Re: torque engine build
[Re: goldmember]
#1069622
09/05/11 02:00 PM
09/05/11 02:00 PM
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Joined: Jan 2003
Posts: 75,004 U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,004
U.S.S.A.
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Quote:
If you want more idle vac I'd try a 2 plane performer RPM intake,that should really boost lower rpm performance without digging into the engine. Proper ignition and carb tuning will also go a long way to clean it up down low. With your compression I would not go to a cam as small as the comp 260H. I wouldn't use Campquest to make a cam choice. If you feel you must change the camshaft just call Tim @ bullet cams. I have given up giving cam suggestions,just too many guru's on the interweb.
What he said, it seems you have a large mismatch of parts so it's not surprising that drivability is less than stellar.
You can also call Dwayne Porter , fast68plymouth , he is very well versed in cams for large engines using stock exhaust manifolds .
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Re: torque engine build
[Re: rbstroker]
#1069627
09/06/11 11:07 PM
09/06/11 11:07 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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Quote:
I wonder what simply changing the intake centerline from the recomended 106* to about 111* would do.
Advancing the cam will help low end. If you do decide to change cams I agree with calling "Dwayne Porter". He speced my cam for my 493 and it works great. Its big enough to make good power but still idles nice enough and sounds great with just enough rump rump. My cam is 264 and 270 at .050 with .634 and .630 lift with 1.6 rockers. I only run 10.6 comp but I use a very fast advance and it has nice low end. I also use the Indy dual plane intake. With standard 906 ports the Performer RPM would work good for you. Ron
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Re: torque engine build
[Re: rbstroker]
#1069630
09/07/11 09:59 PM
09/07/11 09:59 PM
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Joined: Jan 2007
Posts: 7,664 IN
ahy
master
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master
Joined: Jan 2007
Posts: 7,664
IN
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I'm no expert on cams either Since I run a roughly similar combo I feel somewhat qualified to comment though. Mine's an Ed headed 496, 243@.050 .55" lift cam, 108 cl, manual transmission, MP single plane intake, 3.23 rear and 25" tire. It's a little tender launching but does fine with practice. It will accelerate cleanly in high gear from 1200 RPM with part throttle but still may buck a little if I try to run it steady at say 1500. In that situation, I just pull the next gear. With a 30" tire it would possibly be too "tender". With 10:1 (true measured) compression you may be limited in reducing cam duration much as you can run into detonation problems. You are doing well not to have problems now. Also, I think there is a good chance you can get it smoothed out without a cam change or at least without a lower duration cam with the suggestions posted above and one or two more. If you do change cams a wider LSA with about the same duration would be in the right direction. Advancing is worth a try; a lot of the rest is tuning so if you are going to advance it, start with that first. Surging at low RPM may be the result of a lean mixture, excessive advance and/or a big tight CL cam. A dual plane intake should help. Getting it to behave in the 1200-2000 range also takes a lot of tuning. I'm a little surprised reducing spark advance to 5 degrees helped... most moderatly performance cammed strokers like 15-20 initial. It makes me wonder if the rest of the timing curve is off somehow. I'd suggest an initial timing of 15 degrees and a slow advance to 34 degrees at 2800-3000 RPM. Add or re-connect the vacuum advance after you get it smoothed out without vacuum. Vacuum advance will help the engine burn clean and improve fuel economy if you can get it sorted out. The carb likley will need tuning and I'm not a carb guy, mine's EFI and has taken a lot of fiddling to get it to behave reasonably well at low RPM. 750 is a bit small for a 500" engine but may be ideal for your application to help response and low RPM drivability. A vacuum secondary carb is usually considered more street friendly than a DP. It would be worth looking for somebody in your area that's good at tuning carbs. If all of that helps, but doesn't quite get there, a step or two up in rear gear will help. 3.55 isn't much of a change so 3.7x may be the best bet with 30" tires. Good luck!
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Re: torque engine build
[Re: rbstroker]
#1069631
09/07/11 10:15 PM
09/07/11 10:15 PM
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Joined: Aug 2011
Posts: 297 Oklahoma
TinCuda
enthusiast
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enthusiast
Joined: Aug 2011
Posts: 297
Oklahoma
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Lunati voodoo cam p/n 60303 and Rhoads lifters p/n 2018. Just throwing it out there if you want to look at it.
.,
(O O {]{]{]||[}[}[} O O)
1971 Plymouth 'Cuda 440-6
{||O||}
2000 Yamaha V-Max
(O O [========= SRT] O O)
2011 Dodge Challenger SRT 392
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Making as big as a carbon footprint as I can!!!
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Re: torque engine build
[Re: ahy]
#1069633
09/08/11 12:19 AM
09/08/11 12:19 AM
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Joined: Aug 2011
Posts: 297 Oklahoma
TinCuda
enthusiast
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enthusiast
Joined: Aug 2011
Posts: 297
Oklahoma
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If you are using a big cam, look into Rhoads lifters to calm down your idle and still get all the low end torque and all the power at higher RPMs.
I copied this from thier web site.
Orginal Rhoads Lifters reduce lift and duration at idle by approximately .010" to .020". Duration is reduced by approximately 10 to 15 degrees. Total lift and duration are restored at approximately 3500 rpm. Typical vacuum increases range between 1 to 3 inches.
I am a big fan and use them in my 512 stroker 440.
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Last edited by TinCuda; 09/08/11 12:26 AM.
(O O {]{]{]||[}[}[} O O)
1971 Plymouth 'Cuda 440-6
{||O||}
2000 Yamaha V-Max
(O O [========= SRT] O O)
2011 Dodge Challenger SRT 392
.
Making as big as a carbon footprint as I can!!!
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Re: torque engine build
[Re: TinCuda]
#1069634
09/08/11 12:55 AM
09/08/11 12:55 AM
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Joined: Feb 2003
Posts: 10,205 Someplace you aren't
SomeCarGuy
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 10,205
Someplace you aren't
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Scott Brown spec'd a cam for mine that tore the tires off. We camed for use with a small convertor and 3.23 gear. I remember 234 at 50 and .555 lift. Guy I sold it to ran more gear, can't remember but I think it was 3.91. Said the torque was killer for him, but not enough top end charge. Had an Eddy RPM intake and Eddy heads. 10.25 comp.
Just depends on what you want to do with it. Undercam for mostly street is a good route. Really all the way around going small is better for a car thtat is street used a lot.
I want my fair share
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