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Restrictor plate for Time Trials? Experience?

PatientZero

TMO Race
201
135
Kansas City, Missouri
Autocross
10-20 Years
I do not know how to tune but just started with HPTuners for the s550. I think if you need to prove HP on dyno like with NASA ST classes you can tweek throttle position and limit power. One of the NASA ST2 guys did that with ST2 to ST1 cross classing in the C5 vette and it worked fine. SCCA does not require dyno proof so put everyone in the same boat with listed engine mods and restrictor plates. So this same guy swapped plates for T1 and GT2 and used his HPT to download the corresponding tunes per restrictor plate.

That's what I'm doing next week getting 2 dyno tunes one for T1 no plate and T2 with plate and using my HPT to swap tunes as needed. Smarter guys double their costs doubling the number of tunes for 93 pumpgas for when the competition is light and 100 octane for the extra edge when $8/gal race fuel makes sense.
The SCCA class I'm running does require a dyno cert for the season. If I were using an electronic throttle body that would be an option. Unfortunately I have a cable throttle body.
 

captdistraction

GrumpyRacer
1,658
1,128
Phoenix, Az
How does this happen with rich fuel mixture? Lean misfire, knocking, and excessive heat come with lean mistures. All a fat mixture can do is carbon build-up but that does not cause engine failure just dirty motors to de-carbon. What am I missing?
I wouldn't assume that it automatically becomes a rich mixture: Since there's fuel tables / injection settings, but self-adjustment in both long term and short term fuel trims along with mass air flow metering just restricting the inbound air would result in adjustment (and then spark tables would probably need adjustment). I'm not sure the exact mode of failure, but can say for certain exhaust valves and the oem tri-y exhaust manifolds were the victims. I'd almost bet the valve failures were tied to a manifold failure since that's something that can easily kill a valve.). This would be a great question for FRPP if they can track down a calibrator from that time to ask what happened, or a competent coyote tuner.

DISCLAIMER: I'm not a tuner, I just play an idiot on the interwebs :)
 

ArizonaBOSS

Because racecar.
Moderator
8,454
2,200
Arizona, USA
You might want to talk to your tuner, I believe with your LS3 + HP Tuners you would be able to do a "throttle blade closing" tune where the blade would actually begin to close back up at certain RPM ranges to flatten the power curve. Many racers in NASA Super Touring utilize this method to run different tunes that limit their power so they can jump around to different classes with a simple tune upload.

Basically you would have the throttle blade start to close up a certain percentage once you hit that 440 WHP target and then you would just have 440hp from that point until you tap the rev limiter.
 

blacksheep-1

TMO Addict
2,474
1,975
302 HiPo really covered the issues here, I got in with the later (after 2015) song and dance, remember it was PWC that finally drove the final nail into the Boss 302 coffin. That was 2017, when AJ beat the new Gt4 cars and we just can't have that can we? and was legislated into oblivion. it is still competitive in the SCCA classes.
Messing with the restrictor can cause all kinds of issues that you would never even think related to them, but such are modern cars, (believe me, we're going through this right now with the Astin). With regards to the LS series of engines, they are very particular with oiling issues and when first introduced on road courses were popping like popcorn, which is the reason they were allowed to run a dry sump.
 

PatientZero

TMO Race
201
135
Kansas City, Missouri
Autocross
10-20 Years
You might want to talk to your tuner, I believe with your LS3 + HP Tuners you would be able to do a "throttle blade closing" tune where the blade would actually begin to close back up at certain RPM ranges to flatten the power curve. Many racers in NASA Super Touring utilize this method to run different tunes that limit their power so they can jump around to different classes with a simple tune upload.

Basically you would have the throttle blade start to close up a certain percentage once you hit that 440 WHP target and then you would just have 440hp from that point until you tap the rev limiter.
I am my tuner, lol.

I'm using a Holley HP with cable driven throttle body, not a stock ECU. If I were using a Dominator and drive-by-wire throttle body that would be an option.
 

bob

TMO Advanced
103
67
sfo
I am my tuner, lol.

I'm using a Holley HP with cable driven throttle body, not a stock ECU. If I were using a Dominator and drive-by-wire throttle body that would be an option.
I'm trying to learn to tune. I'm starting with a good custom tune from the local hotshot mustang tuner and then might try my hand at tweeking it for 100 octane race gas from 91. Rumor is there is +20hp with a 100 octane tune. I find that a bit of a stretch but...OK. In my class there is not much competition so I only wish for more power when the class size increases and at Runoffs. Otherwise I don't need the $8 bucks a gallon the way this mustang sucks fuel.
 

PatientZero

TMO Race
201
135
Kansas City, Missouri
Autocross
10-20 Years
What software/ecu are you tuning with? Do you have access to a dyno? If you're just trying to get more power by taking advantage of the octane bump there isn't much you can do without a dyno or a controlled and repeatable way to measure acceleration over time(drag strip). You can tune your fuel map on the street or track easily with data logs but trying to tune timing without one of the previously mentioned things is just going to be dangerous guesswork.
 

bob

TMO Advanced
103
67
sfo
I have htTuners. I’m just starting to attempt to learn it. I come from the dial phone generation so....could be a failure. If I can’t learn it then I have bought an expensive way to swap tunes in and out between racing two classes. On my c5 vette racecar I just swapped retuned ecus.
 

