Anyone know Turbonese?

[lilredmachine]

My Bandit has been reliably churning out nearly, if not over 200 rwhp for 5 years now. I know this because it's 1/4 mile time has not dropped and every year it gets the compression test which invariably reveals 155 psi across the barrels. It's heavy old lump and even with a 6" stretch it isn't the longest thing in the world, it's only about 2.5 inches longer than a Hayabusa. It will still eat and spit out most things with a numberplate. However, last year I was racing a 1299 Panigale, I was out about 50 foot on him, missed a shift and he actually started to catch me a bit, nearly pulling level by the finish. The outrage! Makes sense, it has nearly 200 brake, is around 60-70 kgs lighter and is somewhat aerodynamic compared to the brick-for-a-face Bandit, but still, I didn't like it.

I want to increase the boost. However there is an issue which has always been present, known about and ignored with my Bandit, the turbo pressure is unknown. I know it produced 210rwhp on 6psi, and 185 on 5psi, but that was the last time it was dyno'd and it was left on 5 psi as it was standard length. It still wheelied almost uncontrollably in 4th with the lesser power. I know that potential is in there but I now need to extract it. The picture below should explain all:

https://s21.postimg.org/fa249c193/20265084_10155557335473485_6301832054489333651_n.jpg

And herein lies the problem...

It runs an external wastegate. About a year ago I purchased a 7psi spring for the wastegate, and upon going to fit it I discovered that the wastegate had 2 springs in it. The larger spring (on the left) made the 7psi spring I had purchased look like a biro spring. The smaller diameter spring (on the right) was the other spring in there. The spring in the middle is a 12.5psi spring for the same wastegate. I would estimate that the spring on the left (the one that was originally fitted) is a 10ish psi spring based on the length, taking both the 7 and 12.5psi spring as extremes. So it had a 10psi spring, along with another unknown spring to increase the load on the wastegate. Indeed upon fitting the 7psi spring on it's own it proceeded to do absolutely bugger all on boost.

To further the mystery, I have a boost gauge fitted. It's a cheap shit gauge that always used to read about 0.8bar (about 12psi) of pressure at max boost. I figured this was impossible as the bike was supposed to run 5psi and put it down to a hyperactive gauge. However on fitting the 7psi spring, it showed about 0.5 bar, which is actually around 7psi. So the gauge is surprisingly accurate, and is plumbed directly into the feed line for the wastegate, so should be measuring wastegate pressure signal. I'll now go over the specifics:

This bike is a stock motor with a fancy locking clutch hub. Stock Compression ratio, stock timing, the lot. I know it is producing about the power that the dyno sheet suggests as it is a steel framed porker coming in at about 250kg yet runs a 10 flat quarter. Common knowledge of boosting such a motor is:

8psi max if you are pushing your luck on short pulls on pump fuel, circa 250hp.

10 psi max if you are running race fuel, prepared to rebuild the motor and taking your chances, circa 300hp.

10 psi+ race fuel, built motor and billet carb tops as the boost will push the plastic caps over the screws retaining them.

So my question to anyone with experience of building turbo stuff is how the fuck is it reading that much boost and why does it need huge spring load to make very little boost?

Does it have a huge boost leak? If so, why does it read 0.8bar on the gauge off the wastegate pressure line?

I was going to fuck about with making shims to preload the springs to lift boost slightly, but the 12.5 psi spring is 4mm longer so have put that in with the little one for now, will do some gentle boosting to see where the boost pressure sits.

Edit: Wastegates work on spring preload. As I understand it, all the springs for a given wastegate are pretty much the same spring rate as that governs how fast the wastegate lifts once cracked (I.e 2mm per 0.25psi for example). The main difference appears to be the length of the spring, so for example a 7 psi spring will be 100mm long when uncompressed and a 12 psi spring will be 110mm uncompressed. They will most likely be the same spring rate. Hence my original Ida of making 1mm shims to run under the cap to preload the spring to give fine boost control.

I know it's a crappy Chinese built wastegate, but it has always functioned fine, I purchased a new 7psi one to replace the old rather than just change the spring as it's a good idea to either rebuild or replace every now and then. A sticky wastegate can end in a blown motor afterall. However on fitting the 7psi wastegate it had bugger all performance, so began this saga!
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Bikes: too many, too much for one man to maintain anyway.

[Pete.]

Having two springs is normal. Tial do a colour chart for big and small and mixing them just adds the pressure together.

I just pipe some regulated pressure into the gate and observe the pressure it opens at.

BTW where are you taking your boost pressure readings from? Direct off the plenum is best.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[lilredmachine]

Cheers Pete,

Boost reading is being taken from the Wastegate pressure line, plumbed in about 6 inches under the plenum.

I assumed that some wastegates use 2 springs for whatever reason, however the one I purchased to replace (same supplier, same 38mm wastegate) @7psi came with one spring, and indeed read at 7psi on the boost gauge. It just felt like it had no bollocks. Popped the original springs in and read 12ish psi and had the same performance as before.

I have a basic understanding of how it should work, it just seems like this isn't following it. I.e the boost it appears to be running should turn the motor to slag.
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Bikes: too many, too much for one man to maintain anyway.

[Pete.]

[lilredmachine]

Ah, I haven't been clear enough.

It has always read 12psi ever since it was built. I assumed it was a cheap shit boost gauge. I bought a brand new wastegate advertised as 7psi, fitted it after checking it had been built properly, it boosted to 7psi on the gauge but it had no performance compared to the old wastegate. I put the old springs into the new wastegate and I had the old performance back, but with the new wastegate housing, again showing 12psi at max boost.

