[TheCougarine]

So I've got a question for you guys and I want to apologize in advance because I've not got 100% of the info that someone would really need to know to answer it but anyway here it goes.

Currently my car has a 455 bored .40 over, 0 decked and has #17 heads on it. Compression is at 10.7.1. The guy I bought the car from did not know the cam specs but said that he would put a ram air IV cam in the car if he was going to keep it to make the car more drivable and the car does have a rather rough idle and could probably use a 3000 stall. Currently the car has no stall and an open 2.73 rear end so while it drives nice on the highway and will eat its right rear tire on launch its hard to get an idea about what this motor car really do. The main thing is I just haven't found a lot of info about these heads on 455s and was curious if y'all could enlighten me. Thanks in advance.

[ponyakr]

#17 heads originally came on a '68 350 2-barrel engine. They came with small valves & press-in studs. Most head ID sites show 'em to have 72cc chambers. Lots of guys have used 'em in modern day builds.

Most put in bigger valves, and many will port 'em, or pay to have 'em ported. The chambers can be opened up, or they can be machined to reduce chamber size. There are all sorts of upgrades that can be done, for high performance engine builds. With flat top pistons, & a zero deck height, on a 455, they produce too much CR for pump gas, IMO. I feel that combo would require more octane than pump gas 93. If I had to run that engine, I'd use Torco Accelerator octane booster. Some would mix in some 108 octane race gas, or something else to increase octane.

https://www.summitracing.com/parts/t...EaAh5_EALw_wcB

Using the Wallace CR calculator, a .040 over 455, with flat top SP pistons, 72cc heads, .045 x 4.3 head gaskets, & zero deck height, has aprox 11.65 CR. You'd need dish pistons to get the CR down to a pump gas safe level, IMO.

http://www.wallaceracing.com/cr_test2.php

But, Cliff Ruggles and others who know how to build & tune Pontiac engines have reported running high CR, on pump gas. So, it all depends on who you ask, and the exact combination of parts, specs, & tuning.

The RA4 cam you mentioned has long been very popular in high compression Pontiac engines. I ran that cam, along with Rhoads lifters, in most of my 455 bracket cars. Produced a goof enuff idle to launch from an 800rpm idle, using a stock 13" converter. Most of these cars had between 3.55 & 3.73 rear gears, with 13' x 30" slicks. The very few times I tried street tires, just for testing, the traction was basically zero. Nothing but smoke.

Don't know if any of this helps or not.

[steve25]

If those # 17 heads still have the stock valve installed height, no less valve springs then you will not beable to run any Cam like the RA4 that has close to .470" lift.
You don't know what Cam is in there now, but I can tell you from experience that mixing any Cam of more then .450" lift with the stock size pressed in rocker stud is going to bit you in the Ass sooner then later, especially if you try to run poly locks on the stock studs!

And add to this list the need for yanking the the stock rocker arm out and drilling + taping for screw in 7/16" studs .

[J.C.you]

17 heads have a smaller port than other Pontiac heads available. Pontiac engineers designed them for a smaller cube motor. Makes for a combo on a 455+ cube that will spin a tire but falls on its face quickly due to port choke. Not a good combo for a 455 with performance in mind.

I would find a set of 6x heads since you mentioned seeing what it will do.....If you are wanting a tow truck type combo with perhaps better fuel milage 17 heads with pump gas compression, with a performer intake(small ports too) would be desirable.

[TheCougarine]

Thanks guys, thats all good info. I know its hard without having all the info to go on. I'm guessing the heads have had some work done of some kind based on what y'all are saying because the cam in the car is definitely a larger cam than the ram air iv and the motor doesn't seem to have any problem pulling up to 5,000. Since it runs well on 93 I'm guessing the cam is big enough to bleed off some cylinder pressure and is whats allowing it to run on pump gas. I've put a little over 15,000 miles on the car so far and haven't run into any issues yet but I know of course that doesn't mean I won't have an issue tomorrow haha. The guy I got it from seems to have made the mistake of going to a shop and just telling them to build him a motor without telling them what he wanted to use the car for and thats part of the reason he sold it. The rest of the drivetrain is not matched to this motor at all. I'm thinking that once I get some 3.42s and the 4 speed I have waiting to go in it I'll have a better idea about how well this motor combo can perform.

So a follow up question, assuming these heads were modified to work on this motor am I leaving a ton of power on the table running them, in relation to other iron heads of course?

[77 TRASHCAN]

I'm an expert at nothing....but.
Jim Hand, in his book states that nearly all "D" port heads have the same port shape and volume. (intake volume 153 cc's) From the heads I've seen, I agree. I have a set of 17's. I have not looked at them lately, but I saw no real difference in their port size and shape from most other "D" port heads.
My 17's cc'd right at 83.5 cc's. I checked 2 chambers on each head, these heads are untouched.
A member here has a lot of experience with these heads. I have not seen him post in a while, use name, Donovan.
In my opinion, these heads could be used on a 455. It would take a lot of work on your part, including installing larger valves. The larger valves are not the most important part though. Opening up the chambers is.
I don't know what skills or what tools you have available to use. Jim Hands book would help you out.
As J.C. mentioned 6X heads would be a better starting point, and they are plentiful, and not usually expensive...

