[dmac]

I have the original #15 small valve heads off the 455/467, and expect about 450HP around 5000 rpm, MAX. Cam will be done by right about that point in this low CR engine.

Lower rpm should be easier on everything else- kind of how the factory figured it.

I'll never need more than maybe 4000 rpm, but my foot might slip when passing on the freeway or something. Will the stock heads flow enough, and if not, would either larger valves, or porting alone be enough.?

I do want to maintain as much power as possible at lower RPM with cruising rpm to be around 2000 rpm, so if larger valves or if porting means giving up low rpm power for more top power, I don't want it. I understand NOTHING about port velocity except that it somehow matters, and bigger valves and bigger ports matters. 467 ci is a lot to feed but this 455 came from the factory with small valves.

And money is a HUGE issue, . I have a set of large valve 4X heads (no cracks yet) but the chambers are huge. The 15s have the 'perfect' chamber size, but have pressed in studs.

And if pinning the studs is cheaper than converting to screw in studs, then I may do that if I can find a shop

[tom s]

FYI,Dave at SD did a set of 15s with 2.05 intake and a 260 CNC port job and screwin studs.We made 478 HP with a 383 CI 301 stroker with 9.5 CR.Tom

[Rar_421]

Originally Posted by tom s

FYI,Dave at SD did a set of 15s with 2.05 intake and a 260 CNC port job and screwin studs.We made 478 HP with a 383 CI 301 stroker with 9.5 CR.Tom

Which heads Tom,the 68' 400 heads or later 455 heads? Sounds like a real stout motor!

[25stevem]

In terms of port velocity and to tend to your need for maximum average driving power below 4000 or even 4500 with the big stroke of a 455 what matters in terms of porting work is that the amount of intake cfm the porting work picks up will be a larger percentage then the amount of port area increase

In terms velocity of what I did with the 15 I ported here’s the bottom line.
I increased the minimum port area by 20%, yet the rework picked up 50% more air flow.
The result is a 30% increase in port velocity of stock.
This translates directly into no loss of drivability!

Note that I am referring to port area, not overall port volume!

Those small valve heads are the same basic casting as the big valve heads and as such have the same porting potential.

I posted up some 3 years ago here a string on porting the 1968 # 15 castings and was getting 278 intake cfm@28” out of them and there was still more to be had.
Your 455 15 castings have a deeper chamber then the 68 # 15 casting I was working with, so this will limit there high lift flow gain when porting to about 270 cfm.

In regards to your stated hp goal of making a easy 450 hp your casting will need to get ported to attain 240 cfm by .500” lift which can easily be done.

It would be good with the porting work done to get the exh flow numbers up to 170 to 180 cfm .
170 cfm will work find with headers.
This can be had with the stock 1.96” intake valve should you want to stick with that.

In short , when you pass more air through a given port area the velocity goes, and that translates directly into more torque at whatever rpm your talking about.

In terms of a purely street driven motor with less then 3.23 rear gears your driving experience will be much better by gaining power by means of more air flow, not by going with such a big cam that makes the car a Bear to drive below 2500 rpm.
In terms of what I did with the head that I ported
The minimum port area was enlarged by some 20%, yet the air flow picked up by 50% over stock.

This translates directly into a 30% gain in port velocity and that all comes with no loss of drivability, in fact drivability would pick up a lot if the same cam was still being run!

[tom s]

455 15s

[J.C.you]

Not to high jack but what is smallest chamber 67 up small valve heads with screw in studs? Doing a 350ci short deck 301 block circle track motor

[Sirrotica]

1967 326 HO head #141, approximately 68 CC's, 1.92 intake, 1.66 exhaust.

Glad to see you again building a dirt track engine, what's it going in?

[25stevem]

If I recall right those 67 326 heads still have the early chambers in them and not the best starting point in terms of flow, especially on the exh side due to there valve inclination angle.

Of course things will change with porting work, but you can’t change that type of chambers burn rate.

If the class your racing in just limits the compression run and not the pistons, then running a 68 and up head milled and with a slight dome on the piston would be the way I would go.

Sorry for the thread high jack!

[Cliff R]

The small valve heads are fine for high performance use and folks tend to downgrade their potential and/or bypass them looking for the larger valve versions.

I would NOT pin the studs, they convert easily to screw in studs.

Some of the smaller valve heads are missing the end bolt holes but have the casting area for them.

A few years ago we had a well prepared 455 shortblock ready to go less cam and heads, waiting on them from Dave at SD. The engine was headed for a 1981 Firebird and we wanted to make the Tri Power Nat's at Norwalk in August, but the heads and cam weren't going to make it.

I walked over and grabbed a set of 1969 #46 heads out from under a workbench, gently ground the seats (45 degree intake seats) and valves, added better springs and screw in studs. Not a grinder or sanding roll touched them otherwise. I walked back to the parts room and grabbed a lightly used Crower cam used for a dyno session a few years prior. We finished the engine with the #46 heads and Crower cam, bolted one of my TH350's behind it, a custom built Continental converter, quickly prepared a 1978 Olds Q-jet and factory HEI, and got the car ready for Norwalk.

I was expecting maybe low to mid-12's from the combo.

Right off the trailer in the heat of August it went high 11's and ran there all weekend, quite a bit faster than one would ever think you'd go with that set-up. It gave me a new perspective for the smaller valve heads and these weren't even port matched at the intake.........Cliff

[25stevem]

Just curious, what are you planing to run for a intake on that short deck dirt track 350?

[Sirrotica]

670 heads are made in 1967, no one avoids using them, matter of fact many people seek them out.

67 is a closed chamber, but still has the valve angle changed over from the 66 design. If he man is building a short deck engine, he certainly has the means to make the 67 heads suit the design of his engine.

