[67Lemons]

I know this is a silly subjective question but how strong was the 1972 400 in the GTO? Considering a good state of tune, no obvious mechanical issues etc.

I ask because the stock 400 in my 72 GTO can’t spin the tires from a dead stop and needs to be revved to about 3k before it will spin the tires. Basically stock as far as I know with 117k, I see evidence of a cam swap at some time but stock idle, compression is 140-150 across the board, timing optimized with a curve that comes in around 2800 and total at 34 degrees, proper tune on the factory Quadrajet with jetting and rods suggested by Cliff. Car has a factory M20 and 3:23 gears, it feels strong through the gears but wow it feels like a turd off the line.

I always heard that these stock 400’s were pretty strong with a lot of torque so I don’t know if it’s just me or this engine is tired or something else. Again, I know it’s a silly question but figured it will bring some discussion if nothing else.

[JLMounce]

If there is evidence of a cam swap, it may have reduced your low-end torque slightly. Coupled with the weight of your GTO and your gearing, I could understand the car being a little sluggish off the line, but moving nicely through the gears.

Your M20 should have a 2.52 first gear. Multiply your 3.23 rear gear and you get an effective starting line ratio of 8.14:1. Most performance street cars with lower power, would prefer a 9:1 to 11:1 starting line ratio for maximum acceleration out of the whole. If you've got very tall tires on the car, that makes the effective ratio even worse. The factory tire would have been between 26 to 26.5" in diameter. A modern 27" tire is usually used.

The easiest way to skin that cat would be a gear change. A 3.55 gear gets you just under 9:1 starting line, while a 3.73 gets you solidly to 9.4. You'll notice much better first gear performance by doing this, at the expense of highway cruising.

For a best of both worlds approach, you can keep the 3.23 rear gear and go to a wide ratio TKX. You get even better highway cruise ability and the 3.27 first gear gets you a 10.56:1 starting line ratio. That would completely transform how the car behaves.

[PunchT37]

Harmonic balancer timing mark verified?

In other words, slipped outer ring?

[67Lemons]

Originally Posted by PunchT37

Harmonic balancer timing mark verified?

In other words, slipped outer ring?

Yep, verified the mark prior to timing the engine.

[67Lemons]

Originally Posted by JLMounce

If there is evidence of a cam swap, it may have reduced your low-end torque slightly. Coupled with the weight of your GTO and your gearing, I could understand the car being a little sluggish off the line, but moving nicely through the gears.

Your M20 should have a 2.52 first gear. Multiply your 3.23 rear gear and you get an effective starting line ratio of 8.14:1. Most performance street cars with lower power, would prefer a 9:1 to 11:1 starting line ratio for maximum acceleration out of the whole. If you've got very tall tires on the car, that makes the effective ratio even worse. The factory tire would have been between 26 to 26.5" in diameter. A modern 27" tire is usually used.

The easiest way to skin that cat would be a gear change. A 3.55 gear gets you just under 9:1 starting line, while a 3.73 gets you solidly to 9.4. You'll notice much better first gear performance by doing this, at the expense of highway cruising.

For a best of both worlds approach, you can keep the 3.23 rear gear and go to a wide ratio TKX. You get even better highway cruise ability and the 3.27 first gear gets you a 10.56:1 starting line ratio. That would completely transform how the car behaves.

Interesting take on it and a TKX is planned for the distant future so I need to keep that in mind.

[PunchT37]

Cam ICL could be too late. Kind of a pain to check that.

[steve25]

I bet that the new cam that was put in was not degreed during install and is at least 2 degrees retarted currently and maybe more depending on how the timing chain is.
You can check the chain’s condition easily in 25 minutes.

Pull all the plugs out.

Kill power to the coil.

Next remove the distributor cap such that you can see the rotor.
Next grab the balancer and move it back & forth about 1.5 inches and you should see only a slight lag in the rotor responding to the balancer movement if the chain is good.

Do you at least know how much lift that cam has?

[JLMounce]

The OP didn't really indicate that the engine was running poorly. It just lacks performance from what he is/was expecting.

A cam not degreed correctly, or a loose timing chain is always a possibility, but if we're being honest, unless the engine is running really poorly, it's probably not something that's going to be checked or dealt with.

If we take the engine for what it is, a stock 1972 400 with the possibility of a mild cam, I would posit that this car is behaving in a way it always would have and the expectation that it would have great performance isn't necessarily accurate. Especially not against modern vehicles.

