I am building a 383 stroker run with flat top pistons, 081 heads (64cc,1.94/1.60), 268 extreme energy comp cam, performer intake, crane hi-6 ignition, headers, flowmasters. Anyone have a suggestion for a carburetor? Is a holley 750 vacuum secondary too big, what about a 650? The motor is going in an '81 monte carlo. What about jet sizing? I'm mostly looking for torque. Also, should I change the intake to a performer rpm?
04-09-2002 04:41 PM
Well this is one of those areas that you will find many different opinions. If I'm right the 268 series comp cam should be around .454 lift with 218deg duration at .050 lift. I would say that cam would be better matched to the performer manifold and not the performer RPM. The performer RPM is set up for cams that kick between 1,500 and 6,500 rpm's and also sacrifice some of your off idle torque. I would also guess around 650cfm's for a carb. Unless maybe your running a high gear-set in the rear and your engine is building rpm's real quick then maybe a little more carb. Just one opinion for an engine set up to deliver good off idle power/torque.
04-09-2002 05:57 PM
[quote]Originally posted by dmorris1200:
<strong>Well this is one of those areas that you will find many different opinions. If I'm right the 268 series comp cam should be around .454 lift with 218deg duration at .050 lift. I would say that cam would be better matched to the performer manifold and not the performer RPM. The performer RPM is set up for cams that kick between 1,500 and 6,500 rpm's and also sacrifice some of your off idle torque. I would also guess around 650cfm's for a carb. Unless maybe your running a high gear-set in the rear and your engine is building rpm's real quick then maybe a little more carb. Just one opinion for an engine set up to deliver good off idle power/torque.</strong><hr></blockquote>
Thanks for the input. For rear end I'm running a 3.73 posi 8.5 in. My tranny is a 700R4 with a 2500 stall converter.
04-09-2002 06:10 PM
hey monte!,dmorris is right on target in my book.the 650 would be a better choice for your setup,and ditto the performer vs. perf. rpm.however the 750 vacumn secondary has the ability to "size itself"to your application [if you already have it ,use it! a vacumn secondary carb wont open further than the demand that is put on it [straight from the holley gurus!]therefore many overcarbureted engines out there get away with their "phatness",[dmorriss told me to spell it that way] because the secondaries dont open beyond demand!anywho thats my 2 cents,jimm
04-10-2002 11:00 AM
I have found that idle quality suffers with the bigger carb. But wide open power suffers with the smaller carb. The 650 vacuum secounday carb, when jetted and sprung right, will feel better from idle to WOT. But my on track numbers show that the 750 makes more power with 331 cubic inches. The 750 can be tuned to be "ok" for daily driver. I usually go smaller unless I am looking for maximum power. If that's your deal then use the performer rpm, or try to find an old "Torker" manifold and the 750 carb.
04-10-2002 07:16 PM
I would go with the edlebrock 650, electice chock and the performer intake, if torque is the goal, the RPM will be a bad choice until the upper revs. over 1500 and will really pull at over about 3000. I have a mild build 350, 9:1, mild cam ( forget the numbers) and she breathes really well, HP is about 300 and it is a great driver, and highway machine (consistently at 15mpg) good for an aerodynamic shoebox. most folks I spoke to before choosing the setup, said it is common to over carb a motor, by the time you jet it down to idle and run right, it is a waste. the 650 was a piece of cake to set up and doesn't require tweaking at all. set and forget it. that is my two cents, everyone has opinions. later
04-11-2002 03:02 PM
Also to repeat, you want to match your intake/carb to your cam. To go with an RPM or Torker you may as well throw out that cam.
Vancouver Grand Prix
04-12-2002 04:50 PM
650 all the way, don't want to bog it off the line.
04-13-2002 04:37 AM
Hellow Monte,your going to have a bad to the bone monte carlo when you get her going, they are cool looking cars getting to be populer with the performance crowd!!! Say, the 383 produces more tourqe than a 350 anyways,and just does not need to be reved as much. The cam you have is agood choice, the extrem energy 268 has more lift and duration than High energy cams. Yours is about .477/.480, .227/.230 at .050 lift. RPM manifold matches that exactley. I think the 750 vac. carb is a great choice! Remember your 383 is 30ci. bigger than the 350's. also your rear gears and the 700/R4 steeper gears,the 2500 stall converter will help with any tourqe missing down low. 1 5/8' headers help down low, 1 3/4' up a little more, same with exaust stay at 21/2'diameter.I was wondering though, if the heads might be a little small, bigger valves maybe.Just my thougts and 2cents also! Your going to tear em up when your done!!!RSSSCHEVY2
04-13-2002 02:57 PM
I think it's possible we might have a clarification problem here. When you said 268 series cam I looked in my catalog and assumed it was the 268H you were refering to. That has the specs I listed before. The XE268H extreme cam has the larger profile listed by rssschevy2. If you are using the XE series cam yes it would more closely match the RPM manifold but it would be close. My cam has .471 lift and I'm still using the regular performer manifold with pretty good idle characteristics. The larger cam and intake will sacrifice a little of your drivability (you can go to <a href="http://www.compcams.com" target="_blank">www.compcams.com</a> and look at cam characteristics ) but as mentioned the high stall converter will help. If it was my mistake looking up the specs wrong I apalogize. It does sound like a pretty tough set-up though.