Stephtell Posted September 25, 2015 Posted September 25, 2015 Goodmorning, I've a draw though bike that runs great on boost, 285 BHP at the rearwheel so fairly nippy.However, off boost it's not so good and part of that, in my opinion, is the fact that the plenum is rather small. So, I'd like to fit a larger one BUT due to space restrictions I can't just fit something larger. It'll have to be bigger on side than the other to get enough volume but I'm wondering if that's gonna harm the engine because of unequal airflow?What I mean is that it will be (for example) 1" deep on the left side (where the turbo is in the way) and 2" at the right side where there's more space.That's pretty much the only way I can increase plenum volume so....Cheers for the advice! Quote
vizman Posted September 25, 2015 Posted September 25, 2015 bike specs?i wouldn't increase plenum volume on a d/t if you're making 285 on boost... Quote
Gixer1460 Posted September 25, 2015 Posted September 25, 2015 Its the nature of the beast! Carb'd draw through,s are never pretty low down off boost - having a carb a mile away from the valves with gas having to follow a tortuous route to the cylinders doesn't help........add in low gas speed at low throttle openings = nasty. Volume in the plenum is what you don't need ! If you want low end either hop up the compression and use less boost overall or change the turbo to boost earlier which will also compromise the top numbers! You can't have it all! 1 Quote
Stephtell Posted September 25, 2015 Author Posted September 25, 2015 Quick specs (full specs and pics in a month or so when I open a proper topic for the project) 1206 cc 10:1Turbonetics T4/3 hybridS&S Super D carb with thunderjet285 BHP at the rear wheel, 212,3 NM at the rear wheel I know the fuel doesn't atomize very well on a draw through but I was thinking the available airvolume off-boost might be too small for the engine...?I'm thinking of fitting a MIkuni HSR45/48 with enlarged floatbowl as that is a much more sophisticated carb then the S&S (5 versus 3 carb areas to tune with much crisper response, atleast on N/A engines) Quote
Blower1 Posted September 25, 2015 Posted September 25, 2015 If you want a crispier throttle response, you should make the plenum volume smaller.Mikuni HSR carbs are far more better than S&S. S&S carbas are made for Harley Parkinsons 2 Quote
Leblowski Posted September 25, 2015 Posted September 25, 2015 (edited) Let me guess you bought Pascals bike right ?going back to a HSR wil make drivability better but if you install a HSR you wil not be able to get in enough fuel too reach the 285 bhp it gives now. Not even when you install a larger floatbowlI spoke to Sean from Bigg CC about this he told me that he had issues with this on woodys kat they tried upping fuel pressure and tried using rising rate regs but that started pissing all over the carb so that did not work he told me they used a shot of NOS too take over the finish if i recall correctly.Thats the reason that Pascal installed a S & SI had a bike for a couple of years with the same design as your draw through set up cause i copied GJG's design.My bike had a smaller turbo though. Edited September 25, 2015 by Leblowski Quote
Phill106 Posted September 25, 2015 Posted September 25, 2015 @Stephtell Sorry but what turbo is it? A T3/T4 hybrid to me (coming from my skyline background) just means the exhaust housing or flange has been swopped. What actual turbo is it? Quote
Stephtell Posted September 26, 2015 Author Posted September 26, 2015 Errr....the make is Turbonetics, T4 blowerside, T3 exhaust side but the actual name of the turbo? Fuck knows.... Quote
Phill106 Posted September 26, 2015 Posted September 26, 2015 (edited) Errr....the make is Turbonetics, T4 blowerside, T3 exhaust side but the actual name of the turbo? Fuck knows....I'm not getting at you, but, it's kind of important to know what you've got before trying to improve on what sounds like something quite highly tuned. If I were you I'd find the Id plate and number and then phone turbonetics to find out what the .ar is etc. They also may have suggestion on how to improve the response times and plenum sizes that the turbo prefers. Edited September 26, 2015 by Phill106 Quote
Sweary Bob Posted September 27, 2015 Posted September 27, 2015 Super D with a Thunder jet sounds too big for a 1206, always going to be a bit "Boggy" at low revs. Might be better with a Super E and Thunder jet, but you might sacrifice some top end. Could be worth a try. Quote
Stephtell Posted September 27, 2015 Author Posted September 27, 2015 It's not actually THAT bad...but it leaves somewhat to be desired... One point of attention is heat: I can feel the plenum heat up significantly which won't do it any favours so that will be adressed shortly.Can anybody tell me WHY they think the plenum should stay small?I think that, as long as the distance between the butterfly and the intake valves doesn't change, a larger airvolume would indeed aid off boost throttle response... Quote
Gixer1460 Posted September 27, 2015 Posted September 27, 2015 @285hp you must be running 18-20lbs of boost? thats where your heat is coming from and dealing with it in a draw through will always pose problems!Think of the inlet tract you have to deal with - carb with moderately low gas speed and not the best atomisation known, it then gets centrifuged through the turbo compressor whilst increasing its pressure to blow into the plenum where it has to fill the volume and also flow left or right, then do another 90 degree turn into the head inlets and the cylinders. Changing plenum cross section or volume by (say) double will reduce airspeed / pressure by a factor of 4! This volume needs to be filled and re-pressurised and worst of all, the drop in airspeed allows fuel drop out so the mixture goes lean then massively rich as the dropped fuel is re-introduced to the airstream as its speed picks up.If you want bottom end torque improvements you need to spool the turbo faster or earlier whilst keeping the inlet tract cross section relatively constant. If this was a blow through, the bigger volume will have reduced consequence - big up pipes, big intercooler volumes and big plenums are just carrying plain / pressurised air, all regulated pretty much at the end of the inlet tract. Quote
Stephtell Posted September 28, 2015 Author Posted September 28, 2015 Good explanation that, thanks! As for heat: I've a massive blower that can produce the boost relatively easily, so heat not so much of an issue.However, radiant heat from the turbine is! I checked this, deffo coming from the turbine so I will fit reflective foil on the plenum to keep radiant heat out and will fit a turbo blanket as well.Don't get me wrong: it runs great, docile enough around town even though it's a bit of a pig off boost due to running very rich, and it's very quick up top as well (as in: fuck me, it's quick!!) but I'm just looking to improve slightly here and there to make it an even better package for road use. Quote
Gixer1460 Posted September 28, 2015 Posted September 28, 2015 The turbine blanket will certainly help as would ceramic coating the housing first then blanket on top - heat drives a turbo so it may help spool as well. Quote
Stephtell Posted September 28, 2015 Author Posted September 28, 2015 Hence my blanket idea...coating is an idea but I don't fancy taking the turbo apart just yet... Quote
Constant-VCF Posted October 12, 2015 Posted October 12, 2015 Nitrous has been know to spoon up turbos in double quick time. I scooped up an old Edelbrock spray bar that fits in between my HSR42 and Rayjay intake.I've seen guys use a single fogger too. I've seen it where guys have foggers in the turbo inlet before the compressor wheel to cool down the intake but have no knowledge of this being beneficial. 1 Quote
Speedfreak Posted October 20, 2015 Posted October 20, 2015 Hi, can anyone tell me what to do about overflow pipes on a Mikuni CV 40 carb ramp? Just leave them like they are on a non-turbo configuration or connect the pair together with rubber tubing or "inject" to them the pressure coming from plenum? Quote
Captain Chaos Posted October 21, 2015 Posted October 21, 2015 connect them to the plenum/pitot tube. The float bowls need boost pressure. Quote
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