The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by 61 chevy, Aug 22, 2013.
I have a 283, can I get more HP by adv dist timeing? for low end torqe, I am at 4 degree,
It really depends on the rest of the build, you reach a point where spark advance starts to hurt you. If you have a low compression motor it happens a lot sooner then with a high compression motor.
I personally think that 4 is a little slim, look at the timming specs for the corvette motor from the same year start there then back it off if you need to until it runs and starts the best for you.
Start by getting a curve kit...this is a package deal you are starting, not a single mod!
I'm pretty much assuming a '57--window distributor here...
Generally, you will like the change in feel with more initial timing followed by faster rate of centrifugal. Bumping up the syatic timing, though, moves the entire curve up and gives you probably more lead than you want at higher RPM...kit gives you a little bushing to limit total so raising idle timing does not increase top end timing. With that in, bump it to 6--8 degrees, easy to experiment so no big deal. Then put in the middle weight springs, kit gives you 3 sets, and go for a ride. Again assuming window distributor, it is easy to re-test with lighter ones just to see...and you can mix, like one light and one medium, for intermediate results.
Leave vac can disconnected TEMPORARILY while you flog the thing for good full throttle response without significant pinging. Just getting the the faint beginnings of ping is all right.
When you start getting this right, you will get a very satisfying improvement in response and apparent power.
Once satisfied, plug vac can back in and go for a ride, low throttle opening accel and up hill hauls in high gear. If there is pinging, try blocking the thing that moves in slot so that it moves a few degrees less. You want full available power at part throttle, since that is most of real world driving, and lack of vac advance will kill response there.
The first 2 responses are what I was gonna say....
Look up power time-ing..... But you need to have an idea of what cam you have.
If you want more HP or TQ out of your cam, your gonna have to degree it. Degreeing will change the rpm and TQ curve....
I have used Oval track cams in drag cars, by degreeing. with great results
I "built" a 283 with a factory timing curve, then a best timing curve. Assuming your current curve is correct this will illustrate the kind of difference you might get by optimizing the curve.
This is just an example, your mileage will vary.
4 is pretty low . . . I would bump it up in the 8-10 BTDC range.
sorry Bruce, its a HEI, auto 350 trans
When you modify a motor factory specs go out the window. Just remember when you turn the distributor to set the timing you are changing the location of where the fuel starts and ends it's burn. Too early and the charge lights before it all leaves the intake manifold which is why motors run hot if the timing is set too early. Too late and the charge lights while some of it has made it's way to the exhaust pipes which is what is happening when your header pipes glow red at low rpms. You want the sweet spot in the cylinder that gives the most push on the piston while it heads down the cylinder. Too soon and it explodes on the way up and the engine knocks. The engineers go through a lot of testing to find the sweet spot, but change the cam, ignition, pistons, carb, etc, and you lose knowing exactly when to light the plug and start the burn.
I find the new sweet spot by running the motor hard in top gear and listen for knocking or pinging. If I don't hear anything I advance the timing two degrees and retest. Keep going till you hear the engine ping or knock and then back off till it's silent throughout the run in top gear. If you can test going up hill, full throttle in top gear do it.
Either recurrve the distributer or loose it all together and recurve what you get.
The HEI is a smog distributer and is actually worse than an original single point when it comes to performance. It will start dropping voltage around 45-4800 RPM unless you change the control mod for a hopped up one.
on HEI...advance is still up top and easy to tinker, similar spring choices, but with no stop pin so the kits come with special weight shapes to shorten movement. With an HEI, unless you have EGR too you MUST swap the original passenger car vac can for a 1-ton and up version or an aftermarket one...degrees are marked on bracket, what you want has about half the degrees as common stockers. with stock can the thing will ping like crazy at part throttle on an engine without functioning EGR.
PS...recurving a lazy distributor will give you more immediate performance boost than almost anything bolt-on, and is cheap and easy to boot!
These are the 2 different timing curves that produced the above results. These are wot so vacuum isn't involved.
That 283 needs to start moving the advance very quickly. I would like to see all in by 2500. Now because of the small bore we don't need a lot of advance 34 should do. If we can modify the HEI to have 26 then 8 initial would be fine. Add about 16 Vacuum starting at 5-6 and in by 12-14 and you are going to be very close.
thanks guys, I advanced my timing some, now she burning rubber, I have 373 gears
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