Got a 75 this week and is now my new project. I have been a Jeep guy and just finished building my last one, so the Vette thing is a new venture I look forward to.

I am aware of the POOR performance GM did with the L86 and I am wanting to resto-mod this ride for local driving.

What I need help on is what to do with the powertrain?

I know the heads need to go or be bored out for better airflow, but would you:

put in a Stroke kit or build the stock block (130K miles) and juice up the differential, etc?
On a side note - can I get rid of all the emissions crap, but keep the vacuum for the wipers and lights?

I am looking to get up to 350-400hp out of it - anything more is too much $$$

Then - will I need a different transmission and rear end? I am not familiar with the drive train on the C3 Vette.

In other words - what would a C3 owner do for power in this car if it were yours? (within reason!!)

Any input/suggestions would be appreciated! I need to have a "master" plan before I begin the deconstruction.
The forum is always a great place to ask before I run with my own idea and make an expensive mistake someone could have told me not to do...

 

If it were me, I'd drop a crate engine in it and put the original on a skid and keep it.

 

You can get a crate 383 that will drop right in there with zero mods and kick butt. 74 I know was a TH 400 trans, if they used the 400 again in 75, that part is good. As far as the rear end, as long as you stay in the 400 HP range it "should maybe" hold up. But if you hammer on it hard, it can die at any time.

 

What's an L-86?

 

oops...fat fingers.

I meant L-48 engine

 

Crate motor is the easiest route to go and the drivetrain can handle 350 to 400 HP as long as you do not launch at 5000 rpm with slicks. The 75 heads are junk don't waste your time or money on them. The L 48 is just a standard passenger car motor nothing special.

 

Also - you don't need vacuum for the wipers - they are electric. You do need vacuum for the headlights / transmission tube...

Another note. Keep everything (including that "smog crap"). It will help if you ever want to sell it.

My .02

 

He must be thinking of the wiper door, but, again, he doesn't need to worry about it.


Scott

 

Yeah, vacuum wiper doors ended in '72...

 

Change your differential yokes, 75s had a problem with the passenger side yoke breaking inside the rearend, its pretty simple to change out i just got done doing it on my 75 check out the corvette guys on ebay, cheap and good product

 

OK... I've been looking at something similar. I have a 77 that I have just started a body off on. In my case, I have the numbers matching block and, what seems like the original trans.

Getting 350 to 400HP from a 350ci block is pretty simple. It is also not that pricey. Our build list includes a 383 stroker kit, new heads, a proper cam, carburator and sidepipes/headers. We prefer this route just for the sake of keeping the numbers matching block. Look into a book named "How to Build Max Performance Chevy Small Blocks on a Budget". It gives you some great tips/tricks and even gives you combinations with estimated budgets. You'd be surprised what you can do for $3K.

Another option: Look into a GM Performance for an engine. It's P/N 12499529 and it's about $2K.

http://store.gmperformanceparts.com/store/SelectProd.do?prodId=7665&redir=true&man ufacturer=GM&name=350/290%20HP%20Economy%20Performance%20Engin e%20&model=<!--12499529-->

With that as a base, you can modify a tad and likely hit that 350HP figure.

I think you do need to look at the trans and rear end. Off hand I don't know the torque limits though...

In the end... it all depends on the budget... Any idea what you want to spend...

 

If you are going the resto-mod route, do yourself a favour.
Step 1 - remove transmission.
Step 2 - replace with ANY overdrive tranny.
Step 3 - enjoy the BEST move you can make.

 

This is why I love the forums. Thanks to those so far that have posted - GREAT info.
I guess I need to look into the tranny specs and see what it can take - I am getting a little difference of opinion on if it can hold 350hp or not...not a big deal if I need to replace.
Thanks for the info on the yoke assy - good info, and the heads up on the references for the engine building.

Budget - I can go 10K if need be, but I think that might be a bare minimum. Doing all the body work/interior and paint myself so I can save a lot there and put more into the motor/trans.
Not knowing much about corvettes as yet - those little checkered flags and the trim pieces/door panels, etc...holy @!$#!! You guys have an expensive hobby! LOL
However, I can tell the passion of the owners is strong.

