[West Coast GTO]

My 71 GTO with 455 has had numerous upgrades( aluminum heads, intake,carb, distributor/ spark,headers, exhaust system and change to 3:55 gears from 3:08) and this car can't seem to get out of it's own way.The cam IS NOT a very aggressive profile more suited to a Pontiac 350 than a 455. It can break loose the rear tires but it seems a sluggish runner. I know virtually nothing of the auto transmission including what torque converter in installed. Is there a way to check what torque converter is installed and, if is a standard low stall unit, would a different converter make any difference?

[steve25]

You already know the issue because you posted it, it’s the Cam!

The much bigger ports of the heads you now have and the very limited air flow provided by the small amount of open valve time from the cam makes for a small amount of air passing thru that much bigger port, you have lost crucial port velocity which translates directly into lost throttle response and a motor that is slow to gain rpm!

Also have no power band to work with, that amount of CID with too small of a cam will give you a hp peak of 3800 rpm and a torque peak of 2500 rpm.

Putting aftermarket heads on a big cid motor with not enough Cam is like trying to get the complete contents of a liter water bottle into a measuring cup!

You now need a Cam of atleast 225 duration @.050” along with .490” to .550” lift.
If you do not after this work want to send out the Carb to get re-worked to feed this new Cam right then find a chassis dyno to run the car on and have the same recalibration done.

Do you know what the motor has for compression now?

[JLMounce]

Aside from getting under the car and inspecting the torque converter and trying to find a part number, there's no real way to go about finding out what's in there. You can try to measure the diameter and that might give you an idea of what the torque converter, may have capability wise, but that's just trying to make a complete guess a little more educated.

I think steve25 is probably correct here in that you've got more than just an ultra-tight torque converter. The cam is likely all wrong for the application as well.

Since you've done pretty much the entire top-end plus ignition, exhaust and a gear upgrade, I would take that information and talk with a few people (Butler, Kauffman etc. whoever you feel comfortable with) and get a cam recommendation. Do the cam and get a converter matched to the combination at the same time.

I have one of TSP's "Tight" 9" converters and it's quite a bit better than the old B&M holeshot 2000 converter I had behind my aluminum headed 455. While that tight B&M unit wasn't well suited to my engine, it never left me feeling like the car was slow. If I was at lower revs in 2nd or 3rd gear you could tell the engine wanted some extra rpm and torque multiplication, but never sluggish.

[Jay S]

The description of the engine combo is very vague. Could be a number of things holding it back.

But, if you want to get a feel of what converter is in the car…..For testing the converter, first put the car in gear and try holding it back with the brakes and see what rpm the engine overwhelms the brakes and goes forward. Then with the car rolling slow, suddenly go full throttle and check where the engine couples up solid to the drive train. If you have decent brakes the brake test will tell you where the converter is starting to couple up, and the roll test will tell you the flash speed of the converter where it tries to fully couple with the drivetrain. Stock type converter from a big car platform may only make it to 1400-1600 holding the engine back with the brakes, and flash point won’t be that different. Some of the 2000 range stalls are similar, they are loose enough the brake test and the rolling flash test are about the same. A well designed tight street converter may be 2000 rpm by the brakes, and hit’s 4000+ when it goes to full throttle. Most engines with any kind of cam at all the peak tq is 3500+, I have found even the tiny cam engines run noticeable better with a great tq converter. Most that do the small cams go with a lower stall cheaper converter, I think it helps some, but you never really see the engines full potential that a higher end tighter converter provides where the engine pulls the car off line at the tq peak, a well designed converter for the street will still is able to couple up to pull the car cruising without slipping much.

[West Coast GTO]

I do not know what the compression is but the engine had flat top pistons visible with a scope thru the spark plug holes. The upgrades ( including cam) were done before I bough the car, Cliff has rebuilt a Quad for me( not installed yet) to match the engine upgrades and he also recommended a bigger cam.

Originally Posted by steve25

You already know the issue because you posted it, it’s the Cam!

The much bigger ports of the heads you now have and the very limited air flow provided by the small amount of open valve time from the cam makes for a small amount of air passing thru that much bigger port, you have lost crucial port velocity which translates directly into lost throttle response and a motor that is slow to gain rpm!

Also have no power band to work with, that amount of CID with too small of a cam will give you a hp peak of 3800 rpm and a torque peak of 2500 rpm.

Putting aftermarket heads on a big cid motor with not enough Cam is like trying to get the complete contents of a liter water bottle into a measuring cup!

You now need a Cam of atleast 225 duration @.050” along with .490” to .550” lift.
If you do not after this work want to send out the Carb to get re-worked to feed this new Cam right then find a chassis dyno to run the car on and have the same recalibration done.

Do you know what the motor has for compression now?

[JLMounce]

Have you done a cranking compression test? That'd give a bit of information on what's in there now.

I'd almost bet that it pumps pretty high and that it may have a smallish XE style cam in it.

[ta man]

Any 455 with basic aluminum heads with a small cam should be able to roast the tires and pull hard regardless of port size especially with 355 gearing. It may not rev high but should make a ton of torque. Something is wrong...too much cranking compression and the timing set way back to compensate?? Sluggish off the shelf torque convertor slipping...transmission issues...cam installed wrong..

[pastry_chef]

https://www.summitracing.com/parts/edl-2157

If that is the cam, I'd remove it quickly. Makes me wonder about the other parts.

A Pontiac 463 target for 5300 RPM (hyd tappet - 1.65 rockers here).

After a new cam, see how it runs. If you want a new converter I strongly recommend ptcrace.com

[West Coast GTO]

Cam is a Edelbrock performer plus #2157 with valve lift .420" intake, .442" exhaust and 110" lobe separation. I did a compression test when I first bought the car and before repairing/ fixing numerous stupid installation issue from previous owner and believe numbers were consistent around 127 psi dry. I really need to re-check those numbers now.

[pastry_chef]

Originally Posted by West Coast GTO

I did a compression test when I first bought the car and before repairing/ fixing numerous stupid installation issue from previous owner and believe numbers were consistent around 127 psi dry. I really need to re-check those numbers now.

For sure re-check.
127 cranking PSI would also make a dog. Cam install would be off or your static compression sucks.
For a pump-gas performance application I'd hope to see 170 PSI min.

[West Coast GTO]

Yes, the #2157 is the cam installed. Many top end gremlins that I have addressed after buying the car indicate poor assembly/ installation when the car was upgraded. Just lazy on my part not to have changed out the cam previously but, on this car, that means A/C condenser, radiator, shroud, timing/water pump, intake, dizzy,A/C compressor brackets, PS ,alternator, etc.

Originally Posted by pastry_chef

https://www.summitracing.com/parts/edl-2157

If that is the cam, I'd remove it quickly. Makes me wonder about the other parts.

A Pontiac 463 target for 5300 RPM (hyd tappet - 1.65 rockers here).

After a new cam, see how it runs. If you want a new converter I strongly recommend ptcrace.com

[Half-Inch Stud]

Re-adjust you .dizzy for 34* Total ADV at 2800 rpm, dizzy VAC hose plugged.
Then, Verify the idle Timing is between 10* to 18*.

You might be "Tuning" the most important parameter right here.

[West Coast GTO]

Thank you,
No vacuum on MSD mag pick up but will adjust other timing settings.

Originally Posted by Half-Inch Stud

Re-adjust you .dizzy for 34* Total ADV at 2800 rpm, dizzy VAC hose plugged.
Then, Verify the idle Timing is between 10* to 18*.

You might be "Tuning" the most important parameter right here.