#21  
Old 01-31-2020, 07:12 AM
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I had these trw domes in a 71 Ho with ra4 cam. Car went low to mid 12,s on Polyglas tires

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  #22  
Old 01-31-2020, 07:23 AM
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The cam they had used in my 72 was just wrong. The cylinder pressures were crazy high when I did a pre-teardown compression check: https://forums.maxperformanceinc.com...te=1&p=6105727

Cyl 1: 230 psi
Cyl 2: 220 psi
Cyl 3: 225 psi
Cyl 4: 230 psi
Cyl 5: 227 psi
Cyl 6: 230 psi
Cyl 7: 220 psi
Cyl 8: 235 psi

  #23  
Old 01-31-2020, 07:38 AM
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Doug, the stock design seemed to work good as far as I could tell.
The trough (no eyebrows) made a little more CR. The engine with a higher lift roller cam made good power. With the addition of the domed pistons really woke the engine up. (compression to 10.4 to 1)
If it had 12 to one it would have been a beast. But the chambers were too big probably to get that CR. Unless the head was milled of course.
(would have made a killer turbo engine back then )

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  #24  
Old 01-31-2020, 10:42 AM
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I have a set of those domed TRW pistons in the box if anyone is interested. These are new and need to be machined to desired dome height. Standard bore. Got them for my HO build but came across of heads that were milled thus wont be using them.

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  #25  
Old 01-31-2020, 11:16 AM
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Quote:
Originally Posted by Douglas Willinger View Post
What if they instead used the standard SD 455 piston, flat, no dome, with the single-straight trough design value relief cut, instead of the 'eyebrows'?

Of course they would need a smaller chamber SD 455, which would exist in prototype form, or closely as a ported Ram Air II or Ram Air IV set of heads.
That idea works but still doesn't bring the compression up enough, since the chambers in the heads are so large.

Even at zero deck (actually we had the pistons .007" out of the hole) and the HO heads were milled down to 107cc or somewhere in that area (again paperwork not in front of me) I had to use a .045" gasket to keep quench comfortable, and even with that dome on the piston that I pictured above the compression was still only 9.98:1. Take that dome away and you'd have to mill the crap out of the heads to get it back, so far to the point you'll be cutting intakes to fit, valve clearance and geometry becomes an issue etc...Not to mention a set of expensive factory heads that have now been chopped so far they sort of become married to that combo and not much good for anything else.

There is nothing wrong with using a domed piston in a Pontiac as I and many have shown, it works if done properly. Chevy used them all the time. There is something to be said about flat tops and flame travel for sure, but a dome isn't going to hurt anything if the rest of the combo is chosen well. Here's a shot of the narly dome used in my DZ engine. These are NHRA legal reproduction from JE to produce the factory 11:1 compression this engine originally came with, compared next to the original OEM TRW piston that came out of it.

I run an LS7 dome piston in my 454, which is quite common in the BBC world because cylinder head chambers are also quite large for these engines.
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  #26  
Old 01-31-2020, 10:05 PM
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Default SD 455 valve relief design

Someone who sold me one of those pistons told me that the SD 455's single trough was for higher compression.

But Pontiac was adjusting the compression ratio (except for the 428s) by changing the size of the combustion chamber. So a few ccs via the trough design would have been minor.

What I am thinking is that the single trough was for higher compression, as in higher anti knock resistance with such, and hence was developed initially with a smaller chamber head, as part of the high performance Pontiac V-8 engine development during the Ram Air IV/LS-1, and hypothetically, a higher compression version of the SD 455.

Imagine such an engine, with the smaller chambers and the single trough.

What other engines ever used such a design.




Quote:
Originally Posted by johnta1 View Post
Doug, the stock design seemed to work good as far as I could tell.
The trough (no eyebrows) made a little more CR. The engine with a higher lift roller cam made good power. With the addition of the domed pistons really woke the engine up. (compression to 10.4 to 1)
If it had 12 to one it would have been a beast. But the chambers were too big probably to get that CR. Unless the head was milled of course.
(would have made a killer turbo engine back then )

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1970 Lucerne Blue Firebird Trans Am, deluxe blue interior. Original Ram Air III, M-21, 3.73. Being built as a 4" stroke "434" with SR 614 Ram Air IV heads

1972+ Lucerne Blue 4-door hardtop "what if" T-41 Le Mans Sport GT/Grand Am concepts. Equipped with future 3" journal "455 HO"/"what if" prototype "SD 455".
What if GM had continued production of the 1970-72 GM A body somewhere in the southern hemisphere?
  #27  
Old 01-31-2020, 10:14 PM
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Douglas Willinger Douglas Willinger is offline
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Default SD 455 single trough valve relief design

I myself am intrigued by the idea of using the higher compression round-port heads, either the 1968 "96" Ram Air II or the 1969 "722" or 1970 "614" Ram Air IV heads on a 4" stroke.

