Batass

My car is terribly inconsistent. One day it runs great, the next day it breaks up. Out of 8 runs in three days at the track it has made one clean pass(though not the fastest and nowhere near its potential). It runs great at home from week to week then out of nowhere its breaking up and can't rev past 5800 rpm.

Had a problem with a leaky coil, oil soaking the coil wire and cutting out spark.
Then I couldn't have asked it to run better. It sucked another devil through the intake and it appeared to be the power valve not working properly. I plugged that and the car ran flawlessly for 3 months despite severe weather changes.

Prior to plugging the PV my jetting was at 80 pri 96 sec with some ethanol injection. After plugging I went up to 90 primary. Motor ran great.

I'm at 1200 ft and the track is damn near sea level. Temp at the track was 85. Last time the car ran it was mid 70 degrees. No big changes there.

AFR gauge was reading low 12s. I didn't pull any plugs, forgot my gloves. But the motor sounded super rich and my friend noticed black smoke during shifts (open header).

I dropped the primary jets from 90 to 85. I wasn't looking for a subtle change. Car ran a little cleaner but the usual power still wasn't there. AFR didn't change really.

All I want to do is make one clean pass at the power I've felt from this thing and I'm selling the whole FI system and going nitrous. I'm about to do it now, but the sweat equity in this supercharger and carb is killing me.

Here is exactly what I have changed since the motor last ran well-

1. Removed dual 3" exhaust and installed 18" extensions. (Been done before with just a little more power and a LOT more noise).
2. Swapped out ethanol for methanol.

I made my best 60ft today with a 1.6 60ft, 7.04 1/8, 11.2 1/4, 114 crap mph.
Previous best was 11.8 @ 125mph two years ago and the car makes heaps more power than that now. (timing, alky inj, better tune)

It breaks up past 4500 rpm.

I'm beyond annoyed and this motor is about to own me.

vortech s-trim, demon BT carb, msd, msd, msd

and PUKE

Drac0nic

What are your plug gap and your valve springs?

Orr89RocZ

iTrader: (20)

Is the timing system still giving correct timing? IF its failing and screwing with timing, you will see drastically different air fuel ratios at the sensor and could be dropping out lots of timing.

junkcltr

iTrader: (1)

I know people with the same experiences. Throw the carb in the trash can, install EFI, and be happy with your supercharger forever after.
Only a few smart tune oriented carb guys I know got a blow through carb to work. Even then it only works "right" when the weather is "right" for the day it was tuned.

Batass

Gap is .030. Recommended spring is comp 986, I'm running the 987. I've revved the motor over 7000 without a hiccup when its in the mood.

Batass

Timing is locked at 32*. I had it at 26* for a while until I got the afr where I wanted it and added the alcohol injection, bumped it up to 32*. Never any signs of detonation with pump gas, but I run about 100 octane at the track just because the motor gets much hotter and I'm in the throttle longer than the street.

Batass

I think this is what the problem is. I hear a lot of people aren't happy with BG carbs and they recommend I get a real professional blow through carb. I don't know how much happier I would be, but I do know I don't need anywhere near this kind of power on the street. This is why I'm planning on switching to nitrous.

EFI would certainly be a better choice, you're right. Thats why I plugged the PV and just concentrated on WOT. Nevermind trying to get the low speed and cruise decent. I just can't believe how much it changes. One other thing is, I might not even notice the magnitude of change on the street. First gear is about worthless and third is too fast. The problem really shows up in third at WOT. But I can certainly tell when the motor is down on power and not revving clean.

Right now I can't afford to spend much money on the car, I can only sell and swap parts. I'm moving near Pittsburgh for Wyotech. More schooling.

Thanks for the responses.

Orr89RocZ

iTrader: (20)

Nice, Wyotech is out my way near Pittsburgh raceway park. A good blow thru carb from CSU or others will make a difference. Its possible that at 3rd gear doing a WOT pass the carb isnt metering the fuel correctly due to gforces at speed. Not sure, just a guess but the fuel delivery would be something to check.

Batass

Third gear could be a whole different scenario, it only made one good clean pass. When it acts up in first and second, third is always worse which is understandable due to load.

I just don't understand how it can be this inconsistent unless there is something stuck in a circuit that I can't find. I hear many stories about shavings in these carbs.

I'm thinking about swapping out the 750 BG carb for a 600 holley that I modified for blow through on the old 305. I never had a problem with it except the low speed/cruise but I could care less about that for the track.

