View Full Version : Turbos For a 250cc engine
Booma
10-30-2008, 06:53 AM
do any of you guys know what turbo you could run on a 250cc motorcycle engine??
all i can seem to find at the mo thats even remotely small enough is a garrett gt12, but even this suggests a displacement of .4 - 1.2L.
any ideas???
cheers http://fsae.com/groupee_common/emoticons/icon_smile.gif
Booma
10-30-2008, 06:53 AM
do any of you guys know what turbo you could run on a 250cc motorcycle engine??
all i can seem to find at the mo thats even remotely small enough is a garrett gt12, but even this suggests a displacement of .4 - 1.2L.
any ideas???
cheers http://fsae.com/groupee_common/emoticons/icon_smile.gif
Mikey Antonakakis
10-30-2008, 01:17 PM
Just blow into the intake with your mouth!
Superfast Matt McCoy
10-30-2008, 01:17 PM
http://www.geocities.com/buddfab/buddfab3
That guy runs a 50cc engine with a turbo. he might be able to help you if you can find his contact info. Last time I talked to him he said the turbo was too big for him. might be better suited for a 250
Pete M
11-01-2008, 09:18 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Booma:
all i can seem to find at the mo thats even remotely small enough is a garrett gt12, but even this suggests a displacement of .4 - 1.2L.
</div></BLOCKQUOTE>
.4L with what maximum revs? If you're talking a 250 cc engine reving to 19,000 odd rpm, i don't think you can just take the garrett displacement guide as a given. Take the compressor map and plot some points on it, you may find that the turbo isn't as radically oversized as you think (although it probably won't do much until north of 12 grand).
Not saying you shouldn't look at smaller turbos, just saying look at it a bit more scientifically.
VFR750R
11-01-2008, 11:26 AM
Well everyone is limited to the same size restrictor so airflow is the same, so turbo size will more or less be the same as what turbos 600cc teams are using. And gt12's do fine at higher pressure ratios which you'll probably be using with such a small engine.
Chris Lane
11-02-2008, 12:35 AM
What about a turbo from a Suzuki Cappucino? From memory they were REALLY small.
Wesley
11-02-2008, 02:28 PM
You might talk to someone from UTA, they ran a turbo 250 way back when, and the thing still hauls ass.
L B0MB
11-02-2008, 04:50 PM
i read somewhere about single cylinders having issues with spooling turbos due to the large surges of exhaust gas coming from one cylinder as opposed to smaller bursts from multiple cylinders... may have been in the WATARD engine overview
also running 2x the standard torque may tend to smash out gears in the gearbox...
VFR750R
11-02-2008, 05:42 PM
lewis, the engine they are probably referring too is one of the various 250cc 4 cylinder engines only sold in japan.
The commonly used one is the Honda CBR250
I think even the most diehard fly-weight car fans would find little interest in a 250cc single; NA or FI.
Good point about the transmission, even some 600cc 4 cylinder engines can have tranny problems when attached to two 6" slicks.
Grant Mahler
11-02-2008, 06:56 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by lewis:
i read somewhere about single cylinders having issues with spooling turbos due to the large surges of exhaust gas coming from one cylinder as opposed to smaller bursts from multiple cylinders... may have been in the WATARD engine overview </div></BLOCKQUOTE>
My understanding was actually the opposite. I understood that the irregularity of flow at a certain total flowrate meant that the hot side was spun up a little higher during the pulse from the single vs the quasi-steady flow from a 4-cyl. As a result of inertia of the mechanical system after the pulse, the single could potentially spool faster. I don't remember any results (though I read all of Attard's thesis) but they may have been in there and I may have completely misunderstood.
Wesley
11-02-2008, 07:02 PM
No, the Wattard was designed with an exhaust plenum for exactly that purpose - if you have high force gas impingement, not only can it erode the turbines, but it is also less effective than a more regular flow - think area under the pressure curve.
Grant Mahler
11-02-2008, 07:37 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wesley:
No, the Wattard was designed with an exhaust plenum for exactly that purpose - if you have high force gas impingement, not only can it erode the turbines, but it is also less effective than a more regular flow - think area under the pressure curve. </div></BLOCKQUOTE>
I'll admit, looking at page 162 of his thesis (page 212 of the PDF) I am a bit confused. In the middle paragraph of that page he appears to extol the virtues of unequal pulsing. I agree with you in that the result of his simulations suggests that a constant pressure system yields more torque and power. I guess I need to read it again.
Any insights to guide me?
Edit: I think my misunderstanding was a matter of words. I believe he is referring to using unequal runner lengths to provide a constant pressure to mitigate the effects of non-constant pressure generated by the (unusual) firing order of his engine. In this case unequal pulse is referring to the pulse length of the runner, and not the firing of the engine.
VFR750R
11-02-2008, 08:32 PM
Pulses can be taken advantage of with split turbine housings. The idea is to keep them more or less separate all the way to the turbine wheel maintaining their energy, which will help spool the turbo. But when you think about it, the turbine is being constantly hit by at least one 'pulse'. A single will pulse the wheel but then there will be a lapse 3 times longer then the pulse before the next pulse.
The second thing to consider is the intake. With a single the engine is pulling a large 'gulp' on very spaced intervals but the turbo is more or less moving a constant flow rate. This may cause intermitent surge conditions with small intake manifold volumes as the intake valve acts like a throttle that is being closed for 3/4s of the time. The benefit being the turbo will draw constantly on the restrictor, but you'll have to have a very large intake manifold (which you'd have anyways with a single pulling from a restictor).
Kirk Feldkamp
11-03-2008, 04:47 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Booma:
do any of you guys know what turbo you could run on a 250cc motorcycle engine??
all i can seem to find at the mo thats even remotely small enough is a garrett gt12, but even this suggests a displacement of .4 - 1.2L.
any ideas???
cheers http://fsae.com/groupee_common/emoticons/icon_smile.gif </div></BLOCKQUOTE>
IHI makes pretty much the smallest turbos you're going to find available. I think I might have the maps for the RHB3 or RHB4 at home somewhere. As has been mentioned, not all 250's are made equal. If you're talking about a turdly parallel twin EX250 or something, that's one thing... but if it's a little demon CBR250, then the match is quite different. You also didn't mention what the application is (street, fsae, salt flats, etc), so it's kinda hard to tell you much other than to check out the IHI's.
-Kirk
VFR750R
11-03-2008, 09:14 PM
i have seen compressor maps that show the turbo would choke before a 19mm restrictor. I can't imagine why you would want that unless it isn't for fsae.
Kirk Feldkamp
11-04-2008, 11:49 AM
I agree it doesn't make too much sense, but perhaps it's because a lower performance 250 would probably not get a GT12 (or similarly sized turbo) to get into a decent operating region until close to redline? Hard to say without any more information.
-Kirk
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