[78P-T/A]

Originally Posted by SD455DJ

Here is an actual dyno test of a '79 W72, but with an actual 8.1 to 1 static compression ratio. The purpose of the rebuild was to keep the engine as original to factory production as possible. So, this would give you a good idea of what to expect in power output.

"Here are some real-world results of a stock W72 400 rebuild that was relatively low miles (51,000) and starting to lose the original cam. This was Dan’s red ’79 TA W72/WS6 (that he subsequently traded for his current 25,000 mile all original black WS6 TA). Dan pulled the engine due to a little rocker noise and discovered all of cam lobes starting to wear, so decided to tear it down, install new rings and bearings, resize the stock rods, polish the crank, and re-balance the stock rods, pistons, & new rings. His intension was to keep it stock, so he needed a new cam and ordered a custom ground Comp Cams that is somewhat close to the factory cam with 202/219 (255/261 adv.) duration at .050” lift with .420”/.450” lift ground on a 110 lcl. Dan degreed several lobes of the original cam at 199/216 @ .050 and .397”/.406” in worn condition.

He didn’t deck the block to preserve the piston size stampings and measured the factory pistons to be and average of .0114” down (yes, the pistons have the perimeter chamfer). The 6X-4 heads got a slight cut of .002/.003” to true up and new guides and seals with the original valves and springs (that checked out great). The heads measured 91.8 cc’s average and the valve reliefs, above ring and crown chamfer measured 9.8 cc’s that calculated out to 8.1 to 1 static compression…just as advertised. Dan used .046” head gaskets to keep the compression at factory advertised and quench at a high .0574”. Using the Felpro 1016 gaskets with .039” thickness would bump the compression up to 8.22 and lower the quench to .0504”.

The first dyno session they made 23 pulls and found the engine power dropping the last several pulls. Worried, they pulled the valve covers and found lots of glitter! The bearings were toast due to the rod big ends going out of round, even after resizing and using new ARP rod bolts! So, Dan rebuilt the engine with Eagle forged H-beam rods with the original cast pistons…obviously new rings & bearings were installed. (This is the second motor that lost the bearings due to the cast rods going out of round!)

After he reassembled and broke-in the engine he took it to the engine back to the dyno to continue the testing…in 6 variations:

1) With the original ’79 exhaust manifolds through the factory Y-pipe, no ac base
2) With the original ’79 exhaust manifolds through the factory Y-pipe with ac base
3) With ‘71/72 A/F-body log exhaust manifolds with dual 2.25” headpipes with ac base
4) With factory A/F-body Ram Air manifolds with 2.5” mandrel headpipes with ac base
5) Same as 4 with TA air cleaner no scoop
6) Same as 4 with TA air cleaner with scoop (not opened up)

Dyno results (2800 to 5000 rpm):

1) 397.3 tq @ 3400 / 300.0 hp @ 4900
2) 402.0 tq @ 3400 / 305.6 hp @ 5000
3) 413.0 tq @ 3400 / 328.8 hp @ 4900
4) 420.2 tq @ 3700 / 335.3 hp @ 4800
5) 417.6 tq @ 3400 / 331.8 hp @ 4800
6) 412.2 tq @ 3400 / 322.8 hp @ 4700

This is not a max’ed out PSMCDR engine build by any stretch, just a good street rebuild that will perform a little better than original. If you are going to run the stock heads and compression, the Summit 2800 cam (204/214/112 @ .422”/.444”) will be fairly close to these numbers. Since the custom CC cam has the quicker ramps it did build cylinder pressure faster, so is a good cam to use with really low (under 8.5) compression. The Crower 60240 cam is a good choice too, but maybe a little softer down low. Dan was interested in seeing what a very-close-to-factory-original W72 400 would make for power. Installed back in the heavy (loaded) TA with the factory exhaust manifolds, Y-pipe, and test pipe in place of the catalytic convertor, it felt like a low 14 sec. car."

