[enkeivette]

Hooked up the LM2 yesterday, drove the Vette around...

It's about 10:1 under light throttle acceleration, 12.5:1 under part throttle acceleration, and I tipped into the boost real quick and it hit 15:1

If you have any tuning tips feel free to shout them out, a Demon is similar to a Holley for reference, but otherwise I'll be keeping this thread as a log.

If it turns out that I need to upgrade the fuel system and this can't be fixed by carb tuning, the car might have to wait. Unless anyone knows a trick to up the output of a mechanical pump.

[BRIAN]

Take what I say with a grain of salt but isn't 10:1 hella rich for light throttle, It gets leaner as you accelerate but I don't know. I'm used to seeing 10:1 at full throttle but in a boosted car and about 14.7:1 at cruise. This is going to bother me all day

[Vettezuki]

Originally Posted by enkeivette

Hooked up the LM2 yesterday, drove the Vette around...

It's about 10:1 under light throttle acceleration, 12.5:1 under part throttle acceleration, and I tipped into the boost real quick and it hit 15:1

If you have any tuning tips feel free to shout them out, a Demon is similar to a Holley for reference, but otherwise I'll be keeping this thread as a log.

If it turns out that I need to upgrade the fuel system and this can't be fixed by carb tuning, the car might have to wait. Unless anyone knows a trick to up the output of a mechanical pump.

I'm shooting from the hip here, but if a mechanical pump is driven off the accessory drive, is there any such thing as a smaller pulley to spin it faster therefore higher output across the rev band. This might be especially necessary if you're running an underdrive pulley I would think, since you'd just be bringing it back into its designed engine rev : fuel pump turns ratio.

How big is your Carb?

[94cobra69ss396]

What size jets do you have in the primaries and secondaries? When I tuned the Caprice on the chassis dyno I increased the secondaries jet size from 83 to 86 and it went from 15:1 to 14.5:1 and picked up almost 50rwhp. We ran out of time on the dyno but the following day we up'd them to 92 and it felt a lot stronger than it did with the 86.

You'll want to shoot for 14.7:1 at a cruise and 11.5:1 at full throttle. You need to decrease the size of the primaries to bring the cruise ratio up and increase the secondaries to bring the WOT ratio down. However, start with the secondaries first and get the WOT right then move on to fine tuning the cruise ratio.

If you want some help tuning it I'm available this Sunday.

[BRIAN]

ugh I'm too young for carbs

[Damian]

Originally Posted by 94cobra69ss396

What size jets do you have in the primaries and secondaries? When I tuned the Caprice on the chassis dyno I increased the secondaries jet size from 83 to 86 and it went from 15:1 to 14.5:1 and picked up almost 50rwhp. We ran out of time on the dyno but the following day we up'd them to 92 and it felt a lot stronger than it did with the 86.

You'll want to shoot for 14.7:1 at a cruise and 11.5:1 at full throttle. You need to decrease the size of the primaries to bring the cruise ratio up and increase the secondaries to bring the WOT ratio down. However, start with the secondaries first and get the WOT right then move on to fine tuning the cruise ratio.

If you want some help tuning it I'm available this Sunday.

Perfect answer.

[enkeivette]

Originally Posted by BRIAN

Take what I say with a grain of salt but isn't 10:1 hella rich for light throttle, It gets leaner as you accelerate but I don't know. I'm used to seeing 10:1 at full throttle but in a boosted car and about 14.7:1 at cruise. This is going to bother me all day

Yes. Tune was f'd in the A, which is why I blew a piston. Those were base line figures.


CobraSS, Secondary - 80 / Primary - 94

I think you're supposed to keep them within a difference of 10, but at this point I might tell that rule of thumb to suck it.

Today I replaced the stock (33?) high speed air bleeds with some 28s, huuuge difference. Check out the graph, close to 12:1 under boost (only opened it up to about 5 lbs to be safe).

The rpm is not accurate (black line) but at least you can tell when I opened it up.


Tomorrow I plan to drop the primaries, prob down in the 76 range.

[enkeivette]

You can see the AFR (pink) jumps up when I open it up, and when I let off. I think (let me know if you guys disagree) that it's normal to hit 16 or so for a split second when you let off the throttle. I know it shouldn't go so lean when I first open the throttle, but I've been working on that problem for years. Next step is a 50cc pump because my system right now has the biggest pump cam with size 40 squirters and hollow screws. Not much more I can do without bigger pumps.

But the important thing is that it's back down within an acceptable range under boost, for the most part.

[94cobra69ss396]

Originally Posted by enkeivette

Yes. Tune was f'd in the A, which is why I blew a piston. Those were base line figures.


CobraSS, Secondary - 80 / Primary - 94

I think you're supposed to keep them within a difference of 10, but at this point I might tell that rule of thumb to suck it.

Today I replaced the stock (33?) high speed air bleeds with some 28s, huuuge difference. Check out the graph, close to 12:1 under boost (only opened it up to about 5 lbs to be safe).
The rpm is not accurate (black line) but at least you can tell when I opened it up.


Tomorrow I plan to drop the primaries, prob down in the 76 range.

The secondaries should have the larger jets, not the primaries. I hope you have those labeled wrong in your post. If you do have larger jets in the primaries that would explain why your cruise ratio is so rich and you should switch them.

For the lean tip in, that's normal. As long as it isn't lean misfiring your fine. Back when I had the 396 in the Chevelle I had to make my own cam to fine tune the tip in. I just used my Dremal and shaped it until I had the results I wanted.

[enkeivette]

Yeah, switched em. Good catch.