Need input: carb size on LQ4
Need input: carb size on LQ4 For thse who have successfully done a carb swap......
I have a 6.0L, +0.030, looking to do a carb swap.
Eventually I will want to add a small shot of juice to it. It will be an auto car, and I am researching heads (L92, AFR, etc.) at the moment.
But what size carb are you running, or what size is too big? I have read alot of articles with guys running LARGE carbs, on engine dynos. So I need opinions from those who are running these engines in their cars.
Putting it in a 2nd gen Camaro. The car will be streetable, but will definitely be hitting the track!
I have a 6.0L, +0.030, looking to do a carb swap.
Eventually I will want to add a small shot of juice to it. It will be an auto car, and I am researching heads (L92, AFR, etc.) at the moment.
But what size carb are you running, or what size is too big? I have read alot of articles with guys running LARGE carbs, on engine dynos. So I need opinions from those who are running these engines in their cars.
Putting it in a 2nd gen Camaro. The car will be streetable, but will definitely be hitting the track!
I'm running a Holley 750 and its plenty fine. Im also about ot buy a Demon 850 which is not neccessary its probably too big but i got a good deal on it.
Im only running about 74 primary jets, 76 secondary jets, a 6.5pv, a 30cc accelerator pump, a #33 squirter with the hollow screw and a stretched white spring for the vacuum secondarys.
Im only running about 74 primary jets, 76 secondary jets, a 6.5pv, a 30cc accelerator pump, a #33 squirter with the hollow screw and a stretched white spring for the vacuum secondarys.
I will be using a 750 on mine, already have 2 that just need to be freshened up for use. I have been told this is a good size carb until you go huge cam and power adder, but from the looks of the post above me it can handle a good size cam w ease.
SHAWN- have you sprayed the motor yet?
SHAWN- have you sprayed the motor yet?
No not yet. I'm just touching up th elast details. I had the drivetrain complete and unseated my rear from the locating pins on the first launch with the new tires. They are ALOT sticker than the 26x10.5s that were on it before. I just fixed the rear yesterrday and today i have to weld the plates in place.
I could run a 650 on my setup if i wanted to but i chose a 750. I'm moving to an 850 demon because i wanted the mechanical secondaries and i just got a good deal on a particular 850 carb. I would have stuck with a 750 otherwise.
I could run a 650 on my setup if i wanted to but i chose a 750. I'm moving to an 850 demon because i wanted the mechanical secondaries and i just got a good deal on a particular 850 carb. I would have stuck with a 750 otherwise.
I have a 750 Holley on mine also. Interestingly that is the same size carb GM used when they rate their carb'd LS crate motors.
I have a double pumper with mechanical secondaries, I think model number 4779S. I am still fiddling with it, but the idle circuits don't seem to be a good match for the stock cam'd LS2 crate motor. I have the idle screws at about 1/2 turn and it is still a bit too rich at idle.
I have a double pumper with mechanical secondaries, I think model number 4779S. I am still fiddling with it, but the idle circuits don't seem to be a good match for the stock cam'd LS2 crate motor. I have the idle screws at about 1/2 turn and it is still a bit too rich at idle.
I run a 750 Demon on my 6.0L. Its been 10.67 @ 125 mph on a 100rwhp shot. That's with me shifting my 700R4. It has great street manors too. 45* here yesterday two pumps, hit the key and it fired right up, with no choke I have to babysit it for 45-60 secs then it will run on its own just fine. I bought a "BG factory re man" from jegs for $40-$50 cheaper than "new". Came with a 1 year warranty. I had to jet it down to 72 front and 78 in the rear.
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I figured a 650 double pumper would be suffice for my 5.3 w/zo6 cam and a 200 shot. Any input?
Any opinion on a used 750 mighty demon for 200 bones for this 5.3?
Any opinion on a used 750 mighty demon for 200 bones for this 5.3?
Last edited by thedudeZ; Jan 4, 2009 at 07:39 PM.
Will the driveability and responsiveness be the same from 650 to 750? The 650 will be enough even on spray? Should be between 500-550hp on spray.
I'm running about 500hp at the crank now off the spray and my 750 is more than enough. The 750 come stock jetted with 72 primary and 76 secondary jets which were just about dead on for my setup so really you could always jet them bigger. A 650 would work find. A friend of mine Chris-M on here is running a Demon 650 and hes putting down 412rwhp.
You probably wont even notice the different in driveabilty.
The problem with Demons is their quality control. If you see a used one cheap usually the person is getting rid of it because of problems. Out of the box they tend ot have metal shavings in the float bowls which isnt so bad as sometimes the metering blocks are drilled wrong (holes too big or not drilled at all) and ive heard some horror stories of them dumping fuel through the secondaries even while the engine is off.
You probably wont even notice the different in driveabilty.
The problem with Demons is their quality control. If you see a used one cheap usually the person is getting rid of it because of problems. Out of the box they tend ot have metal shavings in the float bowls which isnt so bad as sometimes the metering blocks are drilled wrong (holes too big or not drilled at all) and ive heard some horror stories of them dumping fuel through the secondaries even while the engine is off.
I'm running about 500hp at the crank now off the spray and my 750 is more than enough. The 750 come stock jetted with 72 primary and 76 secondary jets which were just about dead on for my setup so really you could always jet them bigger. A 650 would work find. A friend of mine Chris-M on here is running a Demon 650 and hes putting down 412rwhp.
You probably wont even notice the different in driveabilty.
