Ordered a gear vendor, help with deciding gears
Now if you build a 450-500 horse small block you won't be getting good fuel mileage regardless of rpm. The whole combination needs to work together.
like and agree;
Hiway Fuel economy goes away beginning at about
276/114/105/
286/61/66*/110LSA;
Intake/compression/power/exhaust/overlap/Ica;
and low-rpm is no longer that desireable.
That's my Hughes (HE3037AL) cam btw, and my combo cruises at 65=2240 with 3.55s, with all the timing she can tolerate. This is about as low as I dare go before economy gets worse. She also gets worse with 3.91s. I didn't have 3.73s to try, one of the few chunks I have never had on hand.
The next smaller Hughes cam I tried (HE2430AL),was dynomite easy on gas;
270/116/111/276/53/64/110LSA
These both have had the Scr adjusted to run about 180/185 psi cranking cylinder pressure. And no other changes were made.
IMO
The loss in fuel economy has to be directly related to the power-stroke and overlap differences. Check it out;
276/114/
105/286/
61/66*
270/116/
111/276/
53/64*
Compression difference is only 116 less 114=2*,
Ica difference of 66 less 64=2*,
but
power was 111 less 105= 6*, and
overlap was 53 less 61= 8*
IMO then, power and overlap are the trouble makers. And if I had to guess, I would guess the overlap is the killer at lower rpms with good working headers; as they pull fuel-charge right across the pistons on the overlap cycle. Followed by the shorter powerstroke not able to extract all the energy in the cycle. At Part Throttle and cruising, I doubt the shorter power-stroke played that big a role, but; I cannot guess which cost me more.
That HE2330 easily cruised at 85=2100 returning excellent fuel-economy, which corrects to 65=1606 where it was less excellent.Which I attrinuted partly to the overlap at 1606, and partly to not being able to supply the timing it craved.
After that experiment, I vowed that my next cam would be a solid with the shorter advertised of the 2330 and the longer .050 of the 3037,lol. And so, I am waiting for the 3037 to give up........ since 2005 or 2006,lol; but it just keeps on going.
So like you say;
The whole combination needs to work together.
One of my many uncles, back in the 60s (1964 I think) had a tail-dragging Oldsmobile with a big engine in it, and I distinctly heard/overheard him say that it got better mileage, the faster he drove it, topping out at 85 mph. IIRC that car was a late 50s loooong heavyyy beast.
I was eleven, and not able to formulate an opinion on it. It wasn't until decades later that I began to understand it. My 1970 Swinger340 was like that but in reverse; it got worse mileage at 50/55 than at 60/65. But by 85 it was no longer "sipping gas" any more....... I think 340s were like that, at least every one I have had was. Which only totals three,lol.
