35 replies to this topic

[nafnaforiginal12]

I should add... my cars spec now is as follows:

Minispeed built:
1293cc
stage 3 head
piper bp270i cam
centre main strap
turbo clutch
lightened flywheel
lightened and balanced rods
heat-treated crank
recon gearbox with 3.1 diff
Ramair induction kit

LCB downpipe

Gmax dampers
Front hi-lo's

Minisport 4-pot alloy calipers with vented/grooved discs and EBC greenstuff pads
Rear Minifin drums with mintex shoes
Goodridge braided hoses all round

I suppose i need to know whats next.

[Wil_h]

If you want big power, the turbo chooses itself. Once you go over 10 psi boost, the supercharger requires an intercooler which is more difficult to plumb in than for a turbocharger. A supercharger works best for somebody who would like the 1275 to behave like a 2.0 liter engine (sounds good to me!). The advantage of a supercharger is that it is relatively easy to map the fuel injection. You could probably get it done reasonably well in a single rolling road session. A turbocharger, especially at high boost, is very difficult to map. In fact, if you decide to go with a turbocharger, spend a lot of effort trying to find somebody who has a fully sorted installation and then copy what they have. I cannot over emphasize that it is very difficult to map the injection/ignition of a high boost (12+ psi) turbo. You will likely go through an engine before you get it set correctly.

Just to illustrate the difficulties ahead, with a supercharged engine the fuel demand for a given rpm and throttle position is always the same. The fuel demand for a turbo at any given rpm and throttle position depends on the boost the turbo is delivering that moment. The air/fuel ratio for a turbo needs to change with the boost level to get best performance and low throttle lag, so the mapping is considerably more difficult. When setting up a supercharged car, I could get the fuel injection working reasonably well in about two hours on a rolling road. A custom turbocharged application takes 7-8 hours of rolling road and several days of driving around and fiddling to get right. If you talk to anybody who is actually driving a turbo mini with 12+ psi boost, I am sure they will tell you that they are still working on getting their EFI mapping just right.

I can't really agree with this at all. The turbo setup you were mapping must have been very odd, or something wrong with it. I mapped my hillclimver in a couple of hours upto 18psi, no problems. And I've mapped my road car just on the road with a wideband (12psi) no bother at all. The only thing that has taken time is the cruise and light throttle. But that's not beacuse it was wrong as such, more I wanted it perfect. I can't imagine an SC setup would be any easier to get perfect.

Basically, take the example above as one example. There are loads of us running considerably above 12psi and not come across the issues above to any greater or lesser extent than any other car.

And the "makes a 1275 feel like a 2.0" with an SC may be true, but with a turbo, it can be more like a 3.0. And don't believe all the stories about turbo cars being a pain because boost takes time to build. Mine makes boost from 2k and full at 2800. I've had people drive my car and say how like a 'normal' car it is to drive.

[nafnaforiginal12]

Any one know the difference in lag between the T2, T2.5 and the gt1752?

[Wil_h]

Lag is a confusing term. Once on boost they will have minimal lag.

I presume what you are taliking about is boost threshold, i.e. the point in the rev range where some or full boost is made.

It depends on a lot of things, engine cc, CR, cam profile. Also, T2 and T25 are generic terms for a model of turbo charger, they come in lots of different sizes.

If you use a T2 with an exhaust A/R of 0.35 and a compressor A/R of 0.48 then it will be like a suupercharger on a 1275 or larger, and you'll get boost at 2k on a 998. If you use a GT1752 on a 1275 you'll make a couple of psi at 2k, then rull boost a little over 3k. I have no info on any T25s.

[nafnaforiginal12]

ok, a little more complex than i thought then. hehe

[mini13]

If you want to stay with the a std gearbox then you'll need to stay below about 150hp to keep it reliable, any more than that and you need to be looking at a straight cut box.

what pistons are in your engine now? if they are decent ones and they havent done too many miles then you may as well stay with them, and maybe get them dished out to get the compression where it needs to be,

you'd be best changing that cam for somthing a bit more turbo orientated, or for a standard cam, apart from that you can use what you have, you dont really need anything fancy for a turbo lump, just focus on the pistons, compression ratio and cam.

I'd sugest the GT1752 as its well proven and a more modern turbo than the t2, 2.5, 3 ect. plus mirage do manifolds to fit the 17's now, plus the mirage should fit with a non turbo inlet manifold.

the only other area you might need to look at is the clutch, but I'd say run the turbo one you have then adress it down the line if you get problems with it slipping,

[nafnaforiginal12]

cheers for the advice. i don't know what pistons are in at the moment but i might just leave it as a 1293 and then just rebore when it wears as i'm not planning to get rid of the car... EVER. lol
I've seen the mirage manifolds and they look good.

Just been out in a friends renault 5 turbo which has the t2 turbo i think. it's really nippy, a good argument FOR getting a turbo

[ANON]

i built a few turbo minis years ago, have owned all sorts of turbo charged cars from reno 5's to audi quattros. have been driving a supercharged jag for a few months now and i'd say for a small engine i would go down the route of supercharger.

[nafnaforiginal12]

Why's that just out of interest?

[ANON]

more oomph straight away is the main reason, the worst thing with a high boost turbot is keeping it on boost.
i would try to go for a twin screw charger though over a roots charger.

[Wil_h]

more oomph straight away is the main reason, the worst thing with a high boost turbot is keeping it on boost.
i would try to go for a twin screw charger though over a roots charger.

I've built and run 4 a-series powered minis, and used 6 different turbos. Not once have I ever thought "where is my boost". The only one that has a very high boost threshold is the race car; but this is low geared and as a race car is always at speed. It would not make a nice road car.

But all my road cars drive perfectly, you are never waiting for boost. and the key to this is good, cam, CR and turbo choice.

I personally think the opposite about SCs and engine size. i.e. a larger engine is abetter idea where less % of the engine power is spent spinning the SC.

[nafnaforiginal12]

So, what would you recommend with a GT1752 turbo if i wanted high power but the car will always be on the road and probably not on the track, also reliability becasue it's an everyday car:

CR
Cam
Bore Size & Pistons


Also with turbo's you get to have nice big shiny silicone hoses and a big shiny intercooler

Edited by nafnaforiginal12, 28 November 2011 - 09:19 AM.

[Wil_h]

CR 8.5:1
Cam - MG metro (non turbo) KC500, 274, 266 or Avonbar PH2. (in order of my preferance)
I'd go with a +20 ovebore.
Pistons Omegas

[nafnaforiginal12]

Oky Doky, is +20 overbore 1293cc?

Any idea what sort of power that would give?

Would SC Typhoon ecu be good with that?

Thanks

[Wil_h]

If you are planning a wet manifold injection system yes. If you are planning on some fancy port injection it won't do it.

Yes +20 is 1293

If using the SC kit with wet manifold, I'd keep boost sensible, say 15psi. But this should still give an easy 150 to 170bhp depending on your head and IC.