Author Topic: G40 carb'd turbo  (Read 10420 times)

Offline prankstar2003

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G40 carb'd turbo
« on: June 08, 2011, 07:40:41 pm »
Reet. I'm collecting parts ATM for a carb'd turbo. Currently I have bottom end, Renault 5 turbo carb, intercooler and a few other bits. I know this has been done before, at least I think, can't imagine I'm a pioneer. Anyhow, just wondering what experience other people have or advice etc. If the advice is along the lines of 'don't bother' then take your own advice. I'm aware of the limitations of the set up, and don't hope for injected-turbo outputs. But being as I'm not arsed by electrics, mapping etc, plus this being an exercise in shoestring-blowing (if you like), I'm just after a bit of knowledge. Currently the set up has cost me under £150, so if it goes tita, I've lost little.

So basically, what is required other than what's listed above
Turbo
Piping (including down-pipe)
Dump valve/actuator (if not integrated)
Induction system
G-head
Luck

Not sure what cam to use either. Standard cams, I've heard the gt works beat with a turbo. But a my fuelling won't be as good as injection, will the g40 cam hold it back like it would on a normal turbo? Or would the gt still be better? Not going for custom or turbo cams (see part about shoestring).

Offline cheys03

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Re: G40 carb'd turbo
« Reply #1 on: June 08, 2011, 08:44:01 pm »
First of all - genuine good luck to you, and please make a build thread!
Tommo did this as I'm sure you're aware, he's a top bloke and sure will be willing to point you in the right direction.

Cam-wise it will depend on your turbo - if you let us know which turbo you're using we'll be better placed to help.

Other items worth considering:
Oil cooler with thermo sandwich  plate
Oil feed& return pipes
Coolant hoses for turbo
Boost hoses (if on a budget, get to a scrappy as it's £££s new)
An actuator/bleed screw for your turbo to set boost
Clutch may need uprating depending on your torque
Brakes and suspension to cope
Exhaust
Oil pressure, temp and boost gauge as a minimum really

Offline Winston

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Re: G40 carb'd turbo
« Reply #2 on: June 09, 2011, 02:30:11 am »
Its well worth reading through Tommos posts on here and on clubpolo.. very helpful and knowledgeable guy 8)

Tommo made over 200bhp with a T25 and GT cam.. It might not be perfect but for money its hard to beat. imo

Im in the middle of building one for my Mk1 scirocco it made sense coming from a Renault 5 back ground.. Ive got a build thread on here.

Good luck with the build :D

Offline Winston

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Re: G40 carb'd turbo
« Reply #3 on: June 09, 2011, 02:35:06 am »
I see you know of tommo haha .. I was searching for this thread and spotted you posted on it.

http://www.clubpolo.co.uk/forum/index.php?showtopic=219594&st=0


Offline prankstar2003

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Re: G40 carb'd turbo
« Reply #4 on: June 09, 2011, 11:42:31 am »
Yeah, I have read some of Tommos work. Did he use a carb? I thought it was managed.

All chassis upgrades have been considered, got 256mm for the front, and probs go bigger drums/discs on back. Possible sub frame, but if not, poly bushes

Boost pipes will be made by a mate who welds stainless for a living, so thats free, probably including materials too (check my build thread on club polo for the inlet he made me). He said he'll have a go at the exhhaus mani too!

Cooling and oiling the turbo I had overlooked, so cheers for that.

Regarding turbo, it'll probably be a KO3 or T25. Any recomendations? Also, which cam would be best for which? I have a G40 and GT cam available

Offline Winston

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Re: G40 carb'd turbo
« Reply #5 on: June 09, 2011, 06:30:39 pm »
Tommo used a 5 GTT carb and a late Mk2 Golf vac advance dizzy to run the ignition. Im running a similar setup but ive fitted a vac canister that retards on boost and advances on vacuum.

K03 are easy to get hold of, there are off the shelf manifolds and downpipes, they are limited to 200bhp and im not sure if either G40 or GT cam are really suited to the K03 is the feeling I get after reading into it.

Ive used T2/T25 hybrid because that what I had on my old 5 turbo and a GT cam because Tommo used one with his T25 plus im tight haha, I will see how it goes before I go aftermarket cam hunting.

