#21  
Old 02-21-2021, 07:34 AM
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There was never a head used on any 1970 400 that had under 72 CCs, even the motor that we now call the Ram Air III,

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Old 02-21-2021, 01:52 PM
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Some people (at Pontiac) believed there was.
And so does anyone who has owned a pair or has checked them out.
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  #23  
Old 02-21-2021, 04:57 PM
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I have that same chart and it’s wrong as hell!

It’s showing the 75.7 cc head as making a 10.25 compression, and then the casting 12 head at 9.43 CCs less ( 66.27 CCs ) increasing the compression by only .25 of a point!

And if that is not enough of a red flag the chart shows the RA4 motor with its 69 CC head as only being a 1/4 point higher in compression then the 75.7 cc number 13 casting head used on the 350 hp motors!

When I run the numbers I calculate the 75.7 cc head as making for a 9.8 to 1 compression.

The 66.27 head would make for a 10.8 to 1 compression, when I run the numbers, so in other words your asking me to believe that Pontiac let the RA4 motor out of the factory doors with less compression then the RAIII motor!

I don’t believe that for even half a split second!

So here we go again , anyone have a close to stock number 12 casting sitting around they can CC for us ?

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #24  
Old 02-21-2021, 06:44 PM
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past 35 years i have never seen a proclaimed 72 cc head. last week checked a virgin 1969 #62 casting that was 74.9 cc.
Only head i seen under 72 was a #48 that was milled that came in at 68cc
the 72cc number is just a fallacy.

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  #25  
Old 02-21-2021, 07:07 PM
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Quote:
Originally Posted by steve25 View Post
I have that same chart and it’s wrong as hell!

It’s showing the 75.7 cc head as making a 10.25 compression, and then the casting 12 head at 9.43 CCs less ( 66.27 CCs ) increasing the compression by only .25 of a point!

And if that is not enough of a red flag the chart shows the RA4 motor with its 69 CC head as only being a 1/4 point higher in compression then the 75.7 cc number 13 casting head used on the 350 hp motors!

When I run the numbers I calculate the 75.7 cc head as making for a 9.8 to 1 compression.

The 66.27 head would make for a 10.8 to 1 compression, when I run the numbers, so in other words your asking me to believe that Pontiac let the RA4 motor out of the factory doors with less compression then the RAIII motor!

I don’t believe that for even half a split second!

So here we go again , anyone have a close to stock number 12 casting sitting around they can CC for us ?
Keep in mind that the RA IV used aftermarket forged pistons. Have you ever compared any Pontiac cast pistons to the RA IV forged piston. Could easily be differences in pin height or even deck height. From what I have seen, if the magazines are showing an actual RA IV piston, the tops do have a different valve relief configuration. Maybe a true side by side, measured, comparison between the cast and forged piston would settle it. Maybe you could find an NOS RA IV piston and provide the comparative specs, and then we would have some facts to fall back on for the sake of argument.

  #26  
Old 02-21-2021, 07:29 PM
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The chart in post 22 shows the same .023” deck height for the RA4 as the other 400s shown have, and in 1970 all the 4 bbl 400 motors are showing the same ,028” head gasket.

But you do have a point about the depth of the valve notches that the motors would have needed since the RA4 heads had far shallower chambers, but then again the 1970 RAIII having a 10.8 compression when the maximum ever seen in print in any 70 or pre 70 Pontiac literature is 10.75 is very suspect to me!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #27  
Old 02-22-2021, 05:29 AM
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RAIV has tuliped valve heads and different pistons.
And, 1970 all V/8 400 (exc. 8.6 ratio) uses gasket #9790910 as we learned is .040"/.045" nominal thick, .038" crushed.

Also, as we all learned, advertised compression ratios is nothing but advertising.

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  #28  
Old 02-22-2021, 07:04 AM
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Sorry, I am still calling BS!

There's no way the factory engineers would have given the RA4 motors less compression then the RAIII motors just in light of the RA4 Cam having so much more overlap then either of the two Cams used in the RAIII motors!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #29  
Old 02-22-2021, 08:07 AM
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Quote:
Originally Posted by PontiacJim1959 View Post
Keep in mind that the RA IV used aftermarket forged pistons. Have you ever compared any Pontiac cast pistons to the RA IV forged piston. Could easily be differences in pin height or even deck height. From what I have seen, if the magazines are showing an actual RA IV piston, the tops do have a different valve relief configuration. Maybe a true side by side, measured, comparison between the cast and forged piston would settle it. Maybe you could find an NOS RA IV piston and provide the comparative specs, and then we would have some facts to fall back on for the sake of argument.
How many have actually worked on original RAM AIR IV engines.
I have only worked on two of them as mentioned in previous posts.

