Ronn38

I finally got the c4 I'd coveted since I graduated college in '84--a Polo Green coupe (though mines a '93). And now I'd like to make it more like a Vette, and less like a Cadillac.
52K miles, Auto trans and a 2:59 rear end.

My take on performance starts with getting the most horsepower/torque a car makes to the rear wheel. SO I think the best "bang for the buck" here is a new 3.73 rear end, maybe a shift kit and/or torque converter. Its seems I should just enjoy this motor stock (or mostly stock) and when the Opti gives out again, or the seals, or whatever, I simply do an LS conversion--seems the most cost-effective ('cause the days of the $59.99 hooker heads are clearly long gone;-) )
So my questions are:
1. Thoughts on this approach?
2. Have someone install new ring and pinon in my dana36, or buy an assembled unit from one of our vendors?
I'm an OK wrench, but a rear end is beyond my capacity (could probably drop mine--but I've no lift in the garage, so...). Any advice on the best complete rear end units that don't break the bank?
3. shift kit or torque converter or both?
I put a B&M shift kit in my Z28 when I was a kid, ramps and jacks got that car up high enough. I recall firmer shifts, but if you didn't get into it, wasn't much harsher than stock. I have a built Miata for zoom- zoom, so this is my "fast and Fun" date car--but my smarter half would rather not have a drive remind her of dental work. I've no experience with aftermarket torque convertors, so I pretty much in the dark on them. It seems a higher stall speed would get more RPM's to the rear end efficiently -- but do they make the shifts harsher? Thoughts on this would be most appreciated.
4. Finally, according to the carfax, the Opti was replaced 2.5 years ago (2100 miles--no indication the water pump was replaced) and it's running fine now. But I can see this unit has no venting. The ventilation kit/cap from Petris enterprise is my choice currently. Is it worth it to get a vented cap and hopefully stave off trouble, or is fixing things that ain't broke still a bad idea here?

Thanks in advance!
(and don't tell me to repaint it -- Greens the fastest color ;-) )

Ronn

84 4+3

2.59 to 3.73 is a huge jump. But it wouldn't be bad. Torque converters don't change shifting just the "slip" allowed before its fully transferring power... think torque multiplier. You could go to a 2800 and probably notice no difference just driving it.

The easiest route for the rear would be to find a take out and just swap it honestly. Having gear swaps done could get expensive quick imo. It really depends how much you want to lay out.

KyleF

Completely understand and welcome to the club

Before we get into the other stuff. You want to make sure all fluids are good, idle is good, plugs, wires, fuel pressure, and all filters are up to date and clean. Basically, if it is not healthy and running correctly now, bolting other things onto it isn't going to make it more enjoyable.



Don't pick many races with Cadillacs, especially the ones with a V on them, but heck my '13 ATS had 315hp, a 6-speed Auto Trans, and weighed 3400lbs. It would give most C4s a run for their money, even on a track. Let's not even talk about the V cars.


Yes, this will help a lot to the feeling of the cars performance. The gear with the Converter and a Shift kit will feel much stronger.

You are making life more complicated than it needs to be. You are going to spend way more money and time getting an LS into a C4 than just getting a C5/6. Unless you just have to have a C4, it doesn't make much sense.
Don't guess, get a quote. You know what an assembled unit cost, go to a local performance or 4X4 shop and ask them. Then go with the best price between the two. Both are viable options.

I would say both, but if you are planning on this being a date night car, you may not want the shift kit. The converter will not cause the shifts to be harsher. It will allow the engine to spin freer to a higher RPM, which increases heat in the transmission some. If you are just going up to a 2400-2600 I wouldn't worry about it too much.

With non-vented units it is just a matter of time IMO. Moving to a vented option is predictive maintenance in my book. If you had a vented one I would say don't fix what is not broke.


Nothing dates a car to the 90's quite like forest green metallic with tan interior.

Color Combos go in cycles, drive what you like.

billschroeder5842

Congrats

Fixing things that are not broken is still a bad idea.

Yes, put your money into your rear end and have a pro do it. This will give you a good bang for your buck.

Now, that your engine is turning higher RPMs, it will need to breath better. Take your non broken opti budget and put it into a better exhaust. I'd put on headers, get a hi flow cat and leave the factory mufflers.

Drive that for a while and see what you think.

cv67

Imo the mods you listed (3.73 headers, 2800 stall, firming up shifts) are perfect to start with it will feel like a performance car, rip on the street and still cruise all day on the fwy. Do it!!

The 2800 will behave like a stock one, not feel real loose-sounds like you know when you put your foot into it the converter does its job.

Ronn38

Kyle-- thanks for the thorough response. The nice thing about the shift kit is its an easy DIY addition should I want to try one after the converter and gears. I gentleman I just bought it from, purchased it from a Cadillac dealership about a year ago, and they seem to have made sure the car was up on all the service (carfax says they even did the rear end service.) I mechanic I'm looking to bring it too is a Vette guy, and I'll be asking him to go over the car thoroughly.
In terms of trans temp from a higher stall converter, are you familiar with the Derale cooling pans? Like this one:
https://www.jegs.com/i/Derale/259/14204/10002/-1
More capacity and built-in cooling passages seem a good combination. I'm only concerned it won't fit (Vette's are a lot more cramped down under than my old Z28). The obvious answer is adding a trans cooler up by the radiator-- but I'm wondering if I can limit the amount of cutting and tugging I do on my 27-year-old baby.

