[P@blo]

Cool article kenth. A "slipstick" is a slide rule right ?

[quicksilver97ta]

I wish I could see those little illustrations better but obviously a 6x head and most other D ports are "fully machined wedge with a large squish area".

So where does a closed chamber fit into the mix? I read in the HO Racing manual that the open chamber was a design improvement over the closed chamber but all the new head designs are more like a closed chamber. Maybe thats where the grooves help?

[johnta1]

Nice article kenth.

Interesting that they show the RA IV head with 69 CC's and the RA III head with 66 cc's. I would have thought it would be the other way around.

Also the deck height of the 455 is interesting.

[Skip Fix]

My virgin 614s were actually 69cc with flat valves,can't see the tulip adding 3cc.

[BILTIT]

Originally Posted by quicksilver97ta

I wish I could see those little illustrations better but obviously a 6x head and most other D ports are "fully machined wedge with a large squish area".

So where does a closed chamber fit into the mix? I read in the HO Racing manual that the open chamber was a design improvement over the closed chamber but all the new head designs are more like a closed chamber. Maybe thats where the grooves help?

The closed chamber heads are usually opened up in certain areas to be a semi-closed chamber (similar to the newer chambers maybe?).

Some pics of my closed chambers 670's, semi-closed chamber 670's compliments of Dave@SD and KRE's D-port.

[P@blo]

Kenth, according to your article the Ram Air 4 was "spherized" to complement the higher compression to free up 8 to 10 horse. This would support Jim Hand's recommendation on laying back the eyebrow. Could we be jumping the gun on this new wet flow technology since no Pontiac head has been tested as of yet and it's still in the developmental stages. When the rubber hits the road is where it matters and Jim's Wagon runs pretty darn quick with the chamber mods stated in his book.


Strange how the factory ran double the deck height on a 400 when compared to the 455. What do you think the reason for that was ?

[Skip Fix]

Pablo the RAIVs aren't like Jim's chamber at all. They keep the ridge just moved it out further. The entire chamber diameter is larger also. Since the chamber has a larger diameter than other "72cc " heads the valve seats and edges are closer to the deck/piston. So they would have a different piston to valve clearance than a 72cc D port head or 72cc Edelbrock head with the same cam. A 6X head the valves are actually over 0.200 further away from the deck surface! My RAIV motors did use alot less timing than my D port motors, usually 34 degrees was best.

Pete McCarthy's book has pictures. I might have some on mine somewhere. But RAIVs, HO,SDs all are a way different chamber. Maybe their chambers better effeciency is how they kept the same power band as other 455s with their much bigger ports?

[P@blo]

Thanks for the response Skip. Here is some pictures of a ram air IV chamber beside a 6X so we get a side by side comparison.

[Big Injun]

I talked with Dave Bisschop about this last night. He tested this theory of cutting the ridge in the 6X. Flow increased...but performance lagged. Efficiency was lost and it took 3 degrees more timing to match the uncut chamber.

My take...leave the 6X chambers as designed. Just remove the sharp edge to eliminate potential hot spots.

[sharkbite]

I can't get enough of this post seeing I'm going to have my 6x-8 heads milled and worked first thing next year (Jan 07) and am now trying to decide what action if any to be taken with the modifying the chambers. Jim at MBJ in IL will be doing the work and I'll have to get his take on this whole thing.

A bit surprised we haven't seen any opinions from Mr. Hand on this.

[Skip Fix]

That RAIV looks like it has been smoothed a little on the ridge.

That's an ugly 6X chamber, need a good clean one to compare! A better comparison might be a bigger HO/SD chamber, close to the same size and depth.

I wonder how the even different RAV chamber compares to timing needed also.

These changes as Dave Bisshop noted change performance unrelated to port size.

[P@blo]

Here's is a great link to HPP with a real collection of chamber shots.

http://www.highperformancepontiac.co.../photo_14.html

[Skip Fix]

Great link Pablo for this!! You can see what I mean with the side by sides. the RAIV,HO,SD is alot more open around the valves the way it's machined, you can also see the RAV has no ridges at all. You can see how flow coming in from the intake has alot different path in all of them. You can also see how different the plug is in relation to ridges in all three.

So which Pontiac enginer had it right since they have 3 different chambers and two different ones for their hi perf motors????

That would be a cool thing to see on a wet flow, but any porting is going to change the bias as it comes into the chamber over one ported slightly different.

[KS circutguy]

WOW, glad I posted BEFORE I started cutting.lol
Thanks,
Would like Jim H to chime in too!!

["Puddles the Pontiac"]

Originally Posted by P@blo

Here's is a great link to HPP with a real collection of chamber shots.

http://www.highperformancepontiac.co.../photo_14.html

that 6x looks like it has unshrouding work and touch ups on the ridges (eye brows). the RAV is definately odd compared to the rest.

[Kenth]

"So which Pontiac enginer had it right since they have 3 different chambers and two different ones for their hi perf motors????"

Depending on the application of a certain head the engineers were all right, you don´t see 3 different chambers on the 6X or RAIV heads?

The different chamber styles were aimed at different goals/rpm-ranges/intake-runner-style/camlobe-lift and so on?

[Skip Fix]

But Kenth the HOs and D port 455s had the same rpm range. The RAIII maybe a little less than the RAIV due to the cam. So for us tinkering types which is the best to copy? If the more open chamber of the RA/HO is more performance design than the D port might be better to copy it?

The port size was dramatically different also. My point in other discussions nothing is as simple as just port size when comparing different heads unless they have identical other parts including chmabers.

[Kenth]

Skip, isn´t the 1971-2 455HO Pontiacs considered the most "undercammed" engine due to the heads potential?
I think Pontiac engineering were somewhat compromised by the 1971 emission laws?
There is a lot to consider choosing parts, but one can assume that Pontiac had more resources to find out what works than the average hobbyist, of wich i´m one?

[Skip Fix]

I'll agree the HOs and even SDs have more potential with more cam. The D port crowd will boo me but even the stock 71 HOs I've flowed do better than a medium ported D port head. Pontiac figured out how to keep the rpm range and the HP with the big heads, and give the enthusiasts more potential also. Showing that port ccs is just part of the equation.

[Lee]

I talked with Jim a little over a week ago, on an unrelated subject. I got the impression that he needs to focus on some other things right now. I suspect he'll chime in when he gets caught up on things.

Lee