View Full Version : Has anyone done endurance racing w/ sc 3.8?

matt f
10-10-2011, 02:42 PM
I'm the proud owner of a drivetrain out of an Xr7 5 speed.

I'm looking at installing it into my 88 Turbo Coupe, making it a super turbo coupe. This car is in "24 hours of LeMons" races, where you take a 500.00 car (value of car and modifications) without safety equipment, then cage it, add race seat, extingusher, cutoff switch, etc., then race, anywhere from 14 to 24 hours.


Anyway, I'm looking here for advice on making this engine last for an entire race, if not several. I was thinking about pulling a few degrees of timing and decreasing boost, via an underdrive pulley. If I could run it on e85, that would be a bonus, but no tracks that I've been to sell it, and I rarely see it for sale in the mid atlantic region, only western pa and west...

Does anyone have info on pulleys and belt combinations for 10%, 20%, etc underdriven?

I know the head gasket seems to be a weak point, but the guy I'm getting the engine from had just gone over the top end, including head gasket. I'll also be putting fresh oil into the SC. Should I go synthetic? Mfgr. and weight?

Thanks for your time.

matt f
10-10-2011, 02:46 PM
A pic from the TC's last race...

10-10-2011, 04:27 PM
Wouldn't it just be easier/more appropriate to just remove the SC belt?... :)

10-10-2011, 04:35 PM
Have you ever tried to drive yours with out a belt? It don't really work that easy.

10-10-2011, 08:46 PM
figure out what your rpm range needs to be. That will tell you what you need to do with with anything.

Here is a thread with a spreadsheet that includes the various pulley diameters and how rpm changes with pulley diameter. Remember the stock motor moves 116CI of air with each crankshaft revolution. The M90 blower moves 90CI of air with each rotation of it's shaft (both numbers are assuming 100% VE, thus reality is less). Keep that in mind as you change the SC overdrive, which in stock setup is ~2.5 snout revs for each crankshaft rev. Using a 94/95 blower pulley on a 89-93 blower will underdrive the blower slightly.

If AOD, add a trans cooler, a big one and bypass the radiator one.

big power steering cooler.

Use a high quality full synthetic oil and run it 1/2 quart high or higher? Trying to keep the pickup covered. Don't let it get low for sure. Low enough for the low oil light is too low.

Yank the A/C compressor and pick up the A/C delete bracket and pulley.

Cut some weight.

Swap out wheel bearings if no evidence that they have prevously been done. Likely can get that done on a safety exception. bearings starting on fire and toasting brake lines is not a good thing.

Check the steering column coupling made out fabric. Again, safety might allow replacement with a flaming river solid coupling.

You can yank the octane plug to pull 4 degrees of timing out of the whole rpm range. You could maybe find someone with an old EEC-Tuner module that they will loan you. Value is pretty low. Track down someone then to help you with it to tweak the EEC-IV tune to gain you some MPG, and dial it in on a dyno to eliminate some excess fueling built into them. otherwise, someone with a QH could help you tune your car using their QH. Then you just need to buy an F3 chip which is under $100 to store your tune on.

10-10-2011, 10:54 PM
You probably already ditched your A/C but if the condenser is there, get rid of it so the rad breathes better. Make sure your diffuser is in good shape too.

Miata battery maybe?

Cooler t-stat.

I don't know about having extra oil. I think since you're going to be at relatively high revs a lot of the time, it's better to just keep it at the higher end of the fill section. The pick-up should be fine, but that is smart-thinking to consider it, Mike. Too much oil can cause problems in my experience. Even if the oil pressure doesn't get to "dangerous" levels, you're putting more strain on seals and such, as well as robbing a couple horses that your motor already did the work to make. You do not want this for long races. I think it's better to try to ensure adequate lubrication without over-filling the oil. I would probably use Valvoline VR1 race oil.

I don't think you necessarily need to underdrive the blower, but it might have some effect. Just make sure your exhaust is up for it and your fresh HGs should be fine. The stock pulley is a pretty good choice for racing, actually.

Port the factory 3.8 manifolds if you have access to the tools to do so. They have a stupid inner ridge that should be removed. Even if you have no experience porting, you could do it with the right tools no problem.


E85 is a cool idea (pun intended) if you can make it happen, but you would definitely need better injectors, a decent fuel pump, and probably a good idea to find a way to tune within your budget (if that's even possible). I don't think it's where I'd put my money though.

I don't think you need to pull timing deliberately either. I would just trust your sensor and you can keep more of your low to mid grunt. I'm no expert on that though.

Gap your plugs around .035-.042 perhaps. There are a lot of Autolite 103 fans on here, but I like the NGK V-Power equivalent (TR-6).

I'm not sure what gears are in your fox bird's rear, but I'd recommend 3.27 or 3.55 for the early M5R2 for what you're doing. Depends on where you're racing though. If your car has a 3.08, just stick with that.

Inspect the harmonic balancer.

matt f
10-11-2011, 08:20 AM
I have a 3.55 rear available, but I'd go as (numerically) low as possible. This engine seems to have plenty of torque down low, so that's my target. With the de tuned 2.3 (11 psi max) we saw 130 mph on the straights at Lightning. I imagine we should be more than a couple mph higher.

It's an 89 w/ the 5 speed. We could drive the whole course in 3, 4, 5, and 3 would only be for 1 or 2 turns. I have overfilled every car I've ever had on track by 1 quart, and will probably do the same with this, unless I fab up a ghetto accusump using an old fire extingusher.

What temp t stat, 160?

Since the engine is out, we'll be able to port the ex manifolds pretty easily.

We have fresh rotors w/ new bearings and seals w/ high temp grease. The TC, as of now has the 4 lug setup. As $ allows, we will be going 5 lug, but that's probablt a season away. We're also building our 4 cyl mustang for a T 2.3, and I just picked up a 93 trans am...

fast Ed
10-11-2011, 08:46 AM
For what you plan to do with the car, a normally aspirated 5.0L would be a much better choice, especially since you're doing a complete swap anyway. The 3.8 SC heats up much too easily for both coolant temp and air intake temp when used on track. I used to run my 95 at open-track days, and after 10 minutes on a warm day it would be baking, I would have to back off for a few laps. 24 hours would not be a good idea IMO ... I've done that type of racing as well, I know what's involved.

Ed N.

matt f
10-11-2011, 10:25 AM
For what you plan to do with the car, a normally aspirated 5.0L would be a much better choice, especially since you're doing a complete swap anyway.
Ed N.

Of course it would! But how do you become a LeMons legend? By getting away with ill advised engine swaps, racing French cars, or building your car the night before the race!

I figure on putting in a 5.0 after this engine grenades. I've got 3 of them waiting to run... If the 4.9 I6 wasn't such a boat anchor, I'd be installing thet with some "Ghettocharging".

matt f
10-11-2011, 10:26 AM
has anyone tried water injection???

fast Ed
10-11-2011, 10:34 AM
You would likely need a pretty large tank in the trunk to have enough water to get the job done! :p

I guess it comes down to, do you want a chance at placing well, or do you just want to race? If you want to have a strong reliable car, go with the 5.0L rather than the SC engine.

Ed N.

10-11-2011, 10:52 AM
A centry blower seems to be the fix for this sort of problem.

02-17-2012, 01:06 PM
I like the 4.9L I6 Idea!! That would be BOSS!

03-23-2012, 12:10 AM
There was someone here years ago that tried doing a similar type of racing with a CMRE Stage 2 engine and a MP2 (I believe) and he kept burning up the engine and blower. IMO, the engine will take it but the blower won't. Switch to either a turbo or a centrifugal blower if you really want to road course it.