The Spark

I need to run a restrictor plate on my LS1 engine to bring RWHP down for track events. I'm making 430 RWHP now which is fun for HPDE but need to bring that down to about 390 RWHP for racing.

Anyone know who makes them?
I'm not sure what size I will need so I figure we'd do some dyno tuning to get where we need to be with different size plates. So price is a concern.

Last year we choked off the air filter to bring HP down. Bubba way of doing it but it worked . I have a Blackwing filter and we covered up well over 50% of the filter to get the HP down close to where it needed to be. We tried tuning it first to take out HP but still ended up blocking off the filter. One of the guys at the shop suggested running a little tiny filter. Reminded me of the little air filters we used to put on top of carbs back in my high school days.

I can probably do that again but if I could find a restrictor plate that would be preferable.

zeevette

I'm completely ignorant of racing rules, but what kind of racing specifically targets HP? As far as using some kind of restrictor plate, on a MAF tuned engine, where would you place the restriction?

Dope

Bracket racing maybe?

Dope

The Spark

I'm running time trials with NASA (road race). I have to stay above a weight-to-horsepower ratio to stay in class.

Not to get too much into the rules - I have to be above 8.7 pounds per horsepower. At full power, I'd have to be over 3,700 pounds to stay in class. If I can get HP down to 390 or less, I can get weight down to 3,300.

HP is nice, but you want to minimize the amount of weight you have to slow down, turn, and then accelerate. I've heard it described as run 100 yards as fast as you can - changing directions occassionally like a football player running a kickoff back. Then do the same wearing a backpack with 50 pounds in it. Much easier to do it with less weight.

Also a lighter car is easier on the brake pads.

My engineer friend says you want to put the restrictor plate at the throttle body or the air intake. Choke off the air inlet or the amount of air the engine can suck through the MAF sensor. He says you don't want to put it right at the MAF sensor.

Z06supercharged

Have a tuner just take some timing out to bring you down 50 hp.

Swayse

I see you're from Midland, are there any local tracks, or do you travel?

rebelheart

Is this factory rated HP,or do they actually make you dyno your engine? Dyno numbers can be manipulated,so I really dont see that happening.

The Spark

We brought it down as much as we could by tuning. We need to clean up the tune file but long story short - we did try that route first.

I did heads/cam/intake/throttle body on my LS1 to do HPDE before I got into time trials.

The Spark

Factory HP is 350 at the crank. They use rear wheel horsepower (RWHP). You need to turn in a dyno sheet and weight slip at the start of the season but they can do random checks on you. Sometimes they will run you on a dyno at the track to verify your numbers. At most every event they will randomly pull people over as you come off the track and run you across the scales to check your weight to what you say your car weighed.

You want your weight to be as low as possible on your tech sheet to make sure you are in class and stay above that at the track so you won't be out of class. I'm pretty much at the limit on weight to horsepower for my class (8.7 pounds / horsepower). If I come in lighter or dyno higher, that will put me in the next faster class. They can be down to 5.X pounds / horsepower. So I will be way slow in that class. Plus they have some really good drivers in that class.

I've checked my car on 3 dynos and they all come out about 430 RWHP. Using rule of thumb, I estimate my engine is about 500 HP at the flywheel. Not too bad for a LS1.

Rob's 73

It can be tough to detune. I could only get my friends ls6 with headers down about 25 hp. I think we were only commanding 14 degrees of timing. We tried to keep the tq up the best we could.

What intake are your running? If you are running a FAST maybe you could swap for a LS1 on race days. If you do the restrictor plate I would put it between the throttle body and intake. I would want it somewhere where you could clamp it down with nuts and bolts. You could make it out of sheet metal. Just make sure it doesn't interfere with the throttle body blade.

TT Z06

+1 on taking out timing. If did all you can, there is always more.

The Spark

I am running a FAST 92mm intake with LS2 throttle body.

We tried backing out timing and also adjusting air fuel ratio to take out HP but it was not enough.

My engineer/tuner friend said best place would be restrictor between intake and throttle body. I guess I can take the TB off and get someone to make some different plates for me. I was hoping there was a source that made them at a reasonable price.

But you gotta do what you gotta do. I think changing out plates would be easier than intakes.

TT Z06

putt a bolt behind the gas pedal limiting movement. That's what we used to do to our bracket race car.

J.R.

Tune engine to maximum efficiency.

Take a piece of plastic that is 3.9 inches in diameter and 1 1/2 inches in width. Bore out the center to approx. 45mm.

This piece should be placed directly against throttle body.

Increase center dia. until you reach desired HP. Then chamfer entry which will increase torque and not change HP.

For an approx. 40 HP reduction you should end up with an approx. 54 mm center diameter.

This system was used with ASA engines. You may even be able to contact Lingenfelter and see if they have any laying around. Although the ASA ones were made out of aluminum.

rebelheart

Would it not be easier to simply add some weight low on the chassis?

RX-Ben

Up, any news? Why not just limit how much the TB opens via the tune?

AU N EGL

Louis at LG motorsports.

They had to make one for Lou's World Challenge Cameo

40mm hole in a plate. So much for 92mm tbs

AU N EGL

NASA

8.7:1 hp to wt for the ST2 and STR2 class ~ 370-5 rwhp on 3250 lbs

5.1:1 hp to wt for the ST1 and STR1 class

restrictor or TB plate must go in front of the tb


ballast is limited to 200 lbs, and with all the cars as close to 3250 with driver, that is right were you want to be.

Now if Fast, NickWilliams or TPIS would go back to making 78mm tbs

AU N EGL

a Bit OT, these C5s Ls6s with 375 rwhp, can be so well balanced, that they will just about out lap or get lower lap times than stock C6Z06s

The Spark

I put a twin air filter like this one



I could block off one filter with a rubber pipe cap. On the other end, I found that a metal electrical box cover fit inside just right so it would not move once the filter was installed on the tube. We opened up the plate to fashion our own restrictor plate. It cost less than $3 at the hardware store. I could remove the restrictor and install the other filter to get full airflow again. That way I wouldn't have to have it retuned when going from racing to track days.