Turbo Jetting

[Sparrow]

yeah...

I've just set up a draw thru carby turbo on a 1600 (G161). It's a Garret T25 turbo (carbon seal) stock 8psi drawing thru a 32/36 DGV weber (down draught !!). I havn't started the car yet as i want to know what jetting i should use so it doesn't detonate and damage the engine... any idea ??? (main jet sizes, air corrector, ect.)

[Fastgem]

why have you ran a draw through set up with a 32/36 carb instead of a blow through?

[Ben Wight]

It wont hurt to start the car, and it will probably run slightly lean at 8psi. It may be a bit lean around idle and low throttle as a draw through is typical for this syndrome due to the longer induction.

So a slightly larger idle jet and secondary jet may be required for better running.

But yeah, should have gone blow through.

Ben Wight

[NUT161]

is that u damien?

[Sparrow]

yeah...
(if i wanted a blow thru set up, i'd get a CA-18, FJ20, SR20 DET or the like and do a half decent conversion !!! All i'm trying to do is a bit of a backyard project and i was going to experiment with the old 32/36 downdraught first - i never heard of anyone trying it before with suck thru ... ) !!

...anyway, i've now fucked the 32/36 off now... don't have to cut the hole in my bonnet to fit the fucker either...

i am now exploring the possibility of using a

SINGLE (45mm??) 'SU' sidedraught carby

... i got the thing for free but i don't even know if it is suitable for a small, suck thru turbo application... but it should fit under the bonnet without too much hassle.

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*Has anyone had any experience with tuning a single SU carby...they are way different to the Weber and Nikki !!!
**Will this style carby be suitable for my turbo project ??
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and yeah Danny.

[Nick_H]

Yes it will be fine....ive just finished doing the same as u....suck thru turbo with 1.75 SU...8 psi. i got my complete setup for $400 with the turbo fitted with new bearing and seals....took me about 5 hours from start to finish (running a rebuilt standard engine)

The SU has a pull down jet at the base of the carb. it pulls down for the choke..it also has a nut on it and spring. the nut is for moving the jet up and down which will adjust the fuel mixture.
On the piston inside the carb the is a needle that goes inside the jet.
The further down he jet screws down the richer the fuel mixture will be.
If you remove the piston you can remove the needle and it should have a "E" clip and a few diffrent settings.

U should be able to work it out how it all works now.

That the basics...correct me if im wrong but its worked for me

[Ben Wight]

The reason i suggested a blow through setup is becasue I am using the 32/36 in that config, and when intercooled, you will be able to run a lot more boost than 8psi. So you dont need an EFI based engine as those that you listed, virtually any carb can be made to work in a blow through setup.

SU's are verry common for a draw through setup, I've never tuned one, but they have a tapered needle that controls the mixture over the load range of the engine, ie from idle to WOT.


Are you sure that the turbo is setup for a draw through application, does it have the correct seal? If not, it might blow smoke in high vaccuum situations, such as at idle and light cruise. More typically, after a high vacuum situation, and then when you floor it, the oil will be drawn into the engine from the compressor giving off clouds of smoke.

BTW, I've seen a 32/36 being used draw through before, a special mounting manifold was used so the carb sat really low, sort of dropped the carb so the top was level with the top of the turbo.

Ben Wight