Inliners International Forums General Discussion Hi Performance 302 Jimmy stock head

Hi guy,
I'm back to work on my stock head 302 Jimmy.
Most older posts were in a 2010 thread. I sure got some interesting ideas, and have been following up on them.
Hudson rods showed up. Pistons looking good.
Getting the crank drilled and tapped for extra bolts took a lot more convincing than I had hoped. (Limited choices for machine work).
Today I'm asking for more info on the stock 302 head. Ron G kindly posted flow figures for his #938 head and I have been talking to nearby flow bench specialists.
Most say they have little to no experience with the siamese port.
I would like to hear from anyone who has flow #s to share and porting experts to recommend.
Also, I'm looking for info on grinding each cam lobe on its own individual center (advanced or retarded according to the 3 potentially different port requirements) Reference = maybe Don Hendriks ?
I can't seem to pin down where I got this idea from.
Thanks in advance for any info
Regards, Wilbur

I've ported several of the 983 heads and have gotten similar results. You need to open the intake ports same size as the counterbore for the alignment rings. You will also likely break thru into the head bolt holes adjacent to the ports.
As for advancing the cam lobes seperately, that was done for an entirely different purpose, and only needed if using real high lift roller cams on the later 250 and 292 style engines. You would never need to do this with the GMC or Stovebolt engines.

I am confused...I did not see where a purpose was offered/inferred for Jim Headrick advancing or retarding particular cam lobes. If no purpose was offered then how could it be refuted? I am extremely interested in this subject as I would like to decide for myself its relative merits for my 292 build. What ,then, WAS the purpose of the advanced/retarded lobes? Any information on this subject would render me eternally grateful.

I mostly use the 270H head but Mike Kirby always sleaves the bolt hole close to the ports then does the port work. He only did one head for me and it is that way, my others are not. I have know idea what your plan is for the head but remember the 302 has a lot of shrouding on its valves so the bigger you go the more shrouding you have. I've use a lot of different size intakes and their effiency depends on what I wanted to accomplish. Torque, RPM, Blown, Unblown. Each has it's own needs. Unblown, it's the velocity when the valve opens that is your friend and makes for power, at least it has for me.

For me the 12 port head with no chamber was the best. (Wayne-Shinner) no shrouding at all.........Good Luck

Eddie, as I mentioned, it was only necessary to have the cam lobes ground with a progressive degree of advance from the #1 cylinder down the line to the #6 in these 250-292 engines, and that was when large or huge lift roller cams were used. That purpose was for one reason and one reason only. To achieve the extreme valve lifts used in these engines by Jim, the base circles of the cam lobes had to be reduced so much, that this weakened the cams to the point that they twisted the entire shaft just by adjusting the valves. You wouldn't think that would be possible with a billet roller cam, but when the base circle and cam barrel is ground to less than .875 diameter(necessary to obtain near 1" of valve lift), it would happen every time. He found that after the spring pressure loads(near 1000 lbs. of open pressure) were applied to the camshaft, that the #6 cylinder was retarded as much as 5° from the #1 cylinder. He found that each of the cylinders in between shared a proportionally and consistent degrading of cam timing as well. He simply had the cams ground with a predetermined amount of advance on each lobe to compensate for the twisting of the cam due to spring pressure loads, nothing else. You will never obtain that much spring pressure in a flat tappet cam to have to do that(you will wipe the lobes right off) or most any roller cams up to .800 lift or more as long as the base cirlce on the lobes/cam barrel is .900 diameter or larger.

Big roller cams also deflect downward away from the lifters.

A bunch.

An old friend of mine was running a Buick straight 8 dragster around So Cal in the early 60s. Crower ground the cam and had to compensate for how much it tweaked from #1 to #8. He said that when it hit 6000 rpms it was like shifting gears.

Re: "12 port head with no chamber"

This is also called a "plank" head (since the gasket surface is flat).
The valves are exposed immediately on cracking open, but if the engine has quench they're still shrouded by the "O" or "D" cup in the piston dome B & ATDC during overlap. How quickly the dome "runs away" from the opening intake valve is a function of the cam event (early intake opening or late exhaust closing = worse), the stroke length (short = worse), and the rod ratio (high = worse).
Obviously, after the piston's position passes the cup depth (just a guess: .200" to .300" minimum representing the valve lift during overlap), the valves have radial clearance all around up to the cylinder walls.

A non-quench engine will have no shrouding, since the piston will be flat with whatever negative deck height is needed for the static CR chosen, but IMHO this is a bad exchange.