What I'm getting at is that this bike appears to need to show 12psi on the gauge to boost at 5psi. This phenomena is repeatable on different wastegates. The gauge is relatively accurate. I want to adjust the boost but have an issue where I cannot accurately do a spring upgrade as my system does not appear to adhere to the conventional norms. I don't want to reduce the motor to a 1200 single cylinder, but I want a wee bit more poke, which should be easy as it is at a relatively low boost pressure at the moment.

Unfortunately the rather intriguing boost pressure and selection of springs adorning my wastegate makes that very difficult. I was hoping someone could say 'oh, I've had that before, you need to XYZ' etc.
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Bikes: too many, too much for one man to maintain anyway.

[Hong Kong Phooey]

I'm making the leap of faith that this is a 'simple' setup - carbs, no ECU / MAF metering or lambda/exhaust gas temperature probes.

Boost level is not necessarily how much air is flowing. There may be inlet restriction, or as mentioned already (and more common) a boost leak. PSI measurements are a useful reference but are not the final verdict. Have you done a boost leak test?

Given ideal fuelling, 12psi of hot air is not going to deliver as big a bang as 12psi cold air.
Similarly 12psi via a 1" inlet is bugger-all flow compared to 12psi in a 2" diameter inlet.

You're bum-ometer dyno is probably measuring torque, not bhp. Meaning your mid range might be great but may be losing out top end. Also, missing a gear can lose you a lot of distance on the 'track' / road

I'd probably want to get it dyno'd with air-fuel ratio plotted too. Exhaust gas temps can be calculated, but if there's a bung available I'd use it.

In my experience spring rate changes with the higher rate actuators, they wind using thicker wire stocks. Preload controls the crack open pressure not the rate. I think the internal preload is set higher with the longer springs. It might crack at 5psi, but not be fully open until 21psi with a higher rate spring.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[lilredmachine]

Cheers Phooey,

Yes you are correct it's a simple/dumb setup that runs off wastegate pressure alone with no A/F measurement, maf etc.

This is why I'm trying to eek it up without exploderising it. I get your reasoning that a larger intake equals more air and less boost needed overall but a bike compared to a car generally has a massive intake area if you take the bore of the carbs/throttlebodies into account. For example a boosted 2.0 honda 4 pot may run through an enlarged throttle body (the pinch point in the setup), say with a 64mm bore, which is less than 2 of the 36mm carbs the bandit has. One thing is, the smallest part of the bandit system is the the charge pipe at 60mm in diameter, so this may be affecting it.

Bike runs standard cams, so it's typical bandit 12 - all mid range. It's a hybrid turbo so it is on boost pretty quick for a bike at 4kish and it's peak power is around 7,500, then it's pretty done by 9k. It was setup on a dyno with comfortable A/F ratios which is why it has lasted a good 5 years on a stock motor. Compared to a sportsbike revving to make power, the torque on this is tarmac rippling the moment it builds boost, but actual peak power is not significantly higher in number than peak torque due to the low revving nature

I'm going to suck it and see, gentle boosting, high octane fuel and octane booster to see where the gauge sits as it builds, hopefully being able to reign it in before it holes a piston if it's too much.

I've never done a boost leak test, however my main suspicion regards the wastegate, but it has acted the same over two of them and tuning around it is easier than dealing with it haha.
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Bikes: too many, too much for one man to maintain anyway.

[Pete.]

Just had a thought, If you up the boost you have to up the fuel pressure by the same amount because every psi of boost is acting against the incoming fuel pressure at the float valve . Are you doing that?
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[lilredmachine]

Run a boost reference malpassi so every psi of boost is matched by a psi of fuel pressure. In theory this should keep the A/F where it should be. It's set to deliver about 6psi of fuel pressure at atmosphere, which is just about what it should be. The idle pressure has to be that or on boost no fuel would be able to enter the carbs as their internal pressure is matched to that of the plenum via the pitot tubes.

The malpassi has a far greater effect on the mixture than the jets in the carb do, it runs 136 mains (compared to my gsx12 that runs 155 mains) as they only really dictate the way the bike transitions from atmosphere to boost. Cranking the malpassi up or down dictates how much fuel is forced through those jets when on boost, controlling the A/F.

I presume there would be a point where those jets become a source of bottleneck, but I think it'll be a fair way up there on boost pressure, outside the durability of a stock motor anyway.
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Bikes: too many, too much for one man to maintain anyway.

[Pete.]

I've not done boosted carbs myself but from listening to the ones that do they report the best results from using near-stock jets and tuning the pitot tube. The diameter of the up-pipe has a large part to plat too, too large is generally a bad thing.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[lilredmachine]

Aye, the pitot tubes are incredibly important to get right. Mine run from the just below the neck of the plenum and run into the carbs through the two breathers between 1 - 2 and 3 - 4. They seem to be calibrated nicely as mine is a somewhat well behaved turbo bike. Apart from being * very* sensitive to carb balancing it exhibits no adverse effects from running boost on the carbs such as flooding.

The diameter and length control the volume of air allowed in and speed with which boost pressures the carbs, when i redid mine i extended them by about 6 inches and it got rid of a little bit of pulse/surge i was getting as the bike was building boost. I figured it was pressuring the carbs slightly too aggresively and causing fuel to struggle to enter the carbs until the malpassi caught up.

Little stuff like that is why people are scared of boosting carbs, but done right they can be excellent.
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Bikes: too many, too much for one man to maintain anyway.