CGCBandit

I have an 87 Formula, w/ the LG4 motor. I just built a 383 stroker, w/ LT4 Hot Cam, AFR 190 heads etc.., will the cc qjet handle it. Desktop dyno rates my new motor at 480hp, 505 tq, Also, what should I set the timing at on the new motor, I know the LG4 was 0degrees. Thanks alot to anyone who can help me out.

five7kid

iTrader: (14)

Power-wise, it will handle a lot. Like levels that any 750 CFM carb could produce. In the past couple of weeks, I've seen 750 CFM feed some Novas into the low 12's - one of them was a q-jet equiped stock-class car, another a q-jet equiped, highly modified '70's-style LT1 engine. Don't forget our altitude.

Driveability-wise, could be a different story. Have you read the mag articles on this site by Steve Green? They have "Stroke in the Desert" in the titles. He built a 383 w/Edelbrock heads, one of their cams, headers, and the like. He sent the carb to Jet for them to work over, and used the chip they sent him. He didn't complain about driveability, but you may have a slightly more radical setup than he did.

As to the timing, how about 6 degrees base for a start, and see how it does? You can advance and retard a couple of degrees each way and see what it likes best.

CGCBandit

Thanks for the info. Do you know the cfm raiting on the qjet? I heard somewhere it's a 650, not too sure though.

Sitting Bull

QJets are at least 750 cfm. Some are even 850 cfm. That will produce a LOT of hp

Momar

I think that the computer controlled carbs from our cars are 750 but limited to somewhere around 650 unless you modify the linkage to let it open all the way.

Ben

CGCBandit

OK, thanks for all the info guys, keep it coming!

paul_huryk

The Q-Jet should be able to handle your motor with a bit of room to spare - I guess it starts restricting at 550hp or so.

As for timing - you will have a problem with that. GM detuned the LG4 from the L69 partially with timing. The initial is too low, as is the total (compared to a L69 or other hi-po motor). There is a solution to the timing issue, but you will have to search for it on e-bay or somewhere else. Edelbrock made a add-on computer called a micro-plus in the late 80's - early 90's that pumped up LG4 timing to a high level - even above the L69. It was an add-on piece that plugged into the computer harness and altered the signal going out to the distributor. The cost new was about $200. I have one on my Camaro and had one on the IROC I sold last year - the IROC ran 15.2 at 92 with the computer, banks exhaust, and a dual snorkel air cleaner - the computer is worth about 20hp on a bolt-on LG4. I have a mild 350 in my Camaro and it works great - never had a problem in 13 years, its probably worth 30hp in that case.

Now you need to find one for your car. You can scour e-bay at regular intervals for one. Do note that they made them for various GM cars, so make sure it is for a LG4 car before you buy it. There were ones for the L69, Monte SS, and a few other GM V8's that are different. It should work with the motor you have with no problems.

FYI: even if the distributor is turned by hand to advance, the computer automatically will pull timing until it hits stock specs - that is one reason why the LG4 was so underpowered.

Momar

You might also be able to buy the computer for it from gm that they made for the 350 ho coversion.

99Hawk120

Paul,

Where'd you get that idea?

My car, as well as several other LG4/L69 cars, is simply not capable of doing that. The ECM doesn't even know what the base timing is set at.

The PROM has a timing map programmed into it, which it adds according to RPM, MAP, TPS, and maybe a few other variables. If at stock advance (6*), it gives you a max of 26* at WOT, then advancing the base to 8* will give you 28* at WOT. The problem is that that 2* is added EVERYWHERE, because the ECM can't adjust the base timing. It's highly likely you'll get to much advance at part throttle before you can get enough at WOT simply by adding to the base.

For 85-87 LG4s, the computer has an additional weapon, the knock sensor. It'll retard the timing, sure, but only if it senses detonation. It does not automatically retard the timing just because you advanced the base.

I've observed this behavior with a dial back timing gun and the knock sensor bypassed on my car. If you add 2* to the base, you get 2* more timing everywhere. What are you basing your statement on?

Momar

Does anyone know what kind of timing the computer for this kit runs?

https://www.spoperformanceparts.com/...119&CATID=1099

laiky

I Just went through most of this and am working on the remaining issues, i'm at work now so i don't have time to get into details, but i'll post again ASAP with my issues and solutions

flyway190

The computer in that kit is just a stock '87 LG4 computer, it's the chip that makes the difference (I just wanted to clarify that so someone with an '87 LG4 doesn't go out and buy that computer expecting it to make a difference). Good luck finding that chip though, I ordered one from SDPC a month and a half ago and still haven't gotten it.