The problem with Demons is their quality control. If you see a used one cheap usually the person is getting rid of it because of problems. Out of the box they tend ot have metal shavings in the float bowls which isnt so bad as sometimes the metering blocks are drilled wrong (holes too big or not drilled at all) and ive heard some horror stories of them dumping fuel through the secondaries even while the engine is off.
You probably wont even notice the different in driveabilty.
The problem with Demons is their quality control. If you see a used one cheap usually the person is getting rid of it because of problems. Out of the box they tend ot have metal shavings in the float bowls which isnt so bad as sometimes the metering blocks are drilled wrong (holes too big or not drilled at all) and ive heard some horror stories of them dumping fuel through the secondaries even while the engine is off.
I was honestly just thinking about picking up a plain jane 650 Holley DP to start off with for 75-100 bucks that needed to be rebuilt.
Yeah Demon carbs are kind of a gamble so i've been reading. I really want to run one though but i always have my holley 750 to go back on. I have a dual wide and set up i can use to help tune etc and see if im going to see any real gains. It woulldnt be my first choice of carb to start on a motor. I'd get the motor working, carb tuned to how you want it and then just transfer over what you did to the newer demon carb. Atleast thats what im doing. I'm sure it will save me hours of troubleshooting from a potentially problematic demon carb. I already know mine runs perfect now.
Picking up a carb that needs rebuilts is the BEST way in my opinion. This way you get to see all of the work parts of a carburetor and help you best decide which ones will work best with your set up. having the carb apart is the easiest way to learn them
Back to the origional post i would say 750 double pumper if the setup is under 3600lbs. If its over 3600lbs you might want to go with a vacuum secondary. It'll help you save a good bit of fuel.
Picking up a carb that needs rebuilts is the BEST way in my opinion. This way you get to see all of the work parts of a carburetor and help you best decide which ones will work best with your set up. having the carb apart is the easiest way to learn them
Back to the origional post i would say 750 double pumper if the setup is under 3600lbs. If its over 3600lbs you might want to go with a vacuum secondary. It'll help you save a good bit of fuel.
Advice Lots of advice here about what carb to run.......
I actually posted a timeslip for my N/A stock cu in combination using a Pro Systems carb.
Anyone else want to backup their "advice" with a timeslip?
You want an killer carb for your combo give Patrick James at ProSystems a call he will build you a carb for YOUR combo.
I have run off the shelf carbs from Demon and Holley and they work fine if dialed in properly and the right size/type for the motor.
There is no comparison between an off the shelf unit and one built specifically for you engine/drivetrain combination.
just my 2 cents........
Dave
I actually posted a timeslip for my N/A stock cu in combination using a Pro Systems carb.
Anyone else want to backup their "advice" with a timeslip?
You want an killer carb for your combo give Patrick James at ProSystems a call he will build you a carb for YOUR combo.
I have run off the shelf carbs from Demon and Holley and they work fine if dialed in properly and the right size/type for the motor.
There is no comparison between an off the shelf unit and one built specifically for you engine/drivetrain combination.
just my 2 cents........
Dave
I dont have anny timeslips or dyno number yet. Dyno is on my to-do list. Everything about my carbs gets changed by the time i get them dialed in. I dont see a person getting the carb perfect without it being tested on a car. Kind of like a mail order tune vs a dyno tune.
My carb was dialed in out of the box. Runs the number without changes.
Actually the Idle speed and A/F were adjusted dead on from Pro systems.
Shawn, you are actually making my point for me. The carbs you run require changes to work. The fuel curves that set up in off the shelf carbs are designed for a broad range of applications. Making jet changes and P/V changes are not what I am refering to when it comes to fuel curve.
Pro Systems carbs use a high emulsion sytem that provides a highly emulsified fog of fuel that the off the shelf casrbs can not compete with,(see ET in Sig).
The pump shot, jetting, P/V, Idle speed and A/F are set up out of the box for you combo.
When you buy a carb from them you are supplied a spec sheet with the setup parameters for your carb with lean rich adjustment ranges.
Additionally you get tech support from the owner free, I have called for recomendations for jetting changes for different atmospheric conditions and fuel specific gravity changes..... worth every penny!
I had always thought that an off the shelf design would perform as well as a custom... boy was I wrong.... worth at least 20-30 hp for about 80 bucks more than a new Holley... money well spent.
Do yourself a favor and go to the Pro Systems website and read the tech articles"under the scoop"
Dave
Actually the Idle speed and A/F were adjusted dead on from Pro systems.
Shawn, you are actually making my point for me. The carbs you run require changes to work. The fuel curves that set up in off the shelf carbs are designed for a broad range of applications. Making jet changes and P/V changes are not what I am refering to when it comes to fuel curve.
Pro Systems carbs use a high emulsion sytem that provides a highly emulsified fog of fuel that the off the shelf casrbs can not compete with,(see ET in Sig).
The pump shot, jetting, P/V, Idle speed and A/F are set up out of the box for you combo.
When you buy a carb from them you are supplied a spec sheet with the setup parameters for your carb with lean rich adjustment ranges.
Additionally you get tech support from the owner free, I have called for recomendations for jetting changes for different atmospheric conditions and fuel specific gravity changes..... worth every penny!
I had always thought that an off the shelf design would perform as well as a custom... boy was I wrong.... worth at least 20-30 hp for about 80 bucks more than a new Holley... money well spent.
Do yourself a favor and go to the Pro Systems website and read the tech articles"under the scoop"
Dave