Max Q
Last updated 2007-09-18 11:07 PDT

1986 Audi 5000CS Turbo quattro

Max Q In aerodynamics, particularly rocketry, maximum dynamic pressure (0.5 rho V2); the moment when velocity, trajectory, altitude, and ambient atmospheric temperature and pressure combine to exert the maximum stress upon the vehicle. Most catastrophic failures occur at this moment.

Max Q A quattro or Q-ship with maximized capabilities.

Big photos by S4 owner Geoff Jenkins.
These shots were taken in Graydon's driveway; you can just see
the taillight of Geoff's car in front of mine in the lower shot.

This particular Max Q is an Audi 5000CS Turbo quattro, called a 5kcstq by the cogniscenti. If you want to be one of the groovy people, join the quattro e-mail list.

I purchased this fine German automobile from Graydon D. Stuckey in December of 1998. It had 206,000 miles on the odometer at the time, and I have put another 8,000 on it since. For more complete information on Graydon's modifications to the car, see his Monster 5KCSTQ Page.

You can skip directly to details of some of Max's components:

Here is a table describing the MC motors that were original equipment in the 5k/200 Turbos and the motor in Max Q for comparison. I've fiddled around with a performance simulator using Graydon's measured 0-60 time (5.5 sec) and come up with a figure of about 330 HP, but this seems really optimistic. Graydon said 270 when I asked him to guess; I think he's being pessimistic, not wanting to brag. One thing to note though, is that there is noticeably more power when the weather is cold, probably due to much superior intercooling efficiency.

If you want to guess the HP number, ask me for a ride some time. I might even be persuaded to let you drive.

Turbo quattro Engine Specifications
Model 1986-1989.5 5000 1989.5-91 200 1986 Max Q
Engine Code MC-1 MC-2 MC-1
Horsepower 162 bhp @ 5500 RPM 162 bhp @ 5500 RPM more
Torque 177 ft-lb @ 3000 RPM 177 ft-lb @ 3000 RPM more
Displacement 2226 cc 2226 cc 2226 cc
Bore x Stroke 81mm x 86.4 mm 81mm x 86.4 mm 81mm x 86.4 mm
Compression Ratio 7.8:1 8.4:1 7.8:1
Turbocharger K26 oil/water cooled K24 oil/water cooled K27/K26 oil/water
Ignition Single knock sensor Dual knock sensors Single sensor
Max. Boost 1.4 bar (6 psi) 1.4 bar (6 psi) 2.2 bar (17 psi)
Valve Size (in/ex) 38 mm / 33 mm 38 mm / 33 mm 38mm / 33mm
Cam Followers Hydraulic lifters Hydraulic lifters Hydraulic lifters
Interfering Yes Yes Yes
Transmission Ratios Et Cetera
Gear 1st 2nd 3rd 4th 5th FDR EOT
Ratio 3.60 2.13 1.36 0.97 0.73 3.89 2.84
% RPM Drop -41% 36% 29% 25%
TOP@6500 168 MPH
RPM@70 2707 RPM

Graydon called this car the "Monster 5K", but when I bought it I renamed it "Max Q" (see top of page).

The Powerplant

A quick once-over on Graydon's engine mods follows:

The result? Well, didn't I tell you to come ask me for a ride sometime?

Suspension and Undercarriage

Graydon also tweaked the suspension and brakes by adding the following pieces.

Both front Apex springs have broken, one while Graydon still had the car, the other shortly after I bought it. The springs have a clear vinyl tube over the top 1.5 coils. The spring that I replaced had severe corrosion underneath the tube, and at the point of the fracture there was about 3 mm of metal missing! I have removed the tube from the new spring (also an Apex) and am going to remove the rest of the tube from the already-installed new one the next time I borrow the spring compressors from Peter.

If you look to the right of the MOMO steering wheel you can see the O2 sensor readout (a bank of 10 red LEDs which indicate the relative air:fuel mixture ratio).

