Okay, I'm trying to lay out my game plan for minor modifications to my new (to me) LT4. For no good reason, I'd like to unlock some modest performance gains out of the car. You guys seem to be very knowledgable so I value your opinions and advice.

First observation: The LT4 seems to me to be an LT1 with a focused improvement on airflow....heads, cam, intake. Now, correct me if I'm wrong, but isn't airflow only as good as it's weakest link? If so, wouldn't it stand to reason that these improvements aren't seeing their full benefit because of the t-body? My understanding is that it's still using the MAF and T-body from the LT1. If this is true, would porting the T-body be a good option? I would like to improve the airflow as much as possible, without compromised the manners of the car.

Second: I was considering going to a ceramic clutch and aluminum flywheel. Does anyone here have any first hand experience with this kind of a setup? How much "grabbyness" can I expect?

Thanks in advance for any help. For all of my faults, lack of appreciation is not one of them.

 

I cant answer your questions on the clutch, but IMO the best single mod is 4.10 gears. Then I would follow that with long tube headers and a cam. My choice would be the hot cam.
Good luck with whatever mods you choose to go with, and I look forward to reading about them.

 

I use the stock throttle body and MAF on my 383. I'm at 450rwhp or roughly 500hp at the crank. On an otherwise stock engine, you'll see about 5hp. Hardly worth the $300 cost.

With a throttle body and an aftermarket exhaust you can expect a 10-15hp improvement in total.

To really improve the LT4, you need to port the heads (or go aftermarket) as well as swap the cam, move to full length headers, etc.

Regarding the clutch...it's subjective. Yes you will have some chatter, hard to say if it will be acceptable to you. Having said that, typically the biggest complaint when replacing the dual mass flywheel with an aluminum or steel single mass unit is the noise. At idle with the clutch out/transmission in neutral, it sounds like a box of rocks. You will also hear gear noise below 2000 rpm when accelerating.

 

I would'nt replace the throttle body or the dual mass flywheel/clutch.NO hp to be made with the TB(certainly not enough to justify the cost).I miss my dual mass flywheel every time I drive it.My 383 has an alum flywheel and a spec 2+ clutch.IT is a lot noisier and engages more abruptly although it is needed for 441 rwhp.
Honestly if I were to modify a stock LT4 again I don't know how far I would go.If I did heads I would go straight to some AFR's and a moderate cam upgrade or possibly have advanced induction port my factory ones.
Long tube headers did'nt make a huge gain by themselves on a stock motor for me but would be beneficial with heads and/or a cam.A catback exhaust is a good place to start.Corsa is the best.I wish I had done it first and not tried everything else.lol.
A cut airbox lid and a K&N filter is a good place to start.A dyno tune is usally worth a few hp but I would wait until all of the major mods have been done.
A good tune up to make sure everything is in proper working order should be done first.

 

Thanks for the input. I'm pretty sure I'll not be doing the flywheel and clutch change. 4:10 gears aren't an option for me either, as I like to do long road trips in my cars.

I agree that $350 for the throttle body is not much worth it, but what about porting the stock one? My dealership has a machine shop, as we do quite a bit of racing and fabricating. I have an LT1 engine sitting on a stand that I could rob the t-body from.

I think you guys with the 383's are on a whole different level than I'm heading for. I'm more or less just looking to maximize the engine's potential in stock form. If anything I would probably just port the intake and heads and do the hot cam (unless you guys think there is a better cam option for power AND driveability).

Right now it has a flowmaster catback. I absolutely HATE the sound of this exhaust, so it will be going away soon. Is there much difference between Corsa and B&B? Really, I like the look of the stock exhaust tips the best but my understanding is that the stock mufflers are pretty restrictive.


Please forgive my ignorance. The last LT4 I had was when they were new, so I didn't do much in the way of mods. Just an airfoil, a lid and a filter.

 

Why would a stock tb ported to 52mm be any different than an aftermarket 52mm tb (or 58mm for that matter)? If you can get 5hp for free, then it won't hurt. Would I pay $300+ for the same 5hp?...I personally would not.

