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Some how I managed too delete my last post... Whoops. Anyways so anyways heres the car setup right now.
-87 Monte Carlo SS
-Stock LQ9 with 799 heads and BTR 660 spings
-TSP Tsunami cam .647/.608 235/240 111 lobe sep
-Vic jr intake with 1" carb spacer
-long tubes
-TH400 with PTC 4500 stall
-Ford 9" with 4.11s
Carburetor
-Holley Ultra Xp 850
-80 front jet/ 89 jet in rear with extension
-35 squiters with pink cams
-6.5 pv in front rear blocked
So the car has run a best of 11.71 at 113 but I decided to see if I could dial things in a little more. I bought a Innovate LM-2 A/F fuel meter an installed it to get some readings. Turns out things are on the lean side. I took a recording from 2800 to WOT and there is a massive lean spike then the a/f ratio stays in the 14s.
For fun after this I put on a Holley Ultra 750 street carb from another car I had to see what it read. I set everything the same but 76 jets in the front and 85 jets in the rear. The a/f ratio was alot better maybe slightly rich in the low 12s at WOT. The 750 seems to pull much harder and is alot more responsive as well.
So what do you guys think? Am I missing something with the 850xp? should I jet even bigger? Or should I maybe step down to a 750? Im not a carb expert but any input would help
I have yet to get my LQ9 (232/244 Cam Motion cam) into the truck, but every popular manufacturer recommended an 850 for a limited mileage street/strip setup.
I would at least play with the jets on the 850 and see what you can get out of it. What are you data logging with?
I am using a Innovate Motorsports LM-2 a/f meter which also records/logs runs to a sd card. I was going to maybe try stepping up to a 85/94 jet amd see what happens. but the initial lean spike could mean a bigger squirter or 50cc pump?
What is the intake center line on that cam?]
Does this cam have any advance in it or is it 111 LSA with 111 ICL?
Unless something has changed on those carbs that jetting is pretty big for a cathedral headed 6.0. Especially in the rear.
Sounds to me like your test is telling you it wants less fuel. You could try 78's front and 84's rear on your 850 then tune the shooters. Also it wouldn't hurt to pull a plug and see what its telling you.
A lean spike coming off idle like that it looks like you need to tune the IFR and then the accel pump.
You have a nice carb and the IFR'S are replaceable. Try a size larger.
I wouldn't go to a 50 cc pump cause chances are you don't need it.
Spend some time adjusting the IFR's and airbleeds with slow throttle movement. You can also adjust the power valve restrictor, the LM2 will let you dial that in. It is possible to record a MAP sensor with the unit, but that takes a bit of work. You can usually look at the RPM and tell where you hit the throttle and where the vacuum spikes will be.
When everything is all flat lining on AFR with slow throttle movements then start jamming the throttles and adjusting cams and squirters. Getting the transition circuits right will make the car more enjoyable to drive on the street and will lessen the need for a large accel pump shot.
A lean spike coming off idle like that it looks like you need to tune the IFR and then the accel pump.
You have a nice carb and the IFR'S are replaceable. Try a size larger.
I wouldn't go to a 50 cc pump cause chances are you don't need it.
Spend some time adjusting the IFR's and airbleeds with slow throttle movement. You can also adjust the power valve restrictor, the LM2 will let you dial that in. It is possible to record a MAP sensor with the unit, but that takes a bit of work. You can usually look at the RPM and tell where you hit the throttle and where the vacuum spikes will be.
When everything is all flat lining on AFR with slow throttle movements then start jamming the throttles and adjusting cams and squirters. Getting the transition circuits right will make the car more enjoyable to drive on the street and will lessen the need for a large accel pump shot.
I have yet to check and see what IFR's are even in this carb to see if the lean spike is gone. this still doesn't address the readings on the lean side at WOT tho would it? That's done by adding even larger primary and secondary jets?
It takes some time after mashing the throttle for air flow to increase through the venturi's. This means the main circuits will be lean for a short period of time after the throttle activation. That is the purpose of the accel pump, to dump some extra gas while the venturis come into play.