It's a car that with a driver will weigt somewhere between 4000-4200 lbs. It has an engine that from the factory made 250 net hp, the calculation of which started in 1972. It would have been rated around 325 ft lbs of torque. There's nothing here to indicate that the installed cam is making a punch more power, or that it's install would be robbing a bunch. The engine has to carry somewhere between 15.25 to 16.25 lbs per hp. That's basically the HP to weight ratio of a 2000 Honda Accord v6.

The car in question wasn't fast when it was new and it's certainly not fast now, especially when compared to modern vehicles.

So, if you take the engine for what it is now, and the desire is to increase performance of the car as a whole, it's all in the torque multiplication. The car needs more gear to help motivate it's weight with the power it has. Yes you may gain back a little power and torque by optimizing the cam timing, but it's not going to do what going from low 8:1 starting line ratio to a 10:1 starting line ratio is going to do.

[Formulajones]

A 2.52 and 3.23's isnt going to set the tires on fire at the stop light drags.

It'll be poochy by design till you get going, pretty much exactly what you described.

Gear changes will fix it. I'd suggest a 5 speed swap with more 1st gear, a rear gear swap as well is typically what I do, and then enjoy the benefits of low rpm cruising too. Best of both worlds.

[1969GTO]

Are you getting full throttle when you hit the pedal to the floor?

[steve25]

You did not mention if you are running headers or exh manifolds, but if your running the latter you need to check if the heat riser flap in the passenger side exh manifold is rusted in place and is partially closed .

Tons of folks miss this power strangling problem.

[moneypit]

I just went through a bunch of headaches with my bone stock 71 400/400. TCS was the culprit in my case. Your 72 came with that garbage as well. The factory carb also does not have a provision for ported vacuum. The stock can on my car added 20 degrees of timing off manifold vacuum and the stock "hood hinge" springs wouldn't allow full mechanical advance until 4200 rpm! After putting in lighter springs, limiting the advance can, and bumping initial timing it's like a new car.

[steve25]

Your total mechanical timing does not come in until 2800 and yet your complaining that the car can’t spin the tires until 3000 rpm sounds to me like you can bring in your total mechanical timing a lot sooner.

Have you investigated how much timing you can bring in before you hear the motor ping in 4th gear?

That stock cam is a 067 in that year and by 3000 rpm it’s well into it peak torque range and maybe even on the out bound side of the peak torque band, so by 2500 rpm with the needed proper timing it should be starting to pull hard.

[67Lemons]

All fantastic suggestions and to answer a few questions, the only reason I can assume that the cam was replaced is because there was a box of old factory GM lifters in a tattered Erson Cams lifter box in a pile of spare parts when I received the car, the box looks to be from the 80’s or 90’s based on what I can see online.

I have not checked the timing chain yet but when I replaced the HEI unit (due to sticking weights) and installed the new distributor I didn’t notice any slack when I turned the engine over by hand to align the timing marks. Still want to check for chain slack anyway just in case, great suggestion.

The previous owner owned the car for 25 years and at some point must have switched mechanics because some of the most recent work looked a little shoddy to me which is why I went through the tune up with new plugs, wires, distributor, carb tuning with jets and rods.

Exhaust manifold was leaking when I purchased the car last year due to crack so I replaced the factory log on the passenger side without the flapper valve. I also installed a new 2.5 Pypes system since I was doing exhaust work.

I did verify full throttle opening with the pedal to the floor.

The TCS system appears to be disabled but I should dig in a little deeper to be sure. When I installed the new distributor I used an adjustable vacuum advance can and verified my total timing at 34 degrees so that’s good to go.

All of this work was basic tune up stuff IMO and I did all of it in the winter before I really drove the car last year to make sure that it was safe and sound for the road so I can’t say if it improved vs the way I purchased it or not. It just seems that while the car doesn’t have any major issues the performance is pretty lackluster and maybe that’s the way it’s supposed to be or shall I say the way it was when the car was new? I know a few of you guys had these cars when new so I was hoping for some opinions on that.

I think Jason hit the nail on the head with his assessment, I guess these cars just weren’t “fast” back in the day and all the stories I’ve heard over the years about the impressive Pontiac torque doesn’t apply to these cars once the compression dropped and gas crunch started?

[67Lemons]

Originally Posted by steve25

Your total mechanical timing does not come in until 2800 and yet your complaining that the car can’t spin the tires until 3000 rpm sounds to me like you can bring in your total mechanical timing a lot sooner.

Have you investigated how much timing you can bring in before you hear the motor ping in 4th gear?

