[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

[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