[Ecklund]

Not sure if this is correct forum/area. Concerns a '65 Tempest... (?) Recent new member.

No specific training and limited technical/engine experience. Pardon any jargon misuse.

Getting close to completing a revival of a '65 Tempest Custom four door with 326 2bbl and ST300 from 10-20 years in a back yard.

Looking to replace the 326 and ST300 with a 455 and 200r4 after the car is on the road and drivable again.

The focus of the 455 will be to create as much very low rpm torque as possible with secondary goals of smooth running and quiet operation.

Have seen in the past that small/er valves may create higher charge velocity which would increase low rpm torque. Sounds reasonable but I have no confirmation data for this proposition.

Assuming small valves do benefit very low rpm torque may I ask what head/s would be a good choice/value. As this will be a low rpm daily driver engine even pressed in studs are fine.

A related question is if small ports help low rpm torque would yet smaller valves help more? I assume there may be some point of diminishing returns.

If small valve 389/400 heads would make more low rpm torque would a set of 326 heads with yet smaller valves work even better?

Which ever head would work best it should be a pre '68 closed chamber head. I have seen that there are deeply dished pistons that also match the shape of the combustion chamber that would optimize quench and still create a streetable CR.

Intend to do limited 'clean up' porting and gasket matching.

Also will use 250 (700) Voodoo cam. Appears to have the most appropriate rpm operating range for this application.

Will spend the $ where necessary to gain a significant advantage towards the goal for the 455 but would like to keep the total $ as modest as possible.

Thoughts?

Thanks

[b-man]

Moving to Pontiac Street forum, you’ll get a lot more input there.

[b-man]

Forget about the 326 heads, just a bottleneck and just the totally wrong combustion chamber size. Not only that but heavily restricted breathing may lead to hot running and detonation problems.

The factory already built small valve 455 engines. The 1970 360 hp 455 with small valve #15 heads (1.96”/1.66”) would pretty much fill the bill here with 87cc chambers. Actually there are a lot of 400 small valve heads that would be suitable as well.

Smaller valves really aren’t a necessity and might limit your choices when there are several heads like the popular 6X-8 400 heads that are pretty much perfect when running flat top pistons.

Simply decide your compression ratio if using smaller combustion chambers and then use a dished piston to get exactly where you want to be. My choice would be the 6X-8 (2.11”/1.66”) with up to 105ccs before milling.

The 455 doesn’t need any help producing low end torque by going to extremes, a factory 068 cam would be great and is readily available from the aftermarket. If your compression is low enough (maybe 8.0:1) you could even run the milder 066 cam which was used in the 2-barrel carb 455, otherwise the hotter 067 was used in 4-barrel engines and the 068 in the 455 HO.

Any one of those cams is a low end torque cam. If the Voodoo cam you’re using is ground for low end operation I’m sure it’s fine. Press in studs can be okay but once the heads have been through the shake and bake cleaning process the studs can tend to loosen up. That’s another reason why I like the 6X heads, all of them have screw in studs.

In a nutshell an essentially stock 455 with low compression 400 heads or the high compression #15 455 heads with dished pistons (added expense for those) will get you there. Nothing fancy, keep it simple.

[tom s]

2X the 15 heads.Tom

[J.C.you]

I did a small valve HIgh Port aluminum head on a 389+.030 2.07, 1.625, and made good power. U may consider that route. Better all around heads offered now for the Pontiac faithful. Those heads would be a off idle tire burning brute on a mild cam 455+ci motor. I believe they did 317 cfm on meauxs sf600.

[geeteeohguy]

About 12-15 years ago I installed a set of small valve #15 1970 455 heads on the 400 of my '67 GTO. The only upgrade I did was to install screw in studs. Engine is the original, 068 cam, points distributor, original Q-jet, TH400 trans, with a retrofitted 2.56 posi out back. I like the combo. Very smooth and quiet, plenty of rubber burning torque, even with the lazy gear. The best thing is the fuel economy. I get 21 mpg consistently at 75-80 mph cruise, and even at 90 mph, it motors along nice and cool at 3,000 rpm. It does require 91 octane fuel, but at least it'll run on pump gas, which was not the case with the 670 heads it came with, or the #12 heads I ran for awhile. If I keep the speed down to 65 mph, I can get 23 mpg.