All of the Pistons were supplied by TRW. Both of the RA-IV Engines had Forged Pistons vs stock Pontiac Cast Pistons. The RA-IV pistons also used the 200 gram Piston Pins vs the aftermarket TRW Forged 2262 Pistons which used a 250 gram Pston Pin. Normal Pontiac Pistons were delivered with Cast Aluminum pistons. Put a 200 Gram Piston Pin in a TRW Forged 2262 Forged Piston and you had a RA-IV Piston.

Very likely that the Valve Reliefs on the RA-IV Forged TRW Pistons had a deeper 4 Valve Relief Pocket as the engines were designed for a higher lift .470" valve lift and 1.65 ratio rocker arms. Deeper and Larger Valve Pockets
= a lower measured compression ratio.

So I think that it is possible that Kenth's numbers are close to reality.

I owned a full set of new Forged RA-V Pistons (given to me by the Chief Engineer at TRW Pistons). I later swapped them to Tom Jeffers in Ohio for some Sheet Metal body pieces for my 64 GTO. (Floorboard and Trunk Pans).

Never owned a RA-IV vehicle. Have driven several of them. Have worked on two of them, I have owned all of the unique parts for the engines Valvetrain and Heads/ intakes, Camshafts, Forged Steel RA-IV SD crankshafts.

But I am not a expert on the engines like some here.

Tom V.

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  #30  
Old 02-22-2021, 11:41 AM
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Quote:
Originally Posted by Tom Vaught View Post
... All of the (RAIV) pistons were supplied by TRW. Both of the RA-IV Engines had Forged Pistons vs stock Pontiac Cast Pistons. The RA-IV pistons also used the 200 gram Piston Pins vs the aftermarket TRW Forged 2262 Pistons which used a 250 gram piston Pin. Normal Pontiac Pistons were delivered with Cast Aluminum pistons. Put a 200 Gram Piston Pin in a TRW Forged 2262 Forged Piston and you had a RA-IV Piston....
Thank you for sharing this!

I had read before that the TRW forged piston was the RAIV slug (and was waiting for someone to clearly state this), but have not previously read the pin bit before!
I'm going to try to keep this in mind for my 400 builds going forward.

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2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
  #31  
Old 02-22-2021, 12:37 PM
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If looking at the 1969 Engine Assembly Chart that PontiacJim1959 posted in Post #19, you'll see the actual compression ratios that Pontiac referred to internally. These are NOT the advertised ratios, which, as I have been told was an arbitrary number derived and published by Sales.

According to the 1970 Engine Assembly Chart, Pontiac's actual compression ratio for the 1970 R/A III and R/A IV was 10:1. Those engines carried the highest actual rating that year (along with the WT 400). For note, the number-64 headed L75 455 carried an actual ratio of 9.4:1 despite being advertised at 10.25:1.

Where cylinder head volume is concerned, the number-614 had an actual chamber volume of 69.16 cc while the number-12 had an actual chamber volume of 69.27 cc. The tulip shaped head of the R/A IV intake valve displaced 1 cc. Both 400s used the same 9790910 head gasket.

Looking at the way the two engines (1970 R/A III vs R/A IV) were assembled, the compression ratios should be very much the same and very close to 10:0 despite how far their advertised ratios vary.

The only possible variance could be the valve pocket volume that Tom Vaught noted. I have an NOS R/A IV piston and while I haven't physically measured its volume, the face doesn't look much different than a standard 400 cast piston of the same era. I'd suspect, based on Pontiac showing both the same 10:1 compression ratio for both engine, that the volume differences would be minimal.

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  #32  
Old 02-22-2021, 01:00 PM
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Agree Rocky, we are splitting Frog Hairs Now.

Pontiac Advertising, being a Marketing Game, and a first class Advertising Guy (Wangers)
would push the specs (for the engine) guys in a given direction.

Tom V.

The RA-V engines had a unique long rod for the 303 and 366 engines.
The RA-IV engine parts book (Kenth would know) that Pontiac offered a rerun of the 421 SD Connecting Rods and
the RA-IV SD used those very hard to find 421 SD rod parts in that engine. Forged Pistons, Forged 421 SD Rods, and a Forged Kellogg 3.75 stroke Crankshaft. (And "RACE ENGINE" builders removed those rods and put "better" Pontiac rods in the engines.)

