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Author Topic:   420-430 cu motor
rpm20
Dirt Freak

Total posts: 338
posted December 11, 2004 05:40 PM  
i am planning on building a good motor for open shows and want everyones opinion on this as far as power,reliability and usefullness on the track.

i had 2 schools of thought and they are this

1. build with a 350 block .060 overbore, 3.875 crank,forged rods,forged pistons and sportsman heads with 2.05 valves
full roller 403 cubic inch stroker

or
2. buy a world 4.125 block with std bore and the same parts or a 3.875 or 4.00 stroke for 420-430 cubic inches .
stroked rolled and sportsman big valve heads too.

how useful, and would the better torque work well on our central wisconsin big 1/3 mile low bank clay oval on tacky and dry??

[This message has been edited by rpm20 (edited December 11, 2004).]

[This message has been edited by rpm20 (edited December 11, 2004).]

zeroracing
Dirt Forum Champ
Total posts: 1876
posted December 11, 2004 09:31 PM  
the .060 over will be a bad mistake and not last long. i know some guys claim it will but i would not waste my money on a gamble.

the aftermarket block is the way to go 100% they are alot better than a stock chevy one.

but my take i would build 4.125 bore with a 3.250 crank and long rod. then have the heads ported and roller cam and turn it on.
easy to hook up on slick and ton of power on the top end.
you would be suprised how many big shows are won with little quick reving motors.

rocket36
Dirt Freak

Total posts: 209
posted December 15, 2004 01:42 AM  
we have been running a 415 cube engine for a while now (built from a standard gm 400 block), and i'm still not convinced if its the best way to go because of the amount of torque it produces. i think if i were to do it again i would go for a large bore (4.125 or similar) and end with around the 380 cube mark. but definitely, if given the oportunity, use an aftermarket block.

mod_racer98g
Dirt Roller

Total posts: 25
posted December 28, 2004 02:37 PM  
I'd buid a 283 and run the **** out of it !! oh but i don't have ur money ron !!! just load up and go ump racing if u want to spend it lol

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted December 28, 2004 03:37 PM  
If the aftermarket block is an option then I would go that way no matter what. Then build around that. The larger bore will help it breathe especially with the 2.05 valves.

In my expoerience unless you are on a stop and go track that stays tacky all the time or at least a track that stays heavy all the time and can use all the torque i think the bigger bore smaller stroke like 377 variety are easier to hook up, easier on parts and you can run more gear if you need to make up the torque and turn it more rpms. If I were going to build something big i prob wouldnt go more than 3.75 stroke but thats just me.

sdracer12
Dirt Maniac

Total posts: 180
posted January 04, 2005 09:09 PM  
If you are looking for strength, reliabilty, and USEABLE POWER, I wouldn't go for the biggest 420-430 motor. As someone stated above, you'd be surprised how many shows are won with a little smaller motor which could be lots easier to hook up.

Our open motor is a 400 bore, 5/8"(3.625) stroke, long rod, 385 cu. Sportman Heads, 2.08 / 1.6 valve, full roller motor, with Brodix Intake, and a Braswell carb.

This combination makes broad "seat-of-the-pants" HP and torque, pulls great on the top end, and is prob. a little more forgiving than the 420-430 monsters.

If at all possible, the aftermarket blocks are much more reliable. JMO


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