Don Terrill’s Speed-Talk

Almost all (95%) of the tire grip comes from two parameters: vertical loading and slip angle. All the rest; camber, compound, temp, pressure, etc., comprise the remaining 5%. Vertical loading is determined by a combination of static corner weights and dynamic weight transfer. The best result occur w...

The question regarding fuel enrichment when selecting alternate fuels is not easily answered from simple inspection of presented data. Before we examine the proceedure, let's look some fuel basics. In order to burn, the engine needs both air and fuel. The fuel must be in a vapor form, not a liquid. ...

Well, if nothing else it points out that that particular engine doesn't like a DCR that high. At least that's a conclusion I might draw from that example. DCR is not a stand alone metric to predict octane requirements. DCR must be used in conjunction with inlet air pressure and inlet air temperatur...

As is often the case, an engine built for certain fuel blend must be run on some other blend, either due to dyno issues, track regulations, or availability. Now the problem becomes to determine which alternative fuel will perform similar to our original fuel and is a change in enrichment necessary? ...

Even with all my errors, which of you already posted that DCR results may vary widely? [crickets] Good point. As you said; crickets. But it was not the DCR that varied widely. It was the fact that the engines were not the same. But who knew that DCR, by itself has limited value; its only a ratio an...

DCR is not as valuable as commonly believed. Actually, DCR may be even more valuable than commonly believed. SBC 350 V8, 3.48" stroke, 5.7" rod, same chamber, same spark (using as 1.25 ratio of variable heats) In order to produce the SCR and DCR values listed below, the two engines cannot have the ...

If I was designing a performance engine off of dcr formulas ,my dcr would be higher than allot of guys static number they think to be safe. Perhaps the problem is a lack of understanding of DCR and its function and usage. DCR can never be higher than SCR; but it is still just a ratio of volumes. DC...

Raise the compression ratio. That will improve efficiency across the entire rpm range.

Put it on a dyno and plot the BSFC curves.

Drive the vehicle in the rpm sweet spot. (see typical BSFC curves)

If we were to use a surface profilometer to obtain the Ra of both valve and seat, we would quickly understand that we are attempting to mate two minature mountain ranges. Lapping with a fine compound will reduce the peaks but not eliminate them. When the engine is fired and run for a while, those se...

I wonder what a strip of Plastigage, laid perpendicular cross the seat with the valve pressed in place,
would look like. It might provide a visual of seat width and seat angles.

All I remember is what I was told fifty years ago from a guy who raced something similar. He said, 45-degrees seems like it should be the way to go, but keeping them in line at 90-degrees is what actually works best. Fifty years ago, Porsche linked two 911 engines in series to create the 917. Beat ...

Let's build a paper engine to compare the effects of turbocharging. B = 89.15mm S = 80.0mm R = 135mm Disp = 2.0L NA engine SCR = 12.0 DCR = 9.39 BMEP = 11.03bar Power = 223hp @ 9000rpm (mSp = 24.0 m/s) Turbo engine SCR = 9.39 Boost = 14.3 psi BMEP = 21.75bar Power = 223hp @ 4550rpm (mSp = 12.1 m/s) ...

panic wrote: ↑Thu Jan 19, 2023 11:54 am As air density goes down, heat removal by convection is reduced.
Don't lean it out too much.

Yes, but so is the heat produced by the engine.

Get out the old O2 sensor.

I'm considering purchasing a house in Mexico City in addition to my place in New York City. I ride only air cooled, carbed, single cylinder motorcycles, they're my favorite and that will never change; as such, I'll be taking a favorite moto from NYC to CDMX with me.  But here's the issue: While NYC...

Seems to me that we have two issues: How wide is the seat? How wide should it be? While the seat widths should be similar for consistency, the wrong seat width will affect heat transfer from the valve to the seat. BMW engine specs: intake 0.09 x VHD, exhaust 0.115 x VHD. Each specific engine should ...