Turbo or not turbo, that is the question

[Crawdad]

Hello all,
First time caller, long time listener.
I've settled on building a squishy motor, but keep waffling between NA and turbo. I've never driven a turbo car, much less built one, so I am hoping some of your will share your driving impressions.

What I enjoy above all is driving sideways. So I need torque right now, for the sake of throttle steer. If I go turbo, it will be conservatively sized. But still I fret about turbo lag. Are you turbo guys able to drift your cars without having to plan your throttle inputs way ahead of time, or engage in other turbo-specific shenanigans? I know turbo people tend to get a little evangelical, like converts to the true religion, but still let me ask: do any of you regret going down this (complicated, expensive) road?

My hope is that with the squishies I can run high enough static compression (9.5?) that I will have decent off-boost response. And I gather that having electronic boost control will help the turbo spool faster, since the waste gate stays completely shut till it reaches its set threshold. Is anyone else running squishy pistons with a smallish turbo? I'm thinking 8-12 psig. I'd love to get 200 HP at the wheels, maybe 230 at the flywheel, as long as I have a nice fat torque curve from 2-5k. I'll probably rev-limit at 6k or a little higher.

Here is the recipe I am currently entertaining; suggestions are welcome. All of this will be going in a full-bodied 76 Sedan, stock gear ratios.

82x94 squishy
Web 86a [Maybe a wider than standard LSA, to reduce valve overlap and help the turbo spool?]
1.4 ratio
MS3 for fuel and spark
Heads: Maybe the L5T (40x35) heads that John sells, if I go turbo.
Case: with moderate boost, is an aluminum case still called for, and 10mm head studs? I understand those cases run hotter oil temps than a magnesium case, so I'd run AS41 if it can take the abuse.

Thanks,
Crawdad

[petew]

You're on the right track. 2-5k is the driving range. Above that is where cases start pounding out. The turbo will just help deliver the torque you want at a lower RPM making it more usable (without stealing power like a supercharger does).

So get on with it!

[Wally]

I agree with Pete and I also think you need to specify a wanted torque number at 2-5K rpm.
So, for instance, what torque you want at 3000 rpm and 4000 rpm?

200 WHP is a nice goal, but max power is usually had at +5000 RPM, so outside the 'driving range' you mentioned...

[Chip Birks]

I sure like my turbo'd squishy motor. Not too many pump gas ACVW motors have made 25 psi more than once and lived to tell the tale. I used to daily drive mine at that boost level, 91 octane, no water or meth sprayed into the intake. It is intercooled, but never iced.
It has always been cammed fairly aggressive, with a semi large turbo though, so may be a bit of an apples to oranges comparison. Compression has always been in the 9.4-9.1 range.

The most aggressive cam and turbo combo I had made 236whp at 8psi, with a fairly rough tune and before 6000rpm. It was pretty lame to drive around with though, but its hard to complain about that kind of power easily achieved on pump gas.

My mildest cam and turbo combo made 278whp at 18psi maxing out the fuel system on e85. This combo drove nice, and was good for an 11 second time slip at the track.

My current setup is hopefully in between these two. I'm running e85 again, simply because it provides a lot larger tuning window over gas.

Your proposed combo will probably do pretty well. I might suggest the WEB 86B, but maybe that will move the rpm range up to high to meet you low rpm goal.

[Stripped66]

Also a former N/A squishy user, currently turbo'd.

N/A was a waste of time. Wish I went turbo straight from the start.

[andy198712]

have you got an LSD? for sideways driving?

[Crawdad]

Thanks for the replies. I've followed you guys - Wally and Chip and Stripped66 - from the sidelines for a few years.
As for LSD, I plan to take some. Oops, I mean I plan to get one. I've hear that the old ZF units are pretty clapped out at this point, and overpriced if you can even find one, so I guess at TBD from Quaife or Pelloquin is the only option. That should be fine as long as I keep both rear wheels on the ground.

As for torque numbers at various RPMs, I have no idea what figures to hope for, but think that making peak torque around 4k would be good for my purposes. What I will probably do is build it with turbo in mind, with a turbo-friendly static CR and single throttle body, but run it initially NA. This will be my first foray into electronic engine management, and developing my first spark and fuel maps will be challenge enough without worrying about another variable of boost.

One turner I talked to said that small, quick-spooling turbos are harder to tune for because they come on so quickly, so your transition to boost may occur in just one or two cells of your map. Any thoughts on that?

[Crawdad]

By the way, I neglected to introduce myself. I make parts for customs motorcycles. Metal shaping, in particular. (That is the art of putting compound curves in sheet metal.)
http://www.reclaimed-fabrication.com