Dave_W

Cones - not just for ice cream
73
70
Connecticut
Autocross
20+ Years
There are 2 general types of inlet restrictors, flat plate and nozzle, and both work by "choked flow." The idea is that at some ratio of inlet and outlet pressures of the restrictor, flow reaches Mach 1 and cannot increase due to energy being used by supersonic shockwaves. I think. I don't work for NASA. According to the choked flow Wiki, flat plate restrictors in real air don't really reach a hard limit to flow like the nozzles, though increased pumping and frictional losses at increasing rpm will still create reduction in total engine output. The critical difference across the restrictor is where the outlet pressure is 52.8% of the inlet pressure - that's where choked flow goes Mach 1.

These people make nozzle restrictors and have a couple interesting graphs. Notice that the HP peak not only is reduced, but it moves lower in RPM with each smaller restrictor - the engine falls on its face above the rpm that starts to create Mach 1 flow in the restrictor, and that rpm decreases as the restrictor gets smaller. If you tune for a restrictor, you may want to target increasing torque below the choked flow rpm, and adjust your shift points accordingly.

If I remember right, and I couldn't quickly verify this on the web, the issue with the PWC Bosses was the restrictor location interfered somehow with the MAF sensor getting an accurate reading, causing the A/F ratio to go lean without the ECU realizing it, or being able to compensate for it.
 

blacksheep-1

TMO Addict
2,474
1,975
What you might consider, is just paying someone to do a dyno tune, that you could access with your tuner, that would give you a "safe" baseline, and you could work from there. While "canned" tunes work well, they will never get you all the power you need, BUT... doing a dyno tune will get you closer without blowing your engine apart, then you are on your own.
 

PatientZero

TMO Race
201
135
Kansas City, Missouri
Autocross
10-20 Years
I am my tuner, I'm using a Holley HP EFI system. I had Cam Motion spec out a new cam that is a little smaller and has left lift. They said it should lower my power band at least 400rpm and kill power through the whole range compared to what I have now.
New - 222/232 @ .050 with .553/.553 lift on 112.5 LSA
Old - 232/240 @ .050 with .615/.615 lift on 110 LSA.
I think this combined with a very conservative tune should get me where I need to be. It will also be a little nicer to my valvetrain and hopefully not kill anymore lifters.
 

Fair

Go Big or Go Home
Supporting Vendor
207
318
Plano, TX
I am my tuner, I'm using a Holley HP EFI system. I had Cam Motion spec out a new cam that is a little smaller and has left lift. They said it should lower my power band at least 400rpm and kill power through the whole range compared to what I have now.

New - 222/232 @ .050 with .553/.553 lift on 112.5 LSA

Old - 232/240 @ .050 with .615/.615 lift on 110 LSA.

I think this combined with a very conservative tune should get me where I need to be. It will also be a little nicer to my valvetrain and hopefully not kill anymore lifters.
First of all, SCCA classing is a real gut punch, so kudos for taking that route - its gonna be tough. Unlike NASA, the SCCA never dynos, as far as I can tell.

cover-image.jpg


Yes that smaller duration/lift LS cam will indeed knock out some power. I'd still want the ability to "tune to the edge" in case you add or remove weight, or be able to run "uncorked" at another event with a different ruleset.

ece2dbda-11f5-4b79-919b-f22e403cbe06-jpg.jpg



I just looked at your build thread and see you are using the Holley HP EFI. I don't know what size "Warr performance" TB but since you have an LS3 head I am gonna assume LS3 intake and 90mm TB? Might have been easier to just stick a smaller dia sable throttle body on there, but do they come smaller than 90mm in the LS3/LS7 pattern?


IMG_9884-L.jpg


We built our LS powered Mustang to be flexible, to be able to run several series' rules. For that we used a Holley Dominator EFI, FAST 102 intake and 102mm DBW throttle body. This way we can use the Holley Dominator to make a "Flat tune" via closing the throttle blade on a set "max power targeted" tune.

IMG_9807-L.jpg


It sucks, but maybe converting to a Holley Terminator X-Max with DBW throttle body would make this all so much easier. The newer Terminator X-Max system is REALLY cost effective with the Holley LS harness and Holley ECM coming in around $1200. You can even add some traction control schemes in these systems. Just a thought... we have two cars with Terminator X-Max systems now and they are so simple.

Good luck with the build!
 

PatientZero

TMO Race
201
135
Kansas City, Missouri
Autocross
10-20 Years
Thanks for the tips Terry. Yes, on the 90mm throttle body. I will be running in MiDiv so the rules are slightly altered from standard SCCA Time Trials. They do require dyno runs each season, average of 3 runs I believe with STD correction and 5 smoothing etc. It's laid out in the rules. Once I get some of this figured out I may jump over to NASA but MiDiv runs at all the tracks closest to me so it makes sense.
 

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