Don Terrill’s Speed-Talk

That makes sense.

Tuner wrote: ↑Fri Sep 29, 2017 11:57 am

Ron E wrote: ↑Fri Sep 29, 2017 11:38 am

MadBill wrote: ↑Thu Sep 28, 2017 8:20 pm Wikipedia and some other internet references notwithstanding, O.E.M.s spend a lot of time mapping out MBT during engine development and define it as Minimum spark for Best Torque...

Maybe its the wording, or the intended use but, I remember Warren Johnson saying the most power was up against or even slightly into detonation. So, there could be different positions on timing.

This is only the case when the fuel is not high enough octane to allow MBT. In his case he was limited to a spec fuel and designed the engine to squeeze the fuel to its limit. If the fuel were higher octane the timing could be advanced beyond the point where power output is reduced and have no detonation.

Before they went to a "spec" fuel for the class wasn't one of the areas that Warren Johnson explored the use of specific fuel blends for specific track conditions?

Tuner wrote: ↑Fri Sep 29, 2017 11:57 am This is only the case when the fuel is not high enough octane to allow MBT. In his case he was limited to a spec fuel and designed the engine to squeeze the fuel to its limit. If the fuel were higher octane the timing could be advanced beyond the point where power output is reduced and have no detonation.

Many years ago my pal and I 'tuned up' his new Ram Air III GTO via timed acceleration runs in 3rd gears as we cranked up the timing, listening for detonation. After a while we realized it was getting slower and slower but without a trace of knock, burning Sunoco 260

On the opposite side, with our 93 unleaded. I put a 8V GTI 1.8 in my old Scirocco. Replaced a 1.6.The 1.8 was 10 to 1 and usedknock sensors. My old car did not. By the time I got the detonation stopped it may have been slower than the 1.6.

MadBill wrote: ↑Fri Sep 29, 2017 3:01 pm

Tuner wrote: ↑Fri Sep 29, 2017 11:57 am This is only the case when the fuel is not high enough octane to allow MBT. In his case he was limited to a spec fuel and designed the engine to squeeze the fuel to its limit. If the fuel were higher octane the timing could be advanced beyond the point where power output is reduced and have no detonation.

Many years ago my pal and I 'tuned up' his new Ram Air III GTO via timed acceleration runs in 3rd gears as we cranked up the timing, listening for detonation. After a while we realized it was getting slower and slower but without a trace of knock, burning Sunoco 260

Thats something most people would never think of.

I always back timing out of motors on the dyno to see how it effects the torque curve.i don't think timing is where you are losing power.The question is did this motor lose power from the cumulative effect of a shorter stroke,shorter and heavier rod ,heavier piston, different cam timing or is this set of heads not as good.

Topend was on another engine that made good power.Put new valves,springs & retainers in them.Pretty sure problem is in shorter rods and bigger cam.

I keep going back to heads because on 2 occasions I've had proven combinations be down on power.It was heads both times, specifically it was the valve job on one, the other was a stock, no porting rule, head.

Usually by now there are a bunch of diff. cam suggestions.Where are the cam grinders?I remember a local grinder stating for a sbc 5.7 rod he used a 106 cl and 6 in rod 108, so as far as he was concerned lobe seperation depended on rod length/stroke and duration for track length.

Found the problem.Cam company ground the intake lobe for a .750 wheel and the exhaust lobe for a .850 wheel.

perfconn wrote: ↑Mon Oct 09, 2017 11:20 am Found the problem.Cam company ground the intake lobe for a .750 wheel and the exhaust lobe for a .850 wheel.

Thanks for the update!

perfconn wrote: ↑Mon Oct 09, 2017 11:20 am Found the problem.Cam company ground the intake lobe for a .750 wheel and the exhaust lobe for a .850 wheel.

How much did that drop the duration?

Didn't drop it any.Increased the duration by 2* since I am using a .937 lifter with an .850 wheel on a lobe they ground for a .750 wheel.Kinda of stupid on the cam companys part to think anybody would run two different size lifters.

perfconn wrote: ↑Mon Oct 09, 2017 3:14 pm Didn't drop it any.Increased the duration by 2* since I am using a .937 lifter with an .850 wheel on a lobe they ground for a .750 wheel.Kinda of stupid on the cam companys part to think anybody would run two different size lifters.

Oh ok, I misunderstood what you wrote in your post.