From: Marc Wiese


So, after my latest outing to Thunderhill, I cracked the back of the snail
of my single turbo, likely due to stresses from venting the wastegate back
into the dump pipe which then put unequal forces on the back side of the
turbo. Plus, we're flogging her pretty hard, as God intended.

This was the stock T04S delivered by the RX7 Store some 6 years ago or so. I
elected to go this route vs. a ball bearing turbo because at the time the
ball bearing stuff was just coming on the scene, was more expensive, and
wasn't rebuild able. Prices have since dropped and technology improvements
have been made dual ball bearing the way to go nowadays.

Had Cliff at Turbo Power do the rebuild, since he's about a mile from my
house (right next to Ground Control) and also supply a new turbo blanket
(very nice, very spendy). I figured that while we were there, we might as
well just run through the entire turbo.

The welds holding the down pipe flange on the back of the snail didn't have
very deep penetration - this was one of the reasons it failed. He welded it
up right, along with V-band clamp that is now the standard for single turbos
and will allow some flex.

He added an improved 360 degree thrust bearing for the rear....the stock one
is only 270 degrees, believe it or not. Running higher boost will put more
stress on the back of the turbo - 3psi of pressure on the bearing for every
one pound of boost, according to

We found 18 lbs waste gate springs vs. the  14 lb springs that came with it.
I'm tired of fiddling with my boost controller trying to get the boost to
run at 18 psi....since the car now runs on 100 octane minimum, with at least
11 heat range plugs, we can turn up the wick. This turbo should be good to
20 lbs before getting out of its efficiency range, and I can't go that high
and keep the power on the ground with the 9.5" rear wheels I'm using now.
Those damn waste gate springs are expensive - you need two, and they are
close to $100 bucks for a set.

We're going to have the waste gate vent direct to atmosphere now that this is
a track only race car. More noise is ok now, and venting to atmosphere vs.
trying to blend the waste air into the exhaust should improve boost control
(no weird fluid dynamics blending the two exhaust streams back together).
Also we won't have two different pieces of metal attached to the turbo
causing stress, now only the down pipe will be connected to the back, with
the V-band to relieve more tension.

So, those are the updates for now, fyi for those of you running an out of
the box To4S....if you do have a To4S fail, rather than rebuild, for the
cost, I'd recommend upgrading to something in the GT40 series. It cost me
around 700 for the rebuild, and for 1600 I could have gone with a custom
GT40 dual ball bearing.....still half, but the gross total difference isn't
near what the difference was between T04S and dual ball bearing 6 years
ago.......

Eric Wells