Replacement motor for '85

[bigwingnut]

I'm back into vettes after about a 10 yr drought, and of course am already (only had the car for a week!) thinkin' about another engine. I'm OK on the pre-smog stuff, but need some advice about what works with the 85 ECM and OBD. Logic tells me that one of the World 427 internally balanced small blocks with stock cam, 750cfm maf, 30lb injectors, 58mm throttle body, large tube injector runners, a little less restrictive exhaust with a larger Catalytic converter and a little more fuel pressure ought to sound and work with the ECM about like stock, just with a bit more "OOMPH". Any of you youngsters out there know enough to tell me if that's so, or where I can get an engine that's not too radical, but still with a little more power than stock? Most of my driving is interstate crusing at about 75mph, so driveability is important. Thanks in advance for your help!

 

[69MyWay]

Welcome to CACC.

My first C4 was an 85. Good choice. I bet the 4+3 is a blast.

Okay, you have asked a really huge question here. First of all, are we just dicussing building the "dream motor", or do you have an actual budget in mind and some specific performance goals?

I switched out motors several times in my 85. I went from a freaky roller cam aluminum head motor, to a wicked 383 stroker. In the process I gained a lot of "hard knocks" knowlege about what the stock computer will and won't tolerate.

So, give me some more specifics as noted above. I will be happy to share with you my "dream" engine and whatever I think will fit a real budget. Please let us know if you plan to do the work yourself or pay somebody for the job. That will help us get an idea what you can build.

 

[bigwingnut]

Thanks for the response! Here are the additional details you asked for.

I don't mean this to sound quite like it does...but in this particular instance money is no real object. Not that I've got all the money in the world, but for this project I've got enough. I suppose what I'm tryin' to avoid is doing this more than once.

I do most of the engine work myself...except for farmin' out the machine shop stuff. I've built a bunch of Chevy small blocks (and a couple of big blocks) over they years, but they were all pre-smog. I understand ENGINES pretty darn well, but making them work with modern electronics is a new problem for me. I've always been a beliver in the old addage "there ain't no substitute for cubic inches." When it comes to driveability, a big inch motor workin' a little is easier to live with than a small one workin' hard.

I saw that there was a new 427 internally balanced small block available. Back in 1970 I put a 400 small block with all the 327-350hp innards in it in my 65 vette, and it was the best engine combination I've ever had. Just a driveable as the stock motor, but with more "grunt" when the pedal goes to the metal. In that instance, a little bigger carb plus a free flowing exhaust was all that was required to make it work.

I'm trying to replicate that result here. I just don't know how to make the ECM and fuel injection work together to accomplish that.

The car will likely be driven 800 interstate miles a couple of times a month (Spartanburg-Jacksonville round trip) plus normal in town driving. I'm not likely to race it...more likely to use an onboard computer a couple of time to satisfy curiosity. I don't care much about lookin "kewl", don't care about goin' around corners, and don't really care much about top speed. I just like the kick in the butt on those occasions when I floor it.

I hope this biography helps, and if you wanna know any more just let me know. I appreciate your takin' the time to reply!

 

[69MyWay]

Now that is the kind of budget all of us could use.

Okay, I would do one of two options.

First, I would consider the stroker block, crank, rods, etc, as you have mentioned topped off by a equally nice set of fully worked aluminum heads, and finally a TPiS mini ram and after market computer to keep everything in check. The stock 85 Computer even with a chip does not work all that great when you start strecting out the capacity of the motor.

The TPiS miniram alone will raise hsp by 50-70 and push the RPM curve much higher. This will be done at a significant loss to low end torque. Thus, you up the cubic inches and look for a 3.73 ratio so in the rear axle to make everything work together.

Accel makes a DFI computer that will allow you to dock up with a lap top and create your own fuel curves, etc. Haltech makes a stand alone computer unit that you can program as needed. You will see there are several out there. I would of course speak direct to TPiS about computers they have available to tune it in.

Second, you could consider building a very strong yet mild 350 with as many goodies as you can afford. Then, top it off with a super charger and intercooler. This will allow the best of both worlds and cut down on the guess work. I have been beyond impressed with the MPG, hsp, driveability, and over all fit and finish of the ProCharger, Vortec, and Paxton chargers. IMHO, I think that ProCharger has some of the best products for the C4. The other beauty of the supercharger is you can take it off when you sell the car and install it on the rag top vette that may very well replace this coupe in the future.

Nothing like a six speed, high dollar emission legal exhaust, top down, and th sound of that supercharger spinning under the hood.

You may also get away with the stock computer using a supercharger. I would strongly suggest you locate a complete accessory bracket system for a 1988 and up corvette. This is because you will notice a seperate part number listed by most Supercharger brands for the 85 vette. The newer models had smaller alternaters and a longer production run on that bracket system.

The stock intake will work fine with the supercharger to give you the blend of great low end torque, and added supercharged power.

Finally, if you put the two together........oh mamma. A stroked up, full roller, balanced, highly computerized supercharged 85 Vette would shake the earth when you cranked her up. However, I think I just spend about $12,000 for you.

 

[bigwingnut]

Thanks muchly for the info, that's the kinda help I need! I'm leaning toward the 427 internally balanced engine with their cast iron heads. (2.08 intakes and 1.75 exhausts) using a stock for '85 compression ratio of 9.0. The information on the other items you mentioned ( I haven't really had time to read your post carefully yet, I'm on my way to Florida in a minute and will respond more fully from there) will help me make 'em all work. I'd already intended to add a richmond 6-speed to handle the added torque. I think I'll look toward building it normally aspirated, but the relatively low compression ratio should make it sensible to add the supercharger later...assuming I can work out the pulley ratios! I really appreciate you help, and will respond more fully tonight.

 

[johnny]

stock computer

I'am so sorry to tell you that I tink a stock computer, donot work well. It's at least 16 years old, so if you want to run a smooth engine, than you must adjust the computer. So I choose a DTA racecomputer.
It's 60 x faster and you can put different tracktioncontroles in it. For dry and wet weather. Also it works with ABS.

You can adjust your engine with a laptop in your car, while driving. Or better, on the dyno.

So, this winter a get rid of all the electronic @#%^& and run a smooth engine.

A;so works very good with turbo's or blowers.

John.

Ps. cost a lost $$$

 

[69MyWay]

Jacksonville

Bigwingnut,

Where in Jacksonville do you travel? Orange Park is just South West of Jacksonville/Duval County.