Pro Stock Heads

[DaveRenk]

Does anyone have knowledge of why 500 cid NHRA Pro Stockers use Wedge heads but IHRA Pro Stockers use Hemi heads?

Just a couple of guesses...The small NHRA cylinders have a difficult time getting the high compression ratio? Or, the hemi head's valve train will not rev high enough?

Other thoughts?

 

[Outlaw Eric]

I don't believe the GM or Ford Hemi heads are legal in NHRA.

 

[DaveRenk]

I don't believe the GM or Ford Hemi heads are legal in NHRA.

Both a wedge and hemi head are being developed for (by) Ford and both should be legal soon.

 

[RacerRose]

Bob Glidden said years ago that when the new Ford wedge heads came out for PS, it was because he was only getting around 15 or 15.5-1 compression ratio, while the ohter teams were running 17-18 to 1. That's the best I can remember.

 

[Sean D, shondoo]

Bob Glidden said years ago that when the new Ford wedge heads came out for PS, it was because he was only getting around 15 or 15.5-1 compression ratio, while the ohter teams were running 17-18 to 1. That's the best I can remember.

I remember that same thing. It will be interesting to see if they'll be able to overcome the actual hemi design's original issues with producing adequate cylinder pressure for normally aspirated racing.

Sean D

 

[Nick Name]

I remember that same thing. It will be interesting to see if they'll be able to overcome the actual hemi design's original issues with producing adequate cylinder pressure for normally aspirated racing.

Sean D

Without having to fill the chamber with piston dome.

 

[john]

Without having to fill the chamber with piston dome.

That is really the key. I think with the 500" engines, the wedge works better because of the turbulence when loading and the chamber being in the cylinder and not the head. With the mountain motors, the Hemi adds overall volume to the combustion chamber size, it eats a giant load of fuel on a fill.

 

[70AARCuda]

hemi requires big dome to get compression...and domes add weight to pistons

hemi has complex rocker arm system which has weight to valve train.

 

[Bill]

Somebody correct me if I've got this wrong, but IIRC, about 5 or 6 years ago (maybe more; can't recall) Allen Johnson was running so well in Pro Stock with a HEMI and his own engine program, that he was consistently outrunning the "factory" MOPARS, which had changed over to a new engine configuration that they called a "HEMI," but, really, wasn't...

Rumor was that they had NHRA disallow the engine configuration that Allen Johnson was running and forced him to change over to the new one they'd mandated for Pro Stock.

Is that the way it happened, or did I get that confused?

If it's true, it makes you think about how competitive the HEMI Allen Johnson was running might have been by NOW, had he been allowed to continue developing it. The engine MOPAR has been working with doesn't seem to quite be the answer to domination in Pro Stock, NHRA-style. The old canted-valve GM Corporate "DRCE" motor consistently shows the Hemi the way home... in spite of Allen Johnson's and Larry Morgan's best efforts.

Seems a shame that Allen wasn't able to continue to devolp the HEMI he was working on a few years back. I can't really remember when they made him quit, but it has been awhile.

Anybody else remember that???

Bill

 

[70AARCuda]

Somebody correct me if I've got this wrong, but IIRC, about 5 or 6 years ago (maybe more; can't recall) Allen Johnson was running so well in Pro Stock with a HEMI and his own engine program, that he was consistently outrunning the "factory" MOPARS, which had changed over to a new engine configuration that they called a "HEMI," but, really, wasn't...

Rumor was that they had NHRA disallow the engine configuration that Allen Johnson was running and forced him to change over to the new one they'd mandated for Pro Stock.

Is that the way it happened, or did I get that confused?

If it's true, it makes you think about how competitive the HEMI Allen Johnson was running might have been by NOW, had he been allowed to continue developing it. The engine MOPAR has been working with doesn't seem to quite be the answer to domination in Pro Stock, NHRA-style. The old canted-valve GM Corporate "DRCE" motor consistently shows the Hemi the way home... in spite of Allen Johnson's and Larry Morgan's best efforts.

Seems a shame that Allen wasn't able to continue to devolp the HEMI he was working on a few years back. I can't really remember when they made him quit, but it has been awhile.

Anybody else remember that???

Bill

back in the late 90s...AJ was running a engine that was based off on Dale Eicke mopar combo......which was nothing more then a Pontiac engine with a Mopar part number...

the mopar sponsored team were also using block cast and machined by CAT that were based on the GM block....NHRA made the mopar sponsored team engines ineligable with those blocks....AJ was not currently using that block so his mopar (pontiac) combo was allow .....

but in 1999...mopar brought out the new Hemi....and told NHRA that the 99 Hemi would be the only engine allowed with placing the mopar part number on the heads and blocks...AJ had to change his combo to the current Pro Stock hemi....

aj old engine was not a hemi...but a renamed pontiac...
aj new engie is called a hemi but the chamber is not a true hemi....but is very similar to the drce..,,,combustion chambers are backasswards or something like that...LOL

 

[none]

back in the late 90s...AJ was running a engine that was based off on Dale Eicke mopar combo......which was nothing more then a Pontiac engine with a Mopar part number...

