Street Stock Motor

[ZZZBrahmaBull]

Can anyone tell me what the typical output of a street stock motor is on most track here in Texas?

360something cid in the rules from track to track.What compression?

[4cylfordz]

most average from 9.5-11 to 1 depending on track rules. most of the ones i build are with flat tops and smog heads but the compression ratio will very depending on head chamber cc's and piston dish size since the majority are flat top 4vr usually round 4-6cc's and anywhere between .025 and .001 in the hole with a .041 head gasket. hit up united machine co. web site for a good compression ratio calculatior. or do you mean psi?

[ZZZBrahmaBull]

most average from 9.5-11 to 1 depending on track rules. most of the ones i build are with flat tops and smog heads but the compression ratio will very depending on head chamber cc's and piston dish size since the majority are flat top 4vr usually round 4-6cc's and anywhere between .025 and .001 in the hole with a .041 head gasket. hit up united machine co. web site for a good compression ratio calculatior. or do you mean psi?

Not psi, 360something cid>>>> 362 or 368 cubic inch dia.Most all the track rules I read are all about 362 max cid in street stock but heard some allow few more inches.My first race motor was 327 11 to 1 pistons with 350 heads.Wish I still had that motor.

[4cylfordz]

be careful when saying 11:1 pistons as some manufactures call them that at zero deck with small chamber heads. most flat top pistons create similar compression ratios as long as they carry the same pin height. it's just the way they are advertisized.the differences in the ccs of the valve reliefs will make changes of just .01:1, the only time that pistons start making drastic changes is when they are dish or dome or the pin height is changed. you've got a good example of that there a 327 would most likely be rated by a factory with a 65 cc head since most all of the 327s had hump heads on them but when you put the 350 head on there assuming a large chamber around 71cc you would have dropped the advertised compression ratio to around 9:1 and even less than that if the block wasn't decked

[ZZZBrahmaBull]

be careful when saying 11:1 pistons as some manufactures call them that at zero deck with small chamber heads. most flat top pistons create similar compression ratios as long as they carry the same pin height. it's just the way they are advertisized.the differences in the ccs of the valve reliefs will make changes of just .01:1, the only time that pistons start making drastic changes is when they are dish or dome or the pin height is changed. you've got a good example of that there a 327 would most likely be rated by a factory with a 65 cc head since most all of the 327s had hump heads on them but when you put the 350 head on there assuming a large chamber around 71cc you would have dropped the advertised compression ratio to around 9:1 and even less than that if the block wasn't decked

As that old saying goes "learn something new every day".Back in the days that was the common thought that taking a larger engine heads bolting on a smaller engine gives it more chamber,more air and more horsepower.But instead it dropped the compression.Didn't know that but do now.In that case since chevy made a small block 400 cid engine,you bolt on a set of 283 heads.You just increased the compression?Would that work?Dodge bolt on 318 heads on a 360?

[jwmbishop]

What 4cyl says holds true for small chevy, however Mopar is a different breed.

 

The 400 chevy will take 283 heads - but the steam holes (400 does not pass water between the cyl bores like the other SBCs - called siamesed bores) would have to be drilled in the head. And 283 ports are quite small. Better off using 350 heads and steam drilling them to fit - or even better machining the 400 heads for large valves (you can deck the block and heads and hit 9.2:1 with flattops fairly easily). The siamesed blocks are not real good for racing because of the lack of coolant flow between the bores (causes them to be real suceptable to popping the head gasket and bridging between 2 and 4 or 3 and 5 due to the higher heat from the shared exhaust wall) but it CAN be done with bypasses from rear of manifold to water neck to help even out the temps.

 

On to Mopar - there are two distinct families. 273/318 and 340/360.

 

Many folks have gone both ways - 318block w/ 360 heads or 360 block w/ 318 heads - there are a few considerations that get expensive quick (unless you got your own machine shop) though.

 

318 heads on a 360 block and pistons will give you around 8.5:1 with stock deck - the reason is that stock 360 piston sits between .025 and .080 below deck. Unlike SBC Mopar heads are fit to the bore - that is the difference in flame ring circle is different between both heads, and Mopar chose to use different valve centers (318 valves are closer together than 360). Not a problem but with the valve sitting further in there is less swirl of the charge going into the cyl with a 318 head on a 360 block - with 360 heads on a 318 block you have to "notch" the cyl wall and cant the valve a bit to unshroud the valve (and the notch can't go below the top ring obviously)! Second issue is ports - 318 ports are not as tall so you are giving up big flow characteristics when doing 318 to 360 block. You can use the 360 intake with 318 heads - but would have to port the head runners (disallowed by most street stock rules) to correct the mismatch - leaving the mismatch would kill any gains made by higher compression (you would probably lower the HP). The 318 manifold has a very small and short plenum and the runners are very inadequate for the VE of a 360. Add to the confusion - not all 318 heads will raise the compression on a 360 block. There was only one 273/318 casting, #2843675, from 1968 through 1974. It was of the open chamber design, 61-63 cc's, and the valves were 1.78" and 1.50". In 1975 and '76, the #3769973 casting was used but there were no other significant changes. The next version was from '77-'84? but they were still of the open chamber config. After that came the 'infamous' and soon to be legendary - casting #302's (closed chamber - heart shaped) - these are the ones that would raise compression.

