What size restrictor plate?
 

I've got to drop somwhere between 5-15 ponies out of the new racecar (GT3) in order to make my class. (Depends on the transmission loss)

I'm thinking of going the restrictor plate route to do this. THe question is, where do I start size-wise? The intake is 3.75" in diameter.... Any guru's out there?

...a throttle stop would probably be easiest, but my thought is a restrictor plate might have the benefit of adding a little torque?

THanks!

Chris,

A restrictor plate will not add TQ, a smaller exhaust collector might help to cut some PK HP and build some TQ at lower RPMs. If it makes "too much" HP just at peak RPM turn the revv
Limits down and make it live longer. It all depends on how it is that you have too much power.

I think I'd have to turn down the revs a lot. IIRC peak power is at 7250RPM and rev-limit is at 8k...

Chris,

If that is your only option tell me how much HP you need to kill and where you need to be and I will try to help.

Chris,

The entire tuning equation changes if you go the restrictor plate route. It affects EVERYTHING.

The NASCAR guys, when faced with a restrictor plate change, basically start with a clean sheet of paper.

I would put a 6800 RPM limit in the system and see what that gets you. Is it Bosch Motorsports or Siemens?

How about a cam timing change?

Changing your power band from high RPM performance to low end torque will lower your ultimate horse power and improve low speed /cornering acceleration.
Advancing the cam timing improves low-end power and response.
For a general summary of the affects of camshaft timing, refer to the following table:

Advance
begins intake event sooner
opens intake valve sooner
builds more low-end torque
decreases piston-to-intake-valve clearance
increases piston-to-exhaust-valve clearance

Retard
delays intake event
opens intake valve later
builds more high-end power
increases piston-to-intake-valve clearance
decreases piston-to-exhaust-valve clearance

Is this the first "decrease my HP" thread on the history of the interweb?
:-)

LOL. Well the first one to do it without a mandated method.... :D

Turns out though my weight estimates were off about 50# so I won't have to do this after all. Still an interesting discussion....

50 lb off? Hopefully you've got some more wiggle room so you're not right on the edge. You know the deal with scale variance....... I scaled my car at home on the Proform economy scales and got 2580. Thought it was a reasonable as-raced wet w/driver & gear weight with nearly low fuel. I was surprised back in May when Putnam impound called me 2542.

So what did the dyno number come in at?

Dyno? Hell it's only been started twice. Dyno in 2 weeks or so...

Aw cmon man. Figured the not-knowing-for-sure syndrome would drive you nuts and you would have had that thing over to D&M on Monday morning, after firing it up on Sunday!

As an aside my 2 yr. old son Noah saw the car Sunday at Chris' new car BBQ gathering. Noah sez "Daddy, that car is TOO louuuuuud!!! I'm going to have to put my loud pipes back on because I can't hear my own car (muffler-ed) amongst all the other GTS noise.

Kevin, after the green drops Chris will only be in earshot of the rest of us for a lap anyway, so we won't hear it after that.

Until he comes up to lap you. ;)

Very true. But the 993 boys and Sir Roy are plenty loud too...... My Borla single out muffler setup proved it easily passes sound regs (all my trackside "fans" say they can't even hear me coming) and still makes decent power, so it's back to the raucous racket of the straight pipes. :D

Also very true. I finally managed to keep him from lapping me in a 40 min. race and now he goes and turns it up a notch with a GT3? I got some tricks of my own up my sleeve to keep him at bay..... :p