340 performance...need help!

[Mr.Mopar]

O.K. guys, I rebuilt my 340 with 10:1 cast pistons, moly rings and bowl ported the heads a little more than they had been before. I used to have the stock 8.5:1 cast pistons in it before so I decided to pump up the compression and make some more HP. I use a Comp Cams XE268 cam with .477 lift/intake, .480 lift/exhaust, 2.02 intake valves in J heads, Mopar performance 1 5/8" headers coupled to 2 1/4" pipes into mufflers that dump just in front of the diff. I have an Edelbrock LD340 intake and use a carter 630 AVS. Distributor is dialed in at 13* initial and all in at 35* @ 2600 rpm. 2500 stall convertor in a 727 trans and 3.91 sure grip 8 1/4 diff. I measured the final compression and it came out to 10.2:1 because of the piston design and some milling on the block and heads. I ran a 14.5 @ 95 mph with the low compression and now I run 14.3 @ 97 mph. This is very depressing, I know there is more in this combo. I run street radials and my best 60 ft. was 2.1 sec. I can feel more torque and do have some more tire spin but my 60 ft. times have not varied much from last year. I was doing 2.2 to 2.3 60 ft. times before. I can't believe that I spent all that cash rebuilding to get 2 tenths of a second. Someone, somewhere, what the hell is going on! Do I need more carb or what? The only way I can get into the 13's is on Nitrous. I've got an 800 cfm TQ that I just installed but haven't made it to the track yet. Seems to me I tried that last year on the low comp. engine and it didn't make much difference. Don't tell me this is as good as it gets. Please help!!

[383-man]

I agree it should run much faster. I ran 13.40's at 105 in a 340 Dart that was a stock rebuild with the .474 MP cam and used a LD 318 Edelbrock intake with a Holley 650 DP. Also had headers and a 8 1/4 with 4.10's and a stock 318 904 trans and convertor. Did you degree the cam so you know where its at?? I would also go with a larger carb like a 750 Holley to start with as it should be pulling a better MPH. Definetly need to know where that cam is set at. Ron

[jimbo7074]

What size fuel line are you running?Reason I'm asking is that my Challenger pulled the same 60 foot times on street radials with not much traction,and the car did not seem to pull hard on the top end.I traced it back to a crimped fuel line close to the tank,and am in the process of converting to 3/8 line.

[rumblefish360]

I agree. There should be more in there.
Did you ;
Degree the cam in.
Have a quick advance installed in the distib.
Max the carb out.
Vacumm leak.

Things not mentioned...
Rear springs and shocks.
Front shocks & T-bars.
Front stuts in good shape.
Front end alinment.
Chain or torque arm the engine down.
Fuel line pressure. Along with line size and non crimped line.
Good thinkin jimbo.

Carb;

The AVS spring door adjustments? Did U mess around with the adjustment?
The T-Q will provided more torque and top end just via design of the carb. Spread to square bore will have an effect. Small, but, different.
Remember that the T-Q is 800 cfm vs. the 630 of the AVS.
You should feel a real top end charge with that T-Q.

[Mr.Mopar]

According to Comp Cams, they grind their cams 4 degrees advanced, so mine should be at 106 installed straight up. The cam card and installation instructions tells me this. I am taking their word for it so thats where it should be. Ya, I know, why build an engine and not degree the cam... I have faith in Comp Cams. I ran the Mopar 280 cam last season and got the exact same numbers as the comp cam after I swapped it out for something that would idle better. The comp cam gave me the same performance as the Mopar 280 cam installed at 107 degrees( I degreed this one) plus better idle quality and vacuum. I installed the comp cam straight up just like I did again this year. I am running a carter electric fuel pump with 7 psi. and 3/8 aluminum fuel line, no kinks. I just swapped in my TQ today and it does feel like it pulls harder. I didn't want to grind out my LD340 so I used an adapter on top of the nitrous plate to fit the TQ on. It sits about 1 1/2 inches higher now and I will need a drop base air cleaner to clear the hood. I think the spacer may even help me out on the top end. It feels better in the seat of the pants and at 20 mph. and then step on it, the tires break loose and go up in smoke. Waiting for my snubber from Mancini Racing. Even if the cam was straight up at 110 degrees, wouldn't that help the top end also? Your thoughts?

[1972roadrunner]

how much do you have it bored over? what kind of rockerarms? go to http://tmezz.mezzweb.com/ and check out my 340.

i can run appx. 10's, not sure about mph, didn't look at spedometer. thats not completley accurate though, but ballpark. we have a street that is seldomly used and has mile markers every 1/4 mile. So we got some two way radio's and some stop watches, and got around 10 seconds. can't remember exactly, but it was around 10 seconds. i have 4.10 suregrip rearend, with 50's on the rear.

[Marc]

I have what might be the STRANGEST response?

I ran that combo almost exactly in my Cordoba LS. It was fairly powerful, I had the timing at 36 degrees total.
Always screwing around like I shouldn't, through trial and error (and trial and error) I found the car could pick up five or more car lengths with more timing.
I ended up tuning with NO timing light, and had the car SCREAMING with..... 53 degrees total timing.
I know it SOUNDS stupid, but it turns out my timing marker on my damper wasn't correct.

[Mr.Mopar]

Ya know something, Marc, I just might try that because at 10 degrees, the car was a big pig and the more advance I gave it the better it went. I am at 13 now and no ping. What the heck it won't hurt.