Slow throttle movements take the accel circuit out of it and let you evaluate the jets/bleeds/IFR's directly.
my holley 750 would go so lean at the snap of the throttle that the motor would pop and bang. with a 50cc pump shot it ripped perfect and never went rich. with your car maxing out the lean limit at the initial throttle dump, a bigger pump shot doesn't seem out of the question IMO.
my q850 came from the factory with 50cc front and rear. someone call up quick fuel and tell them they're doing it wrong.
the 750 probably runs richer at the same jet setting as the 850 because the 850 is letting in more air than the 750 causing a lean condition. It would also suggest that your motor can use the 850.[/QUOTE]
my holley 750 would go so lean at the snap of the throttle that the motor would pop and bang. with a 50cc pump shot it ripped perfect and never went rich. with your car maxing out the lean limit at the initial throttle dump, a bigger pump shot doesn't seem out of the question IMO.
my q850 came from the factory with 50cc front and rear. someone call up quick fuel and tell them they're doing it wrong.
the 750 probably runs richer at the same jet setting as the 850 because the 850 is letting in more air than the 750 causing a lean condition. It would also suggest that your motor can use the 850.
[/QUOTE]
I've thought about the 50cc pump and maybe a 37 squirter as well. But jetting even higher from 80/89 seems crazy big for a 6.0 since I'm still not at the 12.5-13 a/f ratio at wot yet
I've thought about the 50cc pump and maybe a 37 squirter as well. But jetting even higher from 80/89 seems crazy big for a 6.0 since I'm still not at the 12.5-13 a/f ratio at wot yet[/QUOTE]
if you trust your wideband, give the motor what it wants. ls engines break the rules all the time.
I didn't notice the size of your jets. You might have some other issue, vacuum leak, bad gasket, warped metering block, cracked part, bad float, blocked orifice/bleed in the carb. Pull up a carb set up guide and check everything.
FWIW, I'm currently running 79/87 jets in my 950hp with 30 primary and 50 secondary acc pumps with 40 squirters front and rear. And according to the plugs it's still lean. They like a lot of fuel. My 780 pro systems had 50cc front and rear with 40 squirters also
It takes some time after mashing the throttle for air flow to increase through the venturi's. This means the main circuits will be lean for a short period of time after the throttle activation. That is the purpose of the accel pump, to dump some extra gas while the venturis come into play.
Slow throttle movements take the accel circuit out of it and let you evaluate the jets/bleeds/IFR's directly.
This is great advice. It is the way to determine if you need more pump shot or an IFR change.
As for if the carb being too big, what you need to look at is the venturi diameter. The typical 750 cfm Holley has a 1 3/8" venturi. A typical 850 cfm Holley has a 1 1/2" venturi. A 1 1/2" venturi carb can be struggle properly metering fuel at lower RPMs and off idle on a 6 liter. So, the carb might feel fussy and lazy at lower RPMs for very little gain at upper RPMs on a typical street/strip 6 liter. If tuned properly it might make a few more horsepower, but might no be worth the aggrivation.
I didn't notice the size of your jets. You might have some other issue, vacuum leak, bad gasket, warped metering block, cracked part, bad float, blocked orifice/bleed in the carb. Pull up a carb set up guide and check everything.
I don't think there are any vacuum leaks below the carb, the 750 I tried actually ran rich at wot with 76/85 jetting. So I'm thinking if anything it would be a carb issue
This is great advice. It is the way to determine if you need more pump shot or an IFR change.
As for if the carb being too big, what you need to look at is the venturi diameter. The typical 750 cfm Holley has a 1 3/8" venturi. A typical 850 cfm Holley has a 1 1/2" venturi. A 1 1/2" venturi carb can be struggle properly metering fuel at lower RPMs and off idle on a 6 liter. So, the carb might feel fussy and lazy at lower RPMs for very little gain at upper RPMs on a typical street/strip 6 liter. If tuned properly it might make a few more horsepower, but might no be worth the aggrivation.
I have tried a 750 ultra series carb on the car, I definitely notice the car a lot more responsive off idle compared to the 850xp, still a slight lean spike at initial wot but isn't as extreme as the log with the 850. The 750 actually did register on the rich side at wot. The only thing is the 750 isn't as nice as the 850 being it still has the choke horn, no jet extensions and the air blends arnt replaceable like the 850.
06-23-2016, 04:21 PM
Too Much Carb for 6.0? 
