JMG2

ok-- not exactly a corvette question, but I generally trust the advice I get in here, so excuse the minor diversion.

I have a 1988 chevy sb350 that I've put into an '88 Cherokee. I'm trying to set the initial timing. right now, its at about 2deg BTDC. what should initial timing be? from what I'm reading, 2deg is too low, and should be around 10deg? (btw, the reason I'm doing this is I'm trouble shooting an overheating issue-- I've already eliminated airflow/coolandlow issues, now checking whether I have timing issues)


The motor is a 1988, 4-bolt main with center bolt valve covers.
Stock heads. Holley terminator EFI. old school HEI vacuum advance distributor.

cam specs re:

Crane
SB-Chevy 262-350ci
Lift: .420''/.442''
Duration: 278°/288°
RPM Range: Idle-5500
View Graph
350-2102

I'm running an edlebrock performer intake

tuxnharley

I have a 350 sbc in my '73 Jag XJ6. I run 8* BTDC initial timing.

I think your 2* setting is too low, and might cause lack of initial response, poor mileage, and possibly some overheating - although that usually came with the smog era settings that actually were ATDC in some cases!

Westlotorn

I would run the RPM up to 3,500 and adjust it so you have 35 or 36 degrees at 3,500. Then back off to idle and see where it falls. Should be 8-14 at idle. Far more important than idle timing is the amount at 3,000-3,500. Your advance should max out somewhere between 2,800 and 3,500. For that reason check it at 3,500 and set it for 35 or 36 total advance. If it does not run good at that setting you will need to change your distributor so the advance works well at idle and still gives you 35 or 36 at 3,500 RPM.
Once this is set add in the vacuum advance and see how it runs once again. The vac advance may need a fine tune also to make your car run well.

JMG2

ok-- and excuse my ignorance, I've been spoiled by dealing with EFI---
I set the timing light to 36 degrees advance, rev the motor to around 3500, and adjust cap until the timing mark on the harmonic balancer matches up to 0 deg on the timing tab, right?

plaidside

Yes,
Do exactly what you describe, turn the distributor until the mark on the balancer aligns with the 0 on the timing tab at 3500 RPM.
If you find that the initial timing at idle is below 10 degrees you will have to have the distributor centrifugal advance curve changed.
Do you have a vacuum advance? Make sure it is disconnected when you do this.
Joe

JMG2

Thanks. Yes, it's a vacuum advance. Already disconnected and capped off :-)

kingwoodvette

Once you get the centrifugal advance sorted out, you should check how much vacuum you engine produces and make sure vacuum advance can is correct. There are lots of discussions in the archives covering selecting the proper can. Good luck. Sounds like a neat Cherokee.

I have a CJ-7 with a Mustang 5.0. Ford haters, I know!

JMG2

don't see too many of those :-)

Yeah, the Cherokee is neat, if the @#$@# thing wasn't overheating. It was running great for months, now it's overheating when driving over 2000 rpm or so ... I can't for the life of me figure out what's going on, every part of the cooling system is brand new and was working as of a few months ago, the only thing I can think of is that the last guy to work on it pulled the cap off, I'm guessing he may have screwed up the timing somehow. This is driving me nutz.

I'm sorely tempted to put in a computer controlled distributor--

leif.anderson93

Depending on the stiffness of the springs in your distributor, you may not be able to bring mechanical advance to 36 degrees between 2800-3500RPM. I wouldn't recommend revving the engine beyond 3500 RPM while it's sitting still in the garage. If you can't bring in 36 degrees by 3500RPM you will need to get a spring kit and play around with some lighter springs to accomplish your goal. One other thing, you want to be ALL in by 3500...you don't want it to continue to advance past that...if it does, then you've gone too far with the lighter springs. FYI, I have mine all in by 2800 and idling with ambient at 95 degrees, she never gets warmer than 210.

JMG2

Thanks.. I'll check everything out tonight. Took the truck offroading over the weekend, and ran cool when I was crawling over rocks, but on access roads -- bumpy, but traveling around 15 or so miles an hour on a long uphill grade, I hit 230 before I stopped (as soon as I stopped, it cooled right down). I'm hoping I have a timing issue, these cooling gremlins are killing me.

kingwoodvette

If you're running cool while rock climbing, very slow going, then you probably don't have an initial timing problem or even a vacuum advance prob. More than likely your crawling in a very low gear at barely above an idle <1500 rpm. Not much load on the engine. On the other hand 15mph on a long uphill could cause a problem in any case. Lots of load on the engine and not much airflow. Have ever been in a similar situation and not had a problem?

Rereading your comments you indicate overheating above 2000 rpm. I guess lack of adequate advance at higher rpm could be your problem.

kingwoodvette

PM sent

GTOguy

As others have said, start at 8 degrees BTDC and go up from there. 2 degrees is not enough initial timing for your engine if you're looking for decent performance all around. (fuel mileage, power, cool running)

JMG2

I'll settle for 1 out of 3-- cool running -- for now ;-)

Cooling issue is driving me absolutely insane.

karkrafter

Just for clarification...You ARE running a vacuum advance though...correct?


That car wont run right [at part throttle] with the vac adv permanently capped off....

JMG2

Yes, I'm running with the vacuum advance. I only disconnected it when I was driving.

I readjusted for 10 degrees initial advance
Total timing (at 2500 rpm) was only around 30 degrees, and it wasn't increasing no matter how much I increased rpm. Could this be causing my overheating problems? And if so, how do I fix... lighter weights under the cap ? (sorry, I'm really out of my element with mechanical timing).

GTOguy

Your mechanical advance might be limited. It could have the wrong weights, too stiff springs, or an oversize limit bushing. You need a total of at least 36 degrees for it to run right. The initial of 10 BTDC is set with the vacuum line disconnected. When you re-connect it, the timing should advance about 10-20 degrees, all by itself. When you rev it to 3000, 3500, it should show 36-50 degrees.

JMG2

I know I'm probably losing power at 30degs total timing, but would being 6 degrees retarded cause such massive overheating problems?

Vetterodder

It may not be the only problem but yes, it may be contributing. Unless you know how much centrifugal is in your distributor setting initial is a crap shoot. GM (and the aftermarket) has used many different curves and many distributors get recurved so there is no one initial that fits all. Personally, I run 21º centrifugal with 16º initial. Gives me a better, cleaner idle.

Faslane

You have holley EFI, it/they should tell you what base to work from. the more you drive it it will move the timing to get the 14.7 burn anyway. I bet it needs to be synchronized where you chose the base.