iroc-z_23

iTrader: (1)

i have the lm-2 from innovate motorsports and am running a 750 DP holley on a 350 that runs mid 12's, untuned. i downloaded some data off the lm-2 of just air/fuel ratio; one of a full 1/4 mile pass and one of just cruising at 55 and punching it. it all looks great, but what do i do about my prooblems? i see that its running maybe a little rich and stumble off the start..i guess my question is.. where do i start with "fine tuning"



this is the full out run. it seems to stumble when you nail it and not sure if 12 or 13.1 is too rich? i know 14.7.1 is perfect but the plugs are black..so correct me if im wrong but im thinking change cams on the carburetor and maybe a couple size smaller jets?

AlkyIROC

http://www.hardtail.com/techtips/carbtuning.html
http://www.hardtail.com/techtips/fuelmixtures.html

iroc-z_23

iTrader: (1)

thanks for the sites.. any other tips on tuning send em this way lol. i have read up on a lot of tips on here in the carb forum but any info is awesome

AlkyIROC

You can always try the Innovate forums for help with tuning

iroc-z_23

iTrader: (1)

haha yeah ive been checking it a little, but just starting out with this stuff i feel like i need a better handle on getting closer dialed in so i can start getting picky..i thought maybe somebody on here might be able to clear up a little jiberish for me before i get too carried away

305sbc

iTrader: (3)

I like to start out by getting the steady cruise to stay between 15.0:1 and 16.0:1.

WOT I like to start at 13.0:1 for NA runs.
Generally, nailing the throttle causes the momentary upward spikes into the lean. Letting off the throttle generally causes the dips into the rich.

Sometimes it helps to stretch out your graphs horizontally so they become smoother and easier to tell demarcation points between driving events.
It's really hard to tell just what you are doing by looking at the picture posted.

It might also help to do a WOT run in 2nd gear only, to create a wide RPM sweep for several seconds.

I would see if you can log other items simultaneously with your AFR. Things like RPM and manifold pressure would be handy.

Your black plugs may be from a rich idle or a rich decel.
Several things interact together to give you the end result.
For instance, increasing your spark advance generally shows a leaner AFR. Too little spark advance can show a richer AFR.
Adding octane booster or race-gas can also show a richer AFR.

If your distributor doesn't have a functioning vacuum advance, then that could explain an overly rich decel.


Quickly nailing the throttle with a carburetor will always show at least a very brief lean peak. It's normal and you really cannot make it go away completely. As the fuel catches up with the air, you then see a dip to the rich, then the AFR should settle out in a fairly narrow range. If the dip to the rich goes very low, or seems to last too long, then you probably need to work on your accelerator pumps.

A spark advance change can also help you determine what's going on and what the car wants.
If you have a lean stumble when punching it, then increasing the spark advance in that area should make the stumble worse.
If it was a rich stumble, then increasing the spark should improve it.

iroc-z_23

iTrader: (1)

thanks for the tips on it. im going to mess with the pump cams and this is locked out timing at 40 degrees here. i would have liked to had rpm hooked up to it when i tested this. but as for the lean and rich dips, that makes sense now and ill try the second gear pull next time. problem is it spins so bad its hard to get a good second gear in

AlkyIROC

40 degrees may be a little high for a 350 running gasoline. SBC engines normally like 34-36 degrees.

iroc-z_23

iTrader: (1)

That's what I thought and I had it at 38 but bumped it up and picked up a couple numbers.. Is there any side effects/danger to running that high of timing

AlkyIROC

It can ignite all the fuel before the piston is ready to start pushing back down. Pinging/knocking from incorrect timing can cause lots of damage.

Timing also affects engine temperature, jetting and plug heat range.

We're going to assume your timing pointer is correct. Without using a degree wheel and some sort of piston stop to confirm where TDC is on the balancer, you could easily be off.

Many years ago, I was still making more power at 44*. After rechecking TDC with a degree wheel and piston stop, I found the timing pointer was out 8*. My 44* was actually 36*.

iroc-z_23

iTrader: (1)

Yeah I guess I'll have to recheck it. Whenever I drive it the water temperature raises from 180F to about 210-220F very brief as if it were an air bubble in the water system. Idk if that has anything to do with the timing setting but it doesn't hurt to double check. Also, I have been looking at vacuum advance distributors. I see that crane cams has one and also an msd I'm interested in. I really like all the settings and timing curves to play with..

MSD Ignition #121-8394
Digital E-Curve Pro-Billet Distributor


Crane Cams #271-1000-1500
Pro-Curve Billet Distributor


Any input on these? Will I gain much more than a regular gm hei distributor?

AlkyIROC

I ran a standard large cap, locked out, HEI for years. I had to finally switch to a small MSD distributor when I installed the tunnel ram.

iroc-z_23

iTrader: (1)

I guess it's just a matter of preference for me but id like a small cap distributor just because getting back there to take the cap off can be a pain. Do you see a problem running locked out timing on the street? Everybody says this is why my carburetor is stumbling and an hei distributor or vacuum advance would solve all my problems

dimented24x7

iTrader: (2)

Too much timing can cause issues with the engine as at low speeds, your igniting the mixture way too early. This basically causes the piston to be forced to compress an already burned mixture, which can cause the engine to run rough. There is a lot of performance to be gained by varying the timing.

When I first put my SFI setup together, I made a mistake with setting up the PCM that caused the SA to be locked at about 32 degrees. The engine ran like complete crap like that. Below are the actual SA tables for my setup, and you can see how dynamic the SA requirements are for an engine at various loads and RPMs. At low RPMs, high load, the engine only likes around 15 degrees, where at higher RPMs, low load, it likes 36 degrees for good economy and smooth cruising. At high RPMs and WOT, the timing is essentially locked like yours at 30 degrees.

The locked out SA is only good for the track where the engine runs at high RPMs, where there isnt much advantage to varying the SA. On the street, though, its essential for good operation.

dimented24x7

iTrader: (2)

Also, are you just using the stock computer controlled distributer now? That could explain why you need so much timing. Without the ECM, theres nothing there to control the coil dwell, so the spark is probably pretty weak. You do get a little advance from those due to the AC generator effect that you get from the magnetic pickup, but its not much.

iroc-z_23

iTrader: (1)

Very nice graPhs.. What software is that? This makes me wish my car wasn't trapped in snow so I can put a different set up in it.

I'm using an msd distributor I don't even think they make it anymore.. I tried finding part numbers on it and can't come up with anything. I took it off a 509 BBC that was supposed to be somewhere in the 8s on nitrous.. I had nothin to lose so I figured I'd try it for a while.

-Thanks for your guys's input btw

dimented24x7

iTrader: (2)

Oh, ok.

The software is tunerpro-rt, which is mainly for tuning the factory ECMs and PCMs. Its offered by a user on this form and available for free, or registered for a small fee. The system itself is a stock 98 vortec PCM.

There are stand-alone spark controllers that allow you to run a distributer and specify the timing curve accurately and still run a carb. I know MSD has stuff like that, but its pricey, so the $$$/HP ratio wont be very good. Another thing people have done is use a stock ECM for a timing controller only and use a stock distributer, although the stock CC HEI system does leave a lot to be desired. The easiest option is to simply buy a vacuum adv. distributor and set the springs/weights up to provide the desired timing curve.

I hear ya about the snow. I think even more is on the way. I could go the rest of my life and never miss seeing snow again.

iroc-z_23

iTrader: (1)

interesting/

guess thats my starting point, im gonna give jegs or summit a call and see what theyre tech support says about the 2 distributors i had in mind..always nice to have some input before you go making pricey decisions