[7T2]

if ya wanna know why, look at where the extra "meat" for the new hemi castings resides...

i see your point, old one; for a perfectly mixed mixture you are right. but an incoming air/fuel charge is an amalgamation of righ and lean spots. the burning of such results in fast(lean) and slow(rich) flame propagation. this will distort the flame front and hurt combustion efficiency.
if a hemi chamber really was that efficient, wouldnt all the automakers be incorporating some derivitave thereof in modern engines?
jim

[Region Warrior]

I remember 440 wedges getting better fuel milage then 426 hemis. Can anyone confirm this.
Over the years, every time someone gets close to beating a hemi in NHRA, hemis are allowed new and improved parts, factoring, etc. Thats my beef.

Stock hemi's in the 9's. I agree 100%. Oringinal factory parts were not up to it. They put rods out the side going 10's.

[NHRASuperStock455SD]

Old One,

Once again, you have missed the point entirely. Just because Mopar retools, and comes up with a hugely improved replacement part, doesn't mean NHRA has to accept it. In this case, most NHRA Super Stock racers agree that either they should have accepted it and added HP, or not accepted it.

It isn't really that the "castings" are a gift, the free 75 or more HP capability is the gift. (This is where you missed the point.) A good example was the replacement heads that the 428 CJ Fords got. They were given an instant 20HP if you use the new heads. (probably rightly so). However, they Chevys and the Hemis got no HP adder. This created an uproar in the Ford community as it was clearly unfair. Now at Indy all the CJ Fords are in tear down. Why? because they complained is the conjecture.

I have heard that argument about Pontiac not producing castings before. It really is a lame argument, because Mopar isn't making them either. They have a separate job shop doing it. They just "rubber stamp" the part number. The real job is the NHRA approval process. GM is so bureaucratic that is impossible to get a rubberstamp. Ford has rubberstamped Dove and many other head replacements like the Medium Riser and High Riser heads.

Len Imbrogno the Sportsman director for NHRA is trying to help the combinations that where the OEM is no longer interested.......then accepted reasonable replacements should/will be allowed. I am meeting with him today. Currently Edelbrock heads are under approval considerations, and close to being accepted. Edelbrock has done many replacement heads like the BBC head. Similar to Dove replacements as well. For heavens sakes man it is just a piece of paper difference. Nothing to lay down in front of a truck.

If you look at the obtuse advantage the HEMI's got with the new castings it really is over the top.

However, even with the HP "gift" that the Hemis got, they still cant handle the 400 Pontiac 6X motor with original cast iron heads, block, crank.

If the Hemi head was so good, and it has now all the modern day technological advantages, I still see the same weight heads up RA-V from 1969 competing with it.

You said it yourself on the post about the RA-V engine on Ebay. If it ran 10.11 in a 4000lb car, what would it run in a professionally built chassis with 1000lbs off? 9.11? What if we spent $7500 redoing the intake porting like I did to get 330 cfm from my 455SD heads with 188 cc intake runners? What about reducing the drive train 70lbs like I did in my Super Stocker (which was way lighter than our old 69 TA). What about a killer short block like we do in Super Stock?

What if we get NHRA to approve my RA-V castings as obtusely as they approved the Hemi castings?

Call and ask Bill Foder, he has built and raced both motors. He has also read all your posts.

Ditto to Poncho and 72T. The Hemi combustion chamber has its advantages and disadvantages. The main advantage for a hemispherical combustion chamber was to reduce cylinder wall quench. Cylinder wall quench occurs when flame travel cant reach the area of the cylinder blocked by the shape of the combustion chamber. it is why Open-chambered heads improved HP. Also, near the cylinder wall, the temperature of the combustion gases go down due to the heat transfer to the water jacket. This reduces combustion efficiency due to the depressed temperatures. However, when you fill a block with hard block, this greatly reduces the quenching problem as the head of combustion is not being transferred through the cylinder wall and into the cooler water.

As we come up with the new combustion chambers, we approach the efficiency of the hemispherical combustion chambers. Then the negative aspects of the Hemi design just as Ponch0 describes takes over. This is why the new wedge style combustion chambers are now more efficient than the Hemi in Pro Stock.

Additionally we could virtually write a book on other parameters. Why does a domed piston that is required for a Hemi to maintain any sort of compression require so much timing advance? Because flame travel is less efficient. The dome also is a heavier piston exactly where you don't want it. My 455 piston only weighs 380 grams without the pin.

