Big Valve X Heads on Low Comp 72 340
- Thread starter Dustine
- Start date
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Not sure a 904 transmission came with a stock converter that would have enough stall to make a 340 work well. Plus, none of the 340 cars I have had ever came with a 904 stock. I have swapped them in myself for assorted reasons, including one that is currently behind my 408 in my 72 dart.
You'll gain nothing but the valve sizes difference by swapping on the X heads. Well, you can stand around and brag about having X heads.
ir3333
Well-Known Member
You would be limited to the cam size for either head. I think stock X or J heads flow stalls out around .490
valve lift. Those TV guys can get 400 hp with a cam, headers and carb swap, but you and i can't.
valve lift. Those TV guys can get 400 hp with a cam, headers and carb swap, but you and i can't.
Yeah and they usually have zero accessories attached. electric water pumps and highly tuned carbs etc..
Gross dyno trim hp and we have our engines in a car would be net hp, but people tend to talk in gross dyno trim hp with older performance engines. Like my engine on the dyno would have about 400 hp and that's what I would say it has but it's probably 30-40 hp less as installed in my car. It really don't matter as long your comparing engines in similar state.
With the addition of the 3.73 gears, headers, intake, and ignition curve would make more meaningful gains if you don't want to touch the bottom end and are looking for actual performance gains. The only way I would change the heads in the name of performance improvements is if I happened to have a set of aluminum heads ready to go. As the OP stated, though, even a low compression 340 still can run fairly good in stock form!
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For my 2 cents, air speed is far more important than CFM. If you don't have air speed you have a lazy engine. CFM is important, but air speed is King!
I am going to guess it would run far better with a 1.88" intake valve than it will with 2.02"s
In your combination I wouldn't use a larger valve. Everyone gets caught up in the bigger is better on valve sizes, cam sizes, and carb sizes.
The truth is most guys have all of the above and wonder why it doesn't run that well. It's just like baking a cake you need to have the right portion of
ingredients to get the best possible outcome.
Tom
I am going to guess it would run far better with a 1.88" intake valve than it will with 2.02"s
In your combination I wouldn't use a larger valve. Everyone gets caught up in the bigger is better on valve sizes, cam sizes, and carb sizes.
The truth is most guys have all of the above and wonder why it doesn't run that well. It's just like baking a cake you need to have the right portion of
ingredients to get the best possible outcome.
Tom
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2.02 only has less velocity if the cfm is the same for both the 2.02 & 1.88, question is how much more flow does the 2.02 need to have same or better velocity than the 1.88 valve ?
junkyardhero
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He may have, i'm sure someone will let us know
I can tell you that having a bone stock 72 340 4spd 323 peg leg Demon ( had factory T-quad), only had a set of Hooker super comps on it it ran great for a stocker..lol. when I went back to manifolds, it lost a lot of quick rpms, lost the torquey feel and generally felt like a dog . Headers are a super PITA putting in that A body, but the rewards are worth it in my opinion.
I agree with GTX John too, smaller valves create more velocity. Keep the 202s for when you want to add, pistons, cam, etc.
I agree with GTX John too, smaller valves create more velocity. Keep the 202s for when you want to add, pistons, cam, etc.
The main thing that holds back the later 340's is the compression. Bumping up the compression will yield the best results. Second would be good exhaust.
Back in the day (1978), I put some cheap Blackjack headers in my otherwise stock low-compression daily driver 73 Duster 340, 3.21 open rear, and picked up over half a second in the quarter (15.0s to 14.40s). Would have done even better, but the headers gave me so much more low end that now I had a traction problem. Headers also raised my shift point from 5200 rpm to 5800 rpm. Except for the headers, the exhaust system was factory stock.
I traded that Duster for a 1982 Charger 2.2 in November of 81. My first new car. Dumbest thing I ever did. . . .
I traded that Duster for a 1982 Charger 2.2 in November of 81. My first new car. Dumbest thing I ever did. . . .
My 73 340 Duster has the OE low compression but it has a different cam, 224* @.050, and LD340. Same gearing, 3.21 open. OE replica bent exhaust and tips. She’ll bark when power shifting to second.
I have a set of TTi shorties in the box I am wanting to put on. Peter Bergman also sold me a 2.97 3rd with True Trac for when I switch to the 8.75 and I have a spare 3rd to have optional gearing.
My heads are a Z and a O head, which I’ve heard are good.
Eventually I would like to up the compression and have a friend port the heads and match the intake.
This is good info.
Swinger 340
Well-Known Member
There is a difference between the "J" and "X" heads. "J" heads came on early 360's and I (had done) use to machine them into 2.02's. The trucks ran better, but I also installed a 4 bbl intake and headers on them. Maybe that is the reason they ran better.
Dale Davies
Well-Known Member
To realise any benefit you may be looking at, run the numbers on David Vizard's 128 formula with the intake valve size you have now and the 2.02 heads. To optimize a change of LSA may be required. Higher ratio rockers would also help give more snap.
Not here because I’d bet a pay check your dead nuts accurate.
As far as I’m concerned, you took the words right out of my mouth.
IIRC, I believe that’s the stock head gasket thickness. .027.
He did mention “Possibly look at headers in the future.”I like how the poor guy said he was happy with the stock bottom end and exhaust manifolds, and just asked if the heads would make a difference.
Now everybody wants him to port heads, add headers and intakes...
Not every thread is looking for a max power build.
That always leads to….. LOL! Exactly what you said.
I do like collecting parts to swap at once though. That’s where you really feel the gain.
To the thread starter (OP) A, FWIW stock head flow video set. Both heads are mine and start with stock cylinder head flow. Being. Charlie ports heads, results are also seen. The J heads are a 1.88/1.60 valve set.
“Should you change a camshaft, in the street, not looking for a drag win, I’d lift the valve until the cam starts to fall off and not really anything ore than that. Someone mentioned stock head flow to .500 was accurate in this case and most every other head I’ve personally come across. You can get a lot of performance out of a stock head.
He S heads were previously ported by someone else and not in a fashion I’d suggest. Enjoy!
I had some 2.02 valves put in a J head years ago. Same casting? Yes, but my machinist didn’t do the work the X head came with. I’m taking my J heads I’ve been reworking after reading and watching DV to get a proper throat cut. Here are three pictures; two of the stock X head and J with the half done 2.02 install. The X has a side cut to unshroud the valve and a cut down into the bowl. Most of the green dyed area on the J needs to come out. I’m giving the J heads an overall job to best of my ability. I’m saving the X head as a fallback if I goof it up.
Bubblegum
Active Member
Beware of Fastback he is a Clear Tweaker!
Swinger 340
Well-Known Member
Not sure on how this became my comment, but it is not. Mine was, I have "Z" and "O" heads on my vans 340. I believe they are from 1970 and from a "E" body. They appear to me the same format as the "X" heads. 2.02/1.60
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