Intake volume

[Steve.k]

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I dynoed this 438 cube engine last fall. Had another builder look it over as we getting work done on convertor. He noticed fuel consumption going up high on end of pull. He said normally thats a sign of small intake for engine. The intake here is ur19 cleveland non ported. What do you guys figure? Unfortunately never got cfm numbers sorry.

[MadBill]

Unless that carb has displayed a better B.S.F.C. history on another engine I wouldn't jump to any conclusions with such limited data. If anything, a 'too small' carb is a more likely suspect. Lots of as-delivered carbs go rich to at least some extent at high RPM, so possibly larger high speed air bleeds would straighten up the fuel curve, but much of the value of a dyno is lost trying to tune in the dark, absent AFR data from meters and/or sensors.

[MadBill]

Unless that carb has displayed a better B.S.F.C. history on another engine I wouldn't jump to any conclusions with such limited data. If anything, a 'too small' carb* is a more likely suspect. (*At this power level I'd think it could easily handle over 1,000 CFM.) Lots of as-delivered carbs go rich to at least some extent at high RPM, so possibly larger high speed air bleeds would straighten up the fuel curve, but much of the value of a dyno is lost trying to tune in the dark, absent AFR data from meters and/or sensors.

[mag2555]

What was the fuel curve like before you switched to the fuel used on this run?
Fuels with different specific gravity's need different power valve channel restriction sizes and jetting from one another, but that being said on that run the motor was well on its way to being rich even at 4600 rpm!

Is the motor breathing thru a 2 bbl Dom?

[Steve.k]

Yes these are two old school 1050's 6464. The manifold is a factory ur19 edelbrock tunnel that also untouched. Port match is the only grinding done. We did have probes for temp and afr on runs. The only thing we didn't have was the cfm meter hooked up as dyno operator has only one hat. The fella who looked at sheet figured that since the intake was originally built for 351 c it's likely a little small for 438 cubes.

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Here is the temps and a/f. Thanks guys. Not sure why they loading sideways?? When you click on them they straighten.

[Steve.k]

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This was last run on c-12 before the oxy 112 torco.

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. Notice af 1&2 here. On last dyno they were 9.

[Steve.k]

I just looked back through dyno pages. After we switched to 112 oxy our lam 1&2 all were 9. We were to tail end of session and did not jet down.

[Steve.k]

I just looked back through dyno pages. After we switched to 112 oxy our lam 1&2 all were 9. We were to tail end of session and did not jet down.

Boys i just remembered (oldtimers setting in)we added header extensions with evacs. No o2 sensors available. The one pull we did with o2 sensors in were 12.2-12.3. Range.

[MadBill]

Actual nine point zeros all the way are virtually impossible so something was out of whack beyond the effects of 'oxyied' fuel.

Someone more experienced with such fuels may step in with more info, but my understanding is that there are several possible routes to follow when fuel stoichiometry changes substantially:

1. Leave the O2 table calibrated stoich value unchanged. This way your non-oxy gasoline knowledge and experience re 'correct' AFR is roughly applicable, e.g. whether the actual stoich is 14.7 or 13.0, 10% rich will show 13.2:1, which your experience may say is "about right for an efficient high compression engine", or "too lean for the kind of boost I'm running" or whatever.

2. Re-calibrate the sensor software values for the actual stoich and come up with the new numbers that correspond with it, e.g. 10% rich for 13.0:1 = 11.7:1.

3. If possible, set up the system to read lambda instead of AFR and school yourself on the desired range of same, e.g. λ 0.90 = 13.2:1 for a fuel with a stoich value of 14.7:1.

Personally, I go with option one; if nothing else it basically need no action unless running high percentages of alcohol.

On to your earlier data: If the reported AFRs in the 12.2-12.3 range were based on a calibrated stoich of 14.7:1, that's pretty rich and probably more so at higher RPM, in which case larger high speed air bleeds would address both issues and likely pick up 25 HP or more.

Also, going from 'non' to with oxygenated fuel it's normally necessary to jet up.

[Walter R. Malik]

Yes these are two old school 1050's 6464.

Those are I.R. type carbs so, are you not using a plenum on top the runners...?

How big are the runners of that manifold...? The Weiand manifold runners have about 3 square inches of area.

[Steve.k]

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. Yes walter it has plenum. Here is look inside. We cleaned up also i never measured runner but it is a smidge shorter than wieand but pretty much same diameter.

[Steve.k]

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Here is first pull on oxy. Still had sensors.I just looked at a pull when i had a single 1050 on it. Completely different carb and intake. Still get that mid 500 bsfc. Hmm makes me wonder.

[Steve.k]

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Here is a pull with single 1050 different carb and intake. Note bsfc.

[PRH]

Are you testing at high elevation?

Looking at the fuel flow and bsfc numbers...... theres over 130hp correction.

[Steve.k]

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Yes typically da of 4900-5100 ft. Heres a 408 I did a few years ago. He used to enter da on sheets. Severe handicap.