[AJ-]

I’m about to swap in a fresh mild 400. Lightly ported 6x heads and 8.5:1 compression. The cam is pretty close to a 068 cam (213/218 @0.050 and around 0.440/0.460 lift with the 1.65 rockers and 114 lsa) Th350, 3.42 gears/Truetrac are the rest of the combo.

The questions is I’ve got two convertors sitting in the garage, one is my stock one and the other is a 10” converter from a friend’s car with a similar setup that seemed to flash around 2500-2800. I was going to swap but now I’m leaning towards just keeping the stock converter. The car is mostly just a summer cruiser for around town with the odd 30 min trip on the highway. Will probably take it to the track for a few passes here and there as well just for kicks. Any advice which way I should go?

I’ll also throw this in for some armchair dyno fun: any guesses on reasonable expectations for hp/tq for this engine?

[PunchT37]

I would put the 10 inch. Low compress 400. Yep.


Should make around 340 hp or so with 420`ish torque.

[NeighborsComplaint]

A stock W72 with 6x-4 heads and an 067 cam made 220 HP. I don't see how that 068 spec cam and home head porting could be worth 120hp.

[PunchT37]

A stock W-72 didn`t come with a 067 cam, and didn`t have 440/460 lift.

[Schurkey]

Originally Posted by AJ-

I’ve got two convertors sitting in the garage, one is my stock one and the other is a 10” converter from a friend’s car with a similar setup that seemed to flash around 2500-2800.

My engines tend to idle nice; I put stock converters in all of 'em.

OTOH, if I had a modern, efficient "performance" converter, I'd probably try it and see what happens. If this was an older, mass-market sloppy-loose converter, it'd go on the scrap pile or perhaps I'd see if the guts could be reworked into something usable.

[steve25]

I would run the 10” converter since the 068 was never factory installed in a motor with as little as 8.5 compression!

[PontiacJim1959]

Originally Posted by Schurkey

My engines tend to idle nice; I put stock converters in all of 'em.

OTOH, if I had a modern, efficient "performance" converter, I'd probably try it and see what happens. If this was an older, mass-market sloppy-loose converter, it'd go on the scrap pile or perhaps I'd see if the guts could be reworked into something usable.

X2 - you want what is called a "tight" converter versus one of the "loose" stall converters. The loose style converters have a lot of slip and are more aimed for competition. A quality "tight" converter is designed to have much less slip for general type driving and will snap up to the RPM design of the converter when you hit the gas pedal to the floor.

The tight type converters also run cooler than the loose type. I am one for adding a trans cooler independent of the radiator tank. I mount it in front of the radiator, or some place where it will get good air flow and connect my lines which may require some line fabrication/extension - but that is my choice.

I think 2,500-2,800 is a little much and would shoot for 2,200-2,500 for a street cruiser. Stock converters are said to have an 1,800 stall.

[ta man]

I think 2,500-2,800 is a little much and would shoot for 2,200-2,500 for a street cruiser. Stock converters are said to have an 1,800 stall.[/QUOTE]

What is the reasoning for a lower stall?..A good quality tight convertor in the 2800 to 3200rpm range would be a good addition and would compliment the gearing. The only thing it will hurt will be the tires.

[Formulajones]

Since you have both converters sitting there my vote is to try both of them. If you don't like one, it's only an afternoon to switch to the other converter and have a go at that one.

Having a RAIII car with the 068 cam and racing the car a bunch, I tried a converter just this past year and can tell you it made no difference at the track for me.

Mine with it's stock converter had cut a best of a 1.89 60 foot, and had run a best of 13.10, and would run in the teens and twenties most of the time right around 104-105 mph.

I had the opportunity to purchase a 69 GM L88 converter. Anyone that knows those converters know they drive around pretty tight, they couple well at cruise speeds, and generally flash around 2800 with an engine that will push it. They are a pretty decent all around mild converter.

So I installed it. Drives around almost like the stock converter, however at the track it flashes to about 2600 rpm for me. Best 60 foot with it so far is a 1.91 and the car hasn't run any quicker or faster with it. In fact so far it's been running about dead on the number it's always run.

For me the converter change didn't do anything. I have a couple ideas as to why that I'll experiment with this year. But the reality is, it's not a huge converter change as far as stall speed, and these little engines with 068 cams aren't power houses either so I wouldn't expect to see much at the track with a very mild converter swap. On the street however you might like one over the other, so try both.

[NeighborsComplaint]

Originally Posted by PunchT37

A stock W-72 didn`t come with a 067 cam, and didn`t have 440/460 lift.

"For 1978, Pontiac improved the W72 by changing the specs on their camshafts. Essentially, they added more duration and added 1:50 ratio rocker arms. In cam tests, the W72 grind was every bit as good as the fabled 067 Pontiac grind."

Performed same as 067 so excuse the over-simplification. You're talking a modest increase in duration and lift with the OP's proposed cam which obviously creates a modest HP increase over stock, probably in the area of 20 HP. Unless the OP is going to run 100HP shot of nitrous, the motor won't make 340 HP. It is what it is, a low compression 400 that will run really good.

[tjs72lemans]

My rebuild is close to what you have. I ended up with 310 hp and 400 ft lbs torque.

[geeteeohguy]

Judging by the way you use your car, I would install the stock converter. But I drive on the street and highways all the time, not on the strip.

[Kenth]

Originally Posted by steve25

I would run the 10” converter since the 068 was never factory installed in a motor with as little as 8.5 compression!

FYI, 1971-72 Pontiac 455HO has 8.4:1 static compression, and the 068 camshaft from factory.

[AJ-]

Some good points raised here, thank-you for the opinions and rationale on both sides of the converter coin. I especially appreciate the track times report-#'s don't lie. I guess the main difference would be my compression is lower which may take away on the bottom end a bit. The converter may make it feel a little snappier but I also kind of like the idea of just a nice stockish combo that works well together, too. I will have to chew on it a bit.

In terms of the hp, the W72 220hp rating is net advertised rating, I thought I read somewhere that 260-280hp was more comparable? In that case the numbers from tjs72lemans make sense. Honestly I'd be real happy with 300hp/400tq. It's replacing a stock 7.6:1 350 so that would be a nice jump.

[ta man]

The 260hp to 280hp is about right. I forget what NHRA factors them at.

[PontiacJim1959]

Originally Posted by ta man

I think 2,500-2,800 is a little much and would shoot for 2,200-2,500 for a street cruiser. Stock converters are said to have an 1,800 stall.

What is the reasoning for a lower stall?..A good quality tight convertor in the 2800 to 3200rpm range would be a good addition and would compliment the gearing. The only thing it will hurt will be the tires.[/QUOTE]

The OP is not looking for a race car. 2,500-2,800 is giving up a lot of usable bottom end RPM torque. It's an "068" cam, not an "041" cam. 2,200 - 2,500 would be a far better choice, period.

[Formulajones]

Not from my experience. As I mentioned I went from using the stock converter, flashing about 1800, to an L88 that flashes to 2600, and it didn't do a damn thing at the track. So why would lowering the stall further do anything. It wont. Peak TQ even with my RAIII and 068 cam is still up over 3,000 rpm, and the 400 068 combo isn't a huge power maker anyway.

If you want to see gains with a converter you need one that flashes up in the 3,000+ range with this combo, just like TA Man said.

To go even further, there are converter companies out there that can build a converter to do just that and still be coupled very well for normal day to day driving. Just because a converter flashes at 3400 rpm doesn't mean it's going to give away any bottom end torque or drivability. That's a very common misconception. In fact some will drive around like it's not even there until you whack the throttle if you find a good converter company that knows what they are doing.

[PontiacJim1959]

Originally Posted by Formulajones

Not from my experience. As I mentioned I went from using the stock converter, flashing about 1800, to an L88 that flashes to 2600, and it didn't do a damn thing at the track. So why would lowering the stall further do anything. It wont. Peak TQ even with my RAIII and 068 cam is still up over 3,000 rpm, and the 400 068 combo isn't a huge power maker anyway.

If you want to see gains with a converter you need one that flashes up in the 3,000+ range with this combo, just like TA Man said.

To go even further, there are converter companies out there that can build a converter to do just that and still be coupled very well for normal day to day driving. Just because a converter flashes at 3400 rpm doesn't mean it's going to give away any bottom end torque or drivability. That's a very common misconception. In fact some will drive around like it's not even there until you whack the throttle if you find a good converter company that knows what they are doing.

I see you are still hooked on the "race application." We are going to have to agree to disagree on this one.

[johnta1]

Formulajones, do you run slicks at the track?

[Formulajones]

Originally Posted by PontiacJim1959

I see you are still hooked on the "race application." We are going to have to agree to disagree on this one.

Um no, I'm talking about a multi application. I daily drive the car, and have been racing that combo off and on for more than 25 years.
Aside from maybe Dennis, and a couple other PS racers we are familiar with, I don't think there is anyone on this forum that has exploited that combination more than I have. And I'm saying, if you are looking for a performance advantage, as is generally the case if you're looking at stall converters, anything less than 3,000 rpm isn't going to do much, if anything at all for this mild combo.

In other words, don't waste money on mild 2200-2500 converters, even for a street car, which mine is.

It would be money better spent to have someone like Cliff, using TSP, to build an efficient converter that flashes up near torque peak, yet will still drive around like a pussy cat on the street. It's the best of both worlds.