dogboy

I put in a sumit 1103 cam to my stock 350, only mods are true duals, edelbrock performer intake, and recurve kit with adj vac advance, which I'm still playing with for best set up. I have a slightly higher TC rated at 18-2200 rpm's. I have a very lumpy idle when at a stop light with the idle set at 800-850 in gear it will drop to 750-700 rpm's. still very rough. It will cruise great but as soon as it drops below 900 rpm's roughness. It almost stalled out at one point and I had to place it in neutral. Also smell from exhaust is horrible, smells very rich. What shold I be looking at to correct. Could this cam be too much for this setup? low end take off not very impressive either. This cam wakes up about 2000 rpm to 5000
These are the cam specs:
@ 0.05 intake duration 214
Exhaust 224

Int lift 442, exh. 465
adv duration int 272
exh282
lobe separation 112

Paul 75 L82

Total timing and your carb adjustments play a very important part of how your motor idles. Work with you total timing and maybe a adjustable vac in the dist. Probally from 34 to 36 deg's total. The idle curcit is very important on your carb. There are many articles in Chevy High Performance, Hot Rod & Car craft about this, or call the carb manfucture for info. That's the reason I run a Demon.

Fevre

I checked the specs on that cam and it says rpm range 2000-4500 so sounds like it is responding when it should. Did you set timing, hook vac adv to ported vac and adjust idle screws? I tried my adv on an unported source and it wanted to stall below the 7 reading on my vac gauge when taking off.

Kingt

I run a similar cam (Crane 272) it idles fine.

PatsLs1vette

like i said before i ran that cam and it idled fine..tons of torque..double check your timing.


[Modified by pats406nitrovette, 11:09 AM 9/11/2002]

70PurpleLS7

Just for poopiez and giggles - when you adjusted the rockers, just how far of an additional turn did you go after you had zero lash???

Could be the valves are adjusted too tight.

dogboy

Paul 75L82 : I now have the crane adj vac advance unit in. Old vac unit was DOA.

Fevre: Initial is at 18deg. I have ported vac which pulls o deg . starts to pull >900rpm's

Pats406nitrovette: I'm still working the curve on the timing adv. Having a little difficulty with the mechanical. I may go back to the stock weights and just play with the springs. I had to drill out the holes a little in order to get the summit center cam to fit my distributor. I'm not up to a total 36-38 advance yet?

70 purple L57: I turned the nut 1/2 turn more as soon as I felt resistence. Did that adjustment twice. Initial and after running for about 10 miles. there was only 1 that really needed a readjust the # 6 intake. It was a little loose.

I'm going to raise idle a little, play with air/feul mix along with a vac gauge, and mess with the mechanical advance.
Thanks>>>>

Brettmc

Lumpy idle? What's wrong with that?! Betcha it sounds good. Your vacuum is low enough that it's prolly opening up your power valve (if your runnin a Holley). I had this problem on a camaro once.

Chuck Harmon

Did you get the cam timed correctly on installation? The timing marks on aftermarket crank sprockets that allow advance or retarded positions can be pretty confusing. I would expect a pretty smooth idle with the specs you show.

Chuck

Paul 75 L82

Don't get hung up on intial timing, it doesn't matter, only total maters. Your cam is screwing up your initial timing from being correct. Set it for total and you will see a difference.

Vetterodder

It's true that, once above idle, initial advance is no longer a factor in performance but the amount of timing at idle has a major effect on how an engine idles, especially with a larger cam. It's no coinicidence that your idle quality drops at the same rpm as your vacuum advance stops adding timing. Going to manifold vacuum from ported will give you a bunch more timing at idle but, once above idle, the engine doesn't see any difference. Also, the increase in advance at idle will probably help combustion and eliminate some of that over rich condition.

Keep in mind that anytime you increase overlap the resulting reduction in intake and exhaust velocity causes combustion efficiency at idle to go down also. That's why bigger cams idle rougher .... not because they're making gobs of power down low, it's because the engine is running crappier at idle rpms.

QuickVet

that cam is small. mabey you have a bad vacume leak. :confused:

nunus79

Provided everything else has been checked out and set properly, the answer is simple, you don't have enough compression to support that cam. What you describe are the classic "under compression" symptoms=big cam idle effect from a mild cam.

Do a cranking compression check. I bet you are in the under 150 psi range.

nunus79

SLICKMAN

That cam you have is not much deferent than an L82 cam (which I have an L82) The specs on the L82 cam is listed below. This cam was used in 1957 – 1987 on 350ci and my 78 has a nice lope and it also wakes up at around 2500 - 3000 rpm which is correct..

Intake = 450 lift
Exhaust = 460 lift
Duration = 272


Just my 2 cents

zwede

I ran that exact cam in a Camaro years ago. Specs were 350 cui, 9.1:1 compression, pocket ported 442 heads, small tube headers, performer intake and Holley 600 carb.

The engine ran very smooth. Barely had a lope at 600 rpm in drive. Pulled lots of vacuum (17") and ran really well. Dynoed over 300 hp at the flywheel, and 380 ft-lbs torque. Excellent street cam. Had a lot of fun with that car.

So something must be amiss on yours... How about tune-up items? Plugs, wires cap & rotor?

dogboy

Just checked the # 1 cyl, cold, all plugs in, pulled about 148 psi I set my total to 38 without vac adv. set idle at 850. plugs look ok and wires are 2 yrs old. Cap, rotor and coil all from accel. runs smooth after idle but still sucky at 750 in gear. vac read 17hg's, pretty steady. If cam is too much for the goodwrench would a comp 260H be a better choice with my compression?

nunus79

I used Rhoads Lifters on my 327/350 cammed L48 shortblock to get 155 psi cranking psi. Even with that, I felt the lazy feeling of low compression. Not until I installed 64 cc Sportsman IIs, did that motor wake up.

I think you got the option to just live with it or to fix the low cylinder pressure. Your thinking about the HE260 is a good one. I believe TNT76Vette is quite happy w/his on a L48. CompCams does recommend using that line of cam with engines w/less than 9:1. The cam gurus will hopefully chime in about that one.

For now, if you have an adjustable mechanical advance distributor, try cranking up the initial advance 20+ and see if the motor wakes up some without predetonation problems. If it works, you'll KNOW you have too low compression for that cam. I ran my L48 with 20+ timing for awhile without any apparent problem. But remember that is just a band-aid kind of thing.

Ybnormal

Dogboy,
I have just installed a cam myself, somewhere close to your specs. (Edelbrock 2103). I found that running (as the directions that came with the kit said) straight manifold vacuum, and it gives a nice idle. Also down sized the primary jetting just a little as I think the Edelbrock 1406 comes with way too big primary jets. Just something you may want to experiment with.

YBNormal..drive a vette
www.angelfire.com/al/swhite7/doug.html

dogboy

What would be the best cam for low compression engines like mine. I do believe that in CHP mag they pulled a 7.7 Comp ratio with this same engine. The only alternative would be to pull the heads , get thinner head gaskets and possibly mill them down a bit. a route that I don't want to go. If I'm going to pull heads I might as well replace them with a set of 64 cc chambers and that would fix that.