Disappointing dyno results?

[RSSweden]

Hi!

Just finished rebuilding my 2.7 litre CIS. 40 mm carb conversion, S cams, larger valves, lightened flywheel, high comp pistons from Wössner, etc. Single plug. Reached 198-205 BHP at the dyno test, but was expecting more. Anyone who has experience from a similar spec and mind sharing your results?

Thanks!

[RSSweden]

Should probably add that I have racing headers and a sport exhaust. Ie nothing that should really hold back performance.

[Tippy]

You getting full throttle?

[Tippy]

Air fuel ratio good? Need to be in the 12's for max power. Leaner or richer will lose power.

[Tippy]

Timing fully advanced? Weights moving freely? Dizzy slop?

[RSSweden]

I am having the engine built abroad, so I cant say for sure. But I assume the carbs are set properly. If not, what can be the BHP difference between poorly and correctly set carbs? Possible to say?

[Tippy]

Impossible to say. Be a little or a lot.

[lvporschepilot]

Originally Posted by RSSweden

Hi!

Just finished rebuilding my 2.7 litre CIS. 40 mm carb conversion, S cams, larger valves, lightened flywheel, high comp pistons from Wössner, etc. Single plug. Reached 198-205 BHP at the dyno test, but was expecting more. Anyone who has experience from a similar spec and mind sharing your results?

Thanks!

205bhp was reached at the wheels or flywheel?

Big question: What were your intake and exhaust ports enlarged to?

An engine such as you describe, if say 36mm intake ports were used, should be good for at least 220-230bhp. As a reminder, a 2.7mfi motor uses 36mm ports and I am told often make in mid 220s at the flywheel despite being factory rated as 210. Your engine should produce similar results as it is not very different.

Please let us know the port size

[lvporschepilot]

Originally Posted by RSSweden

I am having the engine built abroad, so I cant say for sure. But I assume the carbs are set properly. If not, what can be the BHP difference between poorly and correctly set carbs? Possible to say?

If the carb jetting and ignition timing is not optimal then you could easily leave 5-10% of the power on the table. The difference between running overly lean or too rich can be significant

[RSSweden]

205 at the flywheel. I am not entirely sure of the port sizes other than that they are larger than stock. Should know this of course...

Anyway, regardless of port size it certainly sounds as if the output should be 10-20% higher. Might be that the carbs are set to comply with CO emission standards, but that should be easily adjusted.

Many thanks for confirming my suspicion that it is too low and that I need to dig deeper into why performance is off!

Cheers!

[JmuRiz]

Is the engine being built/dyno'd in Colorado?
If so, that makes a big difference due to altitude.

[RSSweden]

It's built at sea level in Europe, so altitude is not an issue.

[clutch-monkey]

dyno'd there as well? dyno's outside the US tend to read lower for a variety of reasons, if the engine feels healthy to drive and the AFR etc are all good i wouldn't worry about it.
could also be a ball breaker of a dyno in general, on top of that.

[lvporschepilot]

Port sizes known yet?

[DRACO A5OG]

For Street or Track use?

If Track use straight bugle type pipes, I observed a dyno set and they swapped 2 in 2 out with SSI headers vs Bugle Type, made a quite a difference in HPs. But loud as Heck.

[Eagledriver]

When you say "S" cams do you mean CIS S cams or real S cams like on a 68-73 911S?