the mopar sponsored team were also using block cast and machined by CAT that were based on the GM block....NHRA made the mopar sponsored team engines ineligable with those blocks....AJ was not currently using that block so his mopar (pontiac) combo was allow .....

but in 1999...mopar brought out the new Hemi....and told NHRA that the 99 Hemi would be the only engine allowed with placing the mopar part number on the heads and blocks...AJ had to change his combo to the current Pro Stock hemi....

aj old engine was not a hemi...but a renamed pontiac...
aj new engie is called a hemi but the chamber is not a true hemi....but is very similar to the drce..,,,combustion chambers are backasswards or something like that...LOL

That is pretty much the way I remembered the Mopar program with A.J. and NHRA going down. About the last true 426 Hemi based motor I can remember still running NHRA prostock was Reid Weisnant around 84 or 85.

 

[headporter]

If you want to make power in PS you WILL have Flat top pistons. And run some pretty high compression.

 

[DaveRenk]

If you want to make power in PS you WILL have Flat top pistons. And run some pretty high compression.

What do the pistons for the IHRA Hemi engines look like? Are they pretty flat or do they have a small dome?

 

[CH3NO2JAY]

Jeff Wick was never a competitive race car on the NHRA circuit, but he did run a "true" hemi, he actually had dual plug heads and I believe he would plug one off once in a while, but he ran the Midwest Pro Stock Association with dual plugs. This is really testing my memory and this was a long time ago, but I think he was off a few tenths back in the day when the Dodge Daytona was the body to use, I'm guessing, early/mid 90's. I think the old MatchMaker ran a best et around a low 7.30...

 

[Bill]

Thanks, Tony and Paul.

The last year the Pro Stock motors were run on a pounds-per-cubic-inch basis (pre 500-cid mandate) (1981 or '82?) at the end of the last season, John Hagen's Minneapolis-based Plymouth Arrow held the mph record (and mph is the best indicator of horsepower, I am told), but lost in the final round at the Pomona NHRA World Finals, to Lee Shepherd in the Reher/Morrison entry, by mere inches.

John was running a 383 Hemi, which was a low-deck (383/400) modified block, massaged by Charlie Malyuke, of Des Moines, IA. It had the top end of a 426 Hemi (with a smaller plenum intake with shorter runners), but the bottom (reciprocating) half of the engine was pure 383 wedge, with the exception of some pistons with some VERY TALL domes on them...

With the shorter stroke and lighter reciprocating assembly, it was a 10.000 rpm motor.

John got the record and that "World FINALS" runner-up, with only ONE YEAR of R & D time.

Given another year to work with it, it might have been awesome...

NHRA killed that 426 motor in Pro Stock competition, by factoring it into a position of having to carry so much weight per-cubic-inch that it couldn't possibly win, so everybody abandoned it, and development stopped.

Later, when NHRA took some weight off the P/S Hemi configuration, Charlie Malyuke built ten of these modified 383 Hemi blocks, and a couple of them became record holders (Waly Dyck's Canadian A/D, for example.)

NHRA's "cookie cutter" rules for Pro Stock motors have stifled development of new and different powerplants, and wil continue to do so as long as they're dictating design parameters to the extent that they do.

Not much wiggle room.

Makes for close racing, but pretty boring, since they're all so similar.

I think it was more exciting when they were running a variety of powerplants.

Bill

 

[Nick Name]

If it was open, and you could run the old style hemi and still limited to one plug per cylinder, it would be hard to make enough power to qualify today.

 

[Mooseman]

If it was open, and you could run the old style hemi and still limited to one plug per cylinder, it would be hard to make enough power to qualify today.

And why is that?

 

[Bill]

The problem with making power with that motor is that the cavernous combustion chamber requires such a monumentally HUGE piston dome, that it adds considerable weight to the piston, which requires a heavier connecting rod, and that total weight requires a commensurately heavier counterweight. The big piston dome does several bad things regarding what goes on inside the combustion chamber having to do with flame fronts and turbulence. A flat top piston works much better, but there goes the compression ratio, and that's a critical consideration running unblown, on race gas. Additionally, the valve reliefs in the piston tops, are at such an angle that they occupy space down farther on the side of the piston, where the top ring would like to be, so they lose power there, too. The higher up you can get the top ring, the better... and they can't get it very high, because of the necessarily "in the way" valve reliefs.

I am not sure what Jay means about running only one spark plug, because these motors had two spark plugs pretty early in the game. I do not undertand the reasoning behind the possibility that NHRA might mandate only one.

 

[Mooseman]

Why not make a titanium piston then if weight is an issue . Someone will say cost but in a class like pro stock where they will spend thousands just to make 1 or 2 extra horsepower and its not like they are going to be replaced all the time . Infact I wouldnt be suprised if Titanium engine components like rods and pistons arent allready out there in pro stock .

 

[Nick Name]

I didn't realize that the race hemi had two plugs. Not much into that old techg stuff. But as you stated when you fill the chamber with piston dome, the flame front is seriously compromised resulting in the need for multiple spark plugs or so much ignition advance that it starts working against itself.