 

My recco if you want to run a Mopar is stay with the 360 block - use the J heads and put 1.88 valves in it (most already are 1.88s). Deck the block to .020 piston height, shave .025 off the heads and run good hyper-u pistons with the correct comp ratio. This will get you to around 9.4:1. BUT word of warning - you MUST work the valve geometry after all the shaving. That would require seats - after all the shaving the valves would be too low and lifter preload as well as rocker tip travel across the valve will be wrong. Trying to grind the seats to raise them back would go thru the nitride hardening layer at the exhaust. As easy as these heads crack I have always hated seeing folks dump machining money into them.

 

SBCs are the favorite for many reasons!

[ZZZBrahmaBull]

What 4cyl says holds true for small chevy, however Mopar is a different breed.

 

The 400 chevy will take 283 heads - but the steam holes (400 does not pass water between the cyl bores like the other SBCs - called siamesed bores) would have to be drilled in the head. And 283 ports are quite small. Better off using 350 heads and steam drilling them to fit - or even better machining the 400 heads for large valves (you can deck the block and heads and hit 9.2:1 with flattops fairly easily). The siamesed blocks are not real good for racing because of the lack of coolant flow between the bores (causes them to be real suceptable to popping the head gasket and bridging between 2 and 4 or 3 and 5 due to the higher heat from the shared exhaust wall) but it CAN be done with bypasses from rear of manifold to water neck to help even out the temps.

 

On to Mopar - there are two distinct families. 273/318 and 340/360.

 

Many folks have gone both ways - 318block w/ 360 heads or 360 block w/ 318 heads - there are a few considerations that get expensive quick (unless you got your own machine shop) though.

 

318 heads on a 360 block and pistons will give you around 8.5:1 with stock deck - the reason is that stock 360 piston sits between .025 and .080 below deck. Unlike SBC Mopar heads are fit to the bore - that is the difference in flame ring circle is different between both heads, and Mopar chose to use different valve centers (318 valves are closer together than 360). Not a problem but with the valve sitting further in there is less swirl of the charge going into the cyl with a 318 head on a 360 block - with 360 heads on a 318 block you have to "notch" the cyl wall and cant the valve a bit to unshroud the valve (and the notch can't go below the top ring obviously)! Second issue is ports - 318 ports are not as tall so you are giving up big flow characteristics when doing 318 to 360 block. You can use the 360 intake with 318 heads - but would have to port the head runners (disallowed by most street stock rules) to correct the mismatch - leaving the mismatch would kill any gains made by higher compression (you would probably lower the HP). The 318 manifold has a very small and short plenum and the runners are very inadequate for the VE of a 360. Add to the confusion - not all 318 heads will raise the compression on a 360 block. There was only one 273/318 casting, #2843675, from 1968 through 1974. It was of the open chamber design, 61-63 cc's, and the valves were 1.78" and 1.50". In 1975 and '76, the #3769973 casting was used but there were no other significant changes. The next version was from '77-'84? but they were still of the open chamber config. After that came the 'infamous' and soon to be legendary - casting #302's (closed chamber - heart shaped) - these are the ones that would raise compression.

 

My recco if you want to run a Mopar is stay with the 360 block - use the J heads and put 1.88 valves in it (most already are 1.88s). Deck the block to .020 piston height, shave .025 off the heads and run good hyper-u pistons with the correct comp ratio. This will get you to around 9.4:1. BUT word of warning - you MUST work the valve geometry after all the shaving. That would require seats - after all the shaving the valves would be too low and lifter preload as well as rocker tip travel across the valve will be wrong. Trying to grind the seats to raise them back would go thru the nitride hardening layer at the exhaust. As easy as these heads crack I have always hated seeing folks dump machining money into them.

 

SBCs are the favorite for many reasons!

Yeah it sound like I will just use my Mopars for street hot rods or hot rodding down the dirt roads out here.Do like everyone else run SBC on dirt track racing.

[4cylfordz]

I agree, unless you went on a hunt and found a 340 mopar than I would stay away from the dodges. or if your track rules allowed aftermarket pistons as they let you get away without the surfacing the crap out of the block and heads by using valve reliefs. The Chevys are allot easier to gain compression out of using bargain parts but be weary of block and head selection as some are gems and some are junk.

[KISS_Racing]

Be prepared to spend 4 times the amount of money on a 318 or 360. We have 3 318's and they arent cheap. If your rules allow put a GM Crate motor in it and enjoy......

[HiTech]

Be prepared to spend 4 times the amount of money on a 318 or 360. We have 3 318's and they arent cheap. If your rules allow put a GM Crate motor in it and enjoy......

yep they cost ..but you get one right ..chevy cant beat it ..on up and up rules . who was that guy who ran that mopar at sas and went over the wall some years back when nick ran sa ..that motor would smoke em ...

[ZZZBrahmaBull]

Be prepared to spend 4 times the amount of money on a 318 or 360. We have 3 318's and they arent cheap. If your rules allow put a GM Crate motor in it and enjoy......

Sooooo if you want to play,you gotta pay.Right now I also got 3 cars with 318's and then got some big blocks too.Passed the thought of would like to open road race the 76 road runner/volare.Geeee that car is so fun to drive with 4 speed and headers.So if GM pretty much got it hands down on Dirt Track,Street Stock,aaaaaahhhh maybe NASCAR.Just how does GM do up against Mopars in Open Road Racing and Drag Racing or the Lucis Oil Offroad Series?Yeah GM might be cheaper.But like Hitech says nothing like a good running Mopar.Then you see GM muscle cars camero,chevelle,malibu,chevy ll.Yeah ok pretty nice pretty cool.Then comes along the tropical fruit colors Mopars,like chargers,challengers,road runners,cudas,darts,dusters,demons,

daytonas,super birds,aspens,and volares.Who has hands down now?