air fuel blues!

[Supervette]

Okay so I got everthing back up and running on the corvette. I installed a innovate wideband to see whats going on. I have a 383 procharged small block with 8.4 to 1 compression with about 30 degrees of timing. My idle is about 12: 1. My cruise is about 9.9, 10.2:1. When i got WOT it drops to to 9.3 to 9.5:1. I know i have to lean it out to about 11.5:1 but how much power loss can you expect from running that rich. Where talking about a motor before the blower was at 400hp, then added 12 lbs of boost to it. It really doesn't feel like it should.

[Supervette]

Any help would be appreciated.

[shmoov69]

I would say that you could be loosing about 50-100 hp. Mine has always ran pig rich and would not even register on the o2 sensor on the chassis dyno years ago, but still ran fine. It actually may have helped it live so long on pump gas by keeping it fat. ??
I know that is a big spread, but with that kind of power, it is fairly easy to loose that much. I thought that I would never see the day that I would say "it feels that I am down about 100hp or so, but still runs mid 11's"! But with forced induction, it is easy to make good power.

[blown69nova]

I bet it feels soft, but thats good, because 30 degrees of timing is too much lead with 12 psi.
I would not have more than 22-24 deg. (at full boost) to start with. Get your afr's around 11.5-.8 and then add 2 deg. at a time.
You will feel 12 psi on top of your 400 hp, trust me.
Good luck, Steve

[DeltaT]

What's controlling your timing? Have your considered a MSD Boost Timing Master?

You can set it up for your straight 30 degrees and have it pull 1 degree of timing out per pound of boost, to get you in the ballpark of what Steve recommends above. It's all adjustable.

You are definitely leaving a lot of power on the table with it that rich, but the same richness is probably saving your motor at 12psi, because your timing is so high.

Jim

[Blown353]

I bet your exhaust valves are hating life-- being that rich a ton of fuel is probably burning out the exhaust ports. That rich can also lead to excessive carbon deposits which bring on detonation earlier... and some is probably sneaking past the rings and diluting your oil. Running really rich is not good any way you look at it.

I'd set the thing for about 36 degrees total timing with the mechanical advance all in and begin by pulling about 1.1-1.2 degrees of timing per pound of boost (assuming you have a BTM or something similar.) That should be very safe on pump gas.

Next, work your A/F ratio leaner. You'll probably end up somewhere in the 11.4-11.8:1 range.

Then go back and start adding timing in a little at a time keeping a very close eye on the plugs.

Also, you are running vacuum advance... right? If not you may have a hard time achieving a good cruise mixture & mileage and also have difficulty keeping the plugs clean during normal driving. Supercharged motors by nature are overcammed/undercompressed when out of the boost and thus need lots of timing to keep the fires hot at light load. That's where vacuum advance comes in. With 8.4:1 compression I wouldn't doubt the thing will take all of 48-50 degrees of timing at steady state light load.

Are you running blowthrough or EFI? If blowthrough, who did your carb prep and what hat are you running?

[Supervette]

okay here is the low down on the situation. The carb is home built, and the hat is extreme velocity. I called the people who built my engine and asked them a few questions like why when I dropped this into my car its getting 9.1:1 air fuel when it was 11.5:1 on the dyno. Two things came up in this conversation which worry me. The fuel at idle is set to 9 9.5 psi and might be going right past the needle and seat. He said i shouldn't go over 7.5psi at idle. This is a 750 double pumper. The next thing is I did all my fuel lines myself and I dont think my lines got purged very well. One of the short ones might not of at all. Maybe some rubber particles made its way into the needle and seat area and are keeping it open and flooding. maybe the 80's and 90's jets were correct and now im jetting down (tuning) for a problem that is my carb??? This is exactly where I'm at right now.

[Supervette]

In reply to the vacuum advance question. Not at this time. Its running centrifigal advance with a lockout bushing and springs. This combo worked on the dyno and I will eventually change it later but for now all I want is my power back and driveability that i feel I have been getting back since ive been jetting down. The surging went away and the power is coming back but what the engine shop told me raises my eyebrow a little.

[Supervette]

fyi about my air fuels ive been getting the first set was on 74 primaries, and 84 secondaries.


The second set im about to give you is on 71 primaries and 82 secondaries. WOT 9.8-9.9:1 cruise is 10.6:1 Idle was 12.3:1 when I was accelerating normally (not racing) I was getting 11.8:1

This is a lot of jets to drop from 80's to 90's running 11.5 to 1 on a dyno?????