Thanks again,

Ronn

Mostmint

My advice is to enjoy the car as is. By standards of 1993 and before this car is fast.

Are you mixing your desire to have a C4 with another desire - to go faster?

Doing major changes is going to cost a good bit of coin - multiplied greatly by needing someone else to do the work. Then you have to find someone who can do the work well. Also you will not have the car while all of this is going on. You can easily put another $10k into this car while not increasing the value much. If you really need a C4 with more power there are ZR1's out there. If it was more about having a Corvette, then consider going to the newest model you can afford.

This car is over 25 years old, and old cars need work. You might consider putting the money into reliability items / preventative maintenance so you can enjoy driving it more.

Since these decisions are so personal, I'm not sure you can go wrong, but you did ask for advice

84 4+3

The pan will fit, but if its the deep style you may lose some ground clearance.

Ronn38

Good to know--yes its deeper (+ 2qts)

Ronn

cv67

Prefer to have a separate trans cooler to the converter doesnt heat coolant but they both work.

After having a Z, if its power youre after build you C4...The Z takes a certain level of commitment to own, cant just swing into Napa and go buy any part you need for it. Love a good OD trans with a firm shift keeps it fun feeling
2800s dont slip like crazy...get a good quality one not the cheap stuff.

375-400 is cake pulling it out of an LT1 car

Ronn38

Thanks for your thoughts--got a TC brand you've used/seen used and can recommend?

Ronn

KyleF

Yes, I am aware. It is also a big thing on trucks to switch to a bigger finned pan made of aluminum to help shed the heat. I just don't see the heat building in a light street car with a slight bump in stall speed. You just won't be working the trans that hard, even in a 1/4 mile shot.

Ronn38

Ah, good to know-- another toy I can add later easily if the need arises.

Thnaks,

Ronn

Mr. Peabody

Welcome to the group!
Many years ago when I had the Hot Cam kit & Stainless works headers installed on my 95, I also bought a Yank SS3200 TC for the built up 4l60e.
I ended up going with a B&M plate cooler for the trans fluid. Mounted it in-front of the AC condenser. For me it works very well. I don't track my car

Similar to this:https://www.summitracing.com/parts/b...IaAtH0EALw_wcB

Just my $0.02 best "bang for the buck" is simply going to from a 2.59 D36 to a 3.07 D36. It like going from a V6 to a V8 from 25 mph to 80 mph.
Also lots of guys eventually swap out their D36 for a D44 setup and thus a D36 pumpkin with the 3.07 gear is relatively easy and inexpensive to find.

Nothing wrong with Polo Green & Tan. One of the BEST colors for C4. Then again I'm very biased.

cv67

Have 2.73 now and feels practically identical to a 3.07...op youll feel lit jumping .5 not a ton though
3.31 to 3.54 hell yes! It will feel like a lot bigger engine and revs will still be reasonable on the fwy.
For once gonna leave mine alone though and focus on the fact its a low rpm cruiser.

drcook

The 3.07 in my '96 will bark the tires when shifting from 1st to 2nd when really getting on it. It actually is a pretty decent ratio for these series of transmissions.

KyleF

I just did a 750 Mile trip running between 75-80 on the highway... got 25mph for an average. If staying between 65-70 that jumps up to 27 or so.

3.54 w M6... don't fear the gear.

I have never found someone who felt like they went too low, but often people mention they wished they would have went a step lower. The LT1 has enough Revs to support a 3.73, but anything will be better than that awful 2.59.

drcook

All of you talking about M6's realize the OP has an auto trans ? With the ultra low 1st gear in the 700r4/4l60/4l60e series of transmissions, you don't need a real stiff gear ratio to get a Corvette moving pretty quick, especially for a street car. (drag racing is a different situation)

The M6's are much better suited to a stiffer gear on a STREET driven car than the autos are. Are least in my opinion. I have an old pickup that I am restoring with a 454 and a 4L80E. The truck has 3.73's for towing. The engine is way to high in the RPM band on the highway. It needs another gear in the trans. Now my 2500HD diesel has 3.73's but has a 5 speed Allison transmission, so the RPM's are where they should be on the highway.

Picking up a 3.07 D36 diff for not much is a lot better bang for the buck and opens up the money to be spent on other engine goodies such as a hot cam kit, with its 1.6 roller rockers.

Other than having to deal with the speedometer issue, a 3.07 and a hot cam would really wake the car up and the computer can deal with the hot cam.

sstonebreaker

You can install a shift kit, but you can also have the shifts tuned in the computer to be firmer. The TC will soften the shift firmness.

As far as the LS conversion goes, I'd probably go halfway - keep the LT1, modify it, but swap the opti for a coil on plug system.

Rear gears - 3.73's are fine. I had them in my 96 impala along with the 4L60e tranny, and even with a heads/cam package, I got 22 mpg on the highway. The 3600 stall Yank converter sent my city mileage to ****, though.

cv67

A 4.10 is fine on an LT, LT5, cammed car that isnt heavy
On a TPI wrong move....youll get tire spin then feels like you put the brakes on. Personally could give a rats butt about mpg, its a toy. 5 or 10bux per tank savings wont make me feel batter when Im WOT and pissed at the gearing.