Has Anyone Sonic Tested the 5.7 Block?

[PowerWagon896]

Since the only real performance potential difference between the stock 5.7 & the 6.1 is .140" bore, just what is the SAFE MAXIMUM OVERBORE for the 5.7 block?

I have seen .080" (4.00") overbores lsited. That is a pretty darned big overbore!

So just how much "meat" is there in the block cylinder walls?

The old pre "62" Chevy "283" small block could be overbored .120". I had 1 of those, a "301". Later years that used different water jacket cores could only stand a .060" overbore.

I have also seen lesser maximum overbores listed for the 6.1 block. (.030")

Are the cylinder wall on the 6.1 block thinner.

Are the same sand cores used for the water jackets on both the 5.7 & 6.1?

If so then the 5.7 could be overbored to the same maximum as the 6.1 (4.090")

So let's hear from those big time engine building shops.

Surely you have done sonic testing before going .080" over on the 5.7 block.

[383HEMI]

PR&D Sonic Checked a couple of blocks before they built my motor with the 4" bore. I'm sure Stu could answer your question.

PH

[392Stu]

I've checked a few out. There is definately more material in the 5.7 block. with a 4.0" bore the thinnest spot I found was in a non thrust direction a bit past half way down the bore wher you can go thinner. It was 0.125". Twards the top in the thrust directions there was still well over 0.200" since that was the first 4" bore I did I checked it pretty extensively.

[PowerWagon896]

I've checked a few out. There is definately more material in the 5.7 block. with a 4.0" bore the thinnest spot I found was in a non thrust direction a bit past half way down the bore wher you can go thinner. It was 0.125". Twards the top in the thrust directions there was still well over 0.200" since that was the first 4" bore I did I checked it pretty extensively.

So if .030" overbore in the 6.1 is max we are looking @ .090 potential bore difference or about 19 cu in potential displacement differnce.

[392Stu]

So if .030" overbore in the 6.1 is max we are looking @ .090 potential bore difference or about 19 cu in potential displacement differnce.

I don't even like going 0.030" on most 6.1's and thats only 5 CI with a stock stroke. A 4" bore on a 5.7 is a 15 ci increase with a stock stroke.

[PowerWagon896]

I don't even like going 0.030" on most 6.1's and thats only 5 CI with a stock stroke. A 4" bore on a 5.7 is a 15 ci increase with a stock stroke.

Yes I know that a 4" bore is a 15 cu in increase W/a stock strock 360 - 345 = 15.

My 19 cu in reference was POTENTIAL increase @ maximum practical bore & stroke for each block & was meant as a ball park figure anyway.


Your reluctance @ boring the 6.1 block .030" over make that POTENTIAL even less.

Any rod length/piston combo (preferebly hypereutectic cast)that will yield the proper compression hieght W/O decking the block @ 3.75" stroke or very close to that?

What is the bore/stroke/rod length of the 381 combo? Sounds like 4.00" X 3.79" bore/stroke to me. (GOTTA LOVE THAT MOVE THE DECIMAL 2 PLACES RIGHT & ADD 2 ON A 4" BORE V8)

I would go for that W/a light reciprocating weight rod & journal/hypereutectic cast piston set-up.

I am looking for that 200,000 mile street engine you mentioned family truckster super sleeper W/lots of flat high end power on the hi-way W/proper gearing for good standing start acceleration for the occassional drag strip thrashing.

[PPP-Tech]

Our engine builders have succesfully bored the 5.7 to 4.055 and put a stock 6.1 rotating assembly in it. If you validate bore centerlines before boring, the 5.7 with a 4.055 bore had almost identical wall thickness compared to a 6.1 with a 4.080 bore. I will get the sonic report and post it on Monday.

[PowerWagon896]

So the gap narrows even more!

So would another .005 bore realy hurt?

That would allow the 5.7 block to utilize various stock bore 6.1 bore aftermarket components.

Now we couls have a 3.79" stroke 392 in the 5.7 block.

I like that idea.

Are you shifting the bores to take advantage of ever bit of wall thickness?

[PPP-Tech]

So the gap narrows even more!

So would another .005 bore realy hurt?

That would allow the 5.7 block to utilize various stock bore 6.1 bore aftermarket components.

Now we couls have a 3.79" stroke 392 in the 5.7 block.

