Draw ( suck) through turbo??

OK guys - I'm looking for a draw through turbo for my KZ750. Don't even try to convince me blow through / injection is better !!! I'm going stone age here - SU carb and as few electronics as possible.

I know I need a turbo with carbon seals, or convert a dynamic seal unit. Not all that plentiful, especially on my meagre budget. A K03-50 ( Audi / VW ) has been suggested.

Why you may ask ??? A result of a late night telephone conversation with the main man over in the KZ forum , the availability of a good spare engine and a desire to go out with a flourish. There wasn't even any alcohol involved !

Plan is to use the part built "Tangerine Dream" Flat Tracker as a base and get it finished in time for Glemseck ( Germany ) this September.

I have all the relevant bits - clip-ons, rear sets, etc. Think mild street / strip drag bike. Initial plan was for a blower - but not enough time to sort out the packaging / drive etc, so it has to be a turbo. ( maybe a whiff of nitrous? ).

I'll be calling in as many mate's rates, favours etc as I can get away with to get it done in time.

All feedback, advice, encouragement gratefully received.

I won't elaborate on the reasons behind the decision - but it has to be done.

I believe this is a 750 twin, rather than the four, the only twin cylinder factory turbos I know of were the Honda CX turbos in the 80s, apparently a twin is difficult to turbo, but in theory a 1600 four cylinder turbo should be about the right size.
Anyway, good luck with it, I think it's going to be tricky to get it running right, even with quite mild boost.

Mild boost .? ........ What's that then !!!!!!

Yes it is the 750 twin - if you're going to go off the wall .....

I'm not looking for a factory turbo bike as a donor. The main issue is getting a unit with as carbon seal.

There are plenty of turbos for choice, even down to being able to size the turbine and compressor ratios.

There were quite a few suitable turbos in the 70's and 80's. - but not very plentiful these days.

Suitable turbos ( ball park ) are available for sub £150 courtesy of Chinabay.

Problem is that all the sellers ( so far ) simply import and flog the units. Ask them if they can fit a carbon seal and - 3 of the 4 I've contacted so far said " What's that"?

Guess you saw my TR1 Turbo build either on here or at VTF. If I were you, I'd get a small and rather common Turbo, which spools up quickly and is rather efficient. Due to the fact that you only have two cylinders instead of four to get that turbo moving a GT1544 out of a small diesel (Vauxhall Vectra is what I am going to use on the Turbo TR1 Mk.2) should be fine up to the power and boost levels where stuff gets expensive pretty fast, i.e. you need forged pistons and other improved internals. Still you should be alright at around 7-8psi.

Another benefit of the GT15: There's carbon seal rebuild kits, which don't cost an arm and a leg and some of the Volkswagen Beetle guys managed to get up to 130-140hp out of a 1600.

I've built a draw-through setup for my TR1, but then failed because the cheap Chinese turbo shat itself. If you're interested you could have the setup as I am going draw-through on the Turbo TR1, mainly because that would open up the option to also make it road legal overhere, which would transform it from a very expensive toy, which is used 3-5 times a year to something I can have some mad fun on back roads.

Cheers,
Greg

A few things I learned tinkering around with an ATP kit for a KZ650.

1] Slide carbs like to freeze up and stick open.
A carb with a butterfly throttle valve is needed.

2] Fuel likes to migrate to the outside of the compressor scroll.
Check out the design of the old turbo intakes for the KZs.
The incoming air/fuel charge hits the back wall, then is distributed to the different cylinders.
This is to reatomize the fuel. A fine wire mesh screen might help also.

And turbos like some plenum volume to smooth out the engine pulses.
This might a problem with a draw thru vs. blow thru. A chamber full of a pressurized
air/fuel mixture could lead to some excitement if ignited. Another option might be to lengthen
the exhaust between the head and the turbo. Seen a you tube video of a XS400 that had the
exhaust run back and then up between the rear tire and swing arm. And mounted the turbo
above the swing arm pivot.


.

Greg, Rex, many thanx for your input - much appreciated.

I've seen your build Greg, currently unable to get back on VTF due to a PC hack last year. I'll check out again. Thanx for the headsup on the Vauxhall turbo.

Can you let me have details of the set up you are replacing ?

Rex I've used a lot of suck through systems ( mechanical supercharger ) and always had good results with SU carbs which I am familiar with.

I'm not looking to build a rocketship here, just a bit of mechanical "what if" and something to exercise the old grey matter.

Keep it coming boys ........