Also, there is combustion efficiency ehancer item called "squeeze". As the piston comes up, if you angle the combustion chamber properly you can squeeze the combustion gases one direction or the other. What are the 3 "T's" of combustion? Time, Temperature, and Turbulence. This squeeze technology creates turbulence at the top of compression like squeezing your hands together at the swimming pool and vastly improves the combustion efficiency. This is accomplished much better with a wedge style head than a Hemi Head, last I heard. Maybe the R&D labs have come up with something, but when I was dealing with GM people at the GM tech center, this was the hot thing.

Lynn

[Bad Karma]

Wow Thanks for the great answers and debates. Very interesting reading. One last thought from me:
Do you ever think the aftermarket will make a hemi head for pontiacs. I could see its use in supercharged or pro charged applications. I just wonder if its a pipe dream.

[tom s]

NEVER happen!At least not for mass production.Tom

[Brian Baker]

It took 20 years for an aftermarket block to surface after Pontiac last made a "real" engine, so I doubt you'll ever see any mass produced hemi heads for a Pontiac, if any will ever get produced.

[Jack Gifford]

Originally Posted by tom s

NEVER happen!At least not for mass production.Tom

Whew! Now I can relax, knowing that my Pontiac hemi will REMAIN one of just a few!

[theoldone]

Originally Posted by NHRASuperStock455SD

Old One,

Once again, you have missed the point entirely. Just because Mopar retools, and comes up with a hugely improved replacement part, doesn't mean NHRA has to accept it. Lynn

It's a moot point, Lynn- the fact is, NHRA did accept the Mopar parts. So the issue changes to, what do we have to run against them ? We can either hope NHRA underfactors Pontiac engines so we get a break in the rules- or we can come up with a new head that Pontiac puts a GM part number on, so we can run against the Hemis heads up and beat them.

8.50's or quicker is the number. Anything else is second best.

The Ebay RA V engine shows that combo's ability- in a 2200 pound tube-chassis race car, it would run in the 8's easily. Rudy D. and Steinbrick proved that. The problem is, you can't run a tube chassis car with Lenco in SuperStock. The best bet for a SS RA V combo would be GT class and run it in a later light body, i.e. Sunbird, Astre, Sunfire, etc.

Otherwise, the best bet would be run it in the 1969-70 Firebird, GTO, Grand Prix body. I don't know where it may fit in exactly. What do you think ?

If the Fords got 20 HP handed to them, that's only one tenth. If the Mopars got 75 HP handed to them, that is only 2-3 tenths for an 8-second car. So instead of running their current 8.50's they'd run 8.80's with their old original stuff ? That is still blistering fast in SuperStock.

[theoldone]

Originally Posted by tom s

NEVER happen!At least not for mass production.Tom

instead an aluminum D-port head was mass produced, our most limited design. that made no sense to me.

Mopar recasts Hemi stuff, Ford guys are making SOHC stuff, while we make aluminum D-ports.

[tom s]

Charlie(theoldone),there was a demand for a alu D port head!There is VIRTUALLY NO demand for a hemi pontiac head.That is why they have not been made.There is a bigger chance for the V head.The hemi head does NOT fit a pontiac block "that" well.Jack and Steve know what has to be done to clearance for the push rods.A block could be modified when cast to allow for it but would be another hurdle for builders to overcome.Tom

[Bad Karma]

Toms
So if they cast say a IIIA hemi block taking in to account these issues it would be easier to manufacture a pontiac hemi head right? I never intended this to be a shat storm topic. It was just a curiosuity I and others obviously had. Again thanks for the answers and info its a great wealth of knowledge.
cheers

[Tom Vaught]

Quote:

"Toms
So if they cast say a IIIA hemi block taking in to account these issues it would be easier to manufacture a pontiac hemi head right? It was just a curiosuity I and others obviously had. Again thanks for the answers and info its a great wealth of knowledge."

You would be surprised how easy it would be to make a PONTIAC
BLOCK with the features that the HEMI possesses:

You could have a 10.72 deck height fairly easily, A cross bolted block, a 2.75 main journal, a 6.8 bore center block, etc etc. BUT THE TYPICAL PONTIAC owner/ racer would not touch it because it violates all of the rules that say "It has to bolt onto that 1955 designed 4.62
bore spaced block or it isn't a "TRUE PONTIAC ENGINE".

Like saying I race a Ford 292 "Y-Blocks" Whoop de do, no one really cares except that overall it is not competitive.

There are a few classes presently where the Pontiac can race competively, very few. Without a different outlook on the way a
racer looks at a PONTIAC block etc, we are fighting a losing battle.

Boosting is the only way to keep an outdated block design and still have a chance of winning in some classes.

JMO

Tom V.

