SUCK THROUGH TURBO SETUP QUESTION?

[TURBO TF]

who here has dont a suck through turbo setup?? and of the people who have, how have u sealed the carby?? or hoe have u got the pipe into the top of the carby? i have been told to make an air titgh box around the carby, but also cant see the drama is clamping a hose straight over the top of the carby, whats the easiest way guys?? this is the only thing standing in my way of getting the gemini on the road.

cheers guys
Hayden

[spud]

do you mean blow through? you dont need a airbox with a draw through system

[Mr bayce]

...just thinking the same thing

[TURBO TF]

i might? i dunno, my mate is doing it all for me and he said we need a box to seal the carby, i have heard of people using saucepans or something? if i dont have an airbox what do i do?? does the pipe just go straight into the carby??
whats the best performance wise aswel??

[KIDACID]

get injection, not that hard to set up.

[Gene FJ20DET]

i think your talking about a blow threw set up not a suck threw
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[spud]

saucepan air box? backyard mechanics is fun. dude if it is a suckthrough system the pipe doesnt go into the carby. that is blowthrough

[20PSI TX]

Geez now you tell me.

Have you ever wired up an injection computer?

[TURBO TF]

OK guya noq i understand the differnece between suck through and blow through, thanks heaps... deicsions decisions.... is either one better performance wise?? and by the way... im not injecting it at the moment, dont have the cash

[Gene FJ20DET]

blow threw u can use a cooler, suck threw u cant
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[zzz]

maybe try searching you will get pages of debates
on this subject some usefull some not try this link
i'm feeling very helpfull to day http://www.hotgemini.com/cgi-bin/forum2.cgi
zzz

[MR_GEMI]

to day = today
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[Simmo]

Hey fella's heres a collection of really good posts that others have put on hotgemini over the years about this topic. enjoy, simmo.

Turboing your Gemini.

its not hard to do, just annoying - getting all the manifolds made up and crap like oil lines etc. I sorted out a garrett T3 turbo with an external waste gate and i had a mate make up some extractors for me, would have been easier to have an internal waste gate for the exhaust setup but anyway.. Then i got a brass T piece for the oil lines, where abouts the oil sender unit is on the left hand side of the block, that screws into the top of it and the oil line at the end going to the turbo, and to return it you will probably need to weld a piece of metal hose on your sump so the oil can be easily gravity fed back in. Then it just depends on if you want to run a draw through or blow through carby set up, each have there own advantages.

The draw through you can just get an adapting manifold and clamp a carby (recommend something like a side draft 40 weber) to the turbo but the problem with this is the fuel vapour droplets don’t remain consistent as they have to travel through the compressor and a fair way to the inlet. Also you cant run massive boost as the air gets to hot and will just detonate and you cant run an intercooler or blow off valve as you would have to be pretty stupid to want air/fuel mixture venting into your engine bay.

If you set it up as a blow through then you can have and intercooler and blowoff valve and more precise tuning as far as a carby goes but you also change how the carby has been designed to run by forcing air through it, you can blow the seals out and also crush the floats. And as Dave said you will want (need) to change the head. I heard someone talking about having a whole lot of metal from the pots in their heads shaved out to lower the compression but I don’t know how much you can remove and you will probably need a thick copper head gasket made up to help lower the compression as well – although it would be a hell of a lot better if you had dish tops pistons in anyway. You will probably need to have your dizzy recurved or the advance welded to stop your engine advancing under boost, maybe a nice cam, water injection (or methanol) to assist the motor in not detonating and then you just need an exhaust to suit. Good luck.
- fastgem


nah, the flat tops should be perfectly flat, the dish tops have a.. well dish in them - like taking a big scoop out of the flat tops, then that’s basically what you will have left, which leaves more room in the cylinder thus less compression, also there’s more clearance for your valves so depending on what sort of cam you want to run and the size of your valves you don’t have to worry about the valves hitting the pistons.

Blow through doesn’t need to bet efi but its a whole lot better for fuel efficiency and power. I’m currently running a draw through setup with twin 1 3/4 Su carbs, they take up a fair bit of space and i had to move the battery but i didn’t pay for them so i don’t really care. It was just easy at the time for that setup.

It basically depends on what sort of compression your running and wether or not you run an intercooler as to what the max boost your engine will be able to handle. The colder the air the better. If you have water injection then the water turns to steam, to do this it takes out some of the heat which stops things from detonating. I don’t think you can really run a draw through much over 10-12psi reliably as the air just gets to hot when its compressed, on a cold winter day with water or methanol injection you might be able to squeeze a little more out if you have fairly low compression but if you want to run it that high to get the power then do it properly with an intercooled efi setup, then you will really notice the difference with both fuel and performance.

Few different things you can do with the water injection, if you go the efi get an aftermarket computer that can control it, get a professional unit or make which can be pretty good, the top of the line ones have a computer and solenoid in them that work out how much water to spray in at any stage, or you can go a bodgy DIY one. I just got a nozzle, drilled and tapped it into position just above the manifold intake and then connected a switch up to my accelerator pedal going to a washer bottle full of water that has a small tap on it so I could slightly restrict the flow of water. the switch is only activated pretty much at full throttle, which I thought would have sucked a little at first but i have just adapted my driving style to suit. Was going to install a second unit to work at mid throttle but so I haven’t got around to it yet.

