Almost ready to start 68 LS1 Firebird, what jets for Holley HP 750?
04-15-2008, 06:41 PM
#21
Yeah! Sorry man i forgot to send you a PM. The fitting at the front of the motor is flowing into the filter, And the rear fitting is flowing out of the filter. If you see in the pic, the one with the T fitting is my oil pressure sensor and that is on the outlet line from my filter (reading filtered oil pressure). Looking at an oil filter the oil flows down through the tiny holes, then back up through the threaded center shaft.
04-17-2008, 01:36 PM
#24
Man, timely thread. I am a few weeks from firing up an LS2 crate motor with a Holley 750 DP and was about to post a thread asking about jets and timing. The LS 364/440 is as I got it from GM with shorty headers.
Anyone with an MSD box want to float me a suggestion for which timing chip I should start out with? I am installing an LM-1 also, but can't believe I got jets recommendations for almost the same set up. Should be one less thing to worry about at startup.
Anyone with an MSD box want to float me a suggestion for which timing chip I should start out with? I am installing an LM-1 also, but can't believe I got jets recommendations for almost the same set up. Should be one less thing to worry about at startup.
04-17-2008, 03:58 PM
#26
Not sure about the woodgrain, its getting sanded off and painted over, its just a chepo decal it seems. AM radio is coming out too for a sirius sattelite radio and mp3 player but that's about the only comfort ill be having. Defrosters are still optional depending on if i can get the blower motor working if not it's all coming out.
Your setup should be pretty close. I'm shooting for my engine to be around 500hp on start up 550-580 when i put heads on it. Around 410rwhp with no heads (just running and alternater, victor intake, LTs, big cam) and around 460-480rwhp with heads. Those are gratutous numbers but one can hope
Your setup should be pretty close. I'm shooting for my engine to be around 500hp on start up 550-580 when i put heads on it. Around 410rwhp with no heads (just running and alternater, victor intake, LTs, big cam) and around 460-480rwhp with heads. Those are gratutous numbers but one can hope
05-04-2008, 09:43 AM
#27
Firebird it up today. It started up instantly! Like no sputter and cut off. Pump the throttle a coupel times and flipped the ignition and starter switch and it came to life. I have another problem though.
The car idles at like 2,000rpm though. I cant get it to go lower. I bought the carb used and it was stated as in good working condition but the flow bowl was loose when i got it so it was leaking fuel and now i cant get it to idle down. The throttle adjsuter is all the way down so that nots stopping it. When i close the choke most of the way i can get it to idle down. Is there anyway to adjust the butterflies on this carb or anything i should look for? There are no vacuum leaks as i checked all the vac ports and have them all blocked off two on the intake and 3 on the carb, and the orings are new on the intake. I can stall it out by putting my hand over the carb.
Should i just go ahead and rebuild it?
The car idles at like 2,000rpm though. I cant get it to go lower. I bought the carb used and it was stated as in good working condition but the flow bowl was loose when i got it so it was leaking fuel and now i cant get it to idle down. The throttle adjsuter is all the way down so that nots stopping it. When i close the choke most of the way i can get it to idle down. Is there anyway to adjust the butterflies on this carb or anything i should look for? There are no vacuum leaks as i checked all the vac ports and have them all blocked off two on the intake and 3 on the carb, and the orings are new on the intake. I can stall it out by putting my hand over the carb.
Should i just go ahead and rebuild it?
05-04-2008, 09:50 AM
#28
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If it's idling at 2000rpm, it's getting fuel AND air from somewhere... I'd pull the carb off so you can get a better look at the throttle blades and linkages. Either something is hanging open, or someone has drilled holes in the blades. Or you have a massive vacuum leak and the idle mixture set mega-rich. My guess is something hanging open...
05-04-2008, 10:14 AM
#29
I was thinkin something with the blades too. I had the idle mixture screws out 1 1/2 turns. It idles down with the choke closing so i dont think it's a vac leak. I can stall it out by almost closing the choke all the way. It's gotta be stuck blades like you said.
05-04-2008, 01:23 PM
#30
Throttle blades wernt centered on the carb. I loosened them forced the blades completely shut and tughtened them down. I stalls out now with the adjuster all the way down so we're good to go! Now i just need to have the driveshaft made and it's off to the dyno!
05-17-2008, 06:08 PM
#32
I rebuilt the carb but havent installed it back on yet. I also took out the rear to install my shock tower relocation crossmemeber. It bassically relocates the shocks a foot inward so you can run wide tires. I also am putting on the lakewood traction bars, summit adjustable shocks, and 8.5 posi rear today.
05-21-2008, 03:29 PM
#35
Thanks man. But i bet your cam has more than .050 intake valve clearence haha. Your motor will last much longer than mine lol. I got my entire ls1 for $710 with computer and all. I sold all the efi and basically only paid $200 for my 2001 LS1 longblock lol. I've been lucky so far. I cant wait to get my driveshaft and see how much wheel lift i can get this thing to do.
08-21-2008, 07:01 PM
#37
I have since rebuilt the carburetor actually. I converted the secondary jets to a metering block and stuck in some 76 jets. so its got 72 primaries, 76 secondaries, a 6.5 power valve and i ended up installed a 50cc acclerator pump because it had a bad off idle lean stumble. This solved it entirely.
