ben wight

FLYINLoW · backyard mechanic Joined: 08 Oct 2001 Posts: 924

hey just a quick qs
ive had a 2litre twincam rebuilt im looking at running fuel injected t03 front mount etc etc but ive had an offer for now that includes a t04 turbo with carbon seal and a single su carby on a manifold to suit twincam basically everything ready to bolt on for a bit of fun now till i have finished my cooler and piping and have enough money for a decent haltech etc. basically in your opinion will my engine which is a fresh twincam block that has been resleeved, with polished and shotpeened rods and crank standard pistons, new cams to suit turbo etc etc will this hold up to uncooled forced induction from the draw through setup ??? im not to keen to run huge amounts of boost with this setup it will just give me something to play around with while the rest of the work is carried out.

also how due you regulate and adjust boost pressure with the draw through setup ???
thanks for your help.

QldRobbo · tinkerer Joined: 11 Apr 2002 Posts: 455

One thing I do know, is that turbo'ing a twin cam apparently isn't a great idea... The oil pump in them isn't the best, basically it's good enough for just the engine, but if you go adding a turbo to it, it can put too much on the pump and it doesn't flow enough oil.

Hope you aren't running the standard oil pump.

FLYINLoW · backyard mechanic Joined: 08 Oct 2001 Posts: 924

ok i dunno where you heard that i know of 2 twin cam turbo gems and they both are A) running standard oil pumps with oil coolers and B) are fine with bolt on turbo's.

i cant see how running a turbo on a twin cam can be differant to running one on a singlecam ???? but we will see.....

QldRobbo · tinkerer Joined: 11 Apr 2002 Posts: 455

I think its more the fact that it is easier to get a high volume oil pump for a SOHC than a DOHC, so if you were to turbo a SOHC you'd want to get a high volume pump. And I have no doubt it would work, it's just you don't really know how well it works till it fails and when it fails.

QldRobbo · tinkerer Joined: 11 Apr 2002 Posts: 455

I was told that the oil pump was shit on DOHC's from the bloke I bought my DOHC off of, and I'd heard it a few other places, so I did a search to see if anyone here had heard that before...

http://www.hotgemini.com/cgi-bin/forum2.cgi?action=rp&mesg_id=114580

QldRobbo · tinkerer Joined: 11 Apr 2002 Posts: 455

What's funny is that you replied to that post, which means you must have read it before, which means you would have already heard about the oil pump being crap...

Josh · backyard mechanic Joined: 04 Oct 2001 Posts: 602

Otherwise, turboing a standard G180w twin cam engine will cause problems due to their naturally high compresion ratios; to decompress them requires the fitment of flat top pistons. Also, valve stem sealing can become an issue as they don't use valve stem seals. The valve stems are lubricated by a 'act of God' system which really defies reason, however judging by the rate of wear I get out of a set of sintered brass guides (and they cost a shitload), they obviously aren't getting oil anyways. My point being that the inlets will blow the crankcase full of boost pressure; these engines already have difficulty keeping the dipstick in unless restrained at over 7000 rpm. All my twin cam engines use a spring to retain the dipstick. It's just a harmonic flutter that the rings seem to get at relatively high revs, and pressurise the crankcase as such...

Geminis have valve stem seals dont they? The black teflon ones?

FLYINLoW · backyard mechanic Joined: 08 Oct 2001 Posts: 924

i didnt refer to the oil pump in the previous post i didnt bother reading it i was interested in stock figures of a g200w. i can gather that the information is speculative and ive seen turbo twincams with both oil cooled and water cooled turbos and they do seem to perform well however with the information passed on it would be wise to research possible aftermarket pumps that are available if any ???

Poida · Posted: Wed Oct 08, 2003 2:32 am Post subject: Re: ben wight

Why not look into a dry sump system as an alternative to the supposedly "bad oil pump", particularly if you are planning on a high performance application?

Seems hard to understand how Isuzu's "bullet proof" twin cam engine is unreliable through a faulty oil pump! These really one tough little engine.
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Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

Andrew, there appears to be questions about the oil pump, and valve stem sealing of a twin cam engine. After saying that, i have 'heard' of a few turbo engines making good power.

I am not familiar with the engines, but I think it would be a safe bet that the 'mushroom' type seals as found on gemini heads could be fitted to a twin cam head with some minor machining.

As far as oil pump, the turbo actually uses very little oil in service. Most turbos I have seen have a small orifice in the oil inlet assembly, which reduces the flow to only what is requred to cool and lubricate the bearings. Does your engine have an oil pressure gauge fitted? do you suffer from any oil pressure dramas? Is your pump in good condition? I cant imagine a factory fitted oil pump would have any problems, factory R&D is very good, and the lubrication of the engine is something that is not something that is ever skimped on as far as I know.

As far as pressurising the crankcase, all engines will do this to varying degrees, that is why oil/air seperators or catch cans were invented. I dont know about the ring flutter business, sounds possible, but if so, then every engine on the road should do it, as they all use the same principles of ring end gap, ring top/bottom clearance in the ring grooves, basic ring design, etc.

If you are keen on getting the turbo on, look into getting a proper valve stem seal. If you cannot afford the efi and IC, then I dont see why you shouldn't try the draw through setup. its your car. Get it running and then take it to a dyno workshop and get the mixtures and inlet temps checked at various boost levels, the dyno operator will be able to advise on boost levels, and ignition timing, etc.

for boost control, try searching the net, try www.autospeed.com.au

Ben

FLYINLoW · backyard mechanic Joined: 08 Oct 2001 Posts: 924

hey thanks for the reply the engine is still in pieces parts are slowly being put back together. basically the head has had $600 worth of machine work and new stems etc etc not including custom cams !!! ouch.
the oil pump is next to brand new and im just sourcing a set of new bearings for some other gear before i put the pump back etc etc. basically my father worked for dynamic turbochargers for 17 years and beleives that the turbocharger will not use much more oil if any and that the blow by etc can be reduced by fitting the oil catch can and then plumbing this back into the sump.
the bottom end was resleeved and has brand new rings so in our opinion we should have minimal piston slap, blow by etc etc even with a heavy amount of boost.
the more we think about longevity of the new engine we keep coming to the conclusion that efi intercooled will be worth the wait.