Dennis

those are some really great numbers! Good information for someone like me who doesn't understand this very well 😅 thank you very much! How does this Summit 2800 compare to the cc xe262h that has been mentioned before do you think?

[Shiny]

Great post, Dennis. Thanks.

I was surprised by such a strong exhaust flow influence. I have read that about these engines on many PY threads but always assumed the exhaust flow benefits were about higher HP builds. Wrong again, Mike...

!!

And sorry for diverting but I'd be upset if I had paid to resize rods and they weren't stable. I would NOT expect this. Good to know! I wonder why? Maybe they creep a little under the loads of new rod bolts? Seems unexpected so thanks for sharing this too.

Mike

[Stan Weiss]

Originally Posted by SD455DJ

Here is an actual dyno test of a '79 W72, but with an actual 8.1 to 1 static compression ratio. The purpose of the rebuild was to keep the engine as original to factory production as possible. So, this would give you a good idea of what to expect in power output.

"Here are some real-world results of a stock W72 400 rebuild that was relatively low miles (51,000) and starting to lose the original cam. This was Dan’s red ’79 TA W72/WS6 (that he subsequently traded for his current 25,000 mile all original black WS6 TA). Dan pulled the engine due to a little rocker noise and discovered all of cam lobes starting to wear, so decided to tear it down, install new rings and bearings, resize the stock rods, polish the crank, and re-balance the stock rods, pistons, & new rings. His intension was to keep it stock, so he needed a new cam and ordered a custom ground Comp Cams that is somewhat close to the factory cam with 202/219 (255/261 adv.) duration at .050” lift with .420”/.450” lift ground on a 110 lcl. Dan degreed several lobes of the original cam at 199/216 @ .050 and .397”/.406” in worn condition.

He didn’t deck the block to preserve the piston size stampings and measured the factory pistons to be and average of .0114” down (yes, the pistons have the perimeter chamfer). The 6X-4 heads got a slight cut of .002/.003” to true up and new guides and seals with the original valves and springs (that checked out great). The heads measured 91.8 cc’s average and the valve reliefs, above ring and crown chamfer measured 9.8 cc’s that calculated out to 8.1 to 1 static compression…just as advertised. Dan used .046” head gaskets to keep the compression at factory advertised and quench at a high .0574”. Using the Felpro 1016 gaskets with .039” thickness would bump the compression up to 8.22 and lower the quench to .0504”.

The first dyno session they made 23 pulls and found the engine power dropping the last several pulls. Worried, they pulled the valve covers and found lots of glitter! The bearings were toast due to the rod big ends going out of round, even after resizing and using new ARP rod bolts! So, Dan rebuilt the engine with Eagle forged H-beam rods with the original cast pistons…obviously new rings & bearings were installed. (This is the second motor that lost the bearings due to the cast rods going out of round!)

After he reassembled and broke-in the engine he took it to the engine back to the dyno to continue the testing…in 6 variations:

1) With the original ’79 exhaust manifolds through the factory Y-pipe, no ac base
2) With the original ’79 exhaust manifolds through the factory Y-pipe with ac base
3) With ‘71/72 A/F-body log exhaust manifolds with dual 2.25” headpipes with ac base
4) With factory A/F-body Ram Air manifolds with 2.5” mandrel headpipes with ac base
5) Same as 4 with TA air cleaner no scoop
6) Same as 4 with TA air cleaner with scoop (not opened up)

Dyno results (2800 to 5000 rpm):

1) 397.3 tq @ 3400 / 300.0 hp @ 4900
2) 402.0 tq @ 3400 / 305.6 hp @ 5000
3) 413.0 tq @ 3400 / 328.8 hp @ 4900
4) 420.2 tq @ 3700 / 335.3 hp @ 4800
5) 417.6 tq @ 3400 / 331.8 hp @ 4800
6) 412.2 tq @ 3400 / 322.8 hp @ 4700

