JRracing

iTrader: (35)

I just recently got my drag car up and running. It's a carbed 383 ls1 with a 750 mighty demonGC, vic jr, 242/248 110lsa cam, afr 205's, 1 7/8" long tubes. going through a th400 with a 4K to 4.5K coverter.

I got the pc hooked up to it today and set the rev limit to 5800rpm to be safe for now and turned the max timing down to 28 degree's. I have never tuned something like this and need a little advice from those who have.

I took the #1 chip out of the box.

What kind of A/F do you guys run? My car idles at 12.5 to 13:1. Is this ideal?

A little insight would be very helpful. Thanks.

xpndbl3

iTrader: (23)

if you are tuning the box yourself then ditch the pills all together. My curve is 22 degrees at 1000rpm up to 28 degrees at 3000rpm. My base timing at zero rpm is 12 degrees and just made a straight line up to 1000rpm(22degrees). This eases the load on the starter during cranking but adds timing once the engine fires up. 13:1 is ok for an idle, try a little leaner if you can. My rev limit I set to 7000 since I plan on shifting it at 6700-6800. My cam is much smaller than yours, you will leave a lot of hp on the table shifting it too soon like that. Also for that type of motor I'd be thinking a 850/950 quick fuel carb, the 650 will be holding you back as well.

Pop N Wood

iTrader: (1)

Start here. Lots of good info on carb set ups

https://ls1tech.com/forums/conversio...-dist-ls1.html


Here is one I started on accel pumps

https://ls1tech.com/forums/conversio...pump-size.html

SMAX

iTrader: (11)

Yeah, if you have a pill in the box it won't matter what you do with the computer because the box will just read off the pill.

Shawn MacAnanny

iTrader: (12)

I can help ya with any questions you might have i have been tunuing mine ALOT. my screen name is ShawnMacAnanny if you have AIM.

JRracing

iTrader: (35)

Thanks for the timing advice. It's a start. I have the rev limiter set low for now just for street driving and to keep me from twisting on a new motor. It will end up at 7500+ when I hit the track.

Thanks, I will look through those threads.

I stated "I took the #1 chip out of the 6010". I put the #1 in there to get a base tune going for now. I will end up with several custom tunes on file by the time I really get rolling.

Shawn, I had AIM but I do not know if I remember my password. What kind of timing do you start with? how about WOT.

A_VAS

iTrader: (16)

for a street car I would shoot for 14-15:1 at idle to really clean it up. But for a drag car you probably don't care as much. Shoot for 12.5-13:1 at wide open...starting richer end and working lean to see if mph pick up (how I would do it)

JRracing

iTrader: (35)

Here is my carb setup out of the box; Mighty Demon model# 5402010GC- Jets 75/83, PV 6.5-PLG, SQ#31

Flow test card; idle 80% wot flow 215 pph.

This info is right off the box and flow test sheet. Do you guys think this is right in the ball park?

JRracing

iTrader: (35)

Thanks for that advice. How do I lean out the idle? Turn the idle circuit screws in?


I was told by a few friend, that with a big cammed race motor, to do away with the power valves. I got a set of PV plugs but have not put them in yet. From looking at the box it came in, "PV 6.5-PLG" does this mean there is a 6.5PV in the front and a plug in the rear?

xpndbl3

iTrader: (23)

yes you are correct. Definitely don't plug the power valves or it will run rich all the time when you're not WOT. a good quality wideband tune would be key by a shop that actually knows about carbs....which is rare if you go to a EFI shop.

A_VAS

iTrader: (16)

yes you have a 6.5 in the front, and plugged rear. I agree with xpndbl3 above...leave the front one in for driving around in the pits, etc. Yes to lean idle just turn the idle mixture screws....if it has 4 corner idle circuit then all 4 should be adjusted the same.
Turning in leans it...doesn't take much...1/4 turn increments can be quite a bit. (edited)
With your high stall, the idle circuit won't affect your transition/launch at all I don't think. Tuning the hit will take some work more than likely..the accelerator pump cams and squirter size may need adjustment. Assuming you'll launch at 4K+ your throttle is pretty far depressed...so you want a "late" acting pump cam. Othewise 1/2 your pump shot is used up when your staged...hope this makes sense.

Keep the rear pv plugged just for easier tuning of the secondary circuits. You want about 8 jet sizes more in the rear with a plugged PV....so if it's 75/83 sounds about right on. I wouldn't depend on Demon to have it set up right though...you may find needing to lean it out.
A small carb will get a strong signal from the motor and actually pull more fuel thru the jets. A wide band will get you real close to optimal, real fast.

rojs234

iTrader: (5)

If you are really interested in learning how to tune your carburetor and you've got a little time, go to www.innovatemotorsports.com and click on forum and then general tuning. There are a number of sharp people on there and you will find out that what you thought you knew about caburetors might not always be true. Better yet, become a member and then you can use the search to get the info you need on power valves and BG carbs, etc. Some of the info might surprise you. Good luck, Ron

JRracing

iTrader: (35)

Thanks for the tip Ron. I have a Innovate LC-1 wideband on the car with the sensor in the left header. It idles at about 13:1 and when I cruise down the street at about 2500rpms it is at 12.3:1. I have not gone wot yet.

Shawn MacAnanny

iTrader: (12)

Those are the same jets that came in my demon 750. The power valve is not plugged in the rear, there is just no provision for one atleast on mine. Did you take the carb apart and make sure there were no metal shavings in the bowls and that the metering plates and jets were correct?

I think thats going to be pretty close to what you're going to need. You'll probably need something like 35 squirters though with hollow screws. thats my next step after i play with the pump cams. I have my idle mixtures out 3/4 turns. I had them at 1 turn out and it was idling at like 11.8:1 now it idles at about 13.8:1. I have 71/75s in mine right now, im working backwards running it leaner and richening it up as i go. I'll be tuning it on a dyno once i get it close.

JRracing

iTrader: (35)

I have not opened the carb up yet. It was on the motor when I got the car. And I have the box and all the paper work with it. I think the guy said it was right out of the box. But I want to go through it pretty soon. I'm going to drive it very soon and see were it rides at and go from there.
It ides good and is very responsive with no bogging or anything wierd.

I got the fenders and the bumper on it tonight. It officially looks like a car again lol. I'll get some pics in a few days. I have some adjustments to make.

A_VAS

iTrader: (16)

start w/ leaning the idle out, that might clean up the cruise afr as well. Then make primary jet changes from there.
These things can get mixed up real quick...so keeping a log book with your settings and what changed what helps for me.

sounds like you picked up a pretty cool car...was it all setup or a roller?

JRracing

iTrader: (35)

I drove the car tonight.it idles at 13.5:1 and It ran about 13.5 to 14.5:1 cruising around at 2500 rpm's. And at WOT it went to 17:1. It leaned out a ton. How do I go about riching it up?

I need to order the gasket set and what ever parts I may need to get it tuned.

JRracing

iTrader: (35)

A few pics I just uploaded.

toxic99

If memory serves me, (it's been awhile since I messed with carbs) pull manifold vacuum and divide that by 2 and that is the size PV you use.

xpndbl3

iTrader: (23)

I'd take that carb apart and blow out all the passages with carb cleaner. Then you will have to up the back jets. Try in increments of 3 or 4 sizes up to get in the ballpark. Then adjust 1 size up or down to get it to 12.8/13.0 or so at WOT.