 

I am completing a full Body OFF restoration and my total is up to $14,000 and I only need to spend another 800 or so to be 100% complete (parts wise) I have done everything myself except rebuild the rear end (had a transmission shop do that). I have gone through this entire car, bought a welder and sandblaster (included in the above) completely replaced and upgraded the suspension various metal peices, new Stainless steel lines... you name it I've done it on this car, I am begining to strip the paint and bought some practice paint, guns, and Paintucation DVD to get ready for that one.. I even have a Keisler 5 speed on the way and a stroker sitting on the stand... Being a little buget minded and if you stay frame on you can do everything you want and then some with your budget of 10K...

#1 tip DO NOT BUY ANYTHING WITHOUT A DISCOUNT!!!!

-Everything I have bought I have received either a group purchase price, corvetteforum discount or waited for some sale getting 15-20% off each purchase (ecklers does this alot)

Something you might be interested for your motor:
I just got a fully forged 383 stroker rotating assembly from CNC-Motorsports for half price... its the current special on their main page

 

Check with a local machine shop for any stroker packages he may have. That's the route I'm taking. I could not touch a crate engine for the price Im paying to have my original block built into a 400+ hp stroker. The engine is getting good parts too, forged rotating assy, full roller cam, with my choice of aluminum heads. From pan to intake, all new and included in the package. The cheapest crate engine that compared was well over 2k more than the builders package price. The best part to me is that ill still have the original block in the car instead of taking up space in my garage.

 

For machine work, my local NAPA has CNC equipment and only charged $289 for hot solvent tank and wash, .03 over bore, new cam bearings, and clearencing work for the stroker kit I bought... All said and done my engine cost only ~$3000 with my new aluminum heads, permastart Edelbrock intake, cam, lifters, timing chain and gears, and chrome waterpump and all required bolts. I'm doing my own assembly..that cost extra

I'll be puting it together in two weeks when I get my block back!

 

$3,000 is pretty inexpensive for a 400+hp stroker.... I especially rebuilding your own. I may have to look into that.
What transmission are you running?
What gear ratio in the rear?

 

I'm on back order for the Keisler RS400 and currently have 3.36 gears.. I might go down to 3.08 depending on how it goes..

 

75VetteMissouri,

I agree with the overdrive trans suggested above. These old cars with carurettors just LOVE petrol. I just purchased a '74 in Washington state and drove it down to Frisco and averaged about 16 mpg. I was pulling just over 3,000 rpm at 60 mph. An OD trans with a 0.66:1 top gear ratio will pull those revs down to about 2,000 rpm and give you much better fuel economy. The engine has enough torque at that speed to pull the car without lugging it.

You did not mention which trans is in the car. If it's an automatic, it will be a TH400, a strong and reliable trans, but handicapped by a 1.00:1 top gear and a non lock-up converter. I would recommend a phone call to BowTie Overdrives who can supply a TH200-4R four speed overdrive transmission with a lock up converter that will noticeably cut your fuel bill when installed.

It is almost the same length as the TH400 and you can even use your original tailshaft, but a new transmission yoke is needed. BTO can supply this. I think you can even use the stock crossmember, as the mounting holes are almost the same, but I could be out here.

If you have a manual trans, then there are several choices out there, but I'll leave the explanations of that to others who have forgotten more than I know about such swaps.

As to the engine, you have seen both camps give excellent advice. The simplest is to yank the original engine and fit a crate engine. You can do this over a weekend and you can buy as much horsepower as you can afford. Plus you can fit all of the "bling" you want to the engine before it's fitted.

It may well be less expensive to do up your original engine, but you will have to pull it out ( to do it properly! ) and then send bits of it away to be modified and all this for what? To keep the original "numbers matching" block! What if your new power punches a hole through the block at some stage? You might well be able to make a claim on the engine builder, but you'll never have your original block, except maybe as a coffee table.

Plus, your car will be undriveable while the engine's away, and there's the chance of losing some of the bolts, etc., or forgetting exactly which bolt goes where. So, while it may well be "cheaper" to do up your original block, your money will be better spent with the crate engine route, and you'll still have the unmolested original engine when the time comes to part with the car and this will more than likely get you a better price for the car.

Just my $0.02 worth.

And congratulations on your purchase and welcome to the "club." Remember, there's no such thing as a stupid question ( just stupid answers), we were all new here at some time, so don't be afraid to ask anything. We're here to help.

Regards from Down Under

aussiejohn

 

Great post aussiejohn
You just reminded me why I recently became a supporting member.....I still can't figure out the picture posting thang....supposed to be easier.....