Just have a question on timing, because I can't seem to get it right...

I have a 350sbc stock bottom end and stock heads, but have RPM combo kit from jegs that consists of (all eldelbrock) a 750cfm 4bbl carb, dual-plane high-rise aluminum intake, and hydrolic cam (480 duration not sure on lift) and hydrolic lifters. I have an Accel HEI ignition and just use 8mm wires with Bosche platinum 4 plugs. Just replaced cap and rotor, plugs and wires. Just can't get the dang timing right. I know a stock 350 should be right at about 8-10 degrees, but I'm not sure how advanced to set my timing. I usually toss the timing gun and adjust it manually till she runs good, but I'm either sacrificing power out of the hole or top end power once I get my RPM's up. Can't seem to get her just right. Can I get any help or suggestions here? Thanks Chevelle lovers! Best source for answers! smile.gif

Nobody has any suggestions? :(

The advertised duration for the RPM cam is 308/318 the .050 is, IIRC, 236/246. It is a big cam that should have 11:1 CR. You probably are in the low 9's or high/mid 8's depending on heads and pistons. With low compression, it will never make any power under 3000 rpm. I had one in a low CR engine and know this from experence.

Try setting the timing at 16º or even 18º. Set the total at 38º. You may need to recurve the distributor and/or shorten up the vacuum advance to keep detonation away. Although, with that cam, it should run on 87 octane.

I realized the issue with power range being after 3000RPM. I actually had someone on a similar forum do the math before I bought the kit and said that the range would start at about 3,400 RPM for good power. So I went out and got a B&M holeshot 3600 (3,400 to 3,800) stall converter since she's an automatic. I'll try using the gun and advance her to around 16 to 18 degrees. What exactly do you mean total of 38 degrees? And do you think I should shorten up my vaccum line to the advance on the distributor? I think it is pretty long and loops around. I think I orginally did that to try and keep the line from kinking. Also, how do you mean recurve the distributor? You mean like I do when adjusting the timing, or something else you're refering to? I appreciate all of the help! Thanks!

your vacuum advance doesn't matter at WOT. you should have the vacuum advance unhooked when setting your timing. by total timing Pat means the initial plus whatever the mechanical advance is in your distributor. if you have 20degrees mechanical advance then you need about 18 degrees initial to reach the 38degrees he recommended. personally i think it might need even more than that if it's a low compression engine, but 38 should be a safe place to run it.

True, the VA isn't an issue at WOT but could be at cruise. What I meant is the amount of advance the vacuum applies when vacuum is high. If you set the total at 38 and the AV adds another 20º at cruse that's 58º and could be too much. I run a 10º VA canister so the total plus VA is about 46º for me. Don't worry about it yet, though. Get the base and total right. If you get pinging at light throttle, then you can address the VA.

Recurving is changing the weights, stops, and springs in the distributer. The easiest way is to have it done at a shop. Should be under $50. You can do it yourself with a kit and a lot of trial and error testing. Do a search in this forum and you'll find a lot of info on doing this.

Okay, I rememeber getting two sets of springs and I put the black heaveier springs on. How do I find out the mechanical advance on my distributor? I have an HEI Accel ignition. I'll have to look on the box unless maybe it won't even be on there. Any ideas? So my mechanical advance and timing advance should add up to about 38 degrees? Thanks guys!

That's pretty much it. Try the lighter springs. That will bring the advance in sooner. Take a look Accel's web site. They may have instruction that will help you. Generally, you want full advance by about 2800-3000 rpm.

I wonder if their information is general or by model numbers of different distributors? Any way to tell exactly which one I have without looking at the box? I'll take a peak at the site and see what I can dig up. Thanks for all the help!

Originally posted by Pat Kelley:
That's pretty much it. Try the lighter springs. That will bring the advance in sooner. Take a look Accel's web site. They may have instruction that will help you. Generally, you want full advance by about 2800-3000 rpm. Okay guys I need some help. I found out that my Accel distributor is the model no. 59107C. The box shows the website www.MrGasket.com (http://www.MrGasket.com) and I can't find any kind of technical information about this distributor or its "mechanical advance" that some of you told me I needed to know. I'm lost and not sure how or where to find the answer...?