Arntzman

I just ordered that chip from gmpartsdirect a month ago. The order just shipped. The chip's eta was Sept 19th. So you should be getting your chip soon. Mine should be here tomorrow.

-Dave

flyway190

Thanks for the info.

laiky

Hawk is right on the timing issue, i have an 84. Right now i have 10 degrees static, with the hypertech chip i installed 12 years ago i get 40 degrees at full advance. I would like about 36-38 degrees total but the idle quality seems better at 10 than the 6 that the factory spec calls for. I just rebuilt and readjusted my carb so i will be trying to reduce the static advance and improve idle quality. I don't get any knock on 92-94 octanebut i do get a little bit of run on if i don't let the car idle for a minute or so before i shut it down. I'm running 9.8 comp with AFR 190's and a flex fan with a 160 degree thermostat, that may be why i don't get a real knock but i still get the run on.

I have modified the secondary air valve to allow the full flow. With out mods it will not open to 90 degrees. There is a little tab on the air valve shaft. I took the time to file it down until it opens to 90 deg. Some people just snip it off. I also have the air valve spring tension loosened 1/2 turn, but i think it may need a little less ( this adjustment seems to produce a good amount of power). i also got a really rich set of secondary metering rods, to be safe.

My advice to you, if you need it that is:

Do a full rebuild to the carb, including throttle shaft bushings on the primary at least, I did primary and secondary. Knock out all of the factory tamper proof plugs. Idle mixture, throttle position, rich stop, lean stop, idle air bleed. there is a tool kit with all the sockets for adjustment, i think it is a real convenience. NAPA sells it and many other parts store, i think Thextron makes it There is also a thextron kit with adjusting gauges, i got that too. the idle air bleed adjusting tool is great to have.

Check all of the sensors and solonoids as per the manual for the car.

Do the by the book rebuild. base line all of the adjustments. Thats where i am right now. I need to do the adjustment procedures for the primary side as per the manual. this will get you in to the carb and computers adjustment window. right now my car starts and idles fine, runs great from idle through the midrange. The one problem i have on the primary side is that the throttle kicker will open and stay thet way once in closed loop. if i load the engine and drop the rpm the kicker retracts and the car idles at 1000 rpm ( a little loapy). I will be backing up the timming to see if my top end gets better and if my run on goes away.

right now i'm real happy with the drivability, but the top end leaves a little to be desired. not that it doesn't make power it just doesn't rev as willingly or freely as i'd like. By the way i am running a cat, my airpump isn't working yet and i DO pass NYS emissions

CGCBandit

Are there any other places that carry the 350HO conversion chip????:hail:

RB83L69

The throttle kicker is designed to stay out as long as the RPMs are ablve about 1400... so if it's set too high, it will never drop out. On the other hand if it's set too low, it will drop out the instant you let off the gas. It's one of those fine tuning driveability things that you have to dink with to get it really right.

Try using a clip lead to energize the solenoid, and set it for 1450 that way, and 850 with it off.

laiky

your right on with the throttle kicker, i bought it back a turn and the high idle drops a second after the rpm drops. I need to bring it back a hair more as it sticks if the idle surges. Its funny i read through the factory servive manual and it states that there is a vehicle speed sensor, and when it drops below a certain speed the kicker will close, I've been through every part of my car and i have never seen a speed sensor!!!

anybody know where i can get an adjustable choke pull off???

Momar

What year car do you have. The sensor is probably in the back of the speedo unless you have a newer car.

ben

five7kid

iTrader: (14)

Jet has their own chips (like I said in my original post). Latest issue of CHP mag had another "My Generation Camaro" article, put in a Hypertech chip, claimed they gained .18 sec in the 1/4 with it alone. But, the timing curve is so advanced that you have to run premium (but then, the 350HO conversion does the same thing). The good news is an '87 LG4 has the knock sensor.

I got my chip from JC Whitney, of all places. I haven't done good back-to-back tests with it and the stock chip, but I've got no complaints about the way it runs or drives, and use regular gas.

laiky

i think it was actually a hypertech and some LCA relocating brackets.

I have a hypertech for an lg4, my problem is i need a hypertech for a rollercam 383 with headers. It needs a different advance curve, i would say more agressive considering the alluminum heads and cam timing

five7kid

iTrader: (14)

Read the article again. It was only the chip and torque arm bushing for their strip testing. They didn't get the LCAR brackets done in time for that (but did some parking lot testing).

laiky

your right