[Sirrotica]

One other question, how many miles on the original engine? That originally came with a nylon timing gear in it, and if it is still in there the cam timing may be way off of spec. Retarding cam timing kills low end, so it may be sluggish because of worn timing components. Or you may have cam lobes going away, one or two nearly flat cam lobes pretty much kill power.

For sake of comparison I had a 68, 400 4 bbl Bonneville with the same gearing, got over 17 MPG on a trip, and would burn the single wheel as long as you wanted to hold your foot into it. Stock cam, and single exhaust.

I wouldn't go with 670 heads with the closed chambers, they have a tendency to detonate when running pump gas. If it were me I'd say with the lower compression heads with small valves. You're never going to be in the RPM range to make good use of larger valves anyway. The 389s used the small valves in them for many years in GTOs and most 4bbl engines previous to 1967. Unless you're building this car to be a street racer no need to build the engine like a drag engine is built, on the street you won't have much occasion to get in the 5000 RPM range very much.

Freeing up the exhaust, optimizing the timing curve, richening the jets up a few sizes, and mostly factory parts should get you some stump pulling torque to pull that heavy barge around.

I used a 1973 400 2 bbl engine with a 067 camshaft, and swapped to a Q jet and factory intake to pull around a 5800 lb Jeep truck. Low compression and small valve heads had more than enough power. Before I put the 400 in, I had a 350 Pontiac engine in it but broke a piston, and ended up swapping to the 400, because I had it already to go. Optimizing what you already have should be plenty to move that wagon around at a satisfactory pace.

I almost forgot, I had 2 of the 71-76 clamshell tailgate wagons with 455s in them, low compression, and I wasn't ashamed of how either of those wagons ran. I just optimized the stock parts on both of them, they are much heavier than a 67 wagon is by about 800 lbs, they weighed 5300 lbs.

Pontiac engineers excelled at making low RPM torque to pull their rather heavy cars around, and still keep the RPM down to get at least decent fuel mileage. Wagons have a higher percentage of rear wheel weight by the body construction, so if it won't spin the rear wheels, that's because you have more weight over them than a coupe has, figure accordingly.

[GTOKIDRH]

Originally Posted by Sirrotica

One other question, how many miles on the original engine? That originally came with a nylon timing gear in it, and if it is still in there the cam timing may be way off of spec. Retarding cam timing kills low end, so it may be sluggish because of worn timing components. Or you may have cam lobes going away, one or two nearly flat cam lobes pretty much kill power.



For sake of comparison I had a 68, 400 4 bbl Bonneville with the same gearing, got over 17 MPG on a trip, and would burn the single wheel as long as you wanted to hold your foot into it. Stock cam, and single exhaust.



I wouldn't go with 670 heads with the closed chambers, they have a tendency to detonate when running pump gas. If it were me I'd say with the lower compression heads with small valves. You're never going to be in the RPM range to make good use of larger valves anyway. The 389s used the small valves in them for many years in GTOs and most 4bbl engines previous to 1967. Unless you're building this car to be a street racer no need to build the engine like a drag engine is built, on the street you won't have much occasion to get in the 5000 RPM range very much.



Freeing up the exhaust, optimizing the timing curve, richening the jets up a few sizes, and mostly factory parts should get you some stump pulling torque to pull that heavy barge around.



I used a 1973 400 2 bbl engine with a 067 camshaft, and swapped to a Q jet and factory intake to pull around a 5800 lb Jeep truck. Low compression and small valve heads had more than enough power. Before I put the 400 in, I had a 350 Pontiac engine in it but broke a piston, and ended up swapping to the 400, because I had it already to go. Optimizing what you already have should be plenty to move that wagon around at a satisfactory pace.



I almost forgot, I had 2 of the 71-76 clamshell tailgate wagons with 455s in them, low compression, and I wasn't ashamed of how either of those wagons ran. I just optimized the stock parts on both of them, they are much heavier than a 67 wagon is by about 800 lbs, they weighed 5300 lbs.



Pontiac engineers excelled at making low RPM torque to pull their rather heavy cars around, and still keep the RPM down to get at least decent fuel mileage. Wagons have a higher percentage of rear wheel weight by the body construction, so if it won't spin the rear wheels, that's because you have more weight over them than a coupe has, figure accordingly.

Currently it has 108K on the clock. I have quite a bit of documentation that came with the car. I'll look into the timing gear. Never crossed my mind. The cam lobe thought too. That's good info!

Sent from my SM-N950U using Tapatalk

[GTOKIDRH]

Originally Posted by GTOKIDRH

Currently it has 108K on the clock. I have quite a bit of documentation that came with the car. I'll look into the timing gear. Never crossed my mind. The cam lobe thought too. That's good info!

Sent from my SM-N950U using Tapatalk

I run pump gas in my '67 GTO with 670 heads and a slightly dished piston (9.5 :1 c.r.) with no issues. I assume that the full point increase in c. r. will add a little more power to the combination?

Sent from my SM-N950U using Tapatalk

[Sirrotica]

Originally Posted by GTOKIDRH

I run pump gas in my '67 GTO with 670 heads and a slightly dished piston (9.5 :1 c.r.) with no issues. I assume that the full point increase in c. r. will add a little more power to the combination?

Sent from my SM-N950U using Tapatalk

Rough figure is 3% of power increase, per 1 point of compression, there are better ways to get that 3% IMO. For sake of discussion, 400 CU IN at 300 HP, raise it i full point of compression and gain 9 HP. You may not be able to run pump gas at that 1 point of compression increase, so then you'll be either changing cams to bleed off low RPM compression, or blending race gas.

I could gain 9 HP with a sharp tune up, bringing the timing in sooner than stock, and richening up the carb and still run pump gas.

I would guess that there is something fundamentally wrong with the OPs engine for it to be such a slug, I worked in a Pontiac dealership in 1970, those cars weren't as slow as he's describing his to be.

I have seen some Pontiacs that someone changed the timing gears, and chain, that were 1 tooth retarded, and run like he's describing. They'll run smooth, but have no low end power whatsoever. Reset the timing gears, and it runs like a different car.

Cutting dishes in pistons is pretty expensive when you can go with a larger CC combustion chamber, and run the stock short block with flat top pistons, but I tend to be practical, and try to save money, especially when it's my money.

I've used Pontiacs from 326 to 455 in daily drivers, used them in Jeep Wagoneers and Jeep tow trucks, plus raced them on oval tracks for years, they aren't slow unless there is something wrong with the internal engine components, or the tune up is way way off. Almost all of my vehicles that were driven on the road would run on pump gas, and were under 9.5 compression ratio. A few of my GTOs were factory rated at 10.5 to 1, and the race car was 12 to 1. I got a lot of work done with relatively low compression Pontiac engines over the last 50 years. All had iron heads.

[GTOKIDRH]

Originally Posted by Sirrotica

Rough figure is 3% of power increase, per 1 point of compression, there are better ways to get that 3% IMO. For sake of discussion, 400 CU IN at 300 HP, raise it i full point of compression and gain 9 HP. You may not be able to run pump gas at that 1 point of compression increase, so then you'll be either changing cams to bleed off low RPM compression, or blending race gas.

I could gain 9 HP with a sharp tune up, bringing the timing in sooner than stock, and richening up the carb and still run pump gas.

I would guess that there is something fundamentally wrong with the OPs engine for it to be such a slug, I worked in a Pontiac dealership in 1970, those cars weren't as slow as he's describing his to be.

I have seen some Pontiacs that someone changed the timing gears, and chain, that were 1 tooth retarded, and run like he's describing. They'll run smooth, but have no low end power whatsoever. Reset the timing gears, and it runs like a different car.

Cutting dishes in pistons is pretty expensive when you can go with a larger CC combustion chamber, and run the stock short block with flat top pistons, but I tend to be practical, and try to save money, especially when it's my money.

I've used Pontiacs from 326 to 455 in daily drivers, used them in Jeep Wagoneers and Jeep tow trucks, plus raced them on oval tracks for years, they aren't slow unless there is something wrong with the internal engine components, or the tune up is way way off. Almost all of my vehicles that were driven on the road would run on pump gas, and were under 9.5 compression ratio. A few of my GTOs were factory rated at 10.5 to 1, and the race car was 12 to 1. I got a lot of work done with relatively low compression Pontiac engines over the last 50 years. All had iron heads.

Thanks for the intel! Again, the stock engine in my wagon has the low compression 8.6:1 pistons as well as the large chambered heads. My thought is I already own the 670 small chambered heads which will only push me into rhe mid 9s compression wise which is still pump gas friendly and I will gain 3% more power than why not? It's free. I won't change the heads until I do the cam swap. I'll be in there anyway. I admit that i know just enough about engines to get myself in to trouble. Still much to learn. Thoughts?

Sent from my SM-N950U using Tapatalk

[Formulabruce]

Originally Posted by GTOKIDRH

Thanks for the intel! Again, the stock engine in my wagon has the low compression 8.6:1 pistons as well as the large chambered heads. My thought is I already own the 670 small chambered heads which will only push me into rhe mid 9s compression wise which is still pump gas friendly and I will gain 3% more power than why not? It's free. I won't change the heads until I do the cam swap. I'll be in there anyway. I admit that i know just enough about engines to get myself in to trouble. Still much to learn. Thoughts?

Sent from my SM-N950U using Tapatalk

That 3% Increase in power is NOT going to be in your normal driving RPM range, IF it was, Pontiac would have done it..... ALL, and I mean ALL, Horsepower increases are at higher RPMS, and Most all are Not used in normal driving.
ALL Horsepower is calculated, even at the dyno, its Never measured.
You have a nice car, hate to see it get into "mission creep" and not enjoyed..

[amcmike]

Originally Posted by Formulabruce

That 3% Increase in power is NOT going to be in your normal driving RPM range, IF it was, Pontiac would have done it..... ALL, and I mean ALL, Horsepower increases are at higher RPMS, and Most all are Not used in normal driving.

Actually it is, and today's OEMs do.

Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.