Re: Pontiacs
 

THAT isn't the only advantage of the 6X head on the 400.....They have a very (very very) benevolent combustion chamber spec. ;-)

Re: Pontiacs
 

At Indy this year, the bump spot was only .536 under, in Stock, & only .350 under, in SS.

https://www.dragracecentral.com/DRCS...r2021#indextop

https://www.dragracecentral.com/DRCS...r2021#indextop

It has been said that many of the quicker cars did not go to Indy, for a variety of reasons.

I think there have been some years when you had to be nearly .900 under to make the 128 car field. I'll find one of those & post a link to it.

The Stock bump spot was .893 under, in '16 & '17.

https://www.dragracecentral.com/DRCS...r2016#indextop

https://www.dragracecentral.com/DRCS...r2017#indextop

The '19 SS bump was .783 under.

https://www.dragracecentral.com/DRCS...r2019#indextop

As Billy said, at MOST nat events, all cars that pass tech can run, no matter how slow.

That's how some really slow cars have won big races. They just didn't have a same-class heads-up round.

So, if you're trying to do some class racing on a small budget, you might wanna choose a class that does not usually have very many entrants, especially not any quick ones.

Sometimes you may be able to change classes up or down 1, by adding or removing weight, depending on car & class. This might help avoid a heads-up race with a quicker car, at a particular race.

Re: Pontiacs
 

I was the last one to race Tibor's 77 before he sold it in 2014.
I went 11.77 on the 12.70 L/SA index..
The way I see it, a single plane intake, healthy cam, trans brake ,and ditch the alternator...easy half second under SS car,...if that's your pleasure.

Re: Pontiacs
 

Yeah, that sounds reasonable to me.

I can remember a few Stockers running in SS, still in legal Stock form.Two I can remember right off were Lindy Lindholm, with his Stock Bird, before it was stolen, & Chris Stephenson with his '68 Bird.

IIRC, they weren't very far under the index, but enuff to have won, if they didn't have a heads-up round.

I'm guessing that most any of the mid 10 sec Pontiac Stockers could easily run their SS index, some without any changes at all.

The D/SA, E/SA, & G/SA Stockers would only need to run 1 sec under, to run their SS index.

And, as Mark said, with a few of the legal changes, it shouldn't be too hard to get a good Stocker quick enuff to run SS. And, since there are plenty of Stockers running low 10's & high 9's with only Cal-Trac bars & 9" slicks, that same set-up should be good enuff for a mid to low 10's SS car. Larry Maxwell is running high 10's with what appears to be a Stock type set-up, in his 350 powered '68 GT Bird.

Don't see a need for fancy high dollar suspension & big tires, unless you just have lots of money & wanna go quicker.

Re: Pontiacs
 

1974 455 rated at 310 hp with 102cc combustion chamber.

1975 and 1976 455 rated at 300 hp in SS with 120 cc chamber.
Looks like piston to valve clearance shouldn't be a problem with flat top pistons.

Re: Pontiacs
 

"1974 455 rated at 310 hp with 102cc combustion chamber.

1975 and 1976 455 rated at 300 hp in SS with 120 cc chamber..."


My guess is that the difference in compression would be worth more than the 10hp difference NHRA allows.

Only advantage I can see to the later models is the 800 cfm Q-jet. But, since the 750 Q-jets are running low 9's & even high 8's, on 428 GT cars, I don't figure the extra 50cfm of carb will make up for the loss of power from the compression difference.

But everybody knows I'm no expert. Does anybody here have the knowledge to accurately figure the power potential difference in these 2 engines ?

I've never read of or heard of anybody running the '75-'76 455 in any Stock/SS car. I'm guessing that the huge chamber volume, together with the 310/300hp numbers, is the reason why.

With that big chamber, I'd think NHRA would have to lower the hp numbers considerably, in order to make those engines competitive.

Considering the chamber size reduction NHRA allows for many other Pontiac engines, that 121.51 number is NOT very generous. Most sources list the factory chmaber size to be only about 124cc. So, NHRA is allowing only a VERY small reduction.

IMO, NHRA should either allow smaller chambers or reduce the hp factor. Unless they do one or the other, it's not likely anybody would ever choose to run this engine in either Stock or SS. But, the chances of getting NHRA to to that are probably slim to none.

However, somebody got an aluminum round port head OK'd for use on a 428 Pontiac engine, which came only with D-port heads. So, miracles do happen.

Don't think too many people ran a 428, before that. Since then, there have been lots of GT cars run a 428, including Chevy bodied cars.

If the 87cc Edelbrock alum heads were allowed on a 455, & NHRA gave it a decent hp factor, there would probably be quite a few guys try one. Since the old iron is getting really old now, and since so many aftermarket heads are now legal for Chevy stuff, I don't see why NHRA shouldn't allow alum heads for more Pontiac engines. Hey, there has been nothing "Stock" about many Stock/SS engines, for a long time. So, what difference would it make to allow alum heads on a Pontiac engine ? If they made too much power, for the NHRA hp factor, I'm sure the Chevy guys would raise enuff cane to get NHRA to fix it.

Re: Pontiacs
 

Doesn't NHRA like other engine specs use the Chamber Volume supplied by Pontiac?



Stan

Re: Pontiacs
 

No !

Here's just one good example. It has long been published & is commonly accepted that the '68 400 D-ports had aprox 72cc chambers. Some say that many actually measured a little bigger. NHRA allows 65cc chambers. So, that's roughly a 10% reduction that NHRA allows. Obviously, that will increase compression & power.

http://www.classracerinfo.com/Engine...9&MAKE=Pontiac

Obviously, they didn't do that for the '75-'76 Pontiac 455.

Compression is obviously a factor that must be considered in determining the power potential & thus the competitive possibilities of a Stock/SS engine. The power potential must then be weighed against the current NHRA hp factor of the engine, to decide if it might be a good engine to use, or not.

Re: Pontiacs
 

I believe Lynn McCarty got the Eheads approved for the 428. IMHO this is still a really good combo for a GT car. It would be nice if NHRA would open up the head rules for the 455. I have a SS shortblock ready to go but am undecided about the heads.

Re: Pontiacs
 

The 65 cc camber volume shown on your link came from PMD not anything that NHRA made up.


Stan