Confusedcuda
Well-Known Member
Has anyone ever done this? My ports on my 920 heads are way bigger then a set of 675 heads I have. Thanks
I think a 340 head would work better. Small chamber and small valves on both those heads will slow a 340 down.Has anyone ever done this? My ports on my 920 heads are way bigger then a set of 675 heads I have. Thanks
Someone must have done some porting work if what you say is true. Stock, they should both have the same size intake and exhaust ports. What manifolds are you using? Have they been port matched to those 920's?Has anyone ever done this? My ports on my 920 heads are way bigger then a set of 675 heads I have. Thanks
Just to be clear, cant deny air flow dynamics..but the 340 was rated 340 tq iirr. The 340 I put ported 315 heads on w/1.88 I take 1.50 exh made 380ft lbs. Tq., just at a lower rpm. Heads were 221cfm@142 port volume w/1.88 .It basically just makes your 340 into a 318 power wise. This idea it will produce more torque cause of velocity maybe at the lowest rpms like idle to say 2500 rpm but I really doubt it would be huge over the 340 J or X heads. And not worth the overall power you’d be given up.
Engines Torque is basically engine size, VE% and CR and engine that high lbs-ft per cid are usually big flowing heads solid roller cams big carbs headers High cr etc.. But yes that stuff tends to move the powerband higher up in the rpm range especially on smaller displacement engines.
For a truck or purely street engine you want idle to 4500 rpm power, for a more muscle car streetable .9-1:1 hp:cid you want more 1500-5500 rpm.
So yes you can used them but it’s a step backwards in the power department. The trick for a street hp engine is to try to keep bottom end hp 1500-2500 rpm while Extending the useful rpm from 4500 to more in the 5000 to 5500 rpm range.
#2658920 is a late 66-67 273 and 67 318 head. Closed chamber with 1.78/1.50 valves.I thought the 920 was a big block casting.
#2658920 is a late 66-67 273 and 67 318 head. Closed chamber with 1.78/1.50 valves.