how much HP. can Stock 1971 short block handle?!?!

i have a 1971 302 , 2 bbl ,that came out of a 1971 comet gt , i was wondering using stock short block internials ,the stock pistion , rods and crank how much horse power , they can handle , ?? figure using stock short block , to make 302 motor ,in the 275-300 hp - 320 tq in gross messurment..

 

Any stock block will handle 450Hp, many have lived through 550-600Hp... It's combination of sustained high RPM & HP that busts blocks..

 

They do have a tendency to split with to much HP and detonation.

 

and bad tunes play hell on stock parts too. Especially those cast pistons. Otherwise, as Tom says above.. Horsepower AND rpm is what causes the cracks to start. Stock blocks don't really like the big sudden power surges coming from turbos and NOS either.

You never indicated what fuel you'll run, but here's another quick tip for anyone building a performance motor. Get the compression up. WAYYY up over those puny little stock numbers. At least 10.25:1.. preferably 10.5:1 or more for racers. Motor will make more power everywhere in the range if you have supporting parts to handle the velocity and airflow increases. Quench height should most definitely be no more than .040 of piston to head clearance.

And if you're not stroking it?(poking it will not be enough by itself).. you'll need fairly small chambers in the heads to push compression up. Keep in mind that although they are pricy(about $100 apiece).. Cometic sells .027 thick MLS gaskets to raise compression up higher wthout having to deck the block and/or make the move towards zero deck height with a slightly taller piston pin height. Their bore size is only +.060" which helps improve compression even more over many of the +.100" gaskets out there. Smaller chambers and tighter quench and fewer wasted space voids around gaskets and ring lands helps prevent detonation while still simultaneously allowing more aggressive tunes.

Otherwise, if you must use those OEM parts to get you by for now?.. cam it bigger and rev it higher to compensate for their weaknesses. Narrower and peakier power band will result(especially if you can't get the compression up very much to help the bigger cam out like it needs).. but you'll easily hit those numbers you're after there.

 

lol.. larger stoker motors add more sidewall thrust loading and the piston skirts don't help matters one little bit as they come further out of the bores @BDC.

 

we where just going to plan to use factory 71 short block with the factory pistions and rods and crank ,and put in new comp cam mild cam about .495 lift ,a four barrel carb an and intake , roller rocker,s , poly locks , full length headers, ,new push rods ,and comp cam springs , high voulume oil pump , ARP oil Shaft and double chain timing chain , new gaskets . i like to talk my buddy into buying ARP ,conectiong rod Bolts , i kinda heard 302 blocks like to split ,but i figure spin in RPM, as 5500-5800 at most, My real question u thing it be good or safe using stock pistions ,and rods, and crank to this build to about 275-300 hp Gross. i figure the block it, self shall be fine ,just wondering about the internials with this set up and mark off about 300 hp gross build..

 

Stock parts are easily good to that power level and beyond. Also might want to consider looking into a cheap set of aftermarket rods that already have the heavier bolts included since you may need to resize the rods or at least have them honed after the new bolts are installed. IOW, installing new bolts onto older rods will very likely cause an out-of-round condition due to extra install torque/higher preload and will need to be honed to correct it. So, money spent either way you go there.

Your max RPM estimate may be a hair low if you don't have aluminum or other aftermarket heads that breathe fairly well. If you want to make that power level at lower rpms, especially the higher side numbers, I would recommend using at least an as cast GT40 head or moving to a lightly ported set of older heads. And the higher the compression the better, especially true as the cam gets larger, so don't be afraid to nip them down .030-.040" thou to raise it as much as you can since it will add torque everywhere in the powerband. More compression compensates for the reduction in cylinder pressure that comes with a bigger than stock cam and makes the motor come up on cam quicker.

 

thanks for the heads up on using stronger rod blots on stock conecting rod caps , with extra torque / preload ,we where just planning on using the stock 71 302 heads ,trying to convince buddy to at least do a gasket match porting of the head,s , i never done a gasket match porting of heads, or any porting on heads , but i think it,s in my capabilities and i think it would help out ,ones of the reason i thought we be in 5800 rpm limit ,no $$ for difrent heads ,or milling heads to increase compresssion ratio

 

Some of the 71 blks were made in Mexico & have bigger main caps that are a little stronger.If you get ARP bolts for the mains you would not have to align hone the blk.Recon the rods w/ Arp bolts & for what you are doing you will be fine.289 & 302 rods are very short & quite stout & the early 302s are like the old 289s in that they have very strong caps.Compare the caps on the newer 302s & you will see what I am talking about.Back in the 70s I`ve seen the older rods reconditioned with new bolts hold 8000rpm,Rob & Tom are right in that you want to get your power from a better set of hds.

 

thanks for all your guys input and helpfull imformantion !!!!!!!!!

 

I saw a post on one forum stating the Mex blocks metallurgy had been tested and it's std iron...

Has also been supposed the extra thickness was because of poorer quality iron than US blocks, didn't seem to be case...