chuntington101

Restrictor plates are widely used in racing to limit top end power. But how do they come up with these sizes?? Is there a way of calculating the exact size of a restrictor plate needed to limit an engine to xyz bhp?? Anyone idea of what the calculation is??

Thanks Chris.

Old SStroker

A restrictor limits the amount of air than can flow thru it. Theoretically a given amount of air supports a given amount of peak power. For a round restrictor in the inlet tract as is used in many applications the calculation is fairly straightforward, and can be found in a good engine simulation program. For the four-hole spacer plate between the carb and manifold inlet like NASCAR it is more complex.

The problem with trying to limit peak power to a given number with restrictors is that engine builders figure out how to more effectively use the limited amount of air they are permitted to injest.

chuntington101

thanks Old SStroker.

i was thinking about superchagerd motors and ways to make centrifugal blowers give a more rounded power band.

have you any ideas of the calculations needed to figure out the size of a single hole to the BHP you 'COULD' make??

thanks Chris.

Old SStroker

Do you mean to restrict the supercharged engine to chop of the top of the power curve?

Gee, I hope not!

Please explain.

3.4camaro

iTrader: (1)

Yeah yall are both thinking of the same thing, cept huntington thinks its a good thing, and SS thinks its a bad thing.

Superchargers do tend to have a rounder power band compared to a turbo.

For what you're thinking about, I wouldn't do it. You don't want to restrict the air intake, because you will lose power at every rpm. Not a good idea.

gun5l1ng3r

In the newest issue of GMHTP, they describe the LS7R which runs with two 31.8MM restrictors and makes 640 LBS-FT of torque and 'only' 590 HP. 31.8MM is a little bit over 1 inch on each bank of the intake, which is tiny for a 7.0L motor!

Katech really knows what they are doing to be able to wring that much torque and HP from such little air...

Old SStroker

Restricting the air limits peak power, which is the whole idea. You can still make low-midrange torque with that limited amount of air as the BMEP at peak torque over 15 Bar shows. Katech/GM Racing described the engine as having a torque curve much like a diesel or very flat. That makes it easy to drive for long races and cuts down on the number of gear changes.

One of the nice things you can do with a big, but restricted engine is get to peak hp early and then hold near peak hp for many hundreds of rpm. The area under the curve is very good.

They don't spin that engine very high at all. That's really good for durability as well as not requiring super-strong parts to cope with high rpm inertia.

FWIW, 31.8 mm is just about 1.25 inches or about 157% of the area of a 1 inch hole. To put it in perspective, those two 31.8 mm holes are just about equivalent to one 48 mm throttle body wide open.

ALLBOTTLE

iTrader: (13)

Stroker,

the reason to restrict a centrifical is for more tq on stock motors. You pulley the blower way dow so it comes on boost at very low rpms and use the restrictor to keep the boost at higher rpm manageable. Rather than having a linear boost curve they hit peak boost by 3k and hold it to readline giving them more average power.

chuntington101,

Call A&A corvette or ECS they do a lot of work with restrictors and can give you some suggestions.

gun5l1ng3r

My bad on the millimeter conversion. It was still early in the morning here on the West Coast (9 AM is early for me) and 25.4 mm is about 31.8 mm to me when I haven't had my morning caffeine.

And I realize how huge of a difference there is between diameter and area for the inlet, so my little mistake does make a huge difference. When you hold a your finger apart 1.25 in. you realize still how much effort goes into sucking every last HP out of straw-like intake holes...

chuntington101

thanks everyone!

my idea really was all thearectical. but i saw a guy running a F2 on a vette and it got me thinking about spinning the blower a little fast and running a restrictor plate to cap the BHP and psi, and stop you blowing the engine sky high thanks to 30+psi of boost! lol

after seeing pics of the stuff that Katech and other do i understand just what goes into them. they are fantastic pieces of kit! i always remember the TVR Speed 12 racers (dont think they went to the US so you guys might not have seen them). it was back when there where soo many more GT cars (not prototypes though). the TVR ran a 8ltr V12, basically two of TVRs 4ltr inline six's mounted together, and the unrestriced road car (there was only one!!) made around 900bhp! restricted around 650.

i will try and do some more looking see what i can come up with.

thanks again guys.

Chris.