I like that idea.

Are you shifting the bores to take advantage of ever bit of wall thickness?

Yes, we are not assuming that the factory bores are in the center perfectly, once we validate, the centerline is almost always moved to the correct position. I am almost convinced that have the same amount of thickness. I am building a 3.75/4.055 392 out of my 5.7 right now. It will essentially be the same bottom end as the mopar 392, but I am using the 5.7 heads with 2.05/1.60 valves which should make tons of tq compared to the mopar 392 that is more hp oriented, I am then using my 6.1 intake to put on top with 1/2" spacers to take car of the transition from 6.1 window to 5.7 window.

[Cam]

1/2" eh, that's one hell of a dog leg Andy. Good luck. But those will make mighty nice spacers for juice huh???.

[HEMIDON]

WOW....
Dan and Andy have a discussion on how far you can bore a 5.7

Would I be wrong in saying that this leads us to the potential in depth discussion of my de-stroked nitrous / blower 5.7-351 motor ?

[PowerWagon896]

WOW....
Dan and Andy have a discussion on how far you can bore a 5.7

Would I be wrong in saying that this leads us to the potential in depth discussion of my de-stroked nitrous / blower 5.7-351 motor ?

Don, in all due respect I can not see yoiur obsession W/the destroke nitrous concept.

Yes the shorter stroke engine will be a better road race/NASCAR type engine that will be revved to redline for extended periods.

Your spray set up will preclude that type of scenario won't it?

I agree W/the idea of keeping the stroke down to reasonable levels.

IMO that is in the 3.75" range for a road car W/occasional drag strip use.

A 3.75 stroke engine will twist out 7000 RPm all you want if it is built properly.

If you have your heart set on a 3.50" stroke, the 4.055" Bore will get you a 361 cu in engine. A classic mopar displacement I believe.

[392Stu]

Yes I know that a 4" bore is a 15 cu in increase W/a stock strock 360 - 345 = 15.

My 19 cu in reference was POTENTIAL increase @ maximum practical bore & stroke for each block & was meant as a ball park figure anyway.


Your reluctance @ boring the 6.1 block .030" over make that POTENTIAL even less.

Any rod length/piston combo (preferebly hypereutectic cast)that will yield the proper compression hieght W/O decking the block @ 3.75" stroke or very close to that?

What is the bore/stroke/rod length of the 381 combo? Sounds like 4.00" X 3.79" bore/stroke to me. (GOTTA LOVE THAT MOVE THE DECIMAL 2 PLACES RIGHT & ADD 2 ON A 4" BORE V8)

I would go for that W/a light reciprocating weight rod & journal/hypereutectic cast piston set-up.

I am looking for that 200,000 mile street engine you mentioned family truckster super sleeper W/lots of flat high end power on the hi-way W/proper gearing for good standing start acceleration for the occassional drag strip thrashing.

The 383 I did (actually 381.5) was 3.795 stroke and 4.0 bore. You need to use a custom forged piston though, because there is not a shelf cast or forged piston that will work in this application. Different wrist pin, compression height, you need a floatig piston with the rods you would have to use. Plus you can design the valve notches, compression ratio and quench to work perfectly for your particluar application. I normally will do more lightining machining on an NA engine and then leave more material in the pin bosses and skirts for a forced induction or N2O engine. You just have so much more flexibility with a custom forging. A properlly designed forged piston will handle high milage without a porblem. The idea that the forged piston won't last is from back when the alloys were different and you needed 0.007 to 0.008" clearance to keep from scuffing. The better new forged pistons can go in with 0.0035-0.004" on a round style piston like this settup uses. Also, that napier second ring does wonders for seeling it up. The coated skirts are worth the money too. It used to be a forged piston engine could be counted on to use a 1/2 quart per 1000 miles and since I've been using the CP pistons and the napier 2nd they rarely use a drop. Even with the relatively low tension ring packages I use.

[RacingRev 1320]

thanks for the thread & info re forged pistons. how much $$$ do the forged & coated pistons add versus cast on a build/rebuild? if they really work hi-mileage, i'd probably go that direction when i redo my 5.7(FI probably turbo'd)! i plan on keeping my car so only want to do this once.

[HEMIDON]

Great info Stu. Sounds like you like the 4" bore concept with custom made pistons.