915 Heads On 383

[IQ52]

While on the subject of 915 heads, I read that the Stealth head is an aluminum version of the 915 head. But with slightly larger combustion chambers at 84 cc. Has any one looked at/compared the port shape of the 915 to the Stealth? I believe the Stealth has the 2.14 intake, 1.81 exhaust valve sizes. I am still trying to decide whether to port a set of 915s, or go to an Alum head. Thanks for any ideas.

Aarrgh. If it is just between the 915 and the Stealth, go for the Stealth!

Whoever originally said that the Steath is an aluminum version of the 915, HAD NEVER SEEN THE TWO SIDE BY SIDE, AND DIDN'T KNOW WHAT THE HECK THEY WERE TALKING ABOUT. We have done extensive work with the 915's and the Stealths.

The last Stealth head I tested is now down around 81 cc combustion chamber and the port shape is NOTHING like, and never was anything like the 915. The Stealth head does not flow as advertised OOTB but still out flows the 906/915 heads by some 30-35 cfm. If you do a few minutes of blending to the Stealth, it will flow like the Edelbrock RPM and you will outflow the 915 by 45-55 cfm.

http://forums.moparmusclemagazine.c...formance-discussion/440-source-stealth-heads/

Please note on page 2 of the thread, what a well ported Stealth head can do, which the 915 can't think of touching.

 

[Garys1969RR]

Ok thanks, I Q 52, I read that in a book on how to build max perf Big Blocks. Maybe some day you can write a book and put all these myths and mis information to rest! Or have you already? Lol

 

[RustyRatRod]

Thanks, Jim. Your posts are always enlightening. Preeshunate it.

 

[IQ52]

Ok thanks, I Q 52, I read that in a book on how to build max perf Big Blocks. Maybe some day you can write a book and put all these myths and mis information to rest! Or have you already? Lol

The book? No. But we are building a pump gas 528 all aluminum Hemi that would make a good read I think. Keeping a good record of the trials and travails of rebuilding an engine that had good parts installed in an unprofessional manor, the destruction caused, and the cures we used.

 

[69Bee]

The one thing that no one has mentioned is the deck height of the piston. According to my engine book, the NHRA spec for a 1970 383 4BBL is -0.004". If your deck height is NHRA correct, with a felpro 0.039: compressed head gasket, you are at to just under the bare minimum clearance. The Mopar Engine book gives 0.055"-0.060" minimum, and states 0.040" will result in contact. Depending on rev's, rods do stretch. Measure your deck height (distance piston is from the the deck of the block +/-) to be sure what you have, and then make your decision. The 383's from 68-69 had a +0.020" deck, so you need to measure it.

As far as the other aspects, the heads are the same ports and valve sizes. The only change was from closed chamber to open chamber. There is no problem to put 2.14" intake, and 1.81" exhaust valves in, and for the street, It is not advisable to go to the 1.88" exhaust. Any competent machine shop can cut the intakes for the larger valves, and then clean up the throat. The exhaust is opened up by putting hard exhaust seats (REQUIRED) in, and then cleaning the throats to match also.

Put the money in the 906 heads for new guides, larger valves, hard ex seats, surface heads, proper springs. You will be much happier in the end.

 

[RustyRatRod]

.040" will result in contact with what? The head? That's wrong. There are people running as small as .020" quench distance without issue. Keith Black RECOMMENDS .035".

 

[Garys1969RR]

Yes, I have ran as close as .037" head to piston clearance on a 440 with no probs. Stock rods, auto trans, 6000 red line.

 

[RustyRatRod]

Yes, I have ran as close as .037" head to piston clearance on a 440 with no probs. Stock rods, auto trans, 6000 red line.

Puzackly.

 

[69Bee]

I only said that the book said that was the minimum. I have also seen the 0.035" spec, perhaps in my Kieth Black book. I am sure that they want to be conservative in their claims. Here is a nice article on the subject, by some well known people:

http://www.chevyhiperformance.com/t...shortblock/94138_piston_head_clearance_guide/

I don't believe people running 0.020" clearance, but you might mean a 0.020" deck height. Combine that with a 0.020" gasket, and you get 0.040", which coincides with the stated minimun.

The things to consider when trying to get close is:

1) rod stretch
2) rod bearing oil clearance
3) rod center to center length
4) reciprocating forces
5) thermal expansion
6) carbon build-up
7) piston rock

Number 6 is important because what might be okay today, might not be at a later time. If you any links to any official 0.020" piston to head setups, please post them.

 

[RustyRatRod]

I know all the things to consider. chebbie high performance aint one of them.

 

[RustyRatRod]

I don't believe people running 0.020"...

I dont give a continental **** what you believe. That's your mistake. I know EXACTLY what I am referring to and it's QUENCH DISTANCE. The distance between the flat part of the piston and the flat part of a closed chamberd head. Clear enough? I been tearin down and buildin engines better than thirty (that's 30) years. I do believe I know the terminology. I think you should come into 20th century thinking. Plenty of people run quench distances close as I describe. It's you who needs to educate himself. Trust me. Get back with me when you do that, ok? Until then, you might want to leave the engine discussions to those experienced with it. You mght even learn something. Just a thought.

 

[FirstPolara]

So I went to buy the 915 heads today and I was scared off by two hairline cracks that I saw. I guess I will have to look into other methods of getting more out of my 383. One of them being the intake manifold as discussed earlier. I have a dp4b that I might consider using and keep the existing 906 heads on. Just trying to get the most I can out of it until I have the cash to build a 440.

