[OldSDGuy]

There were several of us 'old Pontiac guys' there at the dyno today. We all go back to the 70's when we hung out together modifying, restoring and racing Pontiacs. Like Eric, I'm not going to spill the beans but let Mike publish and speak to the results....but I can say I think Mike was ecstatic on the final result. The rest of us were too. There were numerous runs after break-in with a lot of carb and ignition tweaking. The engine ran beautifully and sounded great. All of us together again brought back memories of hanging around together back in the day.

[Skip Fix]

Mike did you ever flow the heads also? I did not see any flow numbers in any post. Be interesting to see what the stock SD ports flow. I bet sum of the 455 SD SS guys like Lynn or JB Clegg have numbers -if they would share them.

[b-man]

390 horsepower!

[PAUL K]

SD455TTFMF's!!!

[mgarblik]

I see a bunch of posts beat me to the forum. Yes, it was a good day on the dyno. Took some tuning and tweaking but the results were rather surprising to me. As I said in my first post way back, this is my first experience working on an SD-455. I guess I didn't really know what to expect. So the peak numbers: 405.8 HP @ 4900 RPM. 498.8 Ft. Lbs. @ 3500 RPM . I will post more detailed dyno info when I can figure out how to make that happen.
In summary, I was surprised the peak HP was just 4900 RPM. HP was falling off pretty fast with 392.2 HP @ 5500 RPM. Big Torque!! 484.5 Ft. lbs. @ 3000 RPM.
449 Ft. Lbs. @ 4700 RPM.

8.4:1 compression, iron everything, exhaust manifolds, stamped rocker arms, point ignition, Q-jet. Not what a typical 400 HP looks like. They really are impressive, more so than I imagined.

So much potential too. The 2 1/4" head pipes just kill it. The stock mild hydraulic cam. The EGR valve and compromised intake manifold. Allot left on the table. Congratulations to Herb Adams and the SD-455 team for getting the most out of a smog era, low compression engine. Unequaled by any other V-8 in this time period.

Big personal bonus. Not one drop of liquid leaked out of it . We ran about 10 gallons of 90 octane, zero alcohol "recreation fuel" through it. Probably about 1.5 hours of total running time.

Final tune: 14 degrees initial, 35 degrees total timing 76 primary jets , 47 metering rods, CV secondary rods, F hanger. 1/4" float level, 5 PSI fuel pressure. R44TS spark plugs .035 gap.

[johnta1]

Yes the pipes kill HP.
If Pontiac used the original planned SD cam it would also have made a huge HP increase. Or even more with a good size cam increase.

[mgarblik]

Sorry, I did not flow the heads. I took them apart, cleaned them and lapped the valves. Replaced the seals. That was it.

[Baron Von Zeppelin]

Congrats on the great results !

I owned a bone stock 73 SD TA Auto AC 3.08 for 20 years.
Knew you were way underestimating the power expectation.
These are real heavy cars equipped that way.

It would have been cool to see what headers would have done to it.
Just for knowing.

More congrats and thanks for sharing it with us.
SD455TTF - pokers to the rear

[jhein]

Unbelievably cool project and results. Congratulations!

It's also really cool to know that Pontiac made 400 hp muscle through 1974.

[KSZR]

I thought the SD had a bigger headpiece right off the manifold for a stretch from the factory?

Very neat project, fun test!

[PAUL K]

Great job and congratulations to all involved!

The SD 455 is flat out bad azz engine. Created by all the guys whose input over the years made the cars we love today.

Pontiac engineers knew the exhaust was a huge restriction on the SD engines. After dyno tests it was determined the exhaust needed improvement. From what I remember they ran a small 2.25 pipe of the manifold for about two inches and then welded a 2.5 over that tube and 2.5 was used going into two resonators shaped similar to the old "Cherry Bomb mufflers" and then into the crossflow muffler. 2.25 tail pipes were used from the muffler back. For 1974 the same exhaust was used but the resonators were dropped.

This compares to the LS-6 which received 1 7/8 tail pipes.

[sdbob]

My stk low mileage new SD TA in 74 ran 14.18 at 98 mph. Non air,3.42 gears,heavy car. Low gear was difficult finding traction. I've heard the SD heads tested were better flowing than production heads. 2nd 3rd gear shift from the m40 was scary hard!!

[SD455DJ]

Congrats Mike! Those are great numbers on your ‘pure’ stock SD455! It’s really cool that your engine has the stock internals including the relatively heavy +.030 TRW SD pistons and the original factory exhaust manifolds. Speaking of which, the factory outlet diameters are only 2.06”/2.125” on the RAIV/455HO manifolds, so I’m wondering if they are the same on the SD manifolds??? We have found that using the Pypes 2.5” mandrel bent headpipes with their captured flanges are necked down to roughly 2.20” at that point, then open up to 2.5” once you get past that. Even though, the 2.5” mandrel 90 degree turn seems to be less restrictive than anything smaller, so you could find a few hp and lbft throughout the pull range.

