Thumper
How high do you have to rev them to get the exhaust cleaned out of the combustion chamber at overlap?
IDK I never had one. But I did have a 292/108 Mopar, that by 2400 was pretty clean. I cruised at at 2600=56mph. It still sucked in the fuel-economy department,lol. And you know why? Because compression degrees plus power totaled just 212*. Even advancing it to in at 102 the Ica now up to 68*, but the power extraction now down to 100*........... just like the 279 ThumpR in at 102.5, just like the XE274H in at 104. It is what it is.
IMO a streeter looking to cruise, needs about 227* of compression plus power, to get some decent power extraction
........ unless it has aluminum heads with 11/1 compression, then just crank the cam timing to favor power extraction.
Which is what I did with a 223 Hughes cam, and everyone scorns me when I claim fuel-economy numbers too big for them to imagine.
Consider the Hughes HE2430AL, now obsolete. The specs are
270/276/110; and 223/
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in at 110, the numbers are;
270/276/110/115comp/112pwr/Ica of 65*/50* E-overlap
Notice comp plus power is 227*, no way AJ you did that on purpose. Actually no,lol, I lucked into it.
Now with iron heads, and on the street,you cannot usually make decent cylinder pressure with just 115* of comp duration. But with aluminum and 11/1, I drove the pressure to 178 psi.
And that left 112* Of power extraction. Now that is a great number. Just get the rpm up high enough to clean up the intake, but low enough to cruise comfortably in double overdrive, and excellent fuel economy is practically guaranteed.
