weber tuning w/LM-1
 

Below is a graph of the a/f ratio & rpms. This is the same reading I got a few months back when I dynoed the car. The test was done from 3000-6000 rpm in 3rd gear under load, (long on ramp with slight incline). The motor is a 2.8 twin plug, SC cams (I was told) 46mm Webers with the following jets:
mains 145, air correctors 120, emulsion F3, idle 60, chockes 36mm, pump 40. Max torque @ 5800 rpm, max h.p. 6400 rpm (255 @ flywheel). Any suggestions on how to smooth out the a/f ratio.
http://forums.pelicanparts.com/uploa...1096335831.jpg

bump

good question

How long were you at WOT? Does this include accelerating to WOT or just sustained WOT? If this includes acceleration, the dip toward rich from 3000 to 4500 rpm could be due to the accelerator pump.

Ahh, a test car with Webers and an LM1. You should be able to supply us with some good reference points. Are you sure you only have SC cams and not S cams? SC cams would be a curious modification on an engine you describe.

Traditionally, 46 Webers would be too big for a street engine that sees alot of part throttle operation. 40s would be more like it.

Sherwood

I don't know much about carb prefered afm except what the books may say. I do know that the EGT's jump under acceleration at proper afm. It's been my experience that just about bogging gives great EGT deviation and great power under acceleration. At cruise is another story.

and I can confirm Sherwoods accelerator pump effect initally cooling EGTs and then a few sec later increasing. I tested 2 accelerator pump quantity flow without touching the linkage geometry at all. so figure afm from my EGT bs.

my trip is that engine efficency is related to stable EGTs. Then max out your action in that envelope. Greater max hp with scattered EGTs is ng, in my un-pro opnion.. expecially on a street engine.. a rebuid every 200-500hrs is another story.

Confirming on the problem statement; the problem is that you're running rich in the mid-range -- right? I believe that this suggests that the issue is with the progression circuit which is affected by the position of the throttle plates. Rich in the mid-range means that that the plates are adusted too high.

It's important that you understand which cam is in your car since that appears to be the primary factory in emulsion tube selection. My understanding is that it affects the slope of the line on the right half of your charat. The F3 tubes that you have should be correct for S type cams. Are you sure that you don't have an S-C cam, as in an S cam from a C series (2.4) car?

For the learning experience, you can also try swapping the jets in turn and just see on the graph if the change helps or not, and how they affect the shape of the curve.

Have you talked with either Steve at Rennsport or Richard at PMO about the jetting? It doesn't look right to me. A 2.7 w/RS p&c's and S cam should have 60 idles, 160 mains, 180 air correction and F3 emulsion tubes. Also, Steve specifically told me that when I had 140 mains I was too lean and risked burning a piston.

I don't think it's a prob if this happens under acceleration. If it's at a steady cruise it's a prob imo.

Ron, I agree that the jetting doesn't look "right". But given the A/F chart, it's not clear to me what he is trying to fix? Rich or lean? Where in the rev range?

Just a SWAG, if the 140's are too lean, (but his graph shows 10 parts air / 1 part fuel, or rich), theres more going on here. I wonder if multiple adjustments are off as a result of an incorrect diagnosis of the problem. Keep in mind that he's running Weber 46's, not 40's like most people on this board. For comparison, here is what 906's were jetted with when they used Weber 46's:

Venturi: 42
Aux Venturi: 4.5
Mains: 170
Em Tube: F24
Air Correction: 145
Idle Jets: 70
Pump Jet: 50

yeah, really.. maybe it's info over-load?

maybe the 46's are causing a sloppy mix below 5k or 6k no matter what?.. and "multiple adjustments are off as a result of an incorrect diagnosis of the problem" is like a dog chasing his tail?

I would think that 46's are a wot only routine?

This is a track car, so hard acceleration is important. The a/f is around 12/1-13/1 cruising around on the street. I duplicated the method that was used on the chassis dyno, 3rd gear, pedal to the floor from 3000 to 6500 rpm under a load. What is WOT? I was told the motor was built for the street and SC cams were used. Short of taking one of the cams out I don't know how to check it. The first time I ran the test I had 150 mains instead of 145, 140 a/c instead of 120, and a 50 pump jet instead of 40. The slope was the same but it ran richer. The accelerator pump cams were moditied by JW. Rich at JW said they sometimes they just disconnected the accelerator pumps. After the first dyno test I contacted a local Weber guy and the jetting I used was his recommendation.

Hi,

Maybe some of the info in these threads is helpful:

http://www.innovatemotorsports.com/forums/showthread.php?s=&postid=3454
http://www.innovatemotorsports.com/forums/showthread.php?s=&threadid=244

Regards,
Klaus

Where in the rev range does your engine feel like it is coming "on-cam"?

interesting street-track package

WOT = Wide Open Throttle

You could try going leaner on the mains and then upping the air correctors a whole bunch to help keep the upper AFR's in check. When weird things like this happen, sometimes it's best to try other emulsion tubes as they can have a major effect of the other jets.

Also to ensure that the data your logging is correct, you want to make sure that the accel pump has no effect. It helps to use a hill as you did, but you'll want to use your brakes initially to help. So, the procedure is go WOT with you right foot, brake with your left to keep speed in check temporarily (say 2 secs), turn on logger, and then let her rip. It may help to have a helper in the car for this!

jluetjen: The power band starts at 5000 and pulls to 7000.

RoninLB: We turned it into a track specific car. It was kind of a street/track car when we got it, a little crude for the street though.

Mr Beau: What would the initial braking do? I turned on the logger as I was getting on the on ramp, 4000 rpm in 2nd which puts it at 3000 rpm when I go into 3rd. I disconnected the accel pumps and didn't notice any difference at the track. Rich at JW thought by disconnecting the accel pumps would get rid of the initial bog down when you floor it.

Did disconnecting the accel. pumps cure the bogging (hesitation)?

I suggest the bogging is not due to too much fuel but not enough. You have relatively low revs at 4000 rpm (you say cam comes on at 5000). Upon opening the throttle, the momentum of the fuel is lower than the air, thus a temporary starvation of fuel = bog. The accel. pump circuits momentarily enrich the A/F ratio during acceleration to account for the sudden throttle opening.

If this isn't the case, disregard the above.

Change one thing at a time, then monitor with the LM1 and record your observations.

I concur with John about trying different emulsion tubes first.

Sherwood

I've got some different emul. tubes that I can try this weekend.
I didn't notice any difference with the accel pumps connected or disconnected.

thats a start,

actually I wouldnt worry to much about a graph like that, you in the power part of a/f through most of the rpm range, a different emulsion tube may remove that extra rich area at around 4500 rpms, you could also try one sized smaller main jets, they will raise that whole curve a bit..

10.5 is to rich for power though, you are very close