Greg,

Do you have contact details for the GT15 carbon seal supplier ?

Thanx

I´m in for this watching!

Rex,

Missed your point first time round re: plenum.

Yes, I had already looked at some sort of plenum log before the individual carb runners to smooth out the pulses from the twin.

My actual build thread is currently under "Tangerine Dream" which logs the build to date ( Flat Trackers ). So far it's rolling chassis related. That's virtually completed and won't be affected by the addition of the turbo.

I have had a Weber 40 DCOE intake made and I'm considering fabbing up a plenum / log to bolt to it - fed directly by the turbo outlet.

I need to get the turbo I will use so I can check out packaging requirements .

The IHIRHB31 is a cheap and cheerful little turbo that should do nicely on a 750cc twin.

It's possible to replace the dynamic seal with a carbon one as well.

http://www.smbaker.com/sand-rail/manx/rebuild-ihi-rhb5-and-add-carbon-seal

That said, it's possible to maintain a dynamic seal on a turbo if you add an appropriately sized restrictor to your oil lines.

Sonreir™ said:

The IHIRHB31 is a cheap and cheerful little turbo that should do nicely on a 750cc twin.

It's possible to replace the dynamic seal with a carbon one as well.

http://www.smbaker.com/sand-rail/manx/rebuild-ihi-rhb5-and-add-carbon-seal

That said, it's possible to maintain a dynamic seal on a turbo if you add an appropriately sized restrictor to your oil lines.

Click to expand...

Thanx for the headsup, that turbo is not readily available in the UK, but I'll keep my eyes open.

I have the spare engine arriving next month courtesy of KK over on the Lonesome Twin ( KZ750) forum. Then I can get on with mocking everything up. I'll need a turbo unit PDQ as that will be the biggest item to package.

Here you go, mate: http://www.ebay.co.uk/itm/131693989514

It's the same turbo they slap on those Japanese 660cc KEI cars.

Sonreir™ said:

Here you go, mate: http://www.ebay.co.uk/itm/131693989514

It's the same turbo they slap on those Japanese 660cc KEI cars.

Click to expand...

Wow, instant service - thanx.

We ( RAM ) bought a T3 from this same supplier last year for the Oilhead "Scream" project !

I've also been given a used GT15 in good condition FREE by one of the KZ750 boys.

I'm told there's a carbon seal kit available for that model ?

Not sure, sorry. Most folks I know who go with draw through are putting together a drag setup, not a daily rider. Dynamic seals along with an oil restrictor usually does the job.

Sonreir™ said:

Not sure, sorry. Most folks I know who go with draw through are putting together a drag setup, not a daily rider. Dynamic bearings along with an oil restrictor usually does the job.

Click to expand...

Should have explained - the bike is heading towards off road / race and occasional street use. There's another bike ( oh no !! ) in the wings as a daily ride.

As long as you don't mind a larger amount of maintenance, dynamic seals might be the way to go (or possibly test), since they're way more common.

One of the significant problems with a draw through setup is when you chop the throttle after a hard run. The turbo is still sucking hard, but now it's pulling against a closed throttle body and this creates a significant vacuum in the intake (you may want to consider replacing any plastic or rubber intake pieces of significant surface area). In many cases, this is enough to suck oil through the feed lines of the turbo and into the intake. Generally, you just have to worry about fouled plugs and some smoke, but keeping an eye on the oil level within the engine is a good idea, too.

Another option is to go with a hot cam. Lower vacuum at lower RPMs (when the throttle is usually closed).

For what it's worth, Garrett had a few turbos with carbon seals from the factory. Might be worth looking at those? They'll probably be a bit too big for a 750 twin, but could be fun when it's balls to the wall time.

Hey Beachcomber!

beachcomber said:

Greg, Rex, many thanx for your input - much appreciated.

I've seen your build Greg, currently unable to get back on VTF due to a PC hack last year. I'll check out again. Thanx for the headsup on the Vauxhall turbo.

Can you let me have details of the set up you are replacing ?

Click to expand...

It's pretty much the setup you can see in my post on this blog and in the video, all you'd have to do is fit a different flange. For you I'd even part with my 2in1 inlet manifold. The T3 you see in the clip is both Chinese and shot, so it's more use a lawn ornament...

One thing I wanted to comment on Rex's post: You want the plenum to be AS SMALL AS POSSIBLE with a draw-through and if you plan to participate in races (Santa Pod, etc.) you have to have a little blast window, to relieve overpressure from back fires.

beachcomber said:

Greg,

Do you have contact details for the GT15 carbon seal supplier ?