[J.C.you]

Originally Posted by 77 TRASHCAN

I'm an expert at nothing....but.
Jim Hand, in his book states that (NEARLY) all "D" port heads have the same port shape and volume. (intake volume 153 cc's)
As J.C. mentioned 6X heads would be a better starting point, and they are plentiful, and not usually expensive...

"Nearly all" ....ok. Perhaps a misleading statement in his book.

If one had a 17 head with a 1.96 intake and then installed a 2.11 would the machining process of opening up the seat area alone increase the intake port volume?

[steve25]

Build the motor with the concideration that by 5000 rpm with a 455 under them that those heads are a real good restriction on the motor and don't be loooking for more then some 400 hp and you'll be fine!

[77 TRASHCAN]

Originally Posted by J.C.you

"Nearly all" ....ok. Perhaps a misleading statement in his book.

If one had a 17 head with a 1.96 intake and then installed a 2.11 would the machining process of opening up the seat area alone increase the intake port volume?

Possibly.
The 17's were only used on 350's for 1968, (LOL, I believe).
The 11 castings that came on the 1970 350 currently in my car, necked down considerably beneath the intake valves. That area looked like a choke point to me in a bad way. I performed a bunch or grinding on them to open them up, similat to Jim hands book.
More of a choke point than the push rod area, that most consider to be a choke point in Pontiac heads. I believe that the 17's didn't seem as choked under the valves as the 11's....
Putting 2.11 valves in 11 or 17's would likely drastically change the intake volume.

The "D" port heads that I think about different than most are the monster chambered heads like the 7M5's and such that had the largest chambers. I wonder if those had smaller volume ports that 153 cc's?

Thanks for you perspective.
350 heads and engines are not widely modified or talked about much. I bought the 17's to possibly put on the 350 currently in my car to pump up the compression ratio, thinking that they were close to 72 or 75 cc chambers...

[ponyakr]

"...thinking that they were close to 72 or 75 cc chambers..."


That's a good point. I just looked up about 5 or so head info sites. EVERY one shows #17 heads to have 72cc chambers.


"...My 17's cc'd right at 83.5 cc's. I checked 2 chambers on each head, these heads are untouched..."

So, obviously, those sites must have bad info, at least for the #17 heads.

[77 TRASHCAN]

Originally Posted by ponyakr

"...thinking that they were close to 72 or 75 cc chambers..."


That's a good point. I just looked up about 5 or so head info sites. EVERY one shows #17 heads to have 72cc chambers.


"...My 17's cc'd right at 83.5 cc's. I checked 2 chambers on each head, these heads are untouched..."

So, obviously, those sites must have bad info, at least for the #17 heads.

It's like I said, 350 info may also be less accurate. Maybe mostly because nobody cares about Pontiac 350's. I wonder about the 11's on my 350. I've had 44 degrees total timing in that thing, couldn't make it ping...the 8.8:1 I believe is pretty bogus also. maybe 7.6:1 like the 350's that followed. Some here have possibly measured 11 heads, and say 8.2 or so. The trend in chamber volumes got bigger going from the late 60's into the early 70's. I can't imagine the 11 head having a smaller chamber than the 17's, especially since the 70 50 was just a pedestrian 2 Bbl for Memaws to drive...
Saying all this a stock bore 350 with these 17's comes in at around 8.2:1, still low, although it's what many speak of concerning the other engines being 1/2 point lower than advertised.....

Who knows it's just a 350...

[Will]

Just because the factory advertised a certain CC size for the chambers in a head doesn't mean that's actually what they were.

Numerous other heads show such discrepancies. Take '70 #13s for example - they are closer to 77-78cc than 72.

The ports in every small valve head I've looked at are definitely smaller than the ports in the big valve heads. It appears the factory was attempting to maintain a ratio between throat diameter and valve diameter, therefore the throats in the small valve heads are definitely smaller than the big valve heads and thus the bowls will be smaller also. The port from the short turn back to the port opening is about the same on all D-port heads I've seen.

The pushrod bulge really isn't a big restriction. The throat and short turn areas are where most flow improvement comes from when heads are ported.

Cutting the heads for larger valves should involve opening the throats up as well. This can easily be done at the same time as the valve job with the appropriate cutter. A little blending above the throat cut and a little work on the short turn will get you around 230 cfm flow, a significant improvement over the ~195-200 cfm of a typical small valve head.

A quick look under the valve covers should show you whether these heads have been converted to screw-in studs. Hard to believe that hasn't been done if the engine has a big cam in it.

[grandam1979]

Back in the mid 80’s I had a junkyard 455 with stock 17 heads and a crane r/a IV cam went 13.0’s at 106 +- in a 69 gto and 11.80’s at 115+ with a 125 nos shot

[J.C.you]

Another thing related on the smaller port castings, such as a 17. They can't be opened up as much before hitting water, as compared to a 16 dport for instance.
When the Pontiac engineers designed the smaller port heads with smaller valves they just didn't add material and make the castings thicker, thus heavier.

There is a relationship between how thick a casting is and how quickly it will dissipate heat. A major consideration of a head design. Pontiacs are good designs in that area. Not a lot of cracked Pontiac head castings out there.

[TheCougarine]

Thanks guys, this was all great information to have. I'd say long term I'd like to do aluminum heads anyway but I wanted to have a better understudying of how the car is now and this really helps.

[77 TRASHCAN]

17 heads would be great for a 400, if you wanted to sell them, or build a 400 in future...