Don Terrill’s Speed-Talk

You should be choosing your cam based on when you want the valve to open and when you want it to close in relation to crank degrees. The lobe center is just a byproduct of those two numbers. It makes indexing the cam is the grinder easier and used for marketing To play the devils advocate, given th...

Tom68 wrote: ↑Thu Jan 18, 2024 2:25 pm Good to see we haven't had the old bench racers tale ''it's to allow for timing chain stretch''.

i thought it was because everyone chooses too much duration so needs +4 to make it work semi ok:lol:

How do you determine when the intake and exhaust valves need to be opened and closed.how lobe profiles affect things. for different purposes and parts used. I would like to know how to spec a cam and tailor the events for my usage. Any rules of thumb? I know there is alot of variability in how you ...

are you talking about a radius VJ or radius contact angle i.e. instead of a 45 it is concave seat and convex on valve?

i think whatever differences are needed to control the seating or lifting of the valve would have a small impact on the overlap triangle area. With regards to overlap "amount", Darin has done some talks about the valve placement and the effect on overlap and thus rpm potential so based on ...

Digger, Those equations allow that very understanding. I never suggested it only applied to PT. They render BMEP for a displacement based on HP at any rpm. Yes, it converts HP to torque for that understanding, and yes BMEP is forever tied to torque and displacement. However when someone says their ...

BMEP is a way more effective comparison tool than torque or hp per displacement. Because HP@ RPM for a displacement claims are more commonly encountered, I founds these simple equations useful. BMEP,psi=(150.8*((5252.11*Crankshaft HP)/RPM))/Displacement CI BMEP,Bar=(170.415*((5252.11*Crankshaft HP)...

I am not 100% following the argument but i don't think > 1.4 tested with cold water, open headers no induction, pump fuel etc is that difficult with the parts available today just due to how they are tested. IMO If you are talking a street engine then it shall be tested as installed in the car to be...

While the point is valid that hp in the rpm range matters more than the actual VE itself. The V8/V10 F1 engines when it was interesting had about the same TQ/CI as a good road engine at the time (i.e. nothing to write home about) but rpm does wonders, this is an example of this. Clearly people know ...

so what is the best factory 2V?

LT2 is the only modern one i know and 1.24 ft/lb/ci

anyone know whether the PAC beehives 1200x are better from endurance perspective generally speaking than the old 1500 series beehives?

that not the efficient way to make something loaded like a retainer lighter

Geoff2 wrote: ↑Tue Dec 12, 2023 12:28 am
All the DV haters/detractors carry on about DV & his 128 rule, but as yet I have not seen ONE test that has disproven 128.

what is the specific claim to be disproved exactly? i'm pretty sure ill be able to find a dyno result from the public domain

Somehow, this has turned into my cam choice rather than validation of the David Vizard formula. I have already given a lot of specifics to the cam company and I trust their choice will meet my requirements. I really am curious, as I'm sure a lot of other people are, how a wide LSA cam with longer d...

this is a totally different question. But still arrived at the kind of answer I’m seeking If that spring is the one recommended for the 0.700 cam and you want to use with a 0.650 cam of same "family" and there is nothing closer then id aim for same coil bind/over the nose load So you woul...