Inconsistant Dyno readings
 

Storyline - earlier in the year built up two 454's, new heads, cam, intake, exhaust, dynoed them at 440 hp each.

Something happened with thermostats causing massive overheat and main bearing failure.

Line bored, new crank, pistons, re-size rods, all new stuff, reused cam, intake, exhaust, carb, heads, all the hard parts. Only change was from a shallow dish to flat top piston with valve reliefs cut and balance rotating assemblies.

Now motors make 400 hp, same dyno, after correction factor for weather.

Timing is within 2 degrees (we are still tweaking on that).

Any thoughts why the motors lose 40 hp after rebuild with slightly more compression and all other components the same?

Re: Inconsistant Dyno readings
 

Dean,
There are a lot of factors to consider. The camshafts you are using could possibly have worked great with the lower compression, and just are not "right" for the higher compression engines. How about jetting ? I would almost guarantee you that an increse in compression would require larger jets / metering rods, depending on which carbs you have.

Fuel system ? Might have been borderline with the original combination, now its not enough ? Same with exhaust ? Are you using the same exact fuel ? With the newer formulations showing up, that could be a factor too.

The dyno should be able to give you some clues by looking at the Exhaust gas temps, BSFC etc.

In general, everything has to work together. One wrong number in the equation and it all can go downhill pretty easy.

The other thought is possibly something has happened to the Dyno since you last used it earlier in the year. The only way to possibly determine this is to put the bullets in the boat with the same prop and see what they do.

Thats a few things to think about,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Re: Inconsistant Dyno readings
 

more info:

The cam is the comp cams "Extreme Marine" hydrolic roller cam, 235 duration, 540 lift, elderbrock 750 cfm carb, dual plane air gap intake. I tried to match everything to a 5500 peak RPM curve. First time on the dyno was probably 9.25:1, now it is probably 9.5:1, so a little increase, not a lot. Same dart heads, small chamber large valves, 309 runners.

I am questioning calibration of the Dyno, either first or second time, but not sure which.

The other thing is the torque curve is WAY off from first time, first time peak was 4800, second was 3700, so the torque/HP curve is not only smaller, it is different. Almost like a different cam or something.

Thanks a bunch for your thoughts...

Re: Inconsistant Dyno readings
 

Background, we built two motors, ran on dyno at 440 hp each, motors blew, rebuilt motors with same components, but same dyno showed 400hp on the first of the two motors.

Update:

Just pulled motor 2 off dyno, it is consistent with the first time we ran these motors (before rebuild) at 440 hp, almost IDENTICAL to pre rebuild. I would have expected a small increase, but this is very much within expectations.

We then tried to recreate the lower hp of the first motor with timing adjustments, it appears the timing light was not consistent and when we were running motor 1, and were able to by advancing distributor timing to 38 degrees.

So apparently the inconsistent results is directly from timing being to far advanced by 3 degrees, and that was caused by inconsistent timing light function.

So now they go back into the boat and we pray dearly nothing screws up from there....

Re: Inconsistant Dyno readings
 

After correction factor ? What was the factor ?

Somethings screwed, excuse the french, and I hope for your sake that it was the dyno and not the engines. If it was the engine's then something is badly wrong. I don't believe (from my computer, far far away - so take this lightly) the 3 degrees of timing killed them that bad.

If it is the dyno, then I still feel bad for you got no valid info + would be waste of time and $$$$.

Anyway - good luck to you. Keep an eye, ear on everything and be very careful in case it is the motors.