I don't know if it would be too small or not. "They" say to run the same size carb that motor likes N/A. CFM calculations come out to 598. It doesn't rev too high with a 110 cam. I ran the same pulley configuration with it and higher boost, but its going to see a good bit more airflow on this motor.

They said there was a track right down the road from the school. Hopefully I can find a place to keep at least some of my toys out there.

Batass

I'm wondering if I'm having spark blowout. I shouldn't with a .030 gap but....

Orr89RocZ

iTrader: (20)

Yeah .030" is usually tight enough. I ran about that and then tightened them up abit more to be safe. I havent had any problems yet with .028-.030" or so.

What heat range plugs are you using?

Batass

R44t ac delco. Stock is R45t

Street Lethal

iTrader: (16)

Your running too rich, you need to pull fuel from your secondaries....

Batass

It was actually E85. And swapping it for methanol should have made it leaner.
I haven't been able to work on the car, I have a new truck taking up space in the garage.
I'm a little worried about pulling out jet when the car ran so well before the way it sits.
I'm going to check for fuel leaks in the carb, obstructions in the air circuits, verify plug gap/check condition of plugs. If all is well there, I'll replace the methanol with water. If its a rich fueling issue, yanking the meth will be a clue.

Carb tuning issues seem to be greatly amplified with FI, but 10 jet sizes is ridiculous.

jcamaro91

i have a buddy with ur same set up and his prob turned out to be that he didnt have enough ventilation to his fuel tank and his air fuel mix was a little off after we took care of theese things he nvr had another prob i dont know if this helps u or not but it might be worth looking into

Batass

I'll look into that. I generally have near a full tank of gas at the track, whereas at home I only usually have 1/4. I forget exactly what I have going on for a vent, but I believe I'm using two 3/8 lines. One factory and one is the old factory return into the tank. If something has gotten pinched it would explain severe inconsistencies.

Street Lethal

iTrader: (16)

This depends on the way your explaining things. From what I'm reading, your using methanol (alky injection) as just a coolant for your intake charge during boost like I do, correct, and your not running straight methanol all of the time? We know that E85 is stoich at 10:1, and methanol at 6.4:1, so yes, swapping to straight methanol will make you go lean without changing jet sizes. However, not only are you claiming that your breaking up on, or just after, 4500-RPM, you also stated that not only does she feel pig rich, but that your buddy verified black smoke. Right there that would tell me that your not running straight methanol, and your just using it to cool down the charge during boost. If this is the case, you need to pull fuel from your secondaries if your breaking up past 4500-RPM, not your primaries. Either that, or lower the amount of methanol your using. Your trying to balance out your air fuel ratio of x amount of air entering into the engine, with x amount of methanol at 6.4:1 stoich, and x amount of fuel at 14:7 stoich. Too much of one or the other fuels your using will make you go rich during boost, which is what it sounds like....

Batass

I'm hoping it was just too rich. I just took it out on the road and it ran great, but I didn't get into third gear. I yanked a plug and the porcelain was brown with soot around the edges, but I don't know how much I can count on that being it wasn't immediately after WOT.

Something I forgot to mention. My last run at the track, it was as if I hit a rev limiter. Tach was reading almost 6000 rpm though, which I don't believe to be right. 6000 rpm in 3rd gear with 3.50 gears is over 130 mph. The tach reading that high really confuses me. Could the motor acting up somehow cause it to blow through the converter? Or was it getting a goofy signal? It sure didn't sound like it was doing 6000 rpms.

I'm planning on getting the car to the dyno this friday and seeing what happens. Then running it saturday. It would be cool to go on a friday night for once, but the track condition always seems to suck on street night. The launch and time slip is what I really care about, not beating someone's leaky farm truck.

Batass

I found that the front squirter is leaking so bad that fuel gets into the HSABs.

Orr89RocZ

iTrader: (20)

Have you been able to try a different carb?

Batass

I will tomorrow for sure. The threads are half stripped for the squirter and it doesn't sit straight, therefore it does a great job at leaking. I'm not sure how I will fix it, but I'm not chancing that it falls into the motor.

I'm going to put a 600 DP on it. Hopefully I won't have problems with it being too rich due to being on the small side even though cfm calcs say 598 cfm for a 383 at 6000 rpm.

I might plug the powervalve to reduce risks of not getting a good WOT afr. I ran this carb on my boosted 305 3 years ago and I was pretty happy with it. I had to drill some holes in the butterflies to get the idle mixture right. I'm going to just change the main jets and set it on the 383. I already have new throttle blades in case I don't need the holes.

I don't know why the 305 needed the holes. I was only running an LT1 cam. I was spinning the blower to the max. Maybe it was pushing fuel in somehow.

