TO4E 60 Trim vs. TO4B 60-1... Surge limit??? HUH? :D
 

I am about ready to put a big single on my 1990 TII. The car has the stock (rebuilt) block and a Haltech, FMIC, and 3" exhaust. I've pretty much narrowed my choice of turbos down to two: The TO4E 60 trim and the TO4B 60-1.

Everybody on the forum seems to say "Go with the 60-1!" most of the time, and it looks like it would do a 'pretty good' job based on the compressor map. This is the turbo that I see a lot of people making a lot of HP with, but... If you look at the TO4E 60 trim's compressor map, it looks like it would do a much better job. The efficiency of the compressor is better throughout the rev range, and it seems like you can run a wider range of boost pressures (~8-15 psi is all well within the efficiency range throughout ~4000-8000rpm span) than you can with the 60-1 Turbo.

The 60-1 looks like it'd work best for a motor that is either heavily ported, running a 9000 rpm redline (at least). It also looks like it falls out of the 'efficient' range quite easily compared to the TO4E.

I calculated the lb/min using this site: http://www.grapeaperacing.com/GrapeA.../turbosize.cfm

Also, what is the 'surge limit', and what effect does it have on things?!


Confused in turboland..., :)
Manolis

Surge limit...

A turbo can be described as an inertial compressor. It physically compresses the air (not just cramming it in like a blower) and it does this by slinging the air at a diffuser - basically throwing it into and against a curved wall in a neat and orderly way. (ever ride a roller coaster? sort of the same thing. you accelerate down the first hill, and then you get compressed when you are slung back upwards)

In order to compress air, therefore, it has to be flowing air, in order for it to be accelerated fast enough to compress. the surge limit is the minimum amount of air that the turbo can flow for a given speed. the speed of the turbo roughly defines how much boost there is, of course that is detailed on the compressor map :)

Any less airflow and things get unpleasant. extreme example: you have no blowoff valve and you're at max boost and you let off the throttle at redline. massive compressor surge.

where can you get the #'s the t-04b can do?

try www.turbonetics.com, look under compressor maps.

that's where i got the data

I get a bit of surge when using cruise control on my TII, with T04E, I thought it was a tuning issue, but after much datalogging, I realize its just that I am asking for bit of boost, and my engine is not really making enough exhaust for the boost pressure, the throttle plates are just being cracked by the cruise control, its a bit annoying but nothing to major..Max