Heron head I believe is the name.Used in the past on Chevy 348,large Lincoln V-8's of the late 50's and a bit more recently the Jaguar V12 and Moto Morrini motorcycles.
This type head is supposed to increase mid range torque,that's why Chevy chose it for the 348 truck engine.
A modified form of this head is used on purpose built Nascar Cup engines featuring a very shallow combustion chamber.Probably used to get high compression ratios without a huge dome.
The stock 302 head is a close copy of the 1949 Caddy V8 quench head.A lot is known about quench type heads because so many engines use them

Isn't the 303 (and all Cadillacs) a wedge chamber?

Yes....I misspoke,not a direct copy or true wedge but used a significant amount of quench which came out of the 303 Caddy head engineering.

CNCDude,
Thanks very much for clearing up the camshaft information.
I found my copy of Leos 6 cylinder book and discovered I had highlited his brief discussion of the topic. I now understand exactly what he was trying to say.
I thought for a while that the lobe advance had something to do with the siamesed port.
I had figured out the part about the additional volume of the port and the port velocity/turbulence problem from fooling with my home made flow bench, but I guess I was trying to connect them in the wrong way.
In my experience, anything you spin real fast is going to twist or stretch.
Axles being my personal favorite ($#*&*&^^)
Timing chains and distributor gears are probably my next favorites, but for some reason a camshaft did not enter my mind.
My actual build plan is for a 320" 6000rpm 3 side draft carb torque monster, so port velocity and a lot of static compression is what I'm thinking.
The actual grind will (of course) depend on the flow numbers.
Thanks again for setting us straight on the lobe advance.
Regards, Wilbur

Wilbur46, if you will go back and check Leo's book you'll find that your original conclusion about what Leo was trying to say was indeed correct. Leo clearly states that Headrick advanced/retarded lobes in order to take advantage of the other part of the siamesed port effectively acting as a larger plenum.

Evidently,this view does NOT coincide with CNCdude's view citing compensation for camshaft twist as the reason for lobe advancement. I offer this not as an endorsement for either view, but rather to point out that it is indeed two differing views on the subject, thusly keeping the record straight. I'll leave it up to the individual to which view he'll choose to subscribe, as both views have merit.

Eddie, im not implying that Headrick purposely misled Leo as to the real reason this lobe advancing was done. But I worked for Jim for 15 years and know first hand he many times "shaded" the facts to keep the subjects like this guarded for obvious reasons. Sometimes, the answers he gave was 180° from the actual facts. Jim didn't even tell his top engine customers everything about their own engines, and they were spending thousands of dollars a year with him, thats how he preserved his knowledge and protected those racers status in the racing venues they raced in. So why do you think that just because someone shows up with a tape recorder and notepad he is just going to spill his lifelong secrets that have made him one of the greatest inline 6 cylinder engine builders of all times and risk loosing a lifetime of accomplishments and clientele. Many, if not all engine builders do that when they really don't want to divulge a "trade secret". Don't be surprised if Mike Kirby, Kay Sissell, Glen Self and others did the same.

CNCdude,
I really was not trying to take sides or to lead anyone one way or the other, I promise. Wilbur45 said that he now understood what Leo was trying to say in his book and I was merely trying to point out that Leo was (rightly or wrongly)led to believe that it was done as an enhanced airflow thing. That IS what Leo put in his book (again rightly or wrongly).I have no dog in the hunt and have no reason to doubt your claim, I was merely correcting what Leo's claim was. If this was not evident in my post, then please accept my apologies.

fasteddie

Hey Eddie, we are all here to have fun and help one another. Nothing you said was ever taken to be in an argumentative manner or any thing else. In all fairness, I know Leo has put much time and effort into his research into gathering info for his books and should be proud of that. He has accomplished and provided a great deal by doing this for the Inliner communtiy. No need to apologize, again, nothing you said or did offended me or even got my blood pressure raised. Glad your here, you'll find we have a lot of fun here.

Wow!!! this thread is really one of the most informative I've ever read here. My light bulb just came on.
Not only does the cam need to reflect the potential twist at rpms, but there IS something to the port configuration/ lobe profile.
I wonder if I can use 3D CAD (solidworks or Pro engineer) to help figure this out.
Yikes!, I just realized I'm using this computer too much!
I wish I had a real flow bench!! (that's a little safer than saying "I wish I had a little head"):)
Has anyone fooled with measuring average compression pressure on a dyno? Regards W

The characteristics of a siamese port cylinder (1 vs. 2, etc.) also vary somewhat depending on whether it's the 1st or last in the sequence (HT: Vizard), so even very similar ports are operating in mirror image.

Car companies have been using in-cylinder pressure transducers for years to measure real time pressure rise during the combustion cycle. It has really helped to optimize the characteristics of the engine, leading to power levels unheard of just a few years ago.

Hi panic, thanks for the reply.
Can you give me a specific reference to D. Vizards' comments on this. I have at least one of his very informative books (somewhere)
Regards, W

It's in the "Mini" book, Chapter 11.