302 heads have small exhaust ports.
72 340 pass side manifold
- Thread starter GSS
- Start date
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302 heads have small exhaust ports.
Sorry I should have clarified. I was thinking of opening them up to gasket match and didn’t know if that would be an issue with the little exhaust ports.
Gasket match should be OK. On exhaust I only match top and sides. I also like to have my exhaust manifolds Jet Hot coated, so they are slicker than most.
good to know. About what can someone expect to have manifolds coated like that?
Not sure, they are ceramic coated inside and outside. It also keeps temperatures down under the hood.
Treblig
Well-Known Member
Anyone who isn't concerned about having their car all original should seriously consider the 96, 97, 98 Jeep Grand Cherokee passenger manifold. It has an exit hole very close in size to the 340 driver's manifold and fit extremely well in all A bodies (even early As with mods).
I had considered going that route but if I do the hi po manifolds it’s because I’m wanting to do FAST racing. Wish my car was a 70 lol. Would be super sleeper doing 340 driver side and JGC on passenger side though. And cheaper!
I don't think a 70 would be faster in FAST
Even with the bigger exit?
Treblig
Well-Known Member
Mopar put the larger manifolds on the 340 for a good reason!!!
72 has a significantly bigger carb, which I'm guessing would likely more than offset the exhaust manifold difference in a FAST type motor.
Correct, I meant as an overall package. Carb and intake will make up for the bad exhaust manifold.
Oh gotcha, I appreciate it. I just honestly assumed any 68-70 340 part was superior to 72. Or is the TQ and intake in 72 really good? Part of me wants to make a 340 that can run in fast so use all 72 parts. Part of me just wants to use any stock looking part that makes the best combo. IE JGC manifold on passenger side, whichever intake is best, etc.
There was a 71 Demon at our track that a guy bought new. After the warranty was off he put headers and slicks on it. I think maybe gears also. It ran 12.8 quarter mile times. Kim
It’s crazy how these 340 cars can be woken up. Makes me question why I’m still running my 318 lol
So what makes a 340 so fast? You can do the same to a 318.
Lol I know. I’m working on it. Currently doing head work and decided to pick up headers.
22 cubes shouldn't make that much difference.
318's can run strong if given the performance parts the 340 got but you knew that already.
22 cubes shouldn't make that much difference.
I'm getting lazy, I did not want to list them all out...
Treblig
Well-Known Member
Like your friends that came to your BBQ .....they came with a 6 Pak!!!!!!!!!
While I do like a 6 pack, my favorite is a TQ.
DionR
Well-Known Member
I think maybe that test isn't valid. I am concluding this based on the dyno test on YouTube where a JY 5.9 was compared to a 300hp crate motor and they made within 1 hp of each other.
Exhibit A - even though the crate motor had a better horsepower producing intake (in theory), they made the same power. Everything else should have been the same between the motors other than the intake. So the long runner beer barrel intake isn't the limiting factor.
Exhibit B - the same guy swapped a mild (like 262 duration) cam into the 300 hp crate motor and made 50-60 more horsepower. So I think the cam is the real bottleneck.
Based on this, I think the stock cam is just a little bumpier than a broomstick. And with such a small cam, I doubt the difference between the 318 manifolds and the 340 ones can accurately be evaluated. Same with the headers.
Also, Engine Masters ran that same crate motor with the better cam and saw a difference of 24 hp and 6 lb/#'s between the stock beer barrel intake and the dual plane M1 (with a spacer). So the dual plane is better at making top end horsepower.
All that to say, I'm not going to sell my freeflows and buy some 318 manifolds and pocket the difference because I think (in the end) the 340 manifolds probably make more power than the 318 ones. Regardless of what that test says.
Back in the day - I'm talking sixties, seventies and into the eighties - when 340s were still relatively plentiful and inexpensive, it just made more sense to start with a 340 because it already had the good stuff in it. Whether considering just the motor, or the entire car. Hot Rod Magazine came to that conclusion when it built a 318 Demon project car that ultimately went 12's.
Today is a different world, of course. Not just the scarceness of real 340 cars, or 340 motors, but also the expense of either. Plus, there are so many aftermarket parts you can stuff into a project motor today that provide so much more performance than OEM that the stock equipment is going to be replaced for any high performance build whether starting with a 340 or with a 318. Or even better, a 360.
But I do miss the days when my Dad bought a two year old 71 Duster 340 with less than 20,000 miles for $1750, or when I bought a five year old 73 Duster 340 with 50,000 miles for $1600. I could afford that even on my then meager fresh-out-of-school salary.
(I won't mention the four year old Hemi Charger Dad bought for $1350.)
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