I'm working on a motor for a circle track car. Soon they are going to make us put on a restrictor plate, 4 @ 1" holes for 4 barrel, 2 @1.5" holes for 2 barrel carb. What crank and cam would work best for this in a 350 block? The heads I am planning on using are from a 305 with 60 cc combustion chambers. I also have some 350 heads but they have something like 72 cc combustion chambers. Any suggestions would be appreciated.

Have no idea but do remember reading somewhere sometime that Smokey Y. once said, "since you can't get much in the cylinder, you gotta squeeze h-ll outta what you get!".

I think what he was saying was that you will need a lot of cam and compression to make good power b/c your engine won't be able to suck like it should, therefore won't have as much to compress so you can up the compression to help compensate.. pdq67

I would get an "old" set of camel hump heads which should be around 64 cc's. If you want more compression have the heads angle milled. These heads flow better and make more power. Most tracks say "no strokers" so I'd stay with the 350. I once read that Smokey Yunick said a longer stroke will suck in more air in a restricted engine. So a 350 is a stroked 302 or 327, but not considered "a stroker".

Can you put open spacers between the carburetor and the restrictor plate? The actual flow of the carb/plate combination will dominate the design. I do this type of design, and as the restriction becomes more severe, the analysis becomes increasingly difficult and time consuming (like for 350CFM 2bbl which have only 1 3/16" venturii). The two 1 1/2" holes won't prove very restrictive to a ported stock head in of themselves. A 2bbl carburetor might though, except the Dominator. What kind of intake can you run?

In general, you would select the best carb/plate flow with flow bench measurements. Pick a head with the best flowing intake port (flow them, too). Don't worry about selecting a head with a good exhaust port because the flow bias built into the head will become increasing incorrect as the intake becomes more and more restrictive (like 350CFM 2bbl or high altitude in the extreme case). Maximize compression ratio with head milling and displacement, but not at the expense of intake port flow.

The cam design is rather odd since the exhaust lobe reflects the actual horsepower, and the intake lobe may or may not depending on the restriction. Header design is also somewhat different than for unrestricted engines. Intake valve timing and gear have to be selected based on everything else to produce the fastest torque curve for your particular track. If you get the right setup, you should blow the competition into the weeds immediately after the rule change. Good luck. graemlins/thumbsup.gif

I'm running in a poor boy's class. The motors are supposed to be all stock but you can tell by the sound of the cars many aren't. I pulled the motor out of a recked pickup. You can tell it is a fresh overhauled 350 block with 60 cc 305 heads. We fired the motor up tonight and it sounded good. We were considering changing the cam but might go ahead and try it out the way it is now. We are allowed to use spacers under the carb. We have two carbs we could use, an Edelbrock OE replace Q-jet and a stock Q-jet. How much of a spacer would we want to use?

Those restrictor plates are generous, and will allow more than 500HP. The 2bbl plate has more flow area than the 4bbl plate, but even the 500cfm Holley has a venturi area smaller than the 2 holes. I guess you selected the 4bbl.

You could start with a 1" open spacer under the carburetor, then tune it to see if it works correctly. If you are using a dual plane intake, you should add a 1" spacer under the plate, too, so that suction pulses can use the pressure on the other side of the manifold. This will minimize the effect of the restrictor plate by allowing more uniform flow through the plate. Upper midrange torque will increase from better ram-tune.

With the stock bottom end, you should cam it, spring it and gear it to hit about 6500RPM at the end of the straightaways on a typical 3/8mile oval. A 350Vortec with a compression increase can make well over 400HP on most of the track with this type of setup.

I have some experience with restrictor plate racing on my Brother and friends dirt cars. We found on a 355 c.i.d. engine in the one car ran 410 hp. with a 2" riser and no plate, with the same riser and adding the plate took this engine down to 380 hp. (30 hp loss). The other engine was a 406 c.i.d. that pulled 470 hp with the same 2" riser and no plate, it then went down to 450 hp. (20 hp loss). With that said we noticed the 406 with larger combustion chambers ( bore, stroke) and the larger runners of the world product heads it was able to over come the loss of air better (same cam overlap and lift between the 355 and 406) But the 406 ran at 7000
rpm and the 355 ran at 6200 rpm and that also made a difference between them. It was able to pull more air thru it than the smaller 355 could. We then designed a riser block that tapered down from the Barry Grant throttle plate to the restrictor plate. With this plate the 355 gained 25 hp back and actually produced more torque than it did with just a open plenum. For more info on this "Plate adapter" e-mail me at jimm@irwinenterprises.com and I can give you a picture of what I built.

Thanks for the help!! I should be able to do a little experimenting with the advice you gave. Sure would be nice to have a dyno to test the changes on....
The 4 barrel carbs are just what I have on hand now. I'll have to see how it runs with one of them. Will also try to find out what kind of carb the guy up front is using...

If you just run a open spacer with the plate under it you will lose alot of power. You need to taper the carb bore down to the plate size with a custom made adapter and you will lose very little. Like I had said before with the 355 we made 418hp open, 380hp with the just the plate and 410hp with the plate and the adapter

The tapered 4-hole spacer between the carb and plate sounds like a great idea. It would improve flow through the plate, and would maintain sharper pulsing to the carb so you wouldn't have to jet up like with the open spacer. You should switch to a square bore carb to use the tapered spacer. The spread bore will require some sort of tapered/open hybrid spacer.

I have a jpg. of the solid part I designed to
cut the spacer but I can't figure out how to post
it off my desktop.