turbo setup with stock su carbs

[DISLEXICDIME]

The guys on ozdat say the single large su makes the most power out of all the draw through carb set up's. Ray at garage auto hero told me his lz18 single su draw through set up pulls as hard as a stock sr.

[hacked521]

im pretty sure you wont have to seal the throttle shafts if you put the carb in the box. personally i think puting a carb in a box would work the best, but it wont really look stock. The way i had been explained to about the carb box, it puts the carb in its own atmosphere, so it would be like you were driving and went so far below sea level that it starts to boost your engine. All i was told to do with my turbo with a 32/36 carb in the box setup was to put a plastic float in there and jet accordingly( secondary fuel jet is nearly an 1/8"). im looking for my turbo book to find notes as well haha :D .

[imtb]

Interesting topic. I like the way your write skib. Sound like a professor.

 

I am still in the process of building my LZ 2.2 turbo. you can see my build thread boosted goon.

I was orginally going to blow through using a single side draft dellorto, the carb is ready to bolt on. I had it turbo prepped and emulsion tubes. I was going to buy a turbo top hat like the VW guys use. They have a quite a few setups. check out CB Performance or search VW blow through. I got talked out of it saying it was to danergous but, still thinking about trying it once my engine is built. I have the FI setup but the SDS system is going to cost some bucks and a little more working putting it in, but probably would have better performance in the long run.

[imtb]

I have been checking Julians build on the 510 Relm, project whitebird. he is designing his own system, interesting to see how he is doing it.

[Skib]

The guys on ozdat say the single large su makes the most power out of all the draw through carb set up's. Ray at garage auto hero told me his lz18 single su draw through set up pulls as hard as a stock sr.

 

over all its already been concluded that a draw thru is the easiest and most practical to build for turbo SU's

and over all an EFI set up is best.

 

but for the sake of figuring out how to run a proper blow thru SU set up,

discuss...

 

 

ya my research has already shown thats the best way to do it but this is just for the sake of discussing making the blow thu set up work

 

 

 

im pretty sure you wont have to seal the throttle shafts if you put the carb in the box. personally i think puting a carb in a box would work the best, but it wont really look stock. The way i had been explained to about the carb box, it puts the carb in its own atmosphere, so it would be like you were driving and went so far below sea level that it starts to boost your engine. All i was told to do with my turbo with a 32/36 carb in the box setup was to put a plastic float in there and jet accordingly( secondary fuel jet is nearly an 1/8"). im looking for my turbo book to find notes as well haha :D .

 

 

i agree, from a pressure standpoint being enclosed in a box would be best since you woulnt have to to seal the shafts.

 

you prob just need to block off the overflow vents and make sure the gaskets are all fresh and sealed on the carbs (mainly thinking about the float bowl cap gasket)

 

 

and yes I forgot to add that part in (good call), you will need a plastic float of your using roadster/510 carbs with the free floating brass floats.

the easiest thing to do is snag some float bowl tops from Z car SU's. they have a hinged plastic float attached to the top.

 

Iv also heard of people opening the brass float and filling it with foam or something and resealing it.

[erichwaslike]

ok so for my setup im looking for blow thru, and y cant u use brass floats?

[DISLEXICDIME]

They will crush under boost

[erichwaslike]

oh okthen i guess i will look into the palstic ones

[Skib]

oh okthen i guess i will look into the palstic ones

 

 

just get the float bowl tops from some Z car SU's

 

there hinged solid floats attached to the tops

[hacked521]

yeah opening up brass floats and filling them with foam then resealing them would have to be a last ditch effort. I found it extremely difficult to not only fill the empty float completely but also resealing them.

 

instead of capping the overflow i would run a line from the overflow to the outside of the box, if a boxed blow through is the idea.

[Skib]

 

instead of capping the overflow i would run a line from the overflow to the outside of the box, if a boxed blow through is the idea.

 

 

the box and carbs will be pressurized tho

[erichwaslike]

so if the carbs arent in a box and i have plastic floats how wood the overflow work? wont it leak pressure all the time?

[Skib]

so if the carbs arent in a box and i have plastic floats how wood the overflow work? wont it leak pressure all the time?

 

I think you would have to plug them because the float bowl is going to be pressurized and push everything out of that hole

[erichwaslike]

so then i just hope that the needle and seat never get stuck open and totally flood the engine?

[Skib]

so then i just hope that the needle and seat never get stuck open and totally flood the engine?

 

lol this is why we have a discussion thread :lol: so we can have figure out the details.

 

since I havent found any one running this set up (with pics or write up)

 

 

thinking about giving Z Therapy a ring and trying to catch him when hes got some time

[erichwaslike]

yeah i thought of doing the same... im not sure wat kind of ppl they are but alot of places dont like to give away secrets for u to do wat they do on ur own casue its bad for business.... let me know wat u find i guess

[Skib]

yeah i thought of doing the same... im not sure wat kind of ppl they are but alot of places dont like to give away secrets for u to do wat they do on ur own casue its bad for business.... let me know wat u find i guess

 

 

I know him personally

[datzenmike]

With a pressurized box blow through system the bowl vent(s) cannot come outside the box. If they do boost pressure will blow out. Capping them should work if nothing goes wrong. If the float sticks and it over fills the carb will flood and run lean. Proper float level is essential to having an SU run properly, unlