out closest (~5 lb-ft across the rev range) to the street pull method.
While I would love the control that would be available from a wastegate setup (boost by gear), I’ve heard it can really put a load on the blower. This same pulley combination (4.0”) made 16 psi on the 402 that was in the car previously. I knew it would probably make 20psi on the smaller 347, so I used the restrictor method to keep boost under control for initial tuning. I’ve machined a few orifice plates that I’ve put upstream of the procharger.
I put a 2.4” orifice in the 4” inlet pipe and this limited me to 7 psi for initial tuning. I’ve since upped the restrictor to 2.65” and this has netted me 13 psi. Since boost didn’t flatline, the current restrictor is not choking - It’s just providing some additional loss prior to the compressor. I expect that when I take it out this year, I will start seeing full boost. Before I get there though, I wanted to understand why almost 14 psi of boost wasn’t making the power I thought it should be.
Originally Posted by coltboostin
Looks like Valve float, or pulling ALL timing up top.
With 1k miles on those springs, I'll go with valve float. PAC will even tell you their spring will not last nearly as long as an OE spring, especially with any aggressive cams. Many drag race guys change them every season no matter what as part of their general maintenance program.
That’s good to know on the springs. I have always heard most aftermarket springs have a life of 20k miles, and I’m getting close at 15k. I suppose it’s possible that the boost is putting enough extra stress on the intake springs that they are floating. This is especially true because this ‘small’ cam basically crams a lot of lift into a very short intake duration – which will naturally be harder on the springs than say a mid 230’s duration.
Originally Posted by RonSSNova
I think it just needs more cam. That's pretty small.
I've tuned a few of these on the dyno, but on Hemi's. They benefit from water meth if you insist on pump gas. And of course more boost.
Are you running a 6 rib or 8 rib belt?
Ron
This is an 8-rib belt. I haven’t noticed any belt slip thus far.
I don’t insist on pump gas, I actually ran on E85 for a good while before putting the F1A back on. I went back to pump gas last year to sort out some driveablity and cold start issues. I will probably go back to E85 again this year.
My only guess at the moment is that the valvesprings are responsible for the 6200 tq cliff and the cam/timing is responsible for the torque drop at 5200 RPM.
Originally Posted by winters97gt
Low compression/small motor/small cam. I made 830rwhp on a 9.5:1 347 motor with a similar size blower at 23psi. I also made 850rwhp on a little T trim blower with a 402 with 10.8:1 compression, my custom 232/244-118+4 cam that idled like stock on 13 psi. I think there is about 100hp missing from your combo though.
^That is a good reference point. It’s interesting to know I will probably have to run into the 20 lb boost range to get my power goals. But as you mentioned, it seems like there is something I have to fix with my setup for that to even be possible. I can’t imagine only 10 more psi will get me from 490 to 800…
Out of curiosity, I see several people have mentioned the cam size. It is small as it was originally spec’d for a 5.3L L33. But after getting screwed on two L33’s with junk cylinders, it had to turn into a 5.7. With this said, the cam is still much larger than say the ever popular LS6 cam you see people running. You'd think it would only be responsible for a small power loss up top - not making peak power at 5200 RPM.
Originally Posted by JoeNova
You're running a spring that is rated for a maximum of .600 lift on a cam with .600 lift. If those lobes are even slightly aggressive, its going to float them.
Good catch. I screwed up on listing the valvesprings, I keep thinking they are 1218’s, but they are really the .650” rated 1518’s. With that said, I was wondering if they were getting near the end of their life.
If your going to change the springs I'd recommend the PSI1511ML springs, I've had really good luck with them. I understand them to be the best option on the market, to use the stock retainers, with cams 0.600 and under. They give good life for an aftermarket spring. Otherwise the BTR dual spring setup would work well too. With your setup either would work well. Both are available from Brian Tooley Racing or various other vendors.
The comments confirm what I was thinking on springs - I’m for sure looking to change springs at this point.
I’m also going to throw in my old NA cam. It was pretty healthy in my old 6.0, and I was afraid it would impact driveability on the 5.7. While perhaps not specifically designed for a cetrif blower, it should definitely keep the motor breathing up top. 232/236 .600/.610 with 113 LSA
Also, I’ve got the engine out, so I’m debating taking the 243’s off and sending them off to be ported by AI or someone similar. It will likely be better than the mild port I put on them, and I can bring the chamber size down to try and get the CR back up to maybe 10.0.
I’m hopeful that perhaps the above 3 items will get my power in line with where it should be. Then I can start looking at removing the restrictor, pulleying down on a 12-rib setup, switching back to E85, etc…
^I go back and forth on whether putting $1400 into the heads themselves is worth it for just ~0.6 points of CR and the better port job. Any thoughts here?
