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davecara

Idiots guide to turbos

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Is there such a thing? Not the principles of turbo charging itself, that's pretty straightforward but more the difference in the varying turbos out there and what differing turbine sizes mean in relation to performance etc?

 

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......there are some " books"  that could probably get you closer to your goal.....Corky Bell / Jeff Hartman / Jay K Miller .....to name a few .....but a straight on handbook for numpties...no .

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.....but perhaps we can get all the "heads"  of forced induction to all come together and make our own "idiots guide" .

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40 minutes ago, no class said:

.....but perhaps we can get all the "heads"  of forced induction to all come together and make our own "idiots guide" .

That's more like what i was aiming at! 

Of course some people have years and £££'s of development in their engines so I would never expect someone to hand all the info out on a plate, but some info on how to read compressor maps properly and calculate engine CR and VE would be useful and wouldn't go outside this forum :)

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Insert biggest turbo possible - turn it up till it goes bang - rebuild and turn it up just shy of where it went bang -  repeat for rest of life.

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General rule of thumb, if it works on a 2 litre petrol car it will work on a 1000-1300cc bike that revs roughly twice as high and has similar gas flow. Power output will be somewhere similar to the car.

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from my exploits with tuning old saabs = two routes

1) sledge hammer approach - boost is king = big bang, good for wahoo effect in a straight line - pain in the arse to manage otherwise and typically loses much bang  with heat build after a few slugs

2) jeweler's screw driver approach - use as little boost as possible and tune the cams / ignition timing / fuel injection to suite = a smoother more turbine effect that will deliver with controllable demand all day long - get this right and you can have more top end HP with less psi ( ref reading a turbo chart - look to the RH side - you can see how once you get to the limits more boost doesn't provide more HP so it just spins the compressor faster creating heat ) - - other note is cam timing can make a noticeable effect on the initial rpm you get usable boost at a price - time for early boost = loose top end // time for top end and you induce more lag

experience with the saab turbo's

the Garrett GT25 will marginally beat the Mitsubishi TD04 on early spool, the TD04 will marginally beat the GT25 on top end - std the GT will see about 280hp, the TD04 about 300 ( note you can find the turbo specs for these cars via SAAB forums etc.. but look for the 9000 tdo4 versus the 9-5 it has a larger turbine

if you want to max these out, fit a gt28 compressor to the TDo4 - it works much better than the mitsubishi 19T upgrade - this is what the left hand side of the graph shows if you compare a gt28 to a 19T, the garrett compressor delivers as it spools up, the 19T struggles until its up to speed - with the GT28 compressor on a SAAB td04 + cam timing shift bias to top end I got over 360HP (1.3bar boost )

overall = for the older car turbo's - from my experience, the Garrett GT25 is a very good all rounder with early spool, easy to tune and forgiving when its running outside optimum - the TD04 will give you a bit more, if you can use it but it takes a bit more work to find it and its more focussed ref rpm range

 

 

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the other bit - not often discussed but important is the turbo body size ( the throat ) - one to watch out for when you go looking - bigger CC engines may have the same compressor / turbine wheels but have a bigger throat ( housing )  - go small on this and you'll get improved early spool, go too small and you'll choke top end, conversely go too big and you'll be waiting all day for spool up = previous ref: to +/- 2litre car engine

a small throat with a bit of porting to max the flow to the waste gate is a good balance i.e. so you can bleed past the turbine as the rpm rises to reduce choking = this leads to another tuning tweak = how and where you introduce the WG flow into the ex pipe downstream of the turbine exit - get this wrong and the two flows clash causing back pressure, get it right and the WG flow can help scavenge ( lower the turbine downstream exit pressure )

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Reckon a TD05 off a Mitsubishi EVO4 would be a bit big then? 

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On 8/14/2018 at 5:57 AM, davecara said:

Reckon a TD05 off a Mitsubishi EVO4 would be a bit big then? 

I had one from an EVO 3, that was too big, boost came in at about 4500rpm, and full boost just after 5000rpm.

Advantage was that at normal speeds you never had to worry about that the turbo spooled up when you don't want/expect it.

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On 8/13/2018 at 8:57 PM, davecara said:

Reckon a TD05 off a Mitsubishi EVO4 would be a bit big then? 

Depends on engine size - mine is sufficient for it to work well.

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3 hours ago, Reinhoud said:

I had one from an EVO 3, that was too big, boost came in at about 4500rpm, and full boost just after 5000rpm.

Advantage was that at normal speeds you never had to worry about that the turbo spooled up when you don't want/expect it.

Why would you have a turbo and not want it to be spooled up? Lol

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Cos some of us mere mortals don't want 100+hp worth of boost to arrive mid corner !

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On 8/15/2018 at 10:22 PM, MeanBean49 said:

Why would you have a turbo and not want it to be spooled up? Lol

Where I live a straight stretch of road is rare, and sometimes it's alright not to worry about a lot of power kicking in. ;)

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3 hours ago, Reinhoud said:

Where I live a straight stretch of road is rare, and sometimes it's alright not to worry about a lot of power kicking in. ;)

If its setup well you can keep the turbo spooled up and driving irrelevant of how much you open the throttle. Problem is the transition between off boost and on.

I live in lincolnshire, we dont have a lot of straights, i do trackdays as well. The trick to going quick is not letting it spool down 

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Agree with Reinhoud and Gixer1460; I started with a small turbo as this would spool up nice and early. I soon found out I was fighting the bike all the time, espesh coming out of corners, when just running around town with my buddies. Wheelie/wheelspin (and clutchslip!) madness...

I've now a TD05-16G (Subaru Impreza) and it complements the nice torquey low-down grunt of the 1195cc EFi motor, starting to build boost at 4500rpm. Pootle around when you want, get big wallops of power when you want.

Edited by bruteforce
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