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Author Topic:   Carb and motor help for IMCA Hobby stock
Dirt Newbie

Total posts: 1
posted February 08, 2002 09:16 PM
Does any one have some helpful hints for the IMCA hobby stocks. I am running an olds cutlass with a 355 chevy. What should you use for intake, exhaust, any carb secrets?

Race your best!! Forget the B.S.!

Earl Parker II
Dirt Full Roller

Total posts: 39
posted February 11, 2002 11:29 PM
Can you be a little more specific- it's possible to write a book in all three areas. Anything you can tell us about your engine, track, rules and any problems you're currently having will help quite a bit.

Earl Parker II

Dirt Forum Racer

Total posts: 79
posted February 12, 2002 04:44 AM
Without knowing what your restrictions are I can only give you general rules of thumb.

Consider your motor as a breathing animal. If you put on a carb and intake with a really high CFM, you -must- run headders and pipes with the largest tubes possible. The exhaust -must- be matched to the intake, cam and carb to be able to take advantage of the -potential- power available. Most of us run on short tracks... 3/8mi or less... and this high flow setup would not be good (unless your a perfect driver). It will give you too much power and most of it would be wasted on wheel-spin. Also remember that the more cool air that you can get into the motor, the better your power. You will need to make sure that the fuel line stays away from the block... cool is the rule.

I race on a 1/4mi track with fairly good banking. Our rules restrict me to a rochester 2bbl, factory cast iron intake, factory cam and 2-1/2" exhaust. I may use headders if I choose. I am using the maximum that the rules allow, but will start with the factory exhaust logs and some tractor mufflers from the farm supply. These mufflers are large, high flow glass packs with a large washer-like restrictor which does not add much back-pressure. They flow very much like racing mufflers. I plan to try headders after a few races to see what they will help or harm.

Remember that the better your air flow is comming in, the more your exhaust must flow. More restriction means more back pressure and more power on take-off and lower rpm. Less restriction means less back-pressure and more power on higher rpm. It's a trade-off and you should find out what the fastest people at your track are running.

You don't necessarily need to spend a lot on "faster" parts. These short tracks require a fast chassis setup mostly. The fast motor will lose every time if the chassis is not set up properly.

The best book that I've ever read on motors is HP Books "How to Hot Rod Your Big Block Chevy". They've got one for small block chevy's too. It is about $25 and money well spent for any performance minded person. They even give you a lot of factory part numbers so you can keep it stock.

Hope this helps... Earl is right... I could write a book. I've tried to keep it simple!

An added note: If you put on large exhaust with no mufflers and notice a popping on decelleration, you will need to add more back pressure or richen your jetting. This will burn your valves or pistons if you don't. A friend of mine bought a Harley that was too quiet for his liking, bolted on no muffler headders, got the same effect as I describe and burnt his valves. What happens is the exhaust flows too much for the amount of fuel comming in. Richer jetting is the prefered way to solve this so that you are not restricting horse power and torque. Remember to always balance the flow.

[This message has been edited by Machinah (edited February 12, 2002).]

[This message has been edited by Machinah (edited February 12, 2002).]

Dirt Forum Champ
Total posts: 1565
posted February 12, 2002 12:48 PM UIN: 54865418
racer you will find there are very few guys on here that run imca i don't run imca but we run 95%of the same rules so that imca cars can run with us on specials and our cars can still run imca with little or no changes anyway to your question intake wise find one that is a non egr myself i run and old 400 intake carb wise find one off a school bus or old straight truck or 70's pontiac 400 have good ones on them exaust go with a 73-78 truck manifolds thats what we run and so does most everybody around here

Dirt Maniac

Total posts: 119
posted March 07, 2002 01:10 PM
Originally posted by 00racer:
Does any one have some helpful hints for the IMCA hobby stocks. I am running an olds cutlass with a 355 chevy. What should you use for intake, exhaust, any carb secrets?

I have a 408 and we use to run headers on it. Well I jumped down to street stock and I run stock exaust. The problem with running stock exaust is that it cuts the horsepower back, back pressure, and it don't allow the engine to breath. I Went to running 512 horsepower to 480 with stock exaust. I say go with the headers.

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