I have a 427 390 hp 1968 motor bored 30 over. What do you think the horsepower at the wheels is.


Asked by Jun 12, 2015 at 02:10 AM about the 1967 Chevrolet Chevelle

Question type: Car Customization

I have  a 427 390 hp 1968 motor bored 30 over.  it has a roller rocker setup the cam I believe 540/ 294 I believe. Aluminum heads, Holley  850 double pumper. it has a  700 r4 tranny high performance, 3" headers with flow masters. 12 bolt posi 355 gears

8 Answers

Bob Beaman

Hello again Tom, I would guess your engine is making approx. 500 to 550 hp and combine that with a 17% drive train loss you are likely at 400 to 450 HP at the rear wheels. That should be a pretty strong motor. Only way to tell for sure is put it on the dyno, but you already knew that.

Bob Beaman

Also, my posted guesstimated HP number depends highly on compression ratio, valve sizes and intake manifold selection.

James Kitlas

427/390 heads are small port type unless you changed them to Dart or Eldelbrock aluminum. All your stuff sounds good but what pistons & compression??? My 427/430 L-88 came (actully dynoed 560 hp) with aluminum heads & 10.5:1 compression pistons. A 390 hp big block is basically a low compression truck motor.

James Kitlas

Oh, about 400-450 hp I'd say?

Buzz Waldron

Ah James, the L-88 was actually 12.5:1 compression ratio unless someone detuned it... in which case it prolly wouldn't make the 560 HP anymore... and the 560 HP was with iron heads... aluminum heads pull heat out of the combustion chamber and result in about 530 HP peak, all other things staying the same as the iron head engine... of course, the aluminum heads are lighter requiring less power to accelerate them and they can be ported and corrected for better flow/more power than stock... the aluminum heads were simply iron heads cast in aluminum and all the stock, old big block heads were rather poor flowing by today's standards and, thus, they were crutched by overly long duration cams to get a bigger HP number, but at the expense of MPG and drivability...

My L-88 had aluminum heads with max cam. 560 hp.

And I used a rare Holley 950 cfm 3-bbl. too.

That was back in 1969-70! 69' Camaro A/SA 11.'s in the quarter mile, (turbohydro 400 automatic trans). Not bad for 1969 ! Loved beating up on those (torque-flight) Hemi's!

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