That stock cam is a 067 in that year and by 3000 rpm it’s well into it peak torque range and maybe even on the out bound side of the peak torque band, so by 2500 rpm with the needed proper timing it should be starting to pull hard.

Good point, I have NOT tested for ping in 4th gear and definitely went with a safe curve and tune, maybe there’s a little more to be found by lowering the when I bring in total timing.

[PontiacHO]

Clutch slipping? Absolutely sure it’s a 3.23 rear gear?

[steve25]

Also if the vehicle has AC from the factory it’s very unlikely that it has 3.23 gears out back , the norm I believe by 1972 was 2.73 and that would explain a lot .

I know for a fact that 1970 that with AC and a wide ratio 4 speed that 3.23 was the norm.

With a 14” G70 tire on the car and with 3.23 gears the engine rpm in high gear should be 2510.

[67Lemons]

The build sheet lists the 3.23 and I verified it during the rear end service.

I forgot that I had dyno sheets in the paperwork when I got the car, not sure if it was an engine dyno indicating that maybe it was rebuilt or chassis dyno and the numbers are at the rear wheels?

[JLMounce]

Originally Posted by 67Lemons

All fantastic suggestions and to answer a few questions, the only reason I can assume that the cam was replaced is because there was a box of old factory GM lifters in a tattered Erson Cams lifter box in a pile of spare parts when I received the car, the box looks to be from the 80’s or 90’s based on what I can see online.

I have not checked the timing chain yet but when I replaced the HEI unit (due to sticking weights) and installed the new distributor I didn’t notice any slack when I turned the engine over by hand to align the timing marks. Still want to check for chain slack anyway just in case, great suggestion.

The previous owner owned the car for 25 years and at some point must have switched mechanics because some of the most recent work looked a little shoddy to me which is why I went through the tune up with new plugs, wires, distributor, carb tuning with jets and rods.

Exhaust manifold was leaking when I purchased the car last year due to crack so I replaced the factory log on the passenger side without the flapper valve. I also installed a new 2.5 Pypes system since I was doing exhaust work.

I did verify full throttle opening with the pedal to the floor.

The TCS system appears to be disabled but I should dig in a little deeper to be sure. When I installed the new distributor I used an adjustable vacuum advance can and verified my total timing at 34 degrees so that’s good to go.

All of this work was basic tune up stuff IMO and I did all of it in the winter before I really drove the car last year to make sure that it was safe and sound for the road so I can’t say if it improved vs the way I purchased it or not. It just seems that while the car doesn’t have any major issues the performance is pretty lackluster and maybe that’s the way it’s supposed to be or shall I say the way it was when the car was new? I know a few of you guys had these cars when new so I was hoping for some opinions on that.

I think Jason hit the nail on the head with his assessment, I guess these cars just weren’t “fast” back in the day and all the stories I’ve heard over the years about the impressive Pontiac torque doesn’t apply to these cars once the compression dropped and gas crunch started?

It certainly sounds like for all intents and purposes, this is a well running stock or near stock configured car.

If the engine accelerates smoothly without any hiccups, coughs, bangs or dead spots, it's likely that it just doesn't make the power you were hoping for.

You're correct that smog era engines can't really compare to the pre-smog era stuff. There's a big difference in a 1972 400 with a 7k3 head and a 1969 400 with a 48 head. Remember, it's not just Pontiac that suffered. Everything from that era just sucked.

Your car could absolutely benefit from some extra ponies, and double checking everything discussed here could free up some, but it's not going to radically change anything.

For ****s and giggles I looked up the published 1/4 mile times for a 72 GTO with the 400 engine option. Between 15.5 to 16.5 seconds. If you get the car to a strip, or have other means to run a 1/4 mile, if you end up in that range, you know you're probably where the car should be.

But it does sound like you've got a decently well-sorted car. You get to decide if you want to do anything to it. There's options abound to make power from what you have now all the way to 4 digits.

I think I'd find out for sure what rear gears are in the car, and if possible I'd try to get a TKX in there quickly. The wide ratio trans with the deep 1st gear will absolutely transform how the car behaves without sacrificing on it's ability to cruise. The only real drawback is a lighter wallet.

[67Lemons]

Originally Posted by 67Lemons

The build sheet lists the 3.23 and I verified it during the rear end service.

I forgot that I had dyno sheets in the paperwork when I got the car, not sure if it was an engine dyno indicating that maybe it was rebuilt or chassis dyno and the numbers are at the rear wheels?

Just confirmed from the previous owner that the dyno sheets are at the rear wheels with 100k on the odometer, he even comments that the 250hp was the original factory rating and they got that with 100k on the clock.