SloppyGearhead

Hello! Just wanted to pick some brains on what choice of converter and gears would be appropriate for a 2nd design L88 cammed 427 in a street car that sees some semi-frequent highway miles. The car is a 1975 Camaro (I know, I know, but Camaro guys don't know big blocks!). The engine is a tall deck 427, stock crank, 6.535 rods, 10.5-11:1 cr, big valve oval port heads, Eddy RPM intake and an 850 Holley with the 2nd design L88/ZL1 cam and a TH400. I know the compression is on the low side for this combo, but this is a pump gas motor, and 10.5:1 static lands around 7.5:1 dynamic with that cam.

The general put 2200-2600 converters behind the L88, definitely sounds a little low to me. How well did this combo work together?

I also see that there were numerous gearing options available with the L88, including 3.08(!). I stumbled upon this Nickey Camaro which left the dealer with 3.23 gears. Everything I've seen on the L88 suggests that it would be a total turd with anything less than 3.73's, and really wants 4.10-4.56 gears. This car has to be able to keep up on the freeway, so some more lax gears would really be nice. Thoughts?

I know this is the Corvette forum, but I hope you can forgive this confused Camaro owner, the wealth of L88 knowledge on this site is incredible, and I look forward to hearing what you all have to say.

bjankuski

With the correct stall speed gears are overrated. If you could list the cam specs that would help pick the correct stall speed. The gears could be between 3.08 and 3.5 for decient highway driving, any higher and it will be a buzz box on the highway.

Please provide cam specs.

I found these specs:



With that cam I would run a 3500 stall, that sould b enough to hit the power band and get good acceleration.

gkull

I wouldn't recommend that cam to anyone. It is very poor 60s design before modern spring technology

it is also older thinking to choose poorly designed TC'S. Modern efficient 9.5 inch has very little slip while cruising. So my solid roller 427 had no problems driving around with a 3800 stall. Well it did have a traction problem.

so look at precision industry vigilante tc

cv67

x2
MINIMUM 3500 and 4.11
Id rather see a 4500 and 4.56
Look around and see what kind of modern cams are out there.

SloppyGearhead

jpattt24

373 gears and you can still drive at highway speeds. with out it being reved up to much. it will still be fun to drive!

Kevova

IMO 3500 w/o lockup is the most stall for a street driven car depending on gears. Stall builds heat 4500 is good for the strip but not cruising 55-70 on the highway. Stall speed needs to be near highway cruise RPM. I ran 4.11 a 2500 and 3500 stall converter 3k = 60-65 MPH depending on tires.for 5 years. 8-10 mpg passed everything but a gas station. 27 -29 inch tires can help with the highway RPM. 4l80e would be a good choice if highway driving is important. L88 also had a special governor in transmission allowing higher WOT shift speeds. 6300 I think

gkull

another old school person who has never owned, bought, or even seen a modern high efficiency quality tc

bjankuski

As I mentioned in my first post gears are overrated, unless you are looking to optimise your 1/4 mile time. If you want a good all around gear the 3.o to 3.5 will work great with a good quality torque convertor. The will cruise down the highway well and run the 1/4 mile well.

a good torque convertor is 80% of what you need to get a good 1/4:mile time and gears optimise the combination.

if you highway drive it don't go with too much gear, you will not like it.

Kevova

No "old school builds " follow old school ways. I believe you have a plan to build the whole car, not build and engine then try to make it work. Theoretically you want atleast ten to one out of the hole 2.48 X 4.11 Stall speed matches equal max torque rpm. The efficiency of modern converters is lock up. Lock up allows for high stall and highway gears. There is more to be gained with modern cams, efi, od transmission none apply to this car now. "L88" sounds cool but not street friendly. If OP moves to 4l80e it would be easier to meet his goals. He would gain both lock up and overdrive.

gkull

That's what you don't understand. Lockup TC'S vs highly efficient non lockup in my years of testing might be very few rpm's different while cruising down the freeway at a constant speed of say 70 mph or even 80. I had a manual switched lockup with 3800 stall and it would purr along at 2500 rpm and I would turn on lock and barely a change in rpm's and I have more power than most c3 corvettes on the road

where in years past when I was young and dumber I bought a 3000 stall b&m and that junk ran exactly like you said. Gear matching the stall. My tc ran down the road at 3000 rpm all the time unless you went faster. It was a 8 10 mpg 68 charger rt bored out 440 with a hot cam

I would not recommend anything over 3.73 in a non od car. It gets old of having the motor revved up going down the road. Where a highly efficient stall can cruise at lower rpm and still rip when you push the go pedal
the poster wants to make the best decision with his existing th400. So talk about lockup and modern tranny is N/A

Kevova

To me you are subscribing a "switch pitch" or variable pitch converter used in some 60s THM 400s Kenne-Bell was big into them in the 70's or is this something else.

The Money Pit

I will offer my opinion....though not a 427, my 406 is cammed like an L88,..I have a th400 with a full manual reverse valve body and at the time 3.70 gears. Yes the highway rpms would be high if I tried to do 80 and keep up with everyone else in a 55 mph zone, but with a classic car, registered as an antique, I try and stay at 55 mph and in the slow lane for the short highway time I drive. Most of my commute is back road switchback driving where high speed is not a great idea anyway. Though I've hit 140 mph many times if the conditions were right...……….

One day I was day dreaming, and forgot to downshift at a side street, and pulled out on the highway in drive....the 406 had no problem pulling to 55 mph. It was of course not the usual zippy self, but never the less pulled just fine. Point I'm trying to make is the big motor will work with high gears and a decent converter if you are OK with a slight loss of zip. They are guidelines.....not rules.

If the car is more race than street,.....well that changes everything.

rickimvette

I think the 50 yr old L88 cam was designed for road racing

SloppyGearhead

Anyone ever ran an L88 with the stock-spec converter? I’ve heard some of the racers like it because it helps them hook up a little easier at the strip. I wouldn’t think GM would use a mismatched converter, not to mention reman GM L88 spec converters are much more affordable than a custom 3500 stall would be...

gkull

Vigilante 9.5 TC's are about $800 You tell them the motor specs and they can make the stall. The problem with L-88 cams or should I say one problem is nothing on the low end. so you have to have stall to get it into it's power range. that is why I used a 3800 with my 427. You are instantly in the power.

another thought...…… In the past I destroyed some converters with higher powered motors. Then it fed all the busted aluminum through the tranny. One brand new TCI came apart the first time I power braked my vette. Your 427 is not a slouch and it is better to be safe than sorry. Like my auto tranny blew up a few times, so back then even with only mid 500 hp I bought a bullet proof 800+ hp tanny and TC and never had a problem for many years and 100's upon 100's of runs down the 1/4 mile

SloppyGearhead

larrywalk