Offline prankstar2003

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Re: G40 carb'd turbo
« Reply #6 on: June 09, 2011, 06:59:44 pm »
What's this canister thingy then? Sounds interesting. I'd be using a polo vac dizzy, same as the golf one. Didnt know he'd squeezed 200bhp from a carbed set up, I was hoping for 150-170 max!! He was using an abd block though right? Which is 1.4 and slightly higher c.r.

What difference does the turbo have on the choice of cam? Do the turbos have different boost profiles or something :-?

Offline Winston

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Re: G40 carb'd turbo
« Reply #7 on: June 09, 2011, 07:41:53 pm »
The canister came from a Mk1 Rabbit but some uk cars use the same canister. It was designed to retard the ignition at idle for emissions, its what the yanks use for Kjet turbo conversions. It just means the diaphram goes both ways so the vacuum sucks it and the boost blows it.



He used an ABD but with machined down the pistons to lower the compression. The grungeisdead has his old pistons and rods up for sale.. 200bhp+ was very impressive.

Different sized turbos boost at different power bands. The bigger the turbo the more RPM is needed to spool it up, Different cams have different power bands its just a case of matching it to the turbo. This is something thats out of my knowledge range tho  :-[

Offline prankstar2003

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Re: G40 carb'd turbo
« Reply #8 on: June 11, 2011, 04:27:11 pm »
That looks like the vacuum unit on mine. Guess it's the internals that are different.

Thanks for the knowledge. I saw grunge has the bits for sale, but it was cheaper to buy the g40 bottom end (£80 :-) )

Hopefully someone can advise on cam/turbo matching

Offline Andy

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Re: G40 carb'd turbo
« Reply #9 on: June 12, 2011, 08:59:02 am »
If you're using a K03 get a lairier cam than a GT one. T25 and a GT cam seems to work well though - bigger turbo, smaller cam.

Offline prankstar2003

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Re: G40 carb'd turbo
« Reply #10 on: June 12, 2011, 02:20:25 pm »
How do you mean 'Smaller'? Lift or duration?

Is the T25 bigger than a KO3? Which cam would be best for a KO3?

Is there any turbo that would suit a G40 standard cam? They have milder profile right, so an evn bigger turbo?I have a GT and G40 item, but wanted to save the GT one for the AEA bike carb conversion

Can anyone suggest any useful books for tuning and forced induction?

Thanks for the help

Offline Andy

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Re: G40 carb'd turbo
« Reply #11 on: June 12, 2011, 05:25:07 pm »
"Maximum Boost" by Corky Bell, and "Forced Induction Performance Tuning" By A. Graham Bell are both worth a read.

Depends which T25 you use, but one from a Saab or 200SX is bigger than a K03, and people get better results with a GT cam and T25 than a G40 cam and T25. The G40 cam is milder (less duration), but also the overlap (relationship between exhaust and inlet valve opening) is biased towards a supercharged application. Turbo'd applications generally don't like much overlap, similar to a naturally aspirated engine.

When I say smaller, I meant less duration. If you run something as mild as a GT cam with a K03 you'll find your power band is from 1500-4500rpm. Fit a longer duration n/a cam with the K03, and you get a 3000-6000rpm power band - much more useable.

Personally I'd forget trying to use the G40 cam with a turbo.

Offline prankstar2003

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Re: G40 carb'd turbo
« Reply #12 on: June 13, 2011, 06:34:46 pm »
So a milder cam than the gt may be better for k03 conversion. Interesting. The gt is the most lairy production cam for the mk3 right? So maybe a longer stroked cam may be better, from the aee 1.6, 8v) for example?

Offline cheys03

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Re: G40 carb'd turbo
« Reply #13 on: June 13, 2011, 06:55:48 pm »
^  other way around... a lairier cam than the GT is more suited to the K03. I started with a GT cam but quickly switched to a naughtier item on Andy's advice because a GT cam with a K03 is actually disappointing to drive. I was aiming for a 254/254 as a middle-ground and luckily one needing a little work came up at a good price. It's definitely worth investing in the right cam for your application as otherwise you're sabotaging the setup's capabilities.

Edit: I say a lairier cam than a GT is more suited because the boost is available more where you want it i.e. the higher revs
« Last Edit: June 13, 2011, 06:57:23 pm by cheys03 »

Offline Andy

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Re: G40 carb'd turbo
« Reply #14 on: June 13, 2011, 08:50:20 pm »
That 254/254 works bloody well in your car Chris, in fact the whole setup does. How many miles on it now?