LT4 LT4 Tuning (long)

[rcdk]

Anybody ever do an opti replacement on an lt4? Everything is off except the balancer/pulley and of course, the opti.

The balancer/pulley won't budge. I removed the three bolts, but they don't seem to do anything -- the whole thing acts like one piece.

I have read a couple of how-tos, buth make it sound like the balancer and pulley should be a snap.

 

[vetsvette]

rcdk,
If you will send me your e-mail address I have instructions I can send.

 

[rcdk]

No luck. I beat on that thing half the night and another hour this morning. I am just going to pull the whole thing -- I think I can get a puller on it.

 

[Wheelie]

rcdk,

Those are tough to get off. I got under the car with a big hammer abd a 10" bar and drove it off form behind. Using liquid wrench where the two parts meet will help also. Make sure you hit the hub of the balancer not the outer ring. 4 or 5 good wacks and that thing will pop off.
Getting a puller in with the balancer still on will be tough. You'll need a special one that screws into the crank because of the way the balancer adapter is designed.

 

[maxrevs85]

I'm sorry gentelmen . But beating on the balancer with a hammer is the worst thing you can do. Get the right tool by all means. Your just asking for more trouble.....Just some helpfull advice .

 

[rcdk]

Finally got everything back together and took it for a spin. That optispark is downright evil to get to.

Definite improvement, as it was getting obvious I had a real problem. The water pump was obviously a goner when I pulled it off. I haven't opened up the old opti.

I would love to know what the right tool is for seperating the pulley/balancer from the hub. I ended up using a puller. That gave me just enough room to pull the opti, but there is no way I could get the balancer/hub off together. There just isn't enough clearance.

However, it still just isn't performing up to the standard of even my brother's LT1 Formula, to say nothing of what people say about the LT4. His LT1 smokes the tires from a roll easily.

Below 2k rpm, nailing the throttle just gives me hesitation and bogging that it never seems to recover from as it progresses through the rpm range. At about 2k, it really wakes up and suddenly, but no tire spin at all. It's like someone overcammed it.

 

[maxrevs85]

Clearance is a problem , I believe you have to remove the motor mount bolts and raise the engine to gain clearance. Still , not a fun job.

 

[P-ColaVette]

Bogging below 2,000 rpm....

Hello All !
rcdk, I'm wondering if maybe you have a severe vacum leak on your car as well ? I know that I purchased my LT4 and drove it for probably 2 months before a corvette only shop owner told me I had the major vacum leak. I had just been driving the car thinking that an LT4 engine was supposed to be making that sucking/whistling noise. What is worse is, I had stopped in to this guys shop to get his opinion/price for fixing my power steering pump pulley. The guy walked up, I started the car to show him the wobbly pulley, and when I shut it off, he popped the top plastic cover off the engine, and showed me that the 90 degree rubber elbow ( I will call it a PCV hose) had dry rotted and had a large opening in the hose in the middle of the bend, allowing it to suck vacum majorly. Your car may have a number of small things like this that the previous owner has just allowed to pile up and get worse and worse, until they just sold the car to you. Just my .02,



Steve

 

[rcdk]

Well, it does stumble around just a touch at idle and it seems to have a real problem with transitioning from low throttle at low rpm to full throttle. It performs much better with a slower application of the throttle until it has reached about 2000 rpm.

In researching vacuum leaks, I came across an interesting statement. One source said that a poorly sealed crankcase can effectively be a vacuum leak through the PCV valve.

I ordered the 7777 intake gaskets, I may try doing the intake next weekend and see what effect that has.

 

[rcdk]

I hate to drag this back up since I know I need to change the intake gaskets, but I have noticed something else since changing the opti/water pump.

When I first start the car, the exhaust note sounds great, throaty and kind of sharp sounding.

After it warms up, it loses all definition and just kind of resonates without any definition, kinded of "loaded up." It's what I would expect if the cats were clogged (except I have no other indication of clogged cats.)

Anyway, I am doing the intake this weekend and I will report the results.

 

[69MyWay]

The LT1/4 style intake is not too bad to change. Just don't get into a rush and bend or break anything. The coolant line coming up from the back of the head kind of gets in the way a tad. Be careful with it as you can break that line easy and cause it to leak.

Maybe you can take some step by step photos for others attempting the same project to follow. Nothing better than hearing it and seeing it from a real person vs. a repair manual.

 

[rcdk]

I replaced the intake gaskets and injector o-rings. I cleaned up the block surfaces and the intake and used black permatex.
I let the permatex cure from Saturday night to Monday morning.

The difference: I fixed a minor oil leak. The old gaskets were fine, no evidence of a problem.

No performance difference at all that I can tell. I still have a slightly rough idle with an occasional miss after the engine warms up, and off idle performance is poor. It ranges from an actual bog to just lazy acceleration for the first second or so after you hit the throttle at low (<2k) rpm.

