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Chevy 302 scratch build help

1360 Views 12 Replies 9 Participants Last post by  lookatme
hi guys. im trying to put together a 302 from scratch. im going to be using a 350 sbc block 87 or 88 1 piece rear seal(4 inch bore), and a 1994 265 crank(3 inch stroke) also a 1 piece rear main seal. they both use the 2.45 main bearings, and the 2.1 rod bearings. i dont have the original rods for the 265, which happen to be 5.94 inches center to center, so im looking at trying to pick up some 6 inch rods.

what i dont know is how much of a clearance i need from the deck surface of the block to the top of the piston. about how much is the minimum that i should try to shoot for? i am asking so that i can try to get an accurate figure for what the compression height that the pistons needs to be.

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Well, since no one has responded, I will give my take on the subject.
A 302 has to turn some serious RPM's to make any, real power, and would benefit greatly from a higher than normal (for todays engines) compression ratio. With that said, I believe you should shoot for zero deck height.
I wonder if the late model 265 crank is going to be able to hold up to the the RPM needed for decent power. You might want to look into an after market crank.
With steel rods, shoot for a piston crown to head clearance of 0.035" to 0.040". Juggle deck height and gasket thickness to get there. For instance, with a zero deck you might use a 0.039" or 0.040" compressed gasket. With deck height of 0.024", you might use a 0.016" shim gasket. With a deck height of 0.012" you might use a 0.028" compressed gasket and so forth.
You'll also need the biggest valves you can get in a head with an intake port size of about 160 cc. Unless you plan to turn it above 7000 and make little power below 4500 then you need more.

So you should look at a small chambered head with reverse dome pistons to make the compression adjustment.
thanks for the responses guys.

as for the crank withstanding the rpms...(cast crank)......... it should be good to about 8500 PROVIDED the balancing is close, and i can keep the weight down. as for the powerband, im trying for around 4000+ to be where it shows up. im planning on using some 041 heads, with large valves. not the greatest castings, but i have them and want to get some use out of them.

any recomendations for rings in a higher rpm engine? i usually dont run high rpms or compression, and id like to keep things together for a little bit and i really appreciate the input

thanks chris
Just curious...whats kind of race car is this high winder going in? And a basically stock GM production CAST crank, even prepped ........ 8500 ??? I,m not knocking your combo but I would definately look for a GOOD forged crank. Thats some serious rpm, best bet would be to check out a few complete rotating assemblies from Lunati etc.
a buddy of mine that use to build engines for a living said cast cranks are lighter than the forged cranks & could get them to turn up quicker. i've seen him turn his 8,500 rpm with a cast 350 crank, 6" olds rods, & forged pistons.

i had a 327 that i turned 7,500 all the time. it had a cast 307 crank in it.

don't get me wrong, i would rather have a forged crank, but a lot of times you just have to run what you can afford.
OK then, you need a 180+ cc head with 2.06 valves fully dressed out.

Remember at 6000 rpm there is only about 10 milliseconds to fill the cylinder, and at 8000 about 7 milliseconds. Small ports and small valves won't make it up high.

112* LSA with 1.6 rockers and 250* duration at .050 with 13.5 static compression ought to do it.

Absolutely full circle rings. period.
rod length + stroke/2 - deck height = compression height

6.0" + 1.5" - 9.0" = 1.5"

5.85" + 1.5" - 9.0" = 1.65"

Is this why they sell 5.85" rods? Using 327 pistons to make a 301/302?
thanks guys for the help. i did some more research on parts availability, and from the looks of things im going to go the 5.85 or stock 265 5.94 rods if i can find some( i would be able to use 350 pistons) . the "race car" that its going in is going to be an old beater truck...... with an m20 and a 4.20 posi.

has anyone used "powerhouse" ? they have an ad in Chevy high performance with some CHEAP prices.

thanks chris
Hey I Am New To This Forum And I Am Also Building A 302 And I Was Just Wondering How You 302 Was Coming Along This Is My Engine Combo.......327 Small Journal Block Drilled To A 4 Bolt Main, Steel 282 Crank, Ater Market 5.7 H Beam Rods, 11 To 1 Older Trw Forged Pistons,world Product Heads W/208cc Intake Runner 2.08 Valve With A Little Port Work,crane Solid Roller Cam 258/268 @ 50 585/612 Lift,crane Solid Lifters W/ Rev Kit, Victor Jr Intake Ported To Match Heads, I've Read Alot About These Motors And It Looks Like Either You Love Them Or You Hate Them, Some People Say That I Should Have Went With A 383 And Made More Power, This Is Going In A 1991 Camaro Street/strip Car
xntrik said:
Absolutely full circle rings. period.
Horseapples! They have no advantage over properly gapped Sealed Power, Hastings, or other good, gapped race rings. Unless you own stock in the gapless company.


7735brian said:
Hey I Am New To This Forum And I Am Also Building A 302 And I Was Just Wondering How You 302 Was Coming Along

WELL....... sofar its still in the planning stages, and the gathering stages.

i have my block(87 1 piece rear main seal factory roller), crank (1994 4.3l 265 v8)[2.45 mains and 2.1 rod journals], heads(1971 o41x), and perriphereals (all the other stuff). immona run a weiand tunnel ram with dual holley 660s(have them) have the fuel pump and headers and ignition. i still need to round the valvetrain parts and the cam (300ish duration and a centerline of 114 or 112. but not too much lift ). i need to get the 6 inch rods, and am going to custom order the pistons to get a compression ratio around 9.5 10 tops. plus the machine shop work. all together im about 6 months out on the project.

talking to the local old guys that have had 302s, the bottom should hold together til around 8500-9000 pushing it (cast parts) and the power should start to arrive right around the 5300+ range. one of the guys i talked to had one that produced 750 horses on alchohol, @ 8500. he was using lightweight parts and had some serious dinero in his bottom end, and his was alive till 10000 rpm.

anyhow i figure i can pull conservatively 400 horses at 8000 with what im going to use.

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