Pure stock 340 Mopar

[X-TECH MAN]

Originally Posted by Todd Boyer

1971ls6: I believe you're referring to the "Pure Stock Musclecar Drags" series in which you must run manifolds and bias tires.

Mark: IHRA has a Pure Stock class that NHRA doesn't. Our local series runs under IHRA rules which open things up to more participation from 'different' classes. You can't use a 'stocker cam' as a traditional stocker can. But I've read here that you should have a cam ground which will check within the specs but should work better than a dead stock grind.

Can run headers with mufflers OR open manifolds.

You can check out the rule book at http://www.ihra.com/.

Thanks for the replies guys.

Correct on all the above. You can run 9 inch slicks at 29.5 diameter. The cam MUST check on OEM duration and over lap like in the Jr. stock days of pre 1972. The valve springs must check on OEM open and close pressure specs also.
Just pretend your racing back in 1971 Jr. stock days if your old enough to remember those days.

[KRatcliff]

Is there a list of the current Pure Stock records?

[Todd Boyer]

Originally Posted by A56

Not old enough, im only 43. You need to put a small header on the car to draw as much air into the engine with a cam like that, your lucky though the 340 had a pretty decent cam though. 1 1/2" - 1 5/8" - 1 3/4" Merge Collectors to dual 2 1/2" with an X pipe. Maybe that will be of some help. Sounds like a fun class, wish I had the chance to give it a go.

Mark Lelchook
F/SA #704

Mark, I already have a set of 1 3/4 non-step headers, will I be able to get away with using them with the X pipe and mufflers ??? I'm only 43 also !!!

[mike coates]

Todd,
I have been running 1 3/4 headers on mine with flow master mufflers.
I don't have a cross over pipe. My thought was run the larger pipes since the muffler was required and will create some back pressure.
I haven't done any additional testing with smaller hearders or X pipe.

Mike

[Todd Boyer]

The worst part of this whole deal is that I just sold a set of Hooker 1 5/8" street & strip headers that I think may have worked with this combo. The main reason I'm wondering if the 1 3/4" will work is that I already have them, and will run them when I eventually build the car into a traditional stocker.
Like Mike, my thoughts were that I could get away with the larger pipes with the exhaust system creating at least some back pressure. Mark, I know you're the man for headers, so in all honesty, what kind of ET difference can I expect between the 1 5/8 and 1 3/4 pipes?
For our local series, I'd be really happy to be -.2 or .3.
I used to run my street/strip '69 Dart with a very mild 360, 904 with 3400 stall converter with 4.10s on 26" slicks. It went a best of 12.9 @ 105 (it was a street and strip car). The car had full exhaust including tailpipes and OLD Dynamax mufflers.

[James L Miller]

I had planned on building a 340 to run IHRA pure stock with my 1969 Barracuda street car. The Crandall track closed, so that plan went out the door. I had bought a custom cam from Bullet for that deal, it was something like 250 degrees at .050" on a 109 LSA as I recall. The old factory spec for the 340 cam was something around 336/348 duration at .000" lift, so that gave a lot of leeway in grinding a cam. Not much different from the regular stocker cams from what I know about them. I also have an old Lunati(c) cam and an ancient CD stocker cam from the 1970s that I was going to try. I liked the idea of Pure Stock since I didn't need to put a rollbar in an original 340 car.

[Todd Boyer]

Hi James.
That sucks about your track closing.
On the factory spec cam do you mean the "stock eliminator cheater cam" with 336/348 duration at .000" lift that Mopar had, or are you referring to a factory 340 cam ? I didn't think the duration was that long on a factory 340 cam.

I'm wondering how much a custom cam will be worth.

[Chipper Chapman]

Todd, what A56 is talking about for the exhaust is that it's not the back pressure the system gives to the engine, but the velocity at which the exhaust gases have to travel in a smaller primary tube. The higher velocity (or rate of speed) will help to draw (or scavenge) the air/fuel into the cylinder during that minimal overlap period, effectively cheating the engine into thinking it has more cam duration. On the monte we ran small primary street headers (cheapo flowtechs) that achevied this, but with a 3" system and mufflers to not create excess back pressure. It went .4 under with a 100k mile engine.

[mike coates]

Todd,
The cam specs come from the NHRA / IHRA engine specs. For the high compression 340's, the specs have the 330 ish duration. They don't match the "advertised" specs. I think Danny Waters Sr. may have the specs. Terry Bell used to have them, but I don't think he does anymore.
They have to be the old specs from before they removed the duration requirements, from like 20 years ago. I have them for the '70 340. I am not sure if they are the same for the earlier ones.
I have an ISKY stock grind that is around 348 @ .050. with .478 lift I think. It is the dwell nose type. The higher lift works because I run the stamped rockers and the ratio is off from the 1.5, so the actual lift at the valve is still a little short. It is supposed to be a good cam for a regular stocker, but I think it is too much for a pure stock. I run stock valve springs per the rules and I only get 6200 - 6300 rpm. If I were to get another, I would get one that works more to that rpm range.
Some time ago, I talked to the guy with the pure stock demon. I think he was only shifting @ 6000 and 4.56 gears and he was running around 12 flat. I don't know what his specs were. But as I said, I built my engine and I think he had someone build his. I know there are probably several items that could be improved on mine.

Mike