Random question.. intake exhaust crossover with headers ?
In your application, the shorty headers are acting more or less just free-flowing logs.
And with 3.23s and say 28s, 65= about 2600 rpm.
Everything else I said still stands with one minor diifference; at 2600 it will be easier to give the engine half decent cruise-timing.
Your Mopar Perf distributor has a single straightline advance curve of about 20* . If that is correct then the about best you can do with that will be say 12* idle timing/ 32* power timing. With a 2bbl and 9.2 Scr, you might be able to get away with 36* at 3400rpm on 87E10. BUT
I have never tuned a Poly, so IDK how much timing it will tolerate nor how soon. Below is a curve that should be a good place to start.
> I suggest to install 24* into the Distributor, and set the Power-timing to 36 degrees maximum at whatever rpm; which should give you 12* at idle.
>Then you will have to slow the rate of advance to about 1 degree per 100rpm or so. If it starts at 1000 rpm it will finish at about 3400.
>This means that at 2600rpm cruise, your mechanical timing will be;
{(2600 less 1000) x1* per 100}plus 12= 28 degrees.
The cruise-timing target may be as much as 52*.
Therefor your Advance-can needs to bring in about
52 less 28 =24 degrees. To do this, the external stops on the arm will have to be whittled down quite far. I got 22* out of mine.
@TrailBeast got 24 out of his.
The trick is to not make all the changes at the same time.
> once you are ballparked, Disconnect the V-can and see if you can bring the Power-timing in sooner and or faster.
> do not get carried away with Idle-timing; It is IMPOSSIBLE to give the engine the idle-timing it wants, while simultaneously being able to drive it normally without detonation. The 12* quoted should get the transfer slots of your carb nearly shut off, at a typical idle of 500/550 in gear. If you get a tip-in stumble, increase the idle speed until it goes away. If the idle speed gets uncomfortably high, like 750 in Neutral, Retard the Idle timing a few degrees.
Get your Idle systems working before attacking the Distributor. Else you will end up redping the Power-Timing.
> Do not fall for the idea that your Power-timing has to be at some specific number or at some specific rpm. Here's why;
Even if your Power-Timing was 100% optimized,
It will only be correct with the throttles at WOT, and usually only over a very narrow rpm range, and even in a specific gear.
At all other load settings, and rpms,, it will be between a little wrong to impossibly lousy.
This curve is/should be, the MAXIMUM your engine can stand at WOT, less a a couple of degrees, for "just-in-case".
The rest of the time, your V-can should be providing the difference between what the mechanical curve is giving you and what the engine actually wants. Not what it will tolerate.
>More is Not always better. Two or even three degrees less than optimum Power-Timing is better than one degree too much; detonation must be avoided at all costs.
> The Poly engine is a solid-lifter design. The factory specs are for an engine at a given temperature. If you run your engine warmer or cooler than the spec, you may be able to/ may have to; change the spec. The on-seat time is the cooling system of the valves. My advice is; it's better to be a tad loose than a tad tight. Hot valves can be a source of pre-ignition which usually leads to detonation.
> For fuel economy, I run my engine as hot as I dare; 205* seems to be just right for my combo.
> Chasing fuel-economy can be fun....... but can also be very labor intensive as you go thru the motions of trying one thing after another. It can take several summers to reach the "close enough" point. The Poly is a great design and worthy of the time, IMO. Your three greatest tools are; Rpm, Throttle-opening, and cruise timing. After that is temperature. This assumes the engine is NOT sucking hot underhood air.
> High-octane gas has additives in it that slow combustion down to help prevent detonation. If your engine doesn't need help, don't run it. At cruise-rpm it is a big waste of money, and the slower burn time is not conducive to better fuel economy.
> pick the lowest octane fuel that your engine will not detonate with at WOT with full power-timing, and tune her to run it.
How will you know?
Wait until you tank is empty, then put enough 87 gas in it so that it is at least 90% 87. Set your Power-Timing to 36* at no sooner than 3600rpm. Now roadtest it. Get it up into Second gear/3400. Then begin accelerating and when you get close to 3600, floor it while looking/listening for detonation.
3600 in Second gear with 3.23s and 28s will be around 58 mph; 4000 will be 64/65 and is fast enough. If it downshifts into First, you will have to eliminate that.
Once you have a no-detonation baseline; you can experiment with more or earlier WOT Power-Timing.
If it detonates with 87 at 36* no earlier than 3600, something is probably wrong. The first thing to consider is a carbon build-up in the chamber, or too-hot sparkplugs..
Happy HotRodding
