340 cam help

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mderoy340

mderoy340

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Need some input for solid flat tappet cam street/strip mostly strip.

1970 340 true 10:1 Airgap Demon 750dp J heads 2.02/1.6 home ported summit 1 5/8 headers MSD 6AL

67 dart all steel no interior, 3.91 27x8x15, 904 low gear set, sub frame installed.
estimate 3100 lbs. Will get a converter after cam selection.

Looking to have some fun at the track so I can leave my daily driver stock.
Thanks FABO
 
Not sure how racy you really want to be versus the street, so I removed my original thoughts.

I don't know whether you'll be running more 1/8th or 1/4mi, but while the low gear will give you 60' times, just remember to cam or converter for that rpm drop into 2nd. A tight LSA will give better torque in that range, probably in the 3500/4000 area depending on your shift point.

Keep in mind also, are the valve guides already machined for dual springs? If not you'll definitely have to address that, as any cam in that range will require it.
 
mid to upper 240* duration @ .050 int / 5 more degrees on the exhaust
.904 specific profile from any listed below
Bullet
Hughes
Comp
Lunati
 
Will run 1/4 mile since its the closest track. Heads have been machined for dual springs, manley SS valves, 1.80 spring height, and have Hughes roller rockers. Motor is balanced.
So a 108 or 107 LSA would produce more torque than a 110 at 3000 to 4000?
 
With the 3.91 and that low gear set in the transmission, I like the Hughes grind Beatnik recommended.
 
Old MP .557 296 dur 110cl would work well, but basically something similar with more @.050 would do it.

So far you have recieved different answers from everyone, lol...good luck
 
I expected a lot of different answers, but it looks like a split pattern is recommended from all. Also I wasn't sure a J head with a home done bowl cleanup and port job needed over .500 lift. I'll get with Mike at MRL and buy from him.
When I get this car running at the track I hope to post a 12 sec combo in the racer forum!
 
mderoy340 said:
I expected a lot of different answers, but it looks like a split pattern is recommended from all. Also I wasn't sure a J head with a home done bowl cleanup and port job needed over .500 lift. I'll get with Mike at MRL and buy from him.
When I get this car running at the track I hope to post a 12 sec combo in the racer forum!
Click to expand...

Great choice to get it from Mike @ MRL!!
 
Really in the grand scheme of things all the answers you've gotten are quite similar.
 
mderoy340 said:
I expected a lot of different answers, but it looks like a split pattern is recommended from all. Also I wasn't sure a J head with a home done bowl cleanup and port job needed over .500 lift. I'll get with Mike at MRL and buy from him.
When I get this car running at the track I hope to post a 12 sec combo in the racer forum!
Click to expand...

If you don't have flow numbers and experience porting heads, there is a good chance your heads won't need a cam over .400 lift ...cause they'll have gone turbulent by then.

With ported heads your best chance is to gett some flow numbers before you try picking a camshaft.
It's not really necessary when you have as cast stuff because they flow within a comonly known cfm / lift range.
Who knows...you may have 200 CFM int going turbulent @.400-.450lift...and 190's exh. That split pattern cam is only going to hurt you and more so when you toss a header on it.
 
Good point on getting a flow test done.
This is the article I based my home porting on; nothing radical here. The heads I started with were fairly smooth as cast from the factory. I also cleaned up and highly polished the exhaust ports. http://www.moparmusclemagazine.com/...orting/intake_port_modification_sequence.html
I've run this engine combo on the street with a Comp XE262 4 speed OD 3.91 gear and the combo pulls hard from 1500 to 5500. Cruise at 2300 75 mph and 18 mpg, great torque and throttle response.
My initial thoughts for a cam change to more strip time was something around 230 @ .050 .480 lift. A little more lift and duration to get the trap speed up and use an automatic for consistency.
 
Gonna run at Speed World? I ran there when it was Bithlo dragstrip. Showing my age....
 
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