Quote:
Originally Posted by Formulajones View Post
That idea works but still doesn't bring the compression up enough, since the chambers in the heads are so large.

Even at zero deck (actually we had the pistons .007" out of the hole) and the HO heads were milled down to 107cc or somewhere in that area (again paperwork not in front of me) I had to use a .045" gasket to keep quench comfortable, and even with that dome on the piston that I pictured above the compression was still only 9.98:1. Take that dome away and you'd have to mill the crap out of the heads to get it back, so far to the point you'll be cutting intakes to fit, valve clearance and geometry becomes an issue etc...Not to mention a set of expensive factory heads that have now been chopped so far they sort of become married to that combo and not much good for anything else.

There is nothing wrong with using a domed piston in a Pontiac as I and many have shown, it works if done properly. Chevy used them all the time. There is something to be said about flat tops and flame travel for sure, but a dome isn't going to hurt anything if the rest of the combo is chosen well. Here's a shot of the narly dome used in my DZ engine. These are NHRA legal reproduction from JE to produce the factory 11:1 compression this engine originally came with, compared next to the original OEM TRW piston that came out of it.

I run an LS7 dome piston in my 454, which is quite common in the BBC world because cylinder head chambers are also quite large for these engines.

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1970 Lucerne Blue Firebird Trans Am, deluxe blue interior. Original Ram Air III, M-21, 3.73. Being built as a 4" stroke "434" with SR 614 Ram Air IV heads

1972+ Lucerne Blue 4-door hardtop "what if" T-41 Le Mans Sport GT/Grand Am concepts. Equipped with future 3" journal "455 HO"/"what if" prototype "SD 455".
What if GM had continued production of the 1970-72 GM A body somewhere in the southern hemisphere?
  #28  
Old 01-31-2020, 10:58 PM
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Quote:
Originally Posted by Douglas Willinger View Post
I myself am intrigued by the idea of using the higher compression round-port heads, either the 1968 "96" Ram Air II or the 1969 "722" or 1970 "614" Ram Air IV heads on a 4" stroke.
That's something I've also been wanting to do for quite some time now. I need a set of 614's for what I want to do. Stick them on a 455 or maybe something slightly larger with a 4.250 crank.

Problem is they aren't falling off trees, and I can't see spending $2000 plus for a set of heads that I have to sink another $1000 plus in rebuilding. There has been talk by a couple different people of making an aluminum version to look the part, maybe with modern chambers that I'd love to jump on board with, but that never seems to go anywhere.

  #29  
Old 01-31-2020, 11:04 PM
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My engine build thread:

http://psp.aquacomp.net/topic.asp?TOPIC_ID=13682

Quote:
Originally Posted by Formulajones View Post
That's something I've also been wanting to do for quite some time now. I need a set of 614's for what I want to do. Stick them on a 455 or maybe something slightly larger with a 4.250 crank.

Problem is they aren't falling off trees, and I can't see spending $2000 plus for a set of heads that I have to sink another $1000 plus in rebuilding. There has been talk by a couple different people of making an aluminum version to look the part, maybe with modern chambers that I'd love to jump on board with, but that never seems to go anywhere.

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1970 Lucerne Blue Firebird Trans Am, deluxe blue interior. Original Ram Air III, M-21, 3.73. Being built as a 4" stroke "434" with SR 614 Ram Air IV heads

1972+ Lucerne Blue 4-door hardtop "what if" T-41 Le Mans Sport GT/Grand Am concepts. Equipped with future 3" journal "455 HO"/"what if" prototype "SD 455".
What if GM had continued production of the 1970-72 GM A body somewhere in the southern hemisphere?
  #30  
Old 01-31-2020, 11:15 PM
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Quote:
Originally Posted by Douglas Willinger View Post
That sounds pretty cool. I've always liked the idea. 22 years ago I built a small main 428, turned down a 428 crank and shoved in a 400 block, and then used a #13 head on it with custom dished pistons for 9.7:1 compression. Had 3 different cams in it. Really liked that combo and worked well.

I have a 70 RAIII Formula that I'd like to make a RAIV clone from just for giggles, but I want to do that with a smallish stroker engine, probably end up with 470-480 cubes but dress it to look stock and have some fun with it. I quit actively looking for 614's though as the prices rose, and I'm not going to wait another 10 years for someone to make them. I will likely end up heavily modifying current aluminum round port offerings to look the part.

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