Weber selection and initial jet tuning

[blodi]

Very happy with the results. The F19 was a great call!  As I said before, the car pulls great!  I think the lean spike at the beginning may be due to the 35mm chokes and losing velocity.  I could try the 34's and see if that helps it, but that will hurt the top end a bit. 

 Also it has a nice lean cruise at these setting as well.  I want to try to get the car on the dyno before the snow flies here.  I'll have to call and see when I can get on their schedule.  Thanks for all the help! I want to get a few more weeks of monitoring under my belt and then I'll get the other E Tubes out to you. 

 

[240260280]

Great. No need to rush!

 

Good luck with the dyno tests.

[240260280]

Waiting for paint to dry so I decided to compare your last run against @Chickenman 's  great Holley (page 13 post #316) and against the Australian video Motorbike EFI system (page 13 post #315)

 

Edited October 3, 2018 by 240260280

[240260280]

More thoughts.  The rich dip at  3500rpm could be a few non-carb things:

 

1. Valve, cylinder, and cam geometry with valve opening overlap allowing unburned fuel to escape into the exhaust causing a richer a/f ratio

2.  A too short manifold with too large an opening preventing the air and fuel to mix well resulting in unburned  fuel in the chamber.

3. Non-ideal air horn length. (longer may help with air velocity and low rpm resonance to help mix the air and fuel).

 

For @Chickenman 's great flat curve, I wonder if a manifold/header bung was used as the sensor mount or if the Dyno-shop used a sensor in the tail pipe.  Some A/F transient smoothing does occur in the passage to the tail pipe.

[240260280]

Not  just us with that 45DCOE rich dip: http://speedtalk.com/forum/viewtopic.php?t=45148

[Chickenman]

17 hours ago, 240260280 said:

More thoughts.  The rich dip at  3500rpm could be a few non-carb things:

 

1. Valve, cylinder, and cam geometry with valve opening overlap allowing unburned fuel to escape into the exhaust causing a richer a/f ratio

2.  A too short manifold with too large an opening preventing the air and fuel to mix well resulting in unburned  fuel in the chamber.

3. Non-ideal air horn length. (longer may help with air velocity and low rpm resonance to help mix the air and fuel).

 

For @Chickenman 's great flat curve, I wonder if a manifold/header bung was used as the sensor mount or if the Dyno-shop used a sensor in the tail pipe.  Some A/F transient smoothing does occur in the passage to the tail pipe.

It was a T/Pipe bung, as are most Dyno setups.  I don't think that was a big factor, as we also ran a test day on the same dyno with about 10 other cars. Most were EFI, and my curve was far flatter than any other cars. Some of the aftermarket EFI AFR curves  were all over the place ... 

The tunable Vacuum secondary also helped smooth things out.  The Vacuum secondary carb was really good in Autocross.  Very smooth power delivery.

I later built a double pumper with the same specs and parts. That was much more difficult to drive in Autocross, but proved to be slightly faster on Road Course and Hill climbs. In autocross you would just haze the tires if you got into the Secondaries too quick.  

Hill Climbs with weight transfer to rear tires and Road Races with higher cornering speeds, reduced the tendency to spin the tires on corner exit. So you could jump on the power quicker and harder. 

[240260280]

@Chickenman Wow, you know your stuff!!!  Any thoughts on the rich dip at the start of the main that seems ubiquitous on most 45DCOE applications?  It is very difficult to address. Etube, jets, fuel level,  acceleration circuit, etc barely make a dent in it.  In the thread in the post #376 (two posts) above, the chap also tried different aux venturi and chokes with no luck.  The carbs did not seem to be able to address it. The thread digressed and was never resolved but the racers threw out timing, exhaust reversion/exhaust geometry, resonance, and cam overlap as possible causes.

Edited October 4, 2018 by 240260280

[Chickenman]

Could be a reversion issue. Could be a lot of things. 

I recently tuned a ITB setup with MS3 and it had a huge reversion issue  ( Cam related ) at exactly 2,200 RPM. Had to lock Auto Tune out at those VE Values as it was going mental.  The pulsations in the exhaust were throwing the O2 sensor out of whack. 

Reversion affects both Intake and Exhaust sides.  One of the theories behind anti-reversion headers is to reduce Intake reversion pulses wit Independant Runner manifolds. It is also not uncommon to purposely leave a slight mis-match or step at the intake manifold side. IE: Make the Intake runner port just slightly smaller than the actual Port on the cylinder head. 

Since reversion pulses mainly travel along the outer walls of the runners, like a " Smoke Ring ", a small step at the runner circumference can reduce the strength of the pulse.  But it all varies from engine to engine. Really complicated stuff and above my Pay grade... 

[240260280]

Thanks!  I hear you.  These problems do not seem to exist on 40DCOE but I have not looked in such detail as this thread has done on the 45DCOE.

[blodi]

Got an appt for the dyno for this Saturday. But, right now it looks like rain, so I might have to reschedule.  Number predictions, anyone? 

[Mark Maras]

6 hours ago, 240260280 said:

These problems do not seem to exist on 40DCOE but I have not looked in such detail as this thread has done on the 45DCOE.

 I knew little about DCOE's until I followed this thread. Thanks. Now for my observation and question. Do you think the problem with the 45's is they're a bit to big for the cubic inches and that's why the 40's work better? The reason I ask is this problem seems related to the late 60's when people would install a higher cfm Holley (usually) on a small block Chevy. The results weren't good. I've always assumed the reduced performance was caused by reduced air speed through the venturis.

 

 

[240260280]

It is hard to tell.  I have yet to see graphs of a/f for 40DCOE on an L28 so it may be the same case.

 

From the graph below, a 40DCOE is adequate for 2.8 litre street use (with a 33mm choke).

A 45DCOE is more suited for higher rpm racing with 36mm choke.  Blodi currently has a 35mm.