I'm getting ready to pop for a steel crank for a 350. I noticed they have a stock 3.48 stroke crank as well as a 3.5" crank. #1. Does the 3.5 use the same pistons as the 3.48"? I ***ume that if it does then you'd get an additional .040 of stroke, ie .020 at the bottom and .020 at the top. Deck height will need to be watched then. #2. This brings up my next question...if I go .020 deeper then I'd get more mixture into the cylinder and if it goes .020 higher I'd get more squish (compression)....about how much? If anyone has the software to figure out more specifically what the compression ratio is then here are the two combo's I'm contemplating. A.) 4.030 bore, 5.7 rod, 3.48" stroke and TRW L2441 dished pistons(advertised CR for these pistons is 8.4:1 with 76cc heads), 62cc chamber 461 heads and with the additinal .020 stroke.... B.) 4.030 bore, 5.7 rod, 3.50" stroke and TRW L2441 dished pistons(advertised CR for these pistons is 8.4:1 with 76cc heads), 62cc chamber 461 heads Once I get all this info that will help me pick my camshaft....So far looks like a Comp Cams Nitrous HP cam. This will have a 6-71 huffer and a mild 5-7 lbs boost(underdriven) with an occasional pulley swap for some drag racing. I understand some of this compression could be bled off with the cam and thick head gaskets. I'd rather have too much and detune with cam and gaskets instead of adding more and more boost to compensate for lack of compression.
Bump...I'm hoping one of the gearheads here can help. Maybe I should say that from the outside this will look like it was built in the '60's. Cast Blower, Camel hump heads, zoomies. No high tech stuff on the outside....just a little on the inside!
Good Question - I look forward to hearing the answer. Only thing I can guess is that it raises the piston to zero deck. What you described is what I am building - almost the same motor but with a 283 and 4-71. I got a solid lifter cam from Clay Smith and am going to build some 461 heads I have for it with the springs that cam with the cam,etc. I was also planning to run low boost. It ought to be pretty sick.
Watch the Intake valve diameter and the small bore 283. With a blower you do not have to worry much about the valve being shrouded by the cylinder wall but clearances are real tight if your 461's use a 2.02 intake. Much safer to run 1.94's on a 283. Blowers help overcome alot of Valve/ports issues but clearances.....they don't help clearances!!! By the way...sharp ride....who's exhaust? Looks killer.
Here's one I've used: http://www.turbofast.com.au/Tfcomp.html and did a search - here's one with an explanation of everything... http://www.rbracing-rsr.com/compstaticcalc.html The 3.50" stroke will get the pistons to 'zero deck' on a good undecked block as the pistons are typically .020 in the hole. Just watch that compression with a blower - I'd keep it around 8-8.5:1 max and make up for it in boost
A 3.48" to a 3.50" crank will only rase the piston .010" not .020" [3.48" dia. or 1.74" radis, so 3.50" = 1.75" radis] just my $0.02. j.j.
Most SBC pistons come in at 20 thou in the hole so the 3.5" stoke crank will zero deck the pistons in most cases. The L2441F pistons you are using have 21.3cc dishes and you will end up with about 7.5:1 compression on a 76cc head with a standard 0.042" thick gasket. A thin 0.015" thick gasket on a true 76cc head on a 30 overbored 350 comes out to 7.83:1. A 62 cc head will bump itup to about 8.4:1 in a 30 over engine with a standard felpro gasket. A 3.5" stroke engine will bumpit up to about 8.8:1. For a 6-71, I would clean up the chambers on those heads and relieve them around the exhaust valve. Try to get a few more cc's into them and the compression ratio to 8:1 or less. Then it will be much happier on pump gas. Its much better to add boost than run thick gaskets and detune the motor. Build the motor right the first time. Choose a cam with a wide LSA and lots of extra exhaust duration. Go smaller than you would on an unboosted vehicle.
Thanks - My heads still have the small stock valves. Sounds like you want the shorter crank for the lower compresion. Good luck on the engine build. Jim Simbley on the hamb here made those headers. I dig em.
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