I am taking it to the dealer for an oil change, I will see if they can find the problem for another $80.

 

[Vettelt193]

How many miles do you have on the car? That would help trouble shoot the problem on my end... Also, are you dumping the clutch, or feathering it on a hard start? If you feather it a little you will notice a world of difference on your pickup (for racing)... otherwise, normal starts on an lt4 should be a world better than an lt1

 

[rcdk]

The car has about 43k on the clock. I am running Firehawk SZ50EPs.

The last trip to the dealer, they told me nothing was wrong and they are recording no misses at idle.

However, it did run better and get quite a bit better mileage when I got it back. ??? But still nothing like people claim for these engines/cars.

If I let the clutch out and have it rolling just above idle and punch it, it isn't even close to spinning the tires. A lot of folks claim the ability to light them up all the way through first gear doing that even with a LT1.

Rolling at about 1800rpm, I can let off the gas to transfer the weight to the front then nail it and it has almost enough torque to break the tires lose, but I don't get more than a quick chirp.

The thing comes alive at 2k rpm, below that there just isn't much. I suppose my next step is to take it someplace like MTI for a dyno run. I may just be comparing it to other people's BS. (Although my brother's LT1 Formula will roast tires all day long from a roll. )

 

[69MyWay]

RCDK,

I just learned something interesting about the LT4. G.M. filtered the electronic spark control module to be less sensative to engine noise to avoid pre-mature erronious spark knock retard through false signals. The LT4 engine is noisy by nature compared to the LT1. Any noise (clutch rattle, spark knock, idler pulley, a/c clutch clanking, etc.) can make the computer think you are spark knocking and will start taking timing out. It will make the engine feel dull, and not trigger a trouble code on the puter.

I would highly suggest you invest in a good quality scanner. I have an ACTRON and am happy with it. Set it on monitor of the ESC and drive the car. Watch the read out and see if you are getting knock retard all the time. If so, it will drive like a dog, and get poor fuel economy. Not sure what it would take to fix it, ie, new sensor, checking the engine for noises, etc. But at least you will know.

 

[rcdk]

Yep, but right now if I spend any more maintenance money on this car my wife will make me sell it. It runs well for the most part, so I will probably just lay low for a while on the maintenance/diagnostics. Since the dealer says nothing is wrong, I can't justify messing with it any more.

 

[96Holly]

How it running?

RCDK how is the car running?

I am interested in your post. I beleve that I have somewhat of the same problem. (No horspower in low range) I don't have the miss or lag you are describing though. I can start from a rolling start (ie clutch all the way out) and hit the gas. It accelerates but not like I thought it would. It doesn't break the tires loose like i hear others tell. (Or is it "How big was that fish that got away?")However, I do know that the LT4 is not known for it's low end capibility. Just curious...

'69: Where can I get one of those scanners and how much?

 

[rcdk]

It has its good days and its bad days.

I think it has some tuning potential. It probably needs to be de-carboned and new O2 sensors.

After the dealer reprogrammed it (?) the mileage and performance jumped appreciably, but they are headed down again, especially the mileage. Right after the dealer visit, the mileage started out averaging over 20, but now it is down to about 17 mpg.

Reading some of the "fish stories" I am inclined to think that tires and pavement are a huge factor in off the line impression. Excellent tires + fresh cement = no tire spin at all, mediocre tires + old asphault = lots of tire smoke.

 

[P-ColaVette]

Integrity Check.

RCDK
I can assure you that my LT4's performance is no " Fish Story " and I would be more than happy to let you drive my 1996 CE to prove it. I am regretting your car's lackluster performance, but I would like to ask you not to judge all the apples in the barrell just because there happens to be one or two bad one's in the group.



Steve

 

[Vettelt193]

I don't think I could get my vette to break loose from a slow rolling start on good pavement and good tires... You are talking about alot of tire to break loose at such a low RPM... Corvettes aren't built to smoke the tires, they are built to put the power down to the road... torque and horse power are going to be far greater above 2000 RPM... it is just an obvious thing, more RPM = more power, especially at low RPM.... comparing a corvette to a firebird is ok, but you have to realize that Corvettes should be better at getting the power down to the ground.... If you want to smoke your tires, rev it a little and dump the clutch.... try finding another LT1 or LT4 powered vette to drive... heck, go to the dealer and pretend to want a used one so you can test drive it...

If you still think there is something wrong, it could be the cam... Some LT1 and LT4 cars have had problems with the cam rounding off... I have heard that the synthetic oil is actually too good... If the car wasn't broken in properly it may have a cam that is rounding off...

As far as the sound of the engine goes, The timing should be advancing more as the car warms up, causing the car to get quieter... Most people don't even notice it, but it is more noticable on an aftermarket computer program (if your car has one, it may be advancing the timing too much, causing reduced HP)