The tires are in pretty rough shape now, and one leaks down 10 psi per week, so I'm looking at getting some new 16" wheels with 225/50 tires. I think that with an ETH 45 they will work just fine. Until I get new tires on the car, I am keeping my cruising speed under 100 and not going over 130 even for short periods.

Current Status

In late July, while out picking up a copy of Mad Magazine with Fiona, the turbocharger seized. While taking it out, I noticed that the outlet tank on the intercooler had ruptured. Once the other bits were out of the way, I saw that the one-piece exhaust manifold had cracked (again). Well, it sounds like it's time for some good old fashioned hot roddin'.

After getting rebuild quotes of around US$300-350 for the turbo, I sez to myself, "Self, that money would be a good down payment on an RS2 turbo!" After researching a little, I found that the RS2 is a fairly old design by today's standards, using only oiled bushings and late-'80s impeller design.

Turbonetics hybrid, left,
K26/K27 hybrid, right.

The down payment went towards a Turbonetics T04E-50/T04B hybrid turbocharger. The exhaust housing is a custom piece with a form factor identical to a KKK K26#8 housing. This turbocharger is equipped with the Turbonetics ball bearing center housing, so is good for 150K RPM and can take a lot of abuse. When I received it, I immediately took it apart and measured all the turbines and housings, and the dimensions were surprisingly similar to those of the old K27/K26#6 hybrid, with the expected exception that the exducer for the #8 exhaust housing was much larger than the old #6 housing. The only big difference was that the width of the exducer annulus on the compressor was about 80% as wide on the T04 as it was on the K27.

The Turbonetics salesman, Ola, told me about their development of this turbocharger, which utilized an Audi S4 as the test platform (alrighty now!). The S4 with stock intercooler would produce 370 HP with 24 PSI of boost on street gas (but with some serious retard dialed in to the ignition timing). He also indicated that this turbo should be good for flow volumes supporting up to about 470 HP, which leaves me with some room for further improvements.

Next we come to the pathetic two-pass intercooler with the blown off tank. The Spearco Intercoolers catalog has a wealth of information. Peter got a copy of it and drew up a big replacement cooler that uses their 2-178 core, which gives a pleasing pressure drop of 0.5 psi when flowing 450 CFM. This sounded pretty good to me so I sent them the drawing, had them quote it ($655 plus shipping, cheaper than an OEM replacement) and I bought one.

Intercooler Sandwich

Spearco's service was excellent, with turnaround of about four working days from the time I called with a credit card number to UPS dropping it off at my front door (this is simply amazing, considering they are in California and I live in Michigan). The weld quality is top-notch, too, so I was very pleased with the expenditure.

Intercooler Fitment

Installation thus far has entailed cutting a notch in the front cross member and moving that "motor mount" loop down about a half inch. The new intercooler is lots bigger than the old one and masses out at about twice the original (some 3.5 kg for the original and about 7 kg for the new one; that's one big mama heat sink!).

Then there is that snap-crackle 'n pop single piece EM. I asked the quattro list about their recommendations and the stock Audi 2-piece was the best bet, even though it prices out at near US$800. John Firkins, from the q-list, had a source in Australia for good custom-made tube headers for about US$1000. Being the lazy sort, I decided to go with the 2-piece.

[As an aside, Graydon had priced out the parts to build a 304 stainless one when he did the original engine build, coming up with a price very nearly that of the 2-piece. He thinks you could get the price down to US$500 for the parts if you are willing to move the turbo out away from the motor (which he says will have that added benefit of allowing some kinks to be removed from the down pipe).]

About the time I was ready to buy a new 2-piece, Jeff Goggin changed his life direction (that is, he was going to have only one project car; we'll believe it when we see it :), and sold off a bunch of parts he had been working over for a 2.5 l torque monster motor (search the quattro list archives for "flow bench" or something). I bought the 2-piece he had flow-benched at a pretty good price, so that's out of the way. I've ground the ports to match Graydon's head work, and I'm planning on having it coated with a ceramic heat barrier to keep the heat in and the pressure up.

EM Outlets

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