With lightly ported LT4 heads, matched intake, the HOT Cam, Corsa exhaust, and an electric water pump, my prior engine was 363rwhp. Driveability is subjective. All cams will compromise something. Do you want a lope? Can you tolerate cam surge below 1500rpm? How critical is gas mileage? Do you have to pass emissions testing? Do you plan to have it tuned (or can you do the tuning)?

The Corsa sounds much different than the Flowmaster system (I have had both). The biggest improvement IMO is that with the Corsa, there is no drone/resonance at idle or part-throttle cruise.

 

I wasn't sure if there was a difference other than just the porting on the T-body, so that's the route I'll take with that.

I would rather not have much lope. The LT4s that I have seen with the hot cam seem tolerable. The surge shouldn't be too much issue since it's a manual. Or am I wrong?

I would like to keep the fuel mileage at least close to what it is now. Right now, on roadtrips, I'm getting close to 30MPG. I wouldn't be too upset if that fell to 25. I can skirt emissions pretty easily, although I'm not supposed to

I HATE my flowmaster. HATE HATE HATE. It's the worst exhaust system I've ever seen. EVER. The drone is unbearable in 6th gear. I need to find someone with a Corsa, and hear it run.

 

Yeah, the Corsa system is really the one to have for long road trips. I've had Flowmaster, Magnaflow and Corsa (sorry, no B&B) and would never consider another after the Corsa. It absolutely screams when you want to be loud and is unobtrusive the rest of the time. I suspect the B&B will be similar to the Magnaflow, which is better than Flowmaster, but really just a less annoying version of the same thing. Otherwise you can go back to stock. Since you're not going for bigger cubes, or aggressive mods, it is a valid option since the LT1 exhaust does flow pretty well and is MUCH CHEAPER. I made about 350WHP on the dyno with the stock mufflers, stock heads, stock throttle body, long tube headers, high-flow cats and an LT4 hotcam w/ bolt-ons and a tune, which was pretty strong compared to others with the same mods at the time.

 

You dont need a bigger TB, waste of time/money

96LT4 is right on the money on his other suggestions imo


the lightweight clutch/flywheel thing on the street isnt worth anything imo.
You wont feel anything and requires more attentiveness to operate.
Big fan of keeping some weight to a street clutch setup.

 

Do an electric water pump for around $250 for 8hp and shorty headers for another 8hp for $200-$300 or go long tubes for 2-3 times that but gain 15-20hp. A new shifter makes it more fun to drive too. You could also do underdrive pulleys if you aren't looking to get too in depth for mods.

 

Where's the best place to get the 4.10 gears for a 96 Corvette Dana 44 (and brand)?

 

350 can barely use 650 cfm at 100% VE


Last LT4 I fooled with had ported LT4 heads, intake hotcam shorties and a good tune.

392rwhp

Stock throttle body.

 

 

Good info guys. It's interesting how the opinions vary slightly, but ultimately seem to go in similar directions. It's good to be able to get opinions for different experiences.

Didn't realize the electric water pump would make that much of a difference. Thanks for the tip.

 

Okay, any recommendations on replacing the optispark? I finished changing the plugs and wires (complete pain in the rump) and I still have a slight spark failure while at a level speed (30-40mph) It doesn't do it while accelerating, just at low speeds. I hooked up the tech II and no codes were thrown, so I'm assuming it's the early form of dementia in my opti.

Should I replace it with the MSD, or is the stock part good enough?

 

Here's the Delteq solution...Click on the link below.

http://delteq.com/

I'm not suggesting you do this, nor what your problem is. I'm just throwing this out there, since many don't even know it exists. It's like an LS series coil pack style for your LT series engine.

 

i thought about that myself but had read Delteq no longer exsists.

 

Takes a lot more than ported heads/intake, hotcam and shorties to get 392 RWHP!!!!!

BTW 392RWHP is almost exactly what I dynoed at with my LT4.....

 

Stick with a stock replacement opti.

 

Thats what we got, was tuned at RPM motors in Santa Clarita Ca.
It was at 365rwhp with heads/cam/tune and manifolds then I did the intake shorties/retune brought it to 392. Think there was 400 in it with a little more head work poss longtubes but youre chasing every little bit merely for a hp#.

Ran strong but imo a little weak on low end tq even with 410s
Pulled hard though think it would have taken my ZR1 down with no problem.
Passed Ca smog