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Author Topic:   cam durations/rod lengths
ukandesperate
Dirt Full Roller

Total posts: 45
posted April 11, 2005 04:20 PM  
Just wondering if you guys can help out,were building a 2.0 pinto that has to use a small carb,for better performance would more duration or morelift be better,my guess is more duration is this right????
and also weve got a few 2.4 pinto(long stroke 2.0) engines using long rod configurations,unlimited carbs,would more or less duration help these,they are currently 240 bhp 200 lbft torque. any help or info would be great,cheers in advance

racerman707
Dirt Freak

Total posts: 374
posted April 11, 2005 04:46 PM  
What size carb? We're restricted to a 32/36 and run a lot of duration cam but we also have a lift rule of .425.

racerman707
Dirt Freak

Total posts: 374
posted April 11, 2005 04:59 PM  
For the bigger motors, it all depends on what you're trying to do with it. You can put the duration on up to say 275@ .050 and it'll send the powerband through the roof. However if you put around 99-103 lobe seperation in it it'll narrow up the rpm range and have more torque off the corners for a restricted motor. If your rpm range only varies 1500-2000 rpm shoot for the high duration with a VERY close lobe sep and use the overlap on the cam to pull some dirty air from the exhaust and you'll trick the motor into thinking it has more carb. Hope this helps.

ukandesperate
Dirt Full Roller

Total posts: 45
posted April 12, 2005 12:15 PM  
on the big motors were running inlet full lift around 108 degrees same for exhaust,with about 180 thou lift at tdc on inlet,.130 exhaust, .520 max valve lift (head doesnt flow any more with more lift) do you think we could get away with more lift on the overlap,were only running 12;1 comp.maybe just bring lobe seperation closer to say 103??? on these cars we need good usable power from 4-8000 rpm,at the mo max torque is at about 5200 max power 6500,would be nice if max bhp was a bit higher.

on the restricted motors (yes its 32/36)we were worried about too much overlap making it too cammy bottom end and under carbed top end,weve no lift restrictions but the heads dont flow much after 5oo thou.

racerman707
Dirt Freak

Total posts: 374
posted April 12, 2005 08:11 PM  
I ran a .425 lift with 274 dur.@ .050 and a lobe seperation of 97 on a half mile. The lobe seperation got me off the corner, then it would flatten out mid stretch, then pick back up going towards the corner. With a 32/36 a 2300 is starved for air BUT who said all the air had to come through the carb? With a good header designed not to let the exaust pulses "bang" against each other on the way out you can use the increased overlap on the cam to pull a little in from the exaust. The whole point is to fill the cylinder. 2 years ago we ran cams like 242@.050 and 254@.050 and they ran great. Times change fast though. Don't be afraid to tinker with the high duration and very tight lobe centers. With a wide rpm range like that on the big motors it gets tough because the tighter the lobe sep the more peaked the power curve is. If you draw up the lobes to 103 I would go up on the duration too. Good luck!

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