[tom s]

badkarma,the cost to tool up for aftermarket parts is high,for virtually every mfg. they have to look at return on investment.The demand for true HP pontiac parts is really smal which is why the parts for our"hobby" are more than others.As the amount of a item increase and actually sold it will dictate the cost of the part.I have looked into repoping some parts but the demand would not justify the capital expensive.To put it shortly,"the juice aint worth the squeeze!Tom

[Bad Karma]

Thanks tom S and tom V I understand why its not likely. I dont have a working kowledge of the race rules. Now its cleared up and makes sense why its not going to happen. I just love choices and the more the merrier. To be honest I couldnt afford them anyway I bet.

[GTOGEORGE]

Tom,
I guess you would have to actually race A Pontiac and be a true blue Pontiac person too understand (not some Ford transplant)!

[theoldone]

Originally Posted by tom s

Charlie(theoldone),there was a demand for a alu D port head!There is VIRTUALLY NO demand for a hemi pontiac head.That is why they have not been made.There is a bigger chance for the V head.The hemi head does NOT fit a pontiac block "that" well.Jack and Steve know what has to be done to clearance for the push rods.A block could be modified when cast to allow for it but would be another hurdle for builders to overcome.Tom

I disagree- all the guys buying Wenzlers, E-heads, etc. would opt for the Hemi head instead. And it would bring the price down too on the other stuff.

How many Wenzler heads are sold ? Not a lot.

[theoldone]

Originally Posted by Tom Vaught

Quote:

You would be surprised how easy it would be to make a PONTIAC
BLOCK with the features that the HEMI possesses:
You could have a 10.72 deck height fairly easily, A cross bolted block, a 2.75 main journal, a 6.8 bore center block, etc etc. BUT THE TYPICAL PONTIAC owner/ racer would not touch it because it violates all of the rules that say "It has to bolt onto that 1955 designed 4.62
bore spaced block or it isn't a "TRUE PONTIAC ENGINE".
Like saying I race a Ford 292 "Y-Blocks" Whoop de do, no one really cares except that overall it is not competitive.
There are a few classes presently where the Pontiac can race competively, very few. Without a different outlook on the way a
racer looks at a PONTIAC block etc, we are fighting a losing battle.
Boosting is the only way to keep an outdated block design and still have a chance of winning in some classes.
IMO
Tom V.

Tom,

Very good post I agree on all points, except the Y-block issue.

The 292 Ford Y-block was not a powerhouse- because it didn't have airflow and cubic inches- in top form it was only a 312 CID motor with choked off heads.

The point is, a Y-block skirt design is STRONGER.

If I was redesigning a Pontiac block, this is what I would do.

Keep the 4.62" bore spacing, so all the old top end stuff still bolts on.

Redesign the main bearing size and align bore the new block to 2.75", just like the 426 Hemi-427 Ford-454 Chevy

Redesign the rod journal size to 2.100" like the SBC

Take the RA V and M/T Hemi heads, and improve them and use them on this new block. Cant the valves on the RA V head and improve the chamber to fast burn.

Recast the block so it has a Y-block skirt design like the 426 Hemi/427 Ford to hold the bottom end together better.

Add at least (3) head bolts per head in the middle, one between each cylinder.

Use a solid lifter valley for strength, and siamesed cylinder bores- in this case the new IA block already has that covered.

IMO, we can keep the deck height and bore spacing the same, just improve everything else. The SBC has an even tighter bore spacing and lower deck height than a Pontiac- those SBC guys are not lacking for power though- they make it up with RPM and compression and airflow. Small journals and more head bolts are the key.

You hit the nail on the traditional Pontiac mindset- the racing class issue- and the boost issue. I agree. All the other makes retooled from 1964-69 and came out with new big block engine designs- while Pontiac just changed valve angles and intakes on their old 1955 design. And we've been playing catch up ever since.

[7T2]

i think theres an 11" deck height block mold floating around that got very little use. probably because of the limited cyl head flows. a guy might be able to acquire that pretty cheap and clearance it for a hemi head an reintroduce- that is if it still exists.

[J.C.you]

i do not claim to be an expert on head design, but are there not many variations in current head designs of the hemi chamber in everyday drivers?

am i off base on cfm required to feed a 500+ cube engine to be in the 500+cfm range for max power?

for years the pontiac community has "thought too small" in the mindset of small ports and crummy headflow.

it is time for a new design that will flow well over 500cfm to feed the big cube strokers we have available.

[Tom Vaught]

JC,

According to Buddy Morrison, (who I sold some flow bench stuff to years ago), they were running over 550+ cfm in 500 cid Pro Stock heads even then BUT the heads were designed to still maintain the velocity.

Tom V.