[shmoov69]

Another thing, what fuel pump? Regulator? Lines? And return line? If you got too big of a pump with not big enough return line or regulator, it will just spike the fuel pressure until you get out of boost. On my A1000, the 1/2" return line is barely big enough when I get under boost. The old Mallory regulator was not big enough to handle it also. Now I got a good Aremotive regulator, but have not put the guage on it to see what has happened. Before it would bury the guage at 35psi. So who knows how high it was!

[DeltaT]

Centrifugal advance is the oppostie of what you need. Stop and lock out the disti and run it through a BTM. The last thing you want is added advance as you build boost.

You've put a lot of $$$ into this now - this is not the time to try to fudge things.

My .02

Jim

[Supervette]

I have an10 going to the regulator with an8 as a return. An 6 feeding the carb rail.

I was thinking about this today. Lets say there was something holding the needle and seat open right. Its still to damn rich anyways to get that kind of W.O.T right? Something is fishy here from the dyno to my car.

Is this what you mean by BTM http://www.jegs.com/webapp/wcs/store...10002_31670_-1
Can I hook this to my digital 6?

[Supervette]

My centri set up is all in by 2500 rpms anways so its not adding timing while im building the majority of the boost. Is this still bad?

[Supervette]

Sorry to post to many times, the fuel pump is a A1000 with a aeromotive regulator we used on the dyno with their walbro pump. Not my A1000

[shmoov69]

Try a #10 on the return. It quite possibly is backing up in the return line & pushing by the needle, mine does!

[Adam's 55 Chevy]

Your not going to get any advance on the timing under boost regardless of where your are in the RPM. The dizzy advances due to vacumn. A vac adv dizzy will help mpg in street driving by at lest 3mpg. The return from your regulator should be a minimum of -10 (1/2" is too small, period). The regulator you have is a 132-02? The idle psi should be between 6 & 7. Boost reference the reg to the hat and it should rise 1:1 with boost. i.e. if you have 8# boost you will see 14# fuel pressure (6 idle + 8 boost). Your idle is ok, maybe you could see another .5 on it but you main problem is the very low A/F reading at WOT. You should be aiming at 11 then, 9 is way too low and could even be washing your bores, (check your oil for fuel). Try to get the jets a little closer maybe a 6 point difference, this does help overall jetting of the whole engine at WOT but your first job would be to change the -8 return for a -10 (your reg return fitting should be a -10 anyway) and make sure you have -10 fittings back at the cell / tank. This may cure your A/F issues straight off.

[whytry]

To be sure why don't you just flush out the lines to make sure they got cleaned out. Then change to -10 return. Are you sure your AFR is reading correctly? If you got mid 9's on your AFR and the dyno was getting mid 11's..... How do you know your is calibrated correctly? It could be a simple fix...

I would lock out the dizzy, even if you have full advance @ 2500. Better to be safe than sorry....

[Blown353]

Before changing all your return lines, do a simple restriction check.

Back the adjustment screw on the regulator ALL the way off, then turn on the fuel pump. Whatever pressure the gauge is reading at this point represents the restriction in your return line and the lowest possible pressure you can set the regulator at.

If you have less than 5-6 psi of backpressure then you are fine because you'll probably set the fuel pressure up at 7psi base. If you can't adjust your pressure any lower than the carburetor's base setting (typically 7psi) then your return line is too restrictive and needs some changing. Typical culprits of flow restriction are machined angled pipe fittings, use only swept-tube hose ends if possible.

A -8 return line should be more than enough. I run an SX pump which outflows an A1000 by a little bit and when I was still running carb'd my -8 return line had 3psi of backpressure.

[Supervette]

I backed the regulator out all the way and it dropped to just below 3 psi at the carb feed line. Its now set to 7psi. Ill have to wait until daylight when I can get this car on the rd. I will take it out Friday night see if indeed it was blowing by the needle and seat.

I called the shop again today and asked him how it could be running rich if the carb is jetted down. Well he said that if there is crap stuck by the needle and seat it will blow fuel out the stacks on the side and fall into the venturies and casue a rich condition.

Anyways on Friday I have an extra powervalve 5.5 im gonna put in and im going to clean up the needle and seat area take it for a spin and pray that its cured. This engine has been a problem for a year now

[Supervette]

I know the air fuel is right because i put it on a chassis dyno and saw it peg out 9 to 1. Then when the guy didn't really help me tune it and it was just a dyno session. I realized I can't be paying for a dyno all the time. I need to get something i can monitor myself and tune.

This is my fuel pressure regulator http://www.aeromotiveinc.com/product...tsub=2&prod=15