It runs pretty well, haven’t had the car on the dyno yet so I’m not sure what its putting out but I’m fairly happy with the result. The main reason I put a turbo on was I got everything cheep (basically given the whole set up) and was curious to see what would happen, but I really need to go efi. Just be prepared to visit servo’s twice as often.

fastgem

AS a small note, ive built a few carby fed turbo gems, and my last one was a standard compression 1800, mild ported 1800 head, double row timing chain, and everything else was standard including pistons. I had a draw thru setup using a t03 off a rotary, with a side draught 40mm solex off a Toyota. I comfortably ran 15psi boost, no pinging or anything, and i wound the boost up to 22psi on avgas for race day, but this would be way too much for everyday driving as I’m sure the motor would of blown up on this much boost if done regularly. On 15psi it made 155bhp, which is pretty good considering its still essentially a standard motor. Standard they roll between 45 - 50 bhp. I noticed however that I could only rev it to 4500rpm as the carby was too small to flow the amount of air required to run that much boost and it would lean off above that. I recommend at least a 45mm, even if you can find one use a bigger side draught carby.
The only other notes are fuel pump, I used a Holley blue with boost modified reg so that it ran 3psi fuel pressure at idle and under boost increased to anything up to 14psi.
You’ll need to either lock the mechanical fly weights in the dizzy, or fit a rotary boost retard vacuum diaphragm unit, and for your brake booster make sure the vacuum pickup is in front of the turbo, not after, cos on boost youll have no brakes otherwise, plus the fuel getting into the booster cant be real good for it.

By Mark

I am selling blow through carburettor kits, but you'll have to convert to a downdraught DVG style weber, as I haven't finished the niki carby kit yet.
The basic kit includes turbo manifold, aluminium crossover pipe and airbox, rising rate fuel pressure regulator, and high flow efi fuel pump, cutom oil line and adaptors. This kit is about $800, depending on what turbo you want to run, whether it is water cooled, etc.
You can run whatever turbo you want, as long as you select one with integral wastegate. I can supply various different units pretty cheaply too.
You can get more comprehensive kits including every last bolt and hoseclamp, turbo and dump pipe, with complete fitting instructions, but obviously, these are more expensive.
Power depends hugely on what boost your engine can handle, the efficiency of the turbo you choose and what further mods you are willing to do.
Blow through is a far superior setup to draw through because of several reasons including better air/fuel charge distribution, more efficient use of turbo compressor, al lot less air fuel seperation, much easier plumbing and the possiblity easy upgrades like intercooling and blow off valves.
Email me for further details if you're interested.

By Ben Wight

Carby fed turbo’s are very simple. You buy a sidedraught carby, probably a 40mm weber, dellorto, solex etc, because they seem to hold more boost, it should set you back about $150 to $200 at most. The exhaust manifold is a simple 3 inch pipe running a long the side of the head with 4 entrances for the exhaust, and one flange plate for the turbo to mount to. Should cost $200 to $250. A turbo will last with efi seals for a year at least before it needs rekitting, and can be picked up from any jap importers for $250 or so. and inlet pipe is probably $50, being a 2 inch pipe that runs over the tappet cover to a standard inlet manifold with the standard carby removed. use a throttle cable from an Eb falcon(mpi), about $30, mount the carby to the front of the turbo with rubber hose, ie radiator heavy duty hose suitable for fuel. fit a 21/2 inch dump pie to a 21/2 inch exhaust, another $200. No fuel injection required, no intercoolers or blow off valves. Oil feed is taken from the allen key blank offs down next to the oil pressure switch and you have to weld an oil return pipe to the sump. Fit a double row timing chain in for safety - about $100. Buy a Holley Blue fuel pump from the trading post for about $100. Using standard pistons, you can safely run 14psi boost and you will run low 14sec quarters at the minimum. Total bill is about $1200 plus your motor for $500 and you’ve just broken $1500 to beat a wrx consistently. The dizzy has had the flyweights inside locked up. ie/ the mechanical advance has been stopped, so when the timing is set at 10 btdc, you bring the revs up, it doesn’t advance any more. It stays at 10 btdc, therefore eliminating pinging due to timing. Standard compression is about 8.3:1 or something, and I run a boost controlled fuel reg. That means at idle the fuel pressure is 3 psi, but as boost goes above that, a vacuum line increases fuel pressure accordingly ie 10psi boost uses 10psi fuel pressure, and this stops pinging due to lack of fuel. I am not experiencing any pinging on leaded fuel at 14psi boost and I am not running a decompression plate. Look at the pictures of one of mine at http://isuzu.somewhere.net. It’s a blue panel van. Hope this helps.


By Mark


An intercooler is not required, but it will limit the amount of boost you can run do to the air temps rising too high as you push the WRX unit out of its efficiency range.

The engineers certificate is hard to say about, because depending on who you go to, they will tell you what you have to upgrade, and Then you might have to do a full emissions test. I think the certificate itself is around $3-400, whilst the emissions test is close to $800. You obviously have to take care of the bigger brakes, etc, yourself, and then the engineer checks them out.

Like I said, any turbo can be mounted to the manifold. I just design a flange on CAD, get it laser cut, get it welded on, and then I port it for smooth transitional flow.

As far as mods to your engine, it depends alot on how much power you want. If you are happy to run 7psi, then you wont have to change a thing except having a correctly jetted carb, and drop static timing back a few degrees.

Changing the timing curve altogether is more ideal, and will give the best results, but if you are not confident in doing that, a simple drop in static timing will give good results, with a slight drop in low rpm torque.

You should also install a good ignition coil, and run a hotter range of spark plugs with about a 0.75mm gap.

If you want to run more boost, then I recommend a locked dizzy, or recurved timing, and some form of charge cooling. Water/methanol spray is cheap, but is not as reliable and effective as a good intercooler.

posted by Ben Wight on Sun Sep 9 17:19:38 2001 from 203.87.2.13