Did you calculate your finished static compression ratio to actually be 8.4 to 1?

Dennis

[Skip Fix]

Very cool build Mike!! And a job very well done.
Back when I was in the OLD NMCA there was a guy with an SD that would usually win his Pure Stock class so they definitely can run hard. The Clegg's still run John's 73 SD car he bought new in SS!

[SD455DJ]

Originally Posted by Skip Fix

Very cool build Mike!! And a job very well done.
Back when I was in the OLD NMCA there was a guy with an SD that would usually win his Pure Stock class so they definitely can run hard. The Clegg's still run John's 73 SD car he bought new in SS!

Skip, I wonder if that was Mark Walters in an Admiralty Blue 4-speed SD455 TA that he sold quite a while ago. He comes to the Pure Stock Drags and races a very clean '74 TA 400 4-speed that runs mid 14's at 98 mph. It's Admiralty Blue as well.

Dennis

[mgarblik]

Thanks for the kind comments. But really, the engine speaks for itself. I had little to do with how it performs. I carefully assembled it so it wouldn't fail and made sure everything was as the engineers intended. But didn't modify anything other than the tuning slightly. To answer a few questions. Paul K exactly described the layout of the exhaust system. When I acquired the car it came with a new in box Gardner exhaust system with the only exception being a new NOS GM muffler. So that's what's going on. The head pipes are a complicated, 3 piece affair. As Paul described, it starts with a 2 1/4" flared pipe at the flange and makes the bend. It is about 6" long. It is welded to a 2 1/2" pipe, crush bent in numerous places to clear the floor pan , cross member and transmission, then welded on resonators. From there, over the axle into the cross flow muffler and 2 1/4" inch tailpipes. It's just a tight fit under there. Lots of pipes and little clearance. As far as verifying compression, I did not CC the heads while it was apart. I also did not surface them. I used the middle thickness factory SD head gaskets. I know 3 thicknesses were produced. Can't off the top of my head remember the thickness. Maybe .045" or so. I can look it up later.

[sdbob]

Thanks Mike for the data. Impressive,details. Wish I had that dyno opportunity. MySD stocker is basic same engine. All stk GM parts,stk lift cam,stk intake,carb,ignition etc. Car is 73 F approximately 3700 lbs. Car has gone 12teens 110 with just my backyard tuning. The thing I did find by accident many yrs ago, secondary rods diameter reduced too 'almost' a hair size,car picked up mph.

[PAUL K]

Originally Posted by SD455DJ

Congrats Mike! Those are great numbers on your ‘pure’ stock SD455! It’s really cool that your engine has the stock internals including the relatively heavy +.030 TRW SD pistons and the original factory exhaust manifolds. Speaking of which, the factory outlet diameters are only 2.06”/2.125” on the RAIV/455HO manifolds, so I’m wondering if they are the same on the SD manifolds??? We have found that using the Pypes 2.5” mandrel bent headpipes with their captured flanges are necked down to roughly 2.20” at that point, then open up to 2.5” once you get past that. Even though, the 2.5” mandrel 90 degree turn seems to be less restrictive than anything smaller, so you could find a few hp and lbft throughout the pull range.

Did you calculate your finished static compression ratio to actually be 8.4 to 1?

Dennis

Hi Dennis, I don't think Mike will mind me answering your question. I had two SD manifolds by my workbench, unfortunately both were left sides. They both measured 2.08 across and pretty concentric. Oddly my 70 TA d-port manifolds measure 2.18 across and a little bigger N & S.

Please clarify, you guys like the Pypes head pipes? I thought they were great until they changed the sealing flange. It's been a headache to get them to seal with the large aftermarket port exits.

I should add the RH SD manifold I had nearby measured more like my 70 d-port but I'm not certain it's OEM.

[SD455DJ]

Thanks for checking your SD/RA manifolds Paul! I bet the outlet diameters varied from casting to casting a little bit...maybe .060" to .080".

Yes, we've liked using the Pypes head pipes so far. They do need a little filing to fit along the studs, but we've been lucky to not have any sealing issues...knock on wood...lol.

Dennis

[Skip Fix]

I do not remember if I used RARE or Torque Technology(now retired made great madrel tailpipes for A and F bodies) head pipes on the 2.5" RARE D port manifolds on my 81 TA. They were hard to seal as the area on the manifold is thin once bored out to 2.5", and at 2.5" the nuts on the studs are really close too.

Forgot the name of the old NMCA SD driver I do think he had short red hair.