[25stevem]

I would build it up with a stroker kit to get a 474 cid motor and then try to turn up a set of # 96 head castings to drop on top.

[John Milner]

Hard to beat a flat top 455, 6X-8 heads and a 068 or 2801 summit cam if you want low end torque. I have ran this combination for years in a driver. It’s all done by about 5,000 rpm but makes a ton of low end torque. It is very hard on rear tires. I also run 87 octane gas in it.

[tom s]

Street car!KISS,455 iron head 9.5 CR 2801 or 068.Tom

[77 TRASHCAN]

You have to really screw up a 455 build to make it NOT be a brutal torque producing engine!!

[Schurkey]

Originally Posted by Ecklund

Concerns a '65 Tempest...

...The focus of the 455 will be to create as much very low rpm torque as possible

Originally Posted by 77 TRASHCAN

You have to really screw up a 455 build to make it NOT be a brutal torque producing engine!!

^^^ What he said.

You have a light car, and a reasonably deep first gear. You have no need for, nor will you be able to use a ultra-torque engine. Even with "posi", you'll just melt the tires.

[25stevem]

One thing I should have posted up and the other replies have alluded to is this, if you have never done a A/B test drive of a 326 and a 455 you will in one romp of the gas understand that a 455 is a very different animal then a 326!

The highest torque output of the 326 4 bbl ho option was still 100 ft lbs less then then a average 4 bbl 455!

That’s a lot in and of itself no less when you multiply that thru the gears,

Just keep in mind that 455 with even the factory 068 cam will peak in torque by 3800 rpm, so gear the car accordingly so that 90% of your driving takes place in the 2200 to 3800 rpm torque cradle and you will be super happy.

[android 211]

My flat top piston 455 has the 068 cam and 96 heads. It has 1.6 rockers. It made 524 ftlbs torque at 3000 rpm. It has 1 5/8" headers. My gas mileage with the present 3.23 rear isn't very good. I have to use 93 and it still pings at times. I guess the spark adance curve is too aggressive.

[Ecklund]

Originally Posted by b-man

Moving to Pontiac Street forum, you’ll get a lot more input there.

Appreciated

[Half-Inch Stud]

Think the priority will be Chamber cc, so consider the Big Valve heads to get Compression right.

87 Street and 89 Strip with combo below but have dished slugs.

[Ecklund]

Originally Posted by b-man

Forget about the 326 heads, just a bottleneck and just the totally wrong combustion chamber size. Not only that but heavily restricted breathing may lead to hot running and detonation problems.

Well taken. Have a set from the original Tempest engine so I thought I'd ask.

The factory already built small valve 455 engines. The 1970 360 hp 455 with small valve #15 heads (1.96”/1.66”) would pretty much fill the bill here with 87cc chambers. Actually there are a lot of 400 small valve heads that would be suitable as well.

Sounds like a good head choice. If they are one year only may be tough to find.

Smaller valves really aren’t a necessity and might limit your choices when there are several heads like the popular 6X-8 400 heads that are pretty much perfect when running flat top pistons.

So there is nothing to the idea of a small/er valve promoting low rpm torque?

Simply decide your compression ratio if using smaller combustion chambers and then use a dished piston to get exactly where you want to be. My choice would be the 6X-8 (2.11”/1.66”) with up to 105ccs before milling.

Do the benefits of the 6x-8 head outweigh the absence of a closed chamber with its ability to maximize quench/squish? Or is a closed chamber not worth the effort/cost?

The 455 doesn’t need any help producing low end torque by going to extremes, a factory 068 cam would be great and is readily available from the aftermarket. If your compression is low enough (maybe 8.0:1) you could even run the milder 066 cam which was used in the 2-barrel carb 455, otherwise the hotter 067 was used in 4-barrel engines and the 068 in the 455 HO.