 

[69Bee]

I dont give a continental **** what you believe. That's your mistake. I know EXACTLY what I am referring to and it's QUENCH DISTANCE. The distance between the flat part of the piston and the flat part of a closed chamberd head. Clear enough? I been tearin down and buildin engines better than thirty (that's 30) years. I do believe I know the terminology. I think you should come into 20th century thinking. Plenty of people run quench distances close as I describe. It's you who needs to educate himself. Trust me. Get back with me when you do that, ok? Until then, you might want to leave the engine discussions to those experienced with it. You mght even learn something. Just a thought.

Rusty, you need to put the pipe down, and take a few steps backward...

I NEVER said you didn't know any terms, and I never inferred that you have no clue as to what you are doing, but I will now...

You don't.

You can walk the narrow margin to disaster all you want, but to infer that there is no risk when it is not YOUR money on the line, that is just wrong. Google the piston to head clearance, and you will find a myriad of articles, forums, and tech pages that state emphatically, that 0.035 to 0.045 is the absolute minimum, and you have to add 0.010" to that if you are using aluminum rods.

For your information, physics has not changed in the last 40 years, so the same clearance rule applies to latemodel motors also.

Also, resorting to name calling, throwing insults, and such, really does nothing for any credible response.

I machine and build motors for a living, and do SLIGHTLY know what the hell I am doing. I work on all things from agricultural, industrial, motorcycle, import, and our beloved Domestic.

You build your motors the way YOU want, and I, like the rest of the professional world, will recommend the correct clearances to our customer...

 

[RustyRatRod]

You're right about the personal attack. My apologies, it was uncalled for.

However, show me where I said there was no risk, ok? I didn't. If somebody builds an engine with .020" quench and thinks there's zero risk, they're bout crazy. There's risk with one .200" in the hole. I'm telling you though, there are people walkin on the wild side and gettin by with it. Did I say I was gonna do it? No. In fact, if you look around on here, I have given specifics about my 383 build. 10.4:1, 516 iron heads, KB400s, all with .043 quench. Is that conservative enough? lol

Rusty, you need to put the pipe down, and take a few steps backward...

I NEVER said you didn't know any terms, and I never inferred that you have no clue as to what you are doing, but I will now...

You don't.

You can walk the narrow margin to disaster all you want, but to infer that there is no risk when it is not YOUR money on the line, that is just wrong. Google the piston to head clearance, and you will find a myriad of articles, forums, and tech pages that state emphatically, that 0.035 to 0.045 is the absolute minimum, and you have to add 0.010" to that if you are using aluminum rods.

For your information, physics has not changed in the last 40 years, so the same clearance rule applies to latemodel motors also.

Also, resorting to name calling, throwing insults, and such, really does nothing for any credible response.

I machine and build motors for a living, and do SLIGHTLY know what the hell I am doing. I work on all things from agricultural, industrial, motorcycle, import, and our beloved Domestic.

You build your motors the way YOU want, and I, like the rest of the professional world, will recommend the correct clearances to our customer...

 

[Cranky]

For a steel rod engine, you can run tighter than .035-.040 quench. Put the books down and do some real world testing if you don't believe that. .020 is pretty tight but depending on the combination used, it's possible so it might be a good idea to not be calling someone a crackhead that has experience in doing that. The tightest engine I've ever built was .019 and know many who run .025. Now I would NOT recommend anyone to run those kinds of numbers unless they knew exactly what they were doing and knew what parts to use to make it live longer than a couple of passes....and if it makes a hill of beans, I've been building engines for 38 years.

 

[RustyRatRod]

A lot of the little foreign motors are quench engines. They run some really tight clearances. They are also some of the most efficient.

 

[Supershafts]

You could run as little .02 as long as you got all the particulars covered, p to w clearance, better off with a little more room and a fire groove which makes a better efficient burn

Which foreign motors are quench, the 3v and 4v set ups is what makes them efficient and the chambers don't have any provision for quench, as of the last probably 15 years, the older 60's and 70's import stuff and euro stuff had quench, they're all 3,4,5v heads and pented style chambers, there efficiency is in the multiple valve arrangement.

They run some tight piston to valve though, and with there super easy to bend stems make them a problem when assembling and running and poor machine work and the slightly wrong seat cut and you got a disaster in the making, which is why most imps have those issues, attention to detail.

 

[fatecaptured]

This probably should be another thread topic, but allot of this one has been about quench. So can someone explain how quench affects compression ratio's. So the average cc for pump gas is 8:1? And so if you have a good quench can you run higher compression with the same gas. I focused my previous build around a 9:1-9.5:1 cc because of this issue . So if i had zero deck and say a 915 head and 10:1 or 10.5:1, could it be ran on pump gas?
Just interested and confused. This thread has gotten very interesting as it progressed. Sorry if I seem to be hyjacking this thread, but I am including the 915 head,lol.

 

[Cranky]

With 'good' quench, you can actually run higher compression ratios and use pump gas. Do a search on quench and you should find an article on it by Keith Black Pistons which was reposted with permission from:

By John Erb
Chief Engineer
KB Performance Pistons

Edit, I found it for ya....yeah, I posted it but it's for the good of the Mopar hobby etc. You can do your own research on the subject if you don't like what I post.....

http://www.forbbodiesonly.com/moparforum/showthread.php?t=12581&highlight=quench

 

[RustyRatRod]

Which foreign motors are quench, the 3v and 4v set ups is what makes them efficient and the chambers don't have any provision for quench.......

Here is but one of MANY examples. This is a Nissan head. Note the quench pad. See the FINGER? Lots of 3 and 4 valve motors are quench motors. My wife drives one everyday. The 3.0 Duratec in her Escape is a prime example. ...and you do what for a livin again?