You can't turbocharge a 914, but if you could? Options

[ConeDodger]

I had lunch and hung out with McMark and the Original Customs crew today and an interesting subject came up...

We've all heard the old joke about how you can't turbocharge a 914. In reality, it's been done many times. Mostly badly, but it's do-able. McMark's own car is a 1.7 turbo he built as a proof-of-concept and his build has worked so well, he practically daily drives it!

I know most of you have no reference for what I'm about to say but I'll try to explain; driving a 2270 stroker TypeIV is a great big bowl full of fun. The flat torque-curve means you don't have to shift all the time, just put your foot down and go. No lug, just grunt! Driving McMark's 1.7 Turbo is like driving a 2270. That, and when I have driven it, it was only at about 6# of boost or less. Turn that up, and you've got a serious screamer on your hands...

His execution is about the best I've ever seen (as per usual Original Customs fare). Yet, having very nicely proven the concept, McMark has only built one other turbo engine. What gives? You guys don't like the idea of a turbocharged 914? (IMG:style_emoticons/default/confused24.gif)

Let's discuss this...

[ottox914]

Check out the build threads in my sig.

Get a snickers bar. This could take awhile...

When I did my turbo project, I had 2 goals. Use as many parts as I already had to keep costs down, and keep the engine running cool.

Phase 1 was to turbo my stock 2.0 motor. It already had SDS efi, ITB's, and a kerry hunter exhaust, so all that was to be re-used on the turbo motor. I got my hands on a used 13b turbo off a mitzu 3000gt. On paper, a perfect match for my goals of low boost and fast response. I mounted it on the back of the collector for the KH exhaust. This would keep the heat of the turbo system out of the engine compartment, and keep the intake air to the engine, as well as the cooling air to the engine cooler. There seemed to be 2 schools of thought on exhaust systems. Corky Bell supported equal length headers if you had the room, for better exhaust pulsing to the turbo, and there fore quicker response, and a log style manifold if space was tight. The 13b turbo was a turd. I rebuilt it and it was still a turd. Wouldn't boost beyond 5-6 psi, and all of that at 5k rpm.

A 13g turbo off a subi 2.0 wrx was sourced. Much better. On paper, the bigger turbo should have been a worse choice, in the real world it worked. Response was linear, smooth, and fast. I had a giant intercooler from a wrx mounted between the ITB's, and with that, intake air temps at 10psi were never more than 20 degrees or so above ambient air temp. Monitoring cht, egt, and oil temps/pressures, all were reasonable for driving around, after a good pounding all would be more elevated more than I would have liked, but all returned to "reasonable" very quickly.

So that set up was SDS, with ITB's, KH header, 13g turbo off of a wrx, BIG intercooler with a custom plenum and puller fan, oil cooler with thermostat and fan system, and lots of gauges to keep track of it all. The tune was done by me on the backroads of WI, running around 14.7 afr at steady throttle, dropping to 12.5 under boost, and going a bit lower than that at WOT. The set up was never dyno'd. All this at 8-10 psi or so, as I recall.

I had parts that worked and proof of theory. Now time to ramp things up. After a bunch of consulting with Jake and Len, a new motor was devised. Again, using as many parts as I could from what I already had, I built a 1835, which was the GA case, 2.0 crank, rods, and 1.7 cyls with custom JE pistons to get the right pin height. I already had the case, crank, rods, cyls. Len took some core 1.7Q heads and did his magic. Pistons were ordered, along with a cam Jake thought would work well for the application. The thought process was the smaller bore would seal better, the better cam and head flow would make up for the smaller displacement, and I'd have a motor that would hold 20 psi if I wanted to throw that much at it. My goals were 12-15 psi at 2000-2500 rpm and 7k rpm redline. For autox, I'd rather not have to make the 2-3 shift any more than needed, so more rpms = more speed in 2nd before the next corner.

I built the motor, broke it in, and put some boost to it. Below 3500 it was quick, above 3500 it was scenery blurring fast. Not exactly what I was looking for in an autox motor, but still very much fun. I tried the 13b turbo, still a turd. Back to the 13g. More experiments with tuning, changing timing, AFR's, plug temps, more boost, less boost, still it was a 3500 rpm motor. Tried a 3rd turbo, I don't recall the designation, I think it was a VF 11 or something. Size wise, it was between the 13b and 13g. It performed like the 13g in terms of when it would spool up, but made less boost at top end. On the positive side, with the cam and heads that had an 85% intake to exhaust ratio, the motor ran very cool. Oil temps, cht, egt all were VERY reasonable and super stable. I was convinced I had a cool running motor that would last, I just needed to find the right turbo. So overall, a little disappointed that while I was getting closer, I wasn't there just yet. No dyno on this motor either. This motor was not babied, running 12 psi and 7k rpm every time I turned the key.

Then the money shift. A friend was driving the car while I was tuning, he was WOT 3rd gear, so 13-15 psi or so and somewhere between 7-7500 rpm. I set the SDS to shut down the party at 7500. Heads should have been good to 8k. He shifted from 3rd to 2nd and that was it. The motor is now in parts. Len has the heads back to me. He thought they had been over heated due to the condition of the metal and seats. Based on my observations of egt, cht, and oil temps I don't see how this happened, but his real world observations vs my glance at the gauges, likely it did.

What have I learned. On a turbo 914, heat is the problem, and whatever you can do to control that is job #1. Had the car not been money shifted, 7k rpm and 12psi+ of boost might have been asking a bit much in the long term. The deeper you go in the rabbit hole, the crazier things get. If you are going to turbo a 914 you will need some aftermarket ECU, larger injectors, and exhaust. "Conventional" wisdom on how to size a turbo to this motor is nearly useless. All the books and internet info on turbo sizing told me the 13b was perfect, the 13g to big. 2 valve heads, air cooled, crappy exhaust port flow, lame stock cam, who really knows what the VE is on one of these old things, trial and error was a better tool to pick a turbo with. ITB's made this harder than it needs to be, but thats what I had on hand and was set up to run. E85 would be an additional layer of safety for tuning and keeping temps down.

If I were doing it again: MS was in its infancy when I started this, I went with SDS as a proven, simple solution. I'd consider MS now that it is more mature. I'd go with a single throttle body, on an OEM plenum and runners to keep that part of the deal simple and cheap. While on paper, using the late "log" style factory exhaust, as McMark did is not optimum, I'd give it a shot. I have those parts on hand, and strongly considered it, but went with the KH exhaust. I'd build in as much intercooler as I could, big injectors, and run e85, which may be easier for me in the midwest than for others out there. For the motor, i could go either way, 1.7 or 2.0. Would probably depend on the turbo. No replacement for displacement. I don't think i'd try to push the boost beyond 10-12 psi with out more of a specialty build on the motor. With a stock motor I'd stick with a stock redline. We are doing this to have some fun here, and blown up, broken down, in the garage is not the kind of fun we're looking for, right?