My set up is similar to yours. SBE 5.7, ported 241's, 224/224 cam on 116lsa, 3.73 gear F1a on 11#'s 614/540 through a 6pd and stock 10 bolt with 3.73 gears
^I go back and forth on whether putting $1400 into the heads themselves is worth it for just ~0.6 points of CR and the better port job. Any thoughts here?
What are your goals power wise?
I'd think you already have a power adder that's not being used to it's full potential, so spending money on the heads doesn't make sense from a cost VS performance standpoint. You are making diddly for boost down low and not much up top either. Figure for every 15lbs of boost the best you'll do is double the NA hp. Then you have to account for efficiency losses due to heat, blower, drivetrain. So power numbers seem about right to me. Bump up the cam size and engine/blower speeds and it will pump out much more.
If you need more RPM, and more power after maxing out the power adder on your current head (or you have an endless budget) then by all means go for the nicest head you can afford.
The cam is on the small side, and costing you a little power. But as you mentioned, that's not the reason. I'm guessing valve float too. A boost leak is possible up top, but not likely at that low of PSI if the kit is clamped in good/bov is solid/etc.
Don't waste your time and money porting 243's on a simple blower build. Stock 243's have 1100rwhp on a 347 with a YSI which is about the same as your blower.
Do not try to bring more boost in sooner, or wastegate it. That will only choke the top end power even more.
You obviously have a major power-limiter happening at 5300 rpm. That's right where a centrifugal supercharger starts to shine. The HP line should continue going up at the same rate as it was from 4500 to 5000, and the torque should start to flatten out, not nose dive.
How fast do you have the blower spinning?
I'd first get it on a real dyno and verify that this is accurate. My first guess would be the combination of small cam and poor valve spring choice. I would call Brian Tooley and have him custom spec a cam for you (only $20 extra), which will probably be in the 230/240ish on 115*, and get a set of his .660" platinum springs. I run an F1A-94 with a custom spec'd cam from him, his off-the-shelf .660 springs, and 18 psi. Power never stops climbing.
I don't think it has anything to do with the cam or heads...looks like a restriction on the intake side of the supercharger. I had that happen with a Procharger setup years ago. One of the elbows was sucking shut above 5k and the power curve nose dived just like yours is.
Does it actually feel like power falls off at 5250 rpm? I think your G force reader isn't right. Your torque and hp will always cross at 5250 rpm but here the hp flatlines so I'm guessing your G force dyno isn't accurate. We can rule out what it's not, since your boost pressure is linear past 5250 can rule out belt slip or that an elbow on the intake side of the F1a is collapsing causing a restriction. The size of the blower for the size of the engine you have, you could have a stock cam and have power climb all the way to redline, you are forcing air into this motor so it won't fall off like a n/a motor. Valve springs could be weak for boost, being that boost is trying to push those intake valves open but at 13 psi I don't think that's it. An a/f ratio would help diagnose but unless your losing all fuel psi at 5250 ill guess it's fine. Same thing with timing unless it's pulling all the timing at 5250 I'd rule out the tune as well
My 2 cents: the parasitic loss to run the blower is more than you think.
This is the same reason I am in the process of removing my waste gated system.
Artificial boost leak on top ( waste gate) & restrictor plates = choke.
The power to run the blower goes up exponentially. I didn't believe it until I lived it.
( I'm thick headed).
Something is definitely going on there. The thing about that graph that just jumps straight out into my face is the the torque falling off after the cross at 5250.
Somewhat of an apples to oranges comparison, but I have a decent math channel built into my Holley software that can tell me based on fuel flow and other parameters a general idea of the power curve for my F2 blown 408. Like I said before it is not an "everything identical" comparison, but it is not uncommon to see centri blown cars keep rising in torque much higher in the rpm. This is just the design of centri blowers. More rpm, typically means more air. Looking at the fuel table in some of my tune ups, it actually suggests that my peak torque somewhere near 7500 rpm.
Where am I going with this?.....
I might have missed some details above, but what is the pulley ratio you currently are running on that F1A? If you have it pulley to max speed very early trying to get the most power out of it, it could be a situation where either the blower has long since passed its "happy zone" or you are experiencing some major belt slip. Glancing at that boost line though that seems to be good.
I don't have a ton of experience with the F1a, but I can't imagine that it should be falling off that quick on a small motor like that.
Just my 2 cents. Maybe I missed something written above.
02-27-2017, 08:58 PM
Forged 347 – F1A @ 13psi – Only 490 whp… 
