I am planning on building a 340 for street/strip in my 72 demon. I have a freshly machined .060" over 340 block, stock forged crank, stock rods, and TRW forged pistons. When the engine is built I will have atleast 10.5:1 comp. For heads I will be using some big valve 'J' heads that have had just some gasket matching done to them. I need opinions on an intake and a cam. Also I will be running a set of tti headers and the car is a 4 spd. and will have 3.91 or 4.10 gears.
340 build up
- Thread starter R72Demon
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Air Gap is a good choice and a 625 AFB maybe a 750 on the large side.
I would go solid lifter and on the short side for duration and more lift. Maybe in the .510 to .530 range and some where in the 230 ish range at .050 would be good. I have a Crane that is about .548 lift and longer on duration, but I run a stroker 416. Dont over cam low end really suffers.
I think a lot of guys like the hughes and comp cam grinds, they are less $$ than Crane but I have had good results with Crane.
You do want more than the factory purple series 340 or hemi grinds. They lack on lift, seem to have more overlap and thus cut out some low end. With that much compression do the better head gaskets too and you can get by with a little more cam to help pinging.
I would go solid lifter and on the short side for duration and more lift. Maybe in the .510 to .530 range and some where in the 230 ish range at .050 would be good. I have a Crane that is about .548 lift and longer on duration, but I run a stroker 416. Dont over cam low end really suffers.
I think a lot of guys like the hughes and comp cam grinds, they are less $$ than Crane but I have had good results with Crane.
You do want more than the factory purple series 340 or hemi grinds. They lack on lift, seem to have more overlap and thus cut out some low end. With that much compression do the better head gaskets too and you can get by with a little more cam to help pinging.
moper
Well-Known Member
How certain are you of that 10.5 number? IMO, if you go too high with the static ratio and kep the big iron chambers, you are asking for detonation going with a small cam. Do you have power brakes?
Intake...high rise dual plane (For surley a 750 cfm carb)
Cam, to bleed off some of that pressure, something with a tighter centerline than normal. I'm with moper on that actual number. It is high for an iron head and pump gas. You have an open chamber and what (?) for quench? Are your pistons domed? This could be tuff to feed.
(This cam choice is closer to a guess at this point, but something like a 238/244 - 246 split with .500/.530 lift or so on a 108 or 106 degreed in.
J heads have an exhaust flow inbalance that should have you looking at a 6 - 8 degree split in duration.)
Cam, to bleed off some of that pressure, something with a tighter centerline than normal. I'm with moper on that actual number. It is high for an iron head and pump gas. You have an open chamber and what (?) for quench? Are your pistons domed? This could be tuff to feed.
(This cam choice is closer to a guess at this point, but something like a 238/244 - 246 split with .500/.530 lift or so on a 108 or 106 degreed in.
J heads have an exhaust flow inbalance that should have you looking at a 6 - 8 degree split in duration.)
No power brakes. I was thinking of going with an Edelbrock Air Gap intake, and a Comp XE284H cam. Would that cam be a good choice??? The next step is the XE294H, would this be too big? Heres the pistons I have: http://store.summitracing.com/partdetail.asp?part=trw-l2316f60
lead69
hopeless car junkie
Just my opinion but I would go with the air gap and a comp xhl274-or something similar-it will give you alot better bottom end and driveability and I doubt you would lose any horsepower,I ran the xe 284 in my pontiac 462 and its a brute.I would verify the compression ratio by cc-ing the heads and checking the deck height,every stock uncut 340 Ive seen has had the pistons right at zero deck and considering mopar heads usually cc higher and modern .039 gaskets most 340s Ive seen wind up around 9.5.
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