uneven intake airflow corrective action options

[Larry DeCamp]

My question got lost in all the superb discussion about cutting edge FI activity. Dan H made a convincing argument that intake imbalance is a composite of manifold, runners , heads and exhaust characteristics. the vertical sump is noted to probabably be the worst case.

Don R reported some very encouraging numbers (egt balance ) with mechanical FI. One post referenced a scenario where in a significant CHT imbalance was improved buy manipulating the rubber gaskets in the intake system.

My question is, Why not use restrictors in the tubes between the sump and head to "tune" the air flow rate and thus optimize egt spread. For a carb engine, it would be an option although not as convenient as nozzle change for AFP or pushing buttons for EFI.

[rv6ejguy]

Originally Posted by Larry DeCamp

My question got lost in all the superb discussion about cutting edge FI activity. Dan H made a convincing argument that intake imbalance is a composite of manifold, runners , heads and exhaust characteristics. the vertical sump is noted to probabably be the worst case.

Don R reported some very encouraging numbers (egt balance ) with mechanical FI. One post referenced a scenario where in a significant CHT imbalance was improved buy manipulating the rubber gaskets in the intake system.

My question is, Why not use restrictors in the tubes between the sump and head to "tune" the air flow rate and thus optimize egt spread. For a carb engine, it would be an option although not as convenient as nozzle change for AFP or pushing buttons for EFI.

I'm not sure we can draw any solid conclusions on the matter at this time. We have a few diverging data points and cases and some conjecture.

In Clark's case, 2 different sumps tried and swapping the "hot" and "cold" injectors made no difference. Why the huge imbalance here? What are other Bendix and AFP users seeing with the same combination of parts? Is there a big piece of casting flash in one of Clark's ports? I don't know the answer here.

Interested to see FI data from someone with flow matched heads, equal length exhaust tubes and the same sump.

For carbs, I think we almost always see large GAMI spreads without carb heat. Flowing wet mixture through unequally shaped runners with a small plenum almost universally has to be bad. I'd like to see some carb folks post their GAMI spreads here, with and without carb heat.

Carb users often report throttle angle mixes up the EGT spreads too. Is that what most people see?

[F1Boss]

The engine in my plane is the TCM IO-550 out of a Cirrus. VERY good induction system, with factory balanced injectors. The thing is designed to run LOP throughout it's life.

All this magic happens at 2500RPM. It does not happen at 2200RPM, nor does it happen at 2700, tho at 2700 it is close. I think that's kinda strange for an engine that has an effective RPM range of only ~700RPM, don't you think?

Looking at the induction on my wife's hemi - that setup is likely to be what we want if we are serious about even airflow thru some range of RPMs. Given that the oil sump is where it is, getting airflow corrected might not be so easy. Kevin's sump on the R motor might be correct - or close - I have not seen what it takes to get the GAMI spread right.

The restrictors mentioned by the OP might do the trick, but at a reduced power level (think NASCAR restrictor), and probably at a specific RPM.

One question I have not seen addressed by the folks who have tuned for an even GAMI spread: does the tuning work well over a wide RPM band? I recall tuning the 540s for 2300RPM, but I never took a look at higher or lower RPMs..

Carry on!
Mark

[rv6ejguy]

Since the original thread started some time ago, many people have contacted me to say that their mechanical FI with tuned injector sizes runs a close GAMI spread at one rpm/ MP range but often does not at other rpms/ MP.

What are other people's experience with that? This would be a good place to share data and experiences. If you can, let us know your setup specs- AFP, Bendix, EFI, carb, other, sump type, engine model, exhaust type, flowed matched heads etc.

I'd like to understand the the likely causes and magnitude of imbalances that exist here.

[Raymo]

If you have a Vetterman exhaust, give Clint a call and talk with him about this topic. They have done lots of dyno testing with different setups.

I recently had a discussion with him when trying to decide if I would go with a cold air induction system and associated trombone exhaust from him versus sticking with the vertical intake and using the less expensive cross-over exhaust. Clint said the cold air induction primary improves performance because of the increase in plenum area; not the temperature of the air. I also had a discussion with Don from AFP about the same decision.

In the end, I opted to save a few hundred bucks, sticking with the vertical sump but using an elbow and spacer from Don to point the FM-150 forward (similar to the IO-550 setup) and using the Sam James intake, which provides more pressure to the induction system versus the snorkel.

[DanH]

Ross, a detail please. The new software allows a discrete injector trim setting for each point on a MP/RPM map, or a single +/- trim value for each injector applied across the entire range?

For example, an individual injector can be set with a +2 at 2400 RPM, and -1 at 2000 RPM? Or would both RPMs share the same trim value?

[rleffler]

Originally Posted by rv6ejguy

Since the original thread started some time ago, many people have contacted me to say that their mechanical FI with tuned injector sizes runs a close GAMI spread at one rpm/ MP range but often does not at other rpms/ MP.

What are other people's experience with that? This would be a good place to share data and experiences. If you can, let us know your setup specs- AFP, Bendix, EFI, carb, other, sump type, engine model, exhaust type, flowed matched heads etc.

I'd like to understand the the likely causes and magnitude of imbalances that exist here.

One of the tests that Don had me performed is to measure at multiple altitudes and settings. For example, 23mp/2300rpm/3,000 agl versus WOT(21/22mp)/2300rpm/ 8,000 agl. The results were similar. I've got all the data at home if anyone really wants to see it.

[rv6ejguy]

Originally Posted by DanH

Ross, a detail please. The new software allows a discrete injector trim setting for each point on a MP/RPM map, or a single +/- trim value for each injector applied across the entire range?

For example, an individual injector can be set with a +2 at 2400 RPM, and -1 at 2000 RPM? Or would both RPMs share the same trim value?

The same trim percentage is applied at all rpm/MAP points. It just adds or subtracts a percentage to the base pulse width currently being outputted from the ECU.

The software was designed to allow people to optimize AFRs in all cylinders in cruise during LOP operation primarily. In Clark's case, he found ROP operation also required similar trim amounts but I am not sure if they varied rpm during those tests.

Will have some additional data next week I would guess.

[BobTurner]

Originally Posted by Larry DeCamp

My question is, Why not use restrictors in the tubes between the sump and head to "tune" the air flow rate and thus optimize egt spread. For a carb engine, it would be an option although not as convenient as nozzle change for AFP or pushing buttons for EFI.

I think, for a carb engine, your proposal would "tune" the total volume but would not alter the fuel-air ratio.

[Larry DeCamp]

Wouldnt EGT be a relative indicator of AF ratio. Admittedly, this does nothing to assess the power created by different cylinders, but air/fuel is proportional to EGT, Yes? No?