Thanx

Click to expand...

Sent you a PM, with what I know. You may have to poke those dealers with the proverbial stick though as most (except for this one) are pretty clueless and a merely shifting boxes and that's it.

Sonreir™ said:

The IHIRHB31 is a cheap and cheerful little turbo that should do nicely on a 750cc twin.
It's possible to replace the dynamic seal with a carbon one as well.
http://www.smbaker.com/sand-rail/manx/rebuild-ihi-rhb5-and-add-carbon-seal
That said, it's possible to maintain a dynamic seal on a turbo if you add an appropriately sized restrictor to your oil lines.

Click to expand...

The oil-restrictor has got nothing to do with carbon seal or not. Petrol will eventually wash out the oil from the bearing and thus ruin it. It won't happen instantly, but it will happen.

Sonreir™ said:

As long as you don't mind a larger amount of maintenance, dynamic seals might be the way to go (or possibly test), since they're way more common.

One of the significant problems with a draw through setup is when you chop the throttle after a hard run. The turbo is still sucking hard, but now it's pulling against a closed throttle body and this creates a significant vacuum in the intake (you may want to consider replacing any plastic or rubber intake pieces of significant surface area). In many cases, this is enough to suck oil through the feed lines of the turbo and into the intake. Generally, you just have to worry about fouled plugs and some smoke, but keeping an eye on the oil level within the engine is a good idea, too.

Another option is to go with a hot cam. Lower vacuum at lower RPMs (when the throttle is usually closed).

For what it's worth, Garrett had a few turbos with carbon seals from the factory. Might be worth looking at those? They'll probably be a bit too big for a 750 twin, but could be fun when it's balls to the wall time.

Click to expand...

If the turbo is well maintained and carbon sealed, this isn't much of an issue really. A hot cam will do no good for you on a turbo engine, as you basically blowing out the boost through the exhaust valve due to the prolonged overlap.

Unfortunately the few cars that came with carbon-sealed turbos are rarer than hen's teeth and therefore expecting to stumble over a good (as in usable or even just repairable/restorable) is next to non-existant. Fifteen, twenty years back you could have had a lucky moment in a salvage yard somewhere in the darkest Alabama to stumble over a turbo Corvair, but nowadays even these cars are all either gone or restored.

One of the things nobody has mentioned so far: I assume your KZ750-twin is a ball-bearing crank engine, i.e. low-pressure, high-volume oil-pump? If so, be aware that a turbo wants to be fed exactly the other way round: Lots of pressure, but not exactly a lot of oil (hence the afforementioned restrictor). There's two (three) ways to go about this: 1) tap into the stock oil-system, install a restrictor to raise the pressure and cross your fingers, 2) install an external oil-pump (the ones from Honda minibikes can be adapted quite easily with a bit of lathe/mill work and be run from right-side crank bolt. 3) Just tap into the oil-system and watch that turbo die... (which is what most people sadly do)

Hope this is vaguely useful to you.

Cheers,
Greg

P.S.: I am uber-busy at uni this week, so if you have any pressing matters feel free to send me a PM, as I really should be learning and not enjoying this turbo-build.

Greg / Sonreir,

Thanx for your interest / input.

Greg, can you pm me with a price for your old set up please.

I have a GT15 arriving Friday, but I can easily get T3 carbon seal kits ( UK ) for a very good price.

A guy on the KZ750 forum has made an upgraded oil pump set up by piggy backing the OEM system. I'm trying to track him down. External pump you mentioned would be a plan b. My big problem is lack of facilities for machining / fabrication work.

One of the "hot tips" for the KZ guys is to fit an exhaust cam on the inlet - higher lift but same duration.

Thanx to everyone for taking the time to share.

Err, my setup is intended for a Virago/XV? So not too sure that this will help you?

Cheers,
Greg

der_nanno said:

A hot cam will do no good for you on a turbo engine, as you basically blowing out the boost through the exhaust valve due to the prolonged overlap.

Click to expand...

This has been proven false. It's a commonly held belief that this is true, but it comes from inductive thinking of days gone by rather than any empirical tests. All your boost isn't going out of the exhaust valves because unlike a naturally aspirated engine, a turbo engine has a pressurized exhaust manifold. And because turbos are rarely capable of producing more pressure in the intake than they're receiving in the exhaust, your boost is going nowhere. When you look at a dyno chart, a hot cam on a turbo engine behaves in very much the same way as on a naturally aspirated lump.