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Discussion Starter · #1 ·
Got a 4-bolt main 350 bored .30 over in my 78 1/2 ton Chevy. Getting the heads tweaked, ported and matched with my performer intake. Top end is built for horsepower and I could use more low end torque. I want to stroke it but dont know which way to go. Thought about a 400 crank but really dont want to spend more on machine work. Would a 327 crank hit faster and give me more torque? Also what cam would you suggest for my application? What other mod's should i consider. I race in the mud w 36" swampers, 10-bolt rear w/ detroit locker and dana 44 front. 3.07 (will not change for anything) gears front and back with 4-speed tranny and 205 t-case. All advice considered and appreciated.

 
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Discussion Starter · #2 ·
A 327 is a shorter stroke, which would give less low end torque.
Your gears is whats killing your low end. Most 205s used in GMs are the 2-1 low range type, if you could find one, or already have one with the 2.5-1 low range that would help some. Otherwise with that size tires with those gears you may think about a 540 cid or even 570 cid.
I assume you want to keep those gears for mileage reasons. I think I would save the money of building a stroker and use it to set the truck up different. I would go to a overdrive with better gears. Along with a 2.5 transfer case you could keep the rpms down on the highway and still have plenty of gear in low range for racing. Autos work much better in mud drags too.
The gears multiply the torque, 200 pounds of engine torque times 2-1 gear equalls 400 pounds of torque at the wheel, same deal with 3-1 gear = 600.
You do your own math with your own figuires and see what you think.
Engine torque X trans gear X transfer gear X diff gear = torque to the tire.
And with an auto you get to add in 2-1 for the converter until it goes to 1-1.

 
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Discussion Starter · #3 ·
RolngThun is dead on. You'd actually be DE-stroking your 350 with a 327 crank. In stock form, the only difference between the 302, 327 & 350 (yes, Chevy did make a 302 for a couple of years) is the stroke. All 3 have a 4" bore. The 302 has a 3" stroke (same as 283), the 327 has a 3.25" stroke (307 has 3.25" stroke & same bore as 283), and the 350 has a 3.48" stroke (as does a 305). So, if you put a 327 crank in a 350, what you end up with IS a 327. Don't bother machining a 400 crank either. If you want to stroke it, there are several sources currently that build "383" cranks that are specifically made for stroked 350 applications. The standard 400 crank has a 3.75" stroke. You can also get a forged 3.80" crank specifically made for the new "Vortec 383 crate engine" straight from Chevrolet. The part # is 1248936. 3.07's actually don't make bad mud BOG gears (good tire speed), but that 4-speed has got to go. Even in relatively deep pits, that's a liability. And if you do mud DRAGS, you probably need to do some re-gearing as well as switching to an automatic. You might want to consider a 208 T-case. They're not as durable as a 205 (then again, what is?), but they're not bad. The low range is 2.61 & would make 3.07's react in the same manner as 4.08:1 gears with a 205 & it's 1.96:1 low range. But, back to that engine. If it were me, I'd forget 350's or 383's altogether. I'd go for a 400 small-block or a RAT if it was me (well if it was me, it'd be the 400). You need to get as many cubes as possible under that hood with that kind of gearing. Just my $.02.

TEX

/wwwthreads_images/icons/wink.gif Got Mud?
G.U.M.B.O. Mud Racing
 
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Discussion Starter · #4 ·
Listen to these guys. They are not steering you wrong. You're heading in the right direction with your top end, but you can't expect to win races while hanging on to your 3.07 gears - unless you have MAJOR torque under the hood, which is way beyond a streetable engine. If you are keeping the 3.07's for MPG, they could be costing you MPG, because the engine must be lugging at low RPM trying to turn those 36's. My recommendations, take 'em or leave 'em, put your top end on a 400 short block, TH350 auto, and 3.73 or 4.11 gears depending on the amount of torque you end up with. If the mud is shallow where you race, go to 34 x 9.5 swampers. Yeah, they're skinny and ugly, but they work. This would make your truck competitive at most places I race. Give us the rules you have to meet and we could get more specific.

/wwwthreads_images/icons/cool.gif
'84 K20 driver
'79 K10 mud racer
'48 CJ-2A trail Jeep
 
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Discussion Starter · #5 ·
I'll vouch for the 34's. Used to have 38X12.50's (only 1/2" taller than 36's) & now run Q78's (1/2" shorter than 36's, but considerably narrower). Some of my competition ran 34X9.50's & those suckers just plain work - even in deeper mud. I would have gone to that size but didn't want to lose so much tire speed (my gearing was pretty decent on the 38's & is REAL sweet with the Q's). We mainly run bog-style pits & 34's would have held redline in 2nd low, but wouldn't have let me shift to "Drive", so I'm keeping the Q's at redline in 2nd low (at 35" exactly, they're 1.5" taller than the 34's, which are about 33.5") for more tire speed.

TEX

/wwwthreads_images/icons/wink.gif Got Mud?
G.U.M.B.O. Mud Racing
 
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