Well taken that the 455 doesn't need any help producing low rpm torque. The factory seems to have added ci to its basic V8 with the 455 to achieve just that. So choosing the 455 block as a starting point. But optimizing certain characteristics of an engine for the goals of a build while keeping costs down can be useful.

With the small cams the engine may well require a low CR like 8.0 to be a daily with 87 fuel. Had hoped the quench produced with a closed head and dished piston would allow a slightly higher CR of 8.7-8.9.

Any one of those cams is a low end torque cam. If the Voodoo cam you’re using is ground for low end operation I’m sure it’s fine. Press in studs can be okay but once the heads have been through the shake and bake cleaning process the studs can tend to loosen up. That’s another reason why I like the 6X heads, all of them have screw in studs.

Well taken about the shake and bake loosening up fasteners on decades old heads.

In a nutshell an essentially stock 455 with low compression 400 heads or the high compression #15 455 heads with dished pistons (added expense for those) will get you there. Nothing fancy, keep it simple.

And that of course is the other clear option. And may well be the best option. The benefits of small valves or closed chamber heads, if any, may just not be worth the added expense. A stock 455 with low compression 400 heads, or even the stock 455 heads if they come with the block, are certainly a very viable option.

Thanks

[Ecklund]

Originally Posted by J.C.you

I did a small valve HIgh Port aluminum head on a 389+.030 2.07, 1.625, and made good power. U may consider that route. Better all around heads offered now for the Pontiac faithful. Those heads would be a off idle tire burning brute on a mild cam 455+ci motor. I believe they did 317 cfm on meauxs sf600.

Thanks for the response. Experience from an actual build is some of the best evidence.

Will look but aftermarket aluminum heads sound a bit pricey.

I take it from your response/post that you found that the small valves did in fact promote low rpm torque? That 'off idle' characteristic would be the goal for this engine.

Did the small/er valve 389 lose significant mid range power compared to the improvement in low rpm torque? The operating range of the 455 project engine for the Tempest would likely be limited to 3500-4000 rpm with the 200r and tall rear gears. So if smaller valves cost the loss of upper rpm power its an acceptable tradeoff assuming the smaller valve size does in fact produce significantly better very low rpm torque.

Thanks for the response.

[Ecklund]

Originally Posted by tom s

2X the 15 heads.Tom

Thanks for the response.

Pontiac using small valves on this 455 producing good torque is more evidence that the small/er valves do promote very low rpm torque.

Were these heads closed chamber?

Were these heads a one year only thing? May be harder to find if they were. But even if they are, probably won't be pricey.

[Ecklund]

Originally Posted by geeteeohguy

About 12-15 years ago I installed a set of small valve #15 1970 455 heads on the 400 of my '67 GTO. The only upgrade I did was to install screw in studs. Engine is the original, 068 cam, points distributor, original Q-jet, TH400 trans, with a retrofitted 2.56 posi out back. I like the combo. Very smooth and quiet, plenty of rubber burning torque, even with the lazy gear. The best thing is the fuel economy. I get 21 mpg consistently at 75-80 mph cruise, and even at 90 mph, it motors along nice and cool at 3,000 rpm. It does require 91 octane fuel, but at least it'll run on pump gas, which was not the case with the 670 heads it came with, or the #12 heads I ran for awhile. If I keep the speed down to 65 mph, I can get 23 mpg.

These are exactly the engine characteristics I was looking for. Smooth, quiet, effortless cruising in the high 80s and bags of off idle torque.

As the #15 '70 455 heads are post '67 I assume they are open chamber heads. Would a closed chamber head with dished pistons and machined to match the combustion chamber allow similar compression ratio and be able to burn 87 octane fuel?

With this 455 build I am leaning toward a closed chamber and small/er valves. Are there any heads that particularly recommended? I can always retrofit the screw in studs.

Thanks for the response.

[Ecklund]

Originally Posted by 25stevem

I would build it up with a stroker kit to get a 474 cid motor and then try to turn up a set of # 96 head castings to drop on top.

Very well taken.

if a 455 is a good torque producer a 474 is better. But for the added expense it would be an excellent choice.

Are the #96 heads pre-67 and have the small/er valves?

Thanks for the response.