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  #33  
Old 02-22-2021, 02:39 PM
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I am whole Heartedly sold on the numbers that you have presented here Rocky!

Thanks once again for the info!

None the less if anyone has some stock number 12s to CC please do so if you would , I have a set of very near chamber wise stock 13s that I will CC on tomorrow night .

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #34  
Old 02-22-2021, 03:43 PM
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Quote:
Originally Posted by steve25 View Post
... None the less if anyone has some stock number 12s to CC please do so if you would , I have a set of very near chamber wise stock 13s that I will CC on tomorrow night .
Since you were actively involved in the recent #48 head discussion, I fail to see why you're asking for the same information contained in that thread.

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2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
  #35  
Old 02-22-2021, 04:21 PM
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Well then someone should be able to answer that question once again easily. No?

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #36  
Old 02-22-2021, 05:41 PM
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One other comment on my Post #29.

People might ask: Why did the RA-IV SD engine have a different weight pin in the TRW piston vs the normal 250 gram pin used in the typical TRW Forged Pistons or Cast Pistons in normal Pontiac Engines?

Stock Pontiac Engines for 400 cid engines used a given Bob Weight to balance the cast iron 3.75 stroke crankshaft.

The Ram Air IV SD engine used a Kellogg Steel 3.75 stroke Crankshaft.

"Cast iron is no heavier than steel on a pure density basis. Anything made out of cast iron rather than steel is heavier because it needs to be much thicker. ... Cast iron is usually defined by its carbon content (>2% by weight), and steel typically has <2% carbon."

Simple terms the balance of the engine is slightly different with the steel Crankshaft vs the Cast Iron production weight. As said above, for similar strength the Cast Iron crankshaft needs to be heavier. Steel being lighter = a 200 gram piston pin will work vs the normal 250 gram pin. 50 grams is not a lot of weight but it does help with the balancing of the engine parts. I was told that every one of the RA-IV SD engines was balanced.

Tom V.

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  #37  
Old 02-22-2021, 06:01 PM
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Tom, please prove that there was a production RA4 SD no less a production one with a true steel crank because I have never seen such!

This is going to be another royal battle I can tell so maybe we should start a separate thread?

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #38  
Old 02-22-2021, 06:25 PM
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Here’s info from my old 1986 TRW performance catalog.

It shows the standard forged 2262 piston as fitting all 67 to 69 4 bbl motors including the RAIII as having the 250 gram pin, and optional is the P1206 pin that weighs in at 192 or 194 grams depending on where you look in the catalog!

The catalog list part number 2398 piston as being for a RA4 motor only and comes fitted with the P1206 pin.

When you go to the piston spec section of the catalog both part number pistons are exactly the same in every respect but for what pin they ship out with.

Even in regards to how much the pistons weight which is strange!

This leads me to ask if the basic RA4 piston itself is stouter then we have been lead to believe!
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!

Last edited by steve25; 02-22-2021 at 06:32 PM.
  #39  
Old 02-22-2021, 06:46 PM
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Cast iron and steel info.

Cast iron is about 450 lbs per cubic foot, steel comes in at about 490 per cubic ft.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #40  
Old 02-22-2021, 08:42 PM
PontiacJim1959 PontiacJim1959 is offline
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Quote:
Originally Posted by steve25 View Post
Here’s info from my old 1986 TRW performance catalog.

It shows the standard forged 2262 piston as fitting all 67 to 69 4 bbl motors including the RAIII as having the 250 gram pin, and optional is the P1206 pin that weighs in at 192 or 194 grams depending on where you look in the catalog!

The catalog list part number 2398 piston as being for a RA4 motor only and comes fitted with the P1206 pin.

When you go to the piston spec section of the catalog both part number pistons are exactly the same in every respect but for what pin they ship out with.

Even in regards to how much the pistons weight which is strange!

This leads me to ask if the basic RA4 piston itself is stouter then we have been lead to believe!
Here is a photo from the magazine article on the RA IV. Maybe Tom can ID the piston tops. I know magazines will toss in "parts" just to make the article up, but you can see the piston on the right has different valve reliefs. The article sounds like the piston on the left is the cast RA II piston, and the one on the right is the forged RA IV piston.

The article also states the RA IV forged pistons are 50 grams lighter than the old cast RA II pistons.
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