This is not a max’ed out PSMCDR engine build by any stretch, just a good street rebuild that will perform a little better than original. If you are going to run the stock heads and compression, the Summit 2800 cam (204/214/112 @ .422”/.444”) will be fairly close to these numbers. Since the custom CC cam has the quicker ramps it did build cylinder pressure faster, so is a good cam to use with really low (under 8.5) compression. The Crower 60240 cam is a good choice too, but maybe a little softer down low. Dan was interested in seeing what a very-close-to-factory-original W72 400 would make for power. Installed back in the heavy (loaded) TA with the factory exhaust manifolds, Y-pipe, and test pipe in place of the catalytic convertor, it felt like a low 14 sec. car."

Dennis

Dennis,
A few years ago you post up a W72 that made 371 HP. It had 8.75:1 CR and the Summit 2800. Were those the only differences from this engine?

Stan

[SD455DJ]

Originally Posted by 78P-T/A

those are some really great numbers! Good information for someone like me who doesn't understand this very well 😅 thank you very much! How does this Summit 2800 compare to the cc xe262h that has been mentioned before do you think?

78P-T/A - I think the xe262h would be a solid choice for your engine as well as the 2800...maybe the better cam, as it will build cylinder pressure more quickly as designed. You will need new valve springs to accommodate the higher lift with the 'xe' cam.

Dennis

[Skip Fix]

The XE 262 I put in my 78 motor was a FUBAR initially. Outer cam journal was too big to fit in the motor! It was 0.002 too big compared to every other journal on it and other cams I have. I had to pay for shipping to get the old one back before they would grind a new one so I just paid for a new one and then they refunded that when the old one went back. It ran OK just not any better than the 2801.

[SD455DJ]

Originally Posted by Shiny

Great post, Dennis. Thanks.

I was surprised by such a strong exhaust flow influence. I have read that about these engines on many PY threads but always assumed the exhaust flow benefits were about higher HP builds. Wrong again, Mike...

!!

And sorry for diverting but I'd be upset if I had paid to resize rods and they weren't stable. I would NOT expect this. Good to know! I wonder why? Maybe they creep a little under the loads of new rod bolts? Seems unexpected so thanks for sharing this too.

Mike

Mike - Yes, when properly rebuilt/reconditioned rods go south on you, it convinces you in a heartbeat to go with good new forged rods as standard practice in Pontiac engine rebuilds. We were probably just unlucky, where we know that most of the time this doesn't happen. It's bad enough when it happens in one of your personal engines, but in a customers...more time & money.

Dennis

[SD455DJ]

Originally Posted by Stan Weiss

Dennis,
A few years ago you post up a W72 that made 371 HP. It had 8.75:1 CR and the Summit 2800. Were those the only differences from this engine?

Stan

Stan, Here are the specifics to that '78 W72:

" Long story short, Dan rebuilt the original numbers matching engine with .040" over Icon forged pistons w/4.5 cc valve reliefs that are .006" out of the hole and with .045" x 4.328" Felpro head gaskets to provide .040" quench depth. The 6X-4 heads were minimally cut for trueness and measured 92.45 cc's average for a final static compression ratio of 8.75 to 1. Dan replaced the cast rods with forged Eagle H-beam rods. New 1-pc valves (2.11/1.66) with CC dual springs were installed. A Summit 2800 cam (204/214/112 @ .422”/.444”) with new 'old' Crane hydraulic lifters along with a new Melling 60 psi oil pump. The one modification was the use of old factory D-port ram air exhaust manifolds with the 2.1" outlets with Pypes 2.5" mandrel headpipes. The original 17058263 Q-jet on the factory cast iron intake with the EGR system and plumbing were reinstalled.

The base runs were made with 42 degrees total timing in by 3000 rpm, 45 primary rods/74 jets/CH secondary rods on an I hanger. The 3rd (and best) base pull made a corrected 360.3 hp