Also, looking at Pat Kelly's quote above, I should use the light springs that bring my full advance in at 2800-3000RPM. I found the little bag with the other two sets of springs and a tech sheet for the advanced curve kit. It reads the following:

GM CURVE ENGINE RPM
-------------------------------------------------
Color___Start___Total
-------------------------------------------------
Gold_____400_____1600
Silver____600_____2800
Black____600_____4000
-------------------------------------------------

I'm not sure which ones to use exactly. I'm currently using the black springs. I'm assuming from Pat Kelly's suggestions that I should probably go with the Silver since the total RPM is at 2800. Is this correct? Thanks for all the help!

Try the silver. Although it starts pretty early. You don't wqant the advance to start at idle but just above it. I don't know how you would control that.

Not sure I'm understanding. No matter if I use the Silver or Black it's going to be starting at 600RPM. My idle is at 900 or so. I do however have the stall converter that is jumping the RPM's right up to 3400RPM before engaging. Just throwing out some more thoughts. Any ideas? I think I'm going to try the silver springs tonight. Last night I bought a new timing light <grin> and set her right at about 17 or 18 degrees and also shortend up my vaccumm line and I can already tell the difference. I'm still needing to find out how to find the mechanical advance on that distributor...? Thanks for all the help!

Hey guys... Still wondering about the above questions ^^^ but I just wanted to put a note on here that I put the silver springs on and set my timing to 17 or 18 degrees and she is running sweeeeet!!! Really clean up in the top end now! Way excited just to drive to work now <grin>!! Thanks for the help guys!

Anyone know how to find out the mechanical advance on my disributor?

Quote:

"...my Accel distributor is the model no. 59107C. The box shows the website www.MrGasket.com (http://www.MrGasket.com) and I can't find any kind of technical information about this distributor or its "mechanical advance" that some of you told me I needed to know. I'm lost and not sure how or where to find the answer...?"

Thanks!

Generally, a 750 cfm carb is too much for a stock 350 engine.

Does your new light have a dial on it? Hopefully someone here can tell you how to work it. I've never used one. If it doesn't have a dial, you can put a timing tape on the damper. Be sure to get one for the diameter of your damper. As you raise the engine speed, the light will show how much advance you have. Just watch the tape as it moves under the "0" advance mark on the timing tab. To set total, disconnect the VA and plug the line to the carb. Bring the engine to 3000 and move the distributor until the 38º mark is under the zero mark on the tab. Drop back to idle and see what the timing is. Subtract that from the total and that is how much advance is in the distributor. If you want more or less initial, you need to change the amount of advance in the distributor. Which I can't help with as I've never done it sucessfully. I have a buddy with a distributor machine who takes care of my needs.

All that said, I have 20º mechanical in both my bracket car and my driver. I run 18/38 in the bracket cart and 16/36 in the driver. Plus the driver has the VA on manifold vacuum so right at idle it has 26º, which drops as soon as the throttle is cracked.

Well, I agree, but the performer RPM kit is all matching specs and RPM ratios with the type of intake and cam, so she does really well. I've been told to try a 600cfm before, but honestly haven't wanted to go buy one just to test it out. The techs at Jegs suggested this kit and I honestly don't have any complaints. She has always done great on the street and pulled high 13's and low 14's on the strip! Not bad for a stock 350 huh? The only complaint was the timing, and I think it's just about there. Just need to figure out the mechanical advance to have it right on, but she is running a lot lot better since I did all of the above suggestions. Thanks all! :D

Just adding another comment on here... want to see if anyone knows how to find the mechanical advance on my particular distributor. Thanks!

You might want to try giving Mr. Gasket a call and see what they have to say about it. I imagine someone there would be able to dig the specs up for you.

Okay, hadn't thought of that. I couldn't find anything on the site, so maybe I 'should' give them a call. Thanks!