I am a running a 377 cid in my 82 Camaro with a crane hyd roller .507/.529 284/292 dur cam. My problem is that I have to decrease the distributer timing way back to crank and then pull it back up to idle freely. Why is this ? I have had many , many engines but this build is really picky on timing. Any ideas ? BTW this isnt a destroked 400. Its a 350.

 

Welcome to the boards - just noticed nobody had replied for a day, thought I'd jump in.

No expert on this, but sounds like you have a large cam that wants a lot of timing, which is too much for the starter to handle. You need some way to automatically do the 'start retard' you are doing by hand, assume this is non computer controlled.

For instance: http://www.summitracing.com/parts/MSD-8982/

 

So could I retard my timing on the timing gear and do this too ? or would that be too much ?

 

What distributor are you using?

 

Stock Hei with MSD remote coil. I just got off the phone with CraneCams and they say its a distributor advance issue and to get another distributor with a better curve. So does that sound about right ?

 

Maybe a high torque mini starter would help also ?

 

No, thats valve timing, different thing.

Do you have a timing light so you can measure what the curve is? Needs prolly ballpark 15-20 initial, 35 @ 3000 rpm. With vac adv on top of that.

 

If the starter you have now is turning over the engine, a mini starter isn't going to do anything better for you..

Whoever you talked to at crane cams could be right, but you don't need to buy a new distributor to adjust it. You can buy new weights and springs and just replace them in the distributor you've got for 20 or 30 bucks.

 

IT could be I would get a distributor with Vac advance and an adjustable curve.

 

i just hooked the advance to direct vacuum on the carb and it cranks better. So I think you got it right , my springs and weights are too tight. I will grab a curve kit and see what happens . Thanks for all the help. BTW I have a Unilite that needs a module , would that be better than the HEI ?

 

Have you put a timing light on it yet?

 

The non-EST HEI's centrifical advance is infinitely adjustable. You can buy spring and weight kits that cover a broad range and you can modify the weight stops. You can also elongate the slotted openings in the base plate to allow for more rotation. By experimenting with different weight and spring combos and just spending some time, you can make the advance curve do anything you want. You can set it up to crank at 8-10 degrees, which should be fine, then idle at 18-22 degrees. You don't say what your cam's LSA is. Assuming it's about 112, 18-22 degrees should provide a decent idle. If LSA is closer to 110, you'll have to increase idle spark as needed. You then want about 29 degrees by 2,800 rpm, 31 degrees at 4,200 and max timing of about 38 degrees at around 5,500. Fine tune the timing curve at each rpm range to 2 degrees retarded from the point where you hear pinging.

The only down side to using manifold vacuum on the vac advance to raise idle spark, is the sag you get as the vacuum drops off on throttle tip in. On more radical engines this can be a pain. Better to use a tunable controller or try to dial in the centrifical advance to give a little advance at 850 and set your idle accordingly.

The MSD tunable ignition controllers are a great tool. Not only do they allow you to fine tune your timing curve, but they also provide that great multiple spark that helps modified engines be more drivable with better low end torque.

 

Is this actually a problem in practice? As the vac drops it just equates to the ported situation anyway. My engine is hardly radical, but I have used both and didn't notice any off-throttle difference. I stuck with manifold for the better idle and lower temps it gave.

 

For some cars it is an issue but for most mild street engines it is not a big problem.

If it runs good leave it

 

As the vacuum drops, when using manifold vacuum to control vac advance, it is retarding the timing 6-7 degrees. It can cause a noticable sag on throttle tip in, especially on engines that are on the edge of too lean due to emission compliant tuning. I have dealt with this on several carbureted engines, mostly on 70s era cars. GM used manifold vacuum advance on many engines during the 70s to improve idle quality on its lean running cars. If the carburetor is tuned just right it's not as much of a problem. As midias says, if your car runs good, leave it.

 

Thanks for the input - I was playing around with this a fair while ago, and concluded that for my case the manifold source was just a smidge 'nicer' quality-wise than ported. Plus it noticeably dropped the running temps. Motor is very well-behaved, no complaints.