358 DIRT Modified Motor

[900HP]

OK CNC
is this a weight limit class or does everyone have to find parts of unobtanium?
If he has a minimum weight he could do raised block, if not he can't- how much weight difference is there< would be hard to find that much elsewhere
I'd still think of the raised cam tunnel- btw do they allow gear drive?
can you get a headgasket for a large bore block and lay it over one of those spec heads?
can you match the bores/ new chambers to the heads?
would such a move allow more flow?
cheers

SHP pro-series is 174 lbs and not available in a raised cam. Dart little M is available raised cam but weighs 230 lbs. You can do a block lightening program on the little M to get it down to 165 or so but $$$$$.

Dirt cars are VERY front-weight sensitive, anything you can do to lighten the engine will pay more dividends than just horsepower. I'm talking about handeling and traction here which will have more effect on winning races than a few extra horsepower.

Even if you can't do much with the chambers, the large bore will pick up head flow with no other changes to the head. That's why it's important to know what size fixture a cylinder head was flowed on. Big difference from a 4.030 to a 4.125 to a 4.185

[CNC BLOCKS]

OK CNC
is this a weight limit class or does everyone have to find parts of unobtanium?
If he has a minimum weight he could do raised block, if not he can't- how much weight difference is there< would be hard to find that much elsewhere
I'd still think of the raised cam tunnel- btw do they allow gear drive?
can you get a headgasket for a large bore block and lay it over one of those spec heads?
can you match the bores/ new chambers to the heads?
would such a move allow more flow?
cheers

Circle track racers will not put that much weight on the front of there cars. A gear drive on a circle track engine would not e my first choice, Why add harmonics to the valve train.

[wyrmrider]

Brodix only shows flow at one non designated bore size
Does anyone have any experience with these spec heads?
agree about the bigger the bore the bigger the flow
If I could use a 4 1/4 bore block I'd gladly forget about the raised cam tunnel
OP may be stuck with the 4 1/8 basic bore block which would be better than a 4" bore block IMHO
there may be a track where 3 7/8 x 3.75 basic sizes would work but I'd much rather go the other way

[CNC BLOCKS]

Brodix only shows flow at one non designated bore size
Does anyone have any experience with these spec heads?
agree about the bigger the bore the bigger the flow
If I could use a 4 1/4 bore block I'd gladly forget about the raised cam tunnel
OP may be stuck with the 4 1/8 basic bore block which would be better than a 4" bore block IMHO
there may be a track where 3 7/8 x 3.75 basic sizes would work but I'd much rather go the other way

Curious why so feel the need for a raised cam tunnel block?

[Robbie DeVane]

What is the rule on the carburetor or is there one ? That is the first thing that I would be looking at you can pick up a lot of bottom an mid range power through different size venture's. I would like to to know why you are wanting to go with alcohol an not gas ? there is a lot of burn off an it change's the rear percentage a lot. That is why almost all of the lucas late models went to gas an they are getting just as much power with out the burn off.Not to mention all of the maintenance that you have to do.
As far as the engine stuff, I would like to see the shortest stroke that you can get with the biggest bore that you can get and turn the engine around 8500-8800 rpm's for that short of a track.




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[JDR Performance]

I'd take the other approach after reading your engine rules and the track conditions. If it's a short, hooked up track with a limited motor I'd keep it on methanol. If you go to gas, you'll probably get plastered on restarts and corner exit. You need the torque.

[Cogburn]

I'd say that if you are unwilling to turn 8500 rpm don't build a short stroke motor.

IMHO, a 3.5 stroke engine will beat a 3.25 stroke if rpm is limited to 7500 and cubic inches are the same.I have seen the 3.5's pull a couple of car lengths off the corner and pass a few cars before the 3.25's got going. If slow or many restarts are normal I would definitely go with a longer stroke up to 3 9/16.