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Re: SBC Horsepower estimate

Posted: Mon Nov 06, 2017 10:07 pm
by kirkwoodken
Just realized I typed YOLKS, not yokes! No yoke!

Re: SBC Horsepower estimate

Posted: Mon Nov 06, 2017 10:10 pm
by MadBill
Damn Spellcheck, it shoulda caught that.. :D

Re: SBC Horsepower estimate

Posted: Mon Nov 06, 2017 10:26 pm
by kirkwoodken
MadBill wrote:
Mon Nov 06, 2017 9:55 pm
With plenty of throttle to spare, my '70 -1/2 Z28 with 12:1, xxx140 cam, cross-ram, headers, 3" exhaust, etc. pulled 7500 in 4th with 26.5" tires and 4.10:1 gears. (144 MPH), but then... #-o
.Broken Rod 001.JPG
[/quote

Yours was the kind of crack supposed to be caught in factory magnaflux, but lengthwise cracks were supposed to be OK. When I tore the 1st Z down, 2 rods had lengthwise cracks an inch long in the pin area. The dealer installed a 327 fitted block in my 2nd Z with the original 3" crank. That's the one which was the real slug. Didn't know what was causing low compression until I took it apart. Pistons were 1/8" in the hole. NEVER let a dealer work on your car. This job was performed for the previous owner. I had the paper work for the job, but the fitted block was only identified with part number. Didn't know it was wrong until I chased down the number after seeing the pistons were too far down. One thing I learned about SBC's. You never knew what you would find on a tear down. One I tore down had roller lifters on a 30-30 cam. The owner said it didn't run right after installing a different cam. And it squeeked.

Re: SBC Horsepower estimate

Posted: Mon Nov 06, 2017 10:35 pm
by MadBill
The zinger here was that I Magnafluxed the rods during the engine's first refresh but not during the second, which preceded the failure. For the third, I had then X-rayed. :(

Re: SBC Horsepower estimate

Posted: Mon Nov 06, 2017 11:41 pm
by rustbucket79
That is just bad luck MadBill #-o
That pic makes me wonder just how many more revolutions were in my "overly" beamed and bronze bushed factory large journal rods in my first serious effort small block (327) before suffering the same failure. Daily driver, heavy assed 12.5:1 TRW pistons, 4.88 gears and 24" tall tires, 7500+ shift points unless I saw a cop... :mrgreen: Oh, and original bolts [-o<

Re: SBC Horsepower estimate

Posted: Wed Nov 15, 2017 6:11 am
by wilson1970
Kinda got off topic. Thoughts on increasing rocker ratio from 1.5 to 1.6? Should I do 1.6 intake 1.5 exhaust? Cam is a Comp Cams XE .520 .540 .236/242@.050 110lsa. Thanks.

Re: SBC Horsepower estimate

Posted: Wed Nov 15, 2017 7:45 pm
by lefty o
wilson1970 wrote:
Wed Nov 15, 2017 6:11 am
Kinda got off topic. Thoughts on increasing rocker ratio from 1.5 to 1.6? Should I do 1.6 intake 1.5 exhaust? Cam is a Comp Cams XE .520 .540 .236/242@.050 110lsa. Thanks.
IMO do both I&E.