I have since tuned the MSD box with a MAP sensor as well rather than using the timing pills. The MSD reads in PSI. My car idles around 8.6psi. To convert to HG you take 14.6 (atmospheric presure roughly, with engine off but MSD on you MAP will read your atmostpheric pressure) subtract the reading 14.6-8.6=6psi which is 6 psi less than atmostpheric meaning a vacuum of 6psi then multiply that by 2 and you get 12 which is what you HG reading is roughly. So i have a vacuum of 12hg which means my PV is pretty close to being right as it should be half that of you idle vacuum.
I am running about 24 degrees total timing advance. 15 degrees base with 10 degrees advance. I run 28 degrees timing at WOT with 10 degrees of advance coming in after 8psi or so. I actually got my Denny Nitrous driveshaft a while ago. An exceptional piece of worksmanship there! I was very impressed came painted and all. I also mini-tubbed the rear since the rear ended up being about 1.5" shorter coming from the nova than the origional rear. I made my wheel well about 5 inches wider on each side. I cut out the shock mounts and all since i have the inner shock mount welded in.
I took it for a few drives. It's pretty amazingly fast. It dead hooks at a 3k launch on cold tires. I can get it to spin above that no problem though if the tires arent heated. I have yet to feel even the slightest bit of wheel hop even with my 15x10 et drag radials im running. The suspension is a very good setup IMO. It shifts and lifts the front so smoothly (not off the ground but unloads the front suspension a great bit on accel). I havent gotten it to lift the front wheels yet but havent tried at all either. I really think it will.
The carb still has the silver stiff spring in it that i was waiting to replace until i got my wideband setup. I bought a Fast Dual wideband O2 setup which is pretty amazing. It logs and replays both banks of data on its own screen so i dont need laptop to view it. I have it idling at 14.8 at WOT its around 11.8-12.6 and cruising is like 13.1 or so. I might jet it down a bit i know the secondaries are not opening all the way with the stiff spring i just cant find the purple, yellow and white springs i bought to replace it with. I did order a Jet kit as well to get it dialed in. I estimate the car somewhere around 2800lbs. It has just 2 4th gen seats in it, no interior panels, the wheel wells are aluminum and the engine is very light with just an alternator.
I plan on taggin it the next couple of weeks. I have all the lights working i just need to finish the inside of the drive side wheel well, put carpet down, get the wipers working again, and put the rear window back in and it will be good to go for inspection. I have on 2" true duals i that were on the car when i boguht it. It's the quitest LS1 you have ever heard. I hope to get a video of it on the road shortly. I'll be taking it to the dyno to get it all jetted right once i get it through inspection and put the 3" x pipe/ side pipe exhaust i have for it on sicne its almost more free flowing and extremely loud.
I have since tuned the MSD box with a MAP sensor as well rather than using the timing pills. The MSD reads in PSI. My car idles around 8.6psi. To convert to HG you take 14.6 (atmospheric presure roughly, with engine off but MSD on you MAP will read your atmostpheric pressure) subtract the reading 14.6-8.6=6psi which is 6 psi less than atmostpheric meaning a vacuum of 6psi then multiply that by 2 and you get 12 which is what you HG reading is roughly. So i have a vacuum of 12hg which means my PV is pretty close to being right as it should be half that of you idle vacuum.
I am running about 24 degrees total timing advance. 15 degrees base with 10 degrees advance. I run 28 degrees timing at WOT with 10 degrees of advance coming in after 8psi or so. I actually got my Denny Nitrous driveshaft a while ago. An exceptional piece of worksmanship there! I was very impressed came painted and all. I also mini-tubbed the rear since the rear ended up being about 1.5" shorter coming from the nova than the origional rear. I made my wheel well about 5 inches wider on each side. I cut out the shock mounts and all since i have the inner shock mount welded in.
I took it for a few drives. It's pretty amazingly fast. It dead hooks at a 3k launch on cold tires. I can get it to spin above that no problem though if the tires arent heated. I have yet to feel even the slightest bit of wheel hop even with my 15x10 et drag radials im running. The suspension is a very good setup IMO. It shifts and lifts the front so smoothly (not off the ground but unloads the front suspension a great bit on accel). I havent gotten it to lift the front wheels yet but havent tried at all either. I really think it will.
The carb still has the silver stiff spring in it that i was waiting to replace until i got my wideband setup. I bought a Fast Dual wideband O2 setup which is pretty amazing. It logs and replays both banks of data on its own screen so i dont need laptop to view it. I have it idling at 14.8 at WOT its around 11.8-12.6 and cruising is like 13.1 or so. I might jet it down a bit i know the secondaries are not opening all the way with the stiff spring i just cant find the purple, yellow and white springs i bought to replace it with. I did order a Jet kit as well to get it dialed in. I estimate the car somewhere around 2800lbs. It has just 2 4th gen seats in it, no interior panels, the wheel wells are aluminum and the engine is very light with just an alternator.
I plan on taggin it the next couple of weeks. I have all the lights working i just need to finish the inside of the drive side wheel well, put carpet down, get the wipers working again, and put the rear window back in and it will be good to go for inspection. I have on 2" true duals i that were on the car when i boguht it. It's the quitest LS1 you have ever heard. I hope to get a video of it on the road shortly. I'll be taking it to the dyno to get it all jetted right once i get it through inspection and put the 3" x pipe/ side pipe exhaust i have for it on sicne its almost more free flowing and extremely loud.
