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Old 01-22-2021, 05:29 PM
taktikian taktikian is offline
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Default The 421 SD/455SD

While cruising thru the various Pontiac dyno results on YouTube I came across something which I thought to be interesting. When the 421SD was built and dyno'd by Butler it cranked out 488 horsepower. It was being compared to a 409. Then I saw a 455SD built and dyno'd by Butler crank out 501 horsepower. Assuming both were built to original specs would you not just think the difference would be bigger. I know I did and was wondering what others thought. Thanks,Paul

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Old 01-22-2021, 05:38 PM
Joe's Garage Joe's Garage is offline
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Default 421SD had MUCH nigher compression - big HP difference potential right there

The SD455 was designed to run on low-octane pump gas.

We've swapped out large-chamber (111cc) factory heads for small-chamber (72cc) factory heads on well-built but low-compression 455s and picked up between 50 and 80 horsepower according to the 1/2 mile numbers.

That would make your numbers more comparable.

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Old 01-22-2021, 06:01 PM
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Actually I do not believe for one second that a stock rebuilt SD455 made even 475 hp, no less cracking 500!

To this day I still have a article that was in super stock mag from 1989 where Don Kennedy’s SD 455 with more compression then stock, ported heads , torquer II intake and a bigger then stock HO racing cam made only 456 hp, when they dropped on a stock intake power dropped down to 424 hp.

Hey Joe, half mile numbers, lol!

I would however believe that it made 500 ft lbs of torque. Is this what you had meant to post ?

Note also in this article I am speaking off that Don’s motor with those ported heads,with a Ported Nash intake and a big super stock roller cam when first run on the dyno made 490 hp.

After a day of progressive testing and without changing out any major parts ended up making 600 hp even though it had under 10 to 1 compression.

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Last edited by steve25; 01-22-2021 at 06:48 PM.
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Old 01-22-2021, 06:50 PM
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Default I never said I could type........

and I definitely can't proof-read.

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Old 01-22-2021, 07:04 PM
taktikian taktikian is offline
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I should be able to supply some numbers pretty soon. My 40 over 455 with original RA IV heads, manifolds etc. should be ready to dyno hopefully in a few weeks. With 9.9 calculated compression it should be comparable to the 455 SD. Paul

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Old 01-22-2021, 07:29 PM
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Joe no problem as I have done the same many times !

Paul are your RA4 heads stock, if ported what do they flow at the cam lift you are running, and in fact what cam is your build running?

Would I be wrong in assuming that your running headers seeing that your com is 9.9?

The ported heads I posted about in the SD555 super stock motor flowed 280 intake cfm@28”, if your RA4 heads are stock they do not flow anymore then 240 cfm@28”.

240 cfm per cylinder would make no more then 63 hp if you attain 100 VE, so you would be doing well to make 490 hp if you ask me.

I look forward to your dyno results in two weeks.

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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; 01-22-2021 at 07:42 PM.
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Old 01-22-2021, 10:50 PM
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The 72 455 HO I did for John had it's factory 7F6 round port heads ported to 280 cfm and a custom 239/243 @ .050 hydraulic roller, and 9.98:1 compression, stock HO intake and Qjet, dyno'd with stock RA exhaust manifolds. Made 507hp 571tq

https://youtu.be/Hkm8ip0rmRE

So as Steve said, and I agree, a stock 455SD, with unported heads, stock cam etc.. isn't going to be anywhere close to 500hp, even if it had compression. We'd need to know the specs on that build, to make 500 hp it couldn't be anywhere close to stock.

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Old 01-23-2021, 09:35 AM
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Here are some test results of the SD455 done by Pontiac engineers back in 1971.

The M-7 cam used in the later testing was known to be a RA4 Cam with a revised 105 lobe separation.

This complete story was done by Pete McCarthy and
Can be found in the Sept/Oct issue of Pontiac Enthusiast .

What I would like to know about these factory
test would be if these early stock test where done with a RA4 cam, or with the emission meeting / production version of the 744 cam?

My feeling is that since these where done in 71 that the factory was still flying with the RA4 cam.

Note worthy is the fact that it took well over 11 to 1 compression with stock heads to crack the 500 hp level!

Also note worthy is that a base line / stock motor with open head pipes could crack the 400 hp barrier, plus achieve 477 lbs of torque!
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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; 01-23-2021 at 09:50 AM.
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Old 01-23-2021, 10:58 AM
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Says Holley carb? Wonder what intake they had on it then. Also says tuned headers and 11.9:1 compression. That's not going to run on todays crappy 91 octane. They probably had Sunoco 260 in that thing. It also says the M-7 cam was used in those tests, which you state is the RA IV??

That one sounds pretty far from stock to me.

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Old 01-23-2021, 11:36 AM
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Test 1,2 and 3 where fitted with the stock Q-jet as it would have been produced in 73.

As I have seen in this article, in test 3 they changed over to what where lead to believe was a stock RA4 Cam to what they called the M-7 Cam which was known thru later research to be basically the RA4 Cam, but with a 105 lobe separation.

It was not until test 5 that the Carb was changed to a Holley which was a 850 model.
Now back then in 71 Holley did not make a Q-jet replacement in that size, the biggest they ever offered was a 800, so we must assume that the square bore 850 was used with a adapter.

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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; 01-23-2021 at 11:50 AM.
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Old 01-23-2021, 11:47 AM
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The note from McCully


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Old 01-23-2021, 11:54 AM
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From SD Bob papers


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Old 01-23-2021, 11:58 AM
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Recommendation


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Old 01-23-2021, 01:05 PM
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Thanks for that John, I figured something was up. Good explanation of why the HP was high in that test and not a representation of how it's done today.
So basically, even with compression, cam, carb, headers, the HP numbers are what appear to be inflated a bit.

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Old 01-23-2021, 01:54 PM
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DL McCully.

Thanks for posting the Info SD Bob got from Dudley "Skip" McCully.
He was one of the engineers who worked with Herb Adams and Tom nell on the 1973 and 1974 Super Duty 455 Engine many years ago.

If you can't read the writing on the pages, I can transpose the words onto a post that will at least allow you to see and read what the documents said.

Let me know if members would like to have that info.

Tom V.

ps Dudly "Skip" McCully and I exchanged info on doing a Boosted 455 engine with two of the production dray thru turbos, 2 carbs, a second passenger exhaust manifold to feed the second turbo system, and a few other items for his personal project.

Do not know if he ever put it together but I was sent some manifolds by him to see of I had any ideas to make the system more efficient.

Tom V.

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Old 01-23-2021, 02:17 PM
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Quote:
Originally Posted by taktikian View Post
I should be able to supply some numbers pretty soon. My 40 over 455 with original RA IV heads, manifolds etc. should be ready to dyno hopefully in a few weeks. With 9.9 calculated compression it should be comparable to the 455 SD. Paul
Unless you picked a really lame cam, I'd expect you to beat those numbers.

What intake are you using?

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Old 01-23-2021, 02:52 PM
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I rebuilt a +.030 SD455. Completely stk GM parts. Only difference was an HO racing blueprinted stock lift cam. Heads had stock valve job. 2" headers,3200 converter,4.10 gears,3800 lbs. 12 teens, 110 mph. My tuning I'm just a backyard taught guy.

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Old 01-23-2021, 03:21 PM
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Bob according to my power/ speed/ weight calculator your are making between 360 and 385 hp at the flywheel , right in the ball park we have been discussing.

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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!
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Old 01-23-2021, 08:51 PM
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For all you guys that say factory manifolds are as good as headers look at the results in that factory test!

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Old 01-24-2021, 03:04 PM
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