I actually owned a 67 Firebird 326 HO in 1969, it was no slouch with the 141 heads on it. I wouldn't discount those heads at all.

[25stevem]

Yes, the 670 casting are certainly a option, but a expensive option if you do not already have them sitting on your self!

[Sirrotica]

My point was, the 670s are the same design as the 141 head, I.E. 67 closed chamber head. If a 141 is in the same family, it too is desirable. The main problem will to find some, as there were only a little over 6,000 of these engines built in 67.

If someone is going to the trouble of making a short deck Pontiac Stratostreak engine, the price to use those heads for raising compression, would not stop the project. He's going to have plenty in the shortblock, the cost of using those heads would be minimal over the total cost of the build. This isn't a low budget build, from start to finish. It's going into a dirt track car, the whole engine needs to be geared towards endurance, not running a 1/4 mile in a straight line, then shutting it down. These engines get punished much harder than a straight line engine does. Who would know more about keeping one together than someone that has raced dirt track Pontiacs for many years? If they're not right when the car goes out on the track, before the night is over, you'll know if it was a success, or not.

J.C. has already run some dirt track modified cars with Stratostreak power, he is aware of what it's going to take to have one that can win, as well as last.

[25stevem]

The point is to use your term, that the 670 casting even while it is the first to have the new 14 degree valve inclination is not the same bath tub chamber as the 141 casting.
Here is a photo of a chamber in one of my 670 castings , and it is not of the complete bath tub shape of the earlier heads as the 141 casting is.

[Sirrotica]

And of course you have a picture of a 141 casting combustion chamber to back up your statement, or not?

Post it if you have it I'd like to see it.

[25stevem]

There’s a carved in stone rule of Thumb that any 67 or earlier head that makes use of the 1.92”-1.66” valve size has a bath tub fully closed chamber.
Also just like the 1966 heads these also have the air injection passage running the length of the head.

[Sirrotica]

Where's the stone it's carved into?

I've never seen that stone in 50 plus years of wrenching on Pontiacs.

Post a picture of a 141 head combustion chamber, not just hearsay.

I posted it's a closed chamber, isn't it a closed chamber?

Calling it a bathtub chamber is virtually the same thing, two different terminologies for the same thing.

JC asked about the smallest chamber in a 67, and later head, is the 141 the smallest or not? Here's his question:

Originally Posted by J.C.you

Not to high jack but what is smallest chamber 67 up small valve heads with screw in studs? Doing a 350ci short deck 301 block circle track motor

I answered his question, you have to cast doubt, why is it you're trying to cast doubt?

Did I lie about something?

[25stevem]

I am not meaning to discredit you in the least that it does not have the smallest chamber, just that a later chamber is more efficient then those bath tub chambers that all of those heads used on a 326 had.

[SD455DJ]

Originally Posted by dmac

I have the original #15 small valve heads off the 455/467, and expect about 450HP around 5000 rpm, MAX. Cam will be done by right about that point in this low CR engine.

Lower rpm should be easier on everything else- kind of how the factory figured it.

I'll never need more than maybe 4000 rpm, but my foot might slip when passing on the freeway or something. Will the stock heads flow enough, and if not, would either larger valves, or porting alone be enough.?

I do want to maintain as much power as possible at lower RPM with cruising rpm to be around 2000 rpm, so if larger valves or if porting means giving up low rpm power for more top power, I don't want it. I understand NOTHING about port velocity except that it somehow matters, and bigger valves and bigger ports matters. 467 ci is a lot to feed but this 455 came from the factory with small valves.

And money is a HUGE issue, . I have a set of large valve 4X heads (no cracks yet) but the chambers are huge. The 15s have the 'perfect' chamber size, but have pressed in studs.

And if pinning the studs is cheaper than converting to screw in studs, then I may do that if I can find a shop

Dmac, My brother Dan and I rebuilt a 1970 360 hp YH code 455 (std. in the Bonneville's) using the 100% stock #15 small valve heads (combustion chambers measured 89 cc's after a minimal cut to true them up) at 9.9 to 1 static compression. The block had been previously been bored .040 over with new cast pistons, so we had it honed to provide .0025" - .0030" clearance (we know, not ideal) for the new moly rings. The cast rods were replaced with Eagle H-beams and the factory crank cut .010/.010 with new bearings. The #15 heads had new Ferrea 1-pc stainless steel valves (1.96/1.66) with new CC valve springs and a Summit 2802 cam & lifter kit (224/234/112 @ .466"/.488") installed straight up (4 degree built in advance IIRC). We had the stock pressed in rocker studs pinned too rather than going to the screw in studs (cheap move on our part...and, again, not ideal). Again, the ports on the #15 heads were untouched and are known to flow 190/195 cfm on the intake side and 145/150 cfm on the exhaust both at .450"+ lift. With the factory cast iron intake, Q-jet, and exhaust log manifolds it made 390 hp at 4600 rpm and 512 lb-ft torque at 3400 rpm. With RA manifolds or headers, it would have easily been in the 420 hp/540 lb-ft range.

I'm not sure you could get 450 hp with stock #15 heads and lower compression, but maybe with a roller cam and headers with at least 9.5 compression.

Dennis

[Sirrotica]

Originally Posted by 25stevem

I am not meaning to discredit you in the least that it does not have the smallest chamber, just that a later chamber is more efficient then those bath tub chambers that all of those heads used on a 326 had.

The closed chamber can be made to more of a open chamber design with some chamber work. I'm sure J.C. has someone that can optimize the chamber, he has done some pretty high tech builds in the past, and is acquainted with some of the better engine builders in the industry.

In other words, this isn't going to be a backyard low dollar attempt, if he stays true to his past builds, it will probably be a very well performing HP per cubic inch example. Most likely will be run on methanol, so the need for more compression would be needed if that would be his fuel of choice.