B4Ctom1

What kind of fuel pump, pressure regulator, and spring are you running?

Batass

A1000, aeromotive type boost ref return FPR. Carb spring.

I got the holley on and did some tuning yesterday. I drove it four different times in a 3 mile loop and burned half a tank of race gas.

I now have 78 jets with the PV installed in the primary, and 90's in the rear. And it is still very rich. High 10 afr's throughout and pretty consistent. Probably won't screw with it much more until I get to the dyno. The noise in my community gets old real quick.

It seems to run much better with this carb though. It sounds different, cleaner. It also idles better.

Orr89RocZ

iTrader: (20)

hopefully that helps things out man. Would love to see this setup run like it should

Batass

Car ran well, got to the track and it started breaking up again. My buddy had the bright idea of letting the motor slowly rev while staying in the primaries. It still broke up so we looked at ignition. Didn't find anything wrong, but I turned off the start retard, the rev limiter, and the two step even though it wasn't hooked up. Ran free and clean. Conflicting emotions.

It ran a 10.78 @ 127.5. AFR was in the high 11's. Pulled the plugs and they were just about white. I turned the meth on and got about the same et, but couldn't get faster than 126 mph. The car was having a difficult time starting up too. I think the digital 6 box might be toast.

This was through a 600 carb with 68/74 jetting. When the car ran well with the 750 it had 84/96 jetting.

This was my last race with this setup. I have had so many parts fail its supernatural.
I'm going with a T-56 and nitrous or maybe a roots. Blowthrough isn't working out for me for a street car.

Orr89RocZ

iTrader: (20)

No efi attempts?
Sorry to hear you cant get that setup working. T56 would be fun and nitrous will make for a reliable easy to use setup. I dont think you will be disappointed with that.

Batass

Its been a plan for a while to ditch the blowthrough setup. I just wanted to get some decent times and recieve the effect before doing something else. It doesn't give the type of power I really like.
I simply don't need the power on the street. I get really rowdy sometimes and its not worth losing the car or lifelong consequences. I'm getting rid of my gsxr for the same reason.

I want brutal low end torque and kicked in the chin with a barbaric shift. Maybe a kick of n2o for track days.

Eric89sc

iTrader: (1)

I was having the same problems but I'm so glad I bought my carb from csu, kevin was just a phone call way to help me. Carb all the way I wouldn't switch. I have to switch gears yet then it should run even better. If u need any help I'm not that far from u.

Batass

Well I could go on and on about why I'm ditching it, exchanging power for reliability and reasonable gas mileage, wanting a stick. I love this car and I want to put my effort into many other areas than constantly playing with the motor. I would be completely fine with this car if it was drag only, but I'm picky about street manners. I absolutely hate a high stall auto. When the stick goes in, it won't see the track much and I just don't need much more than 450hp to have a good time on the street.

Not to mention motorcycles have kinda spoiled me.............

Eric, thanks for the offer. It would have been real cool to get together last year...

Batass

Blower is going back on. I swapped my hurricane intake to an RPM laying around, and holy cow what a difference. Runs much better. I just got here to wyotech and I hear nothing but how "fast" so and so's car is. I tend to be pretty modest, but I'm gonna try and hit 9's with this little blower and no nitrous. The only really fast car around here is a 550hp honda. Blasphemy.

Its incredible how much more torque and manners the car has now.

brandoz28

iTrader: (1)

those hurricane intakes are basically only good for a drag only motor, we went from one of those to a super victor on my friend's car and the throttle respsonse/driveability was way better. not to mention the fact that it ran about a tenth quicker on street tires than the hurricane was with the slicks

Batass

Yea, I'm pretty sure I gained more than 40 ft/lbs at low end part throttle. Hell 40 ft/lbs is almost the gain from stroking.

I haven't even hooked up the blower yet. I think its going to pull real nice, not to mention the low speed signal should be much better, letting me tune it better and in turn a better street car. It'll probably eat less gas too.

I can't get a good answer on running a dual plane vs single plane. I'm going to run it, check plugs for cylinder consistency, then put on a 1" carb spacer in case the motor wants more plenum, check plugs again and compare mph. If the motor wants more intake the spacer should show it.

brandoz28

iTrader: (1)

we had to jet up a TON for the hurricane, at first we thought it was moving more air, but i think it was just a total loss of carb signal.


if you need a single plane, the super victor is WAY better

Batass

I was running 98 jets in the rear, WITH pure alcohol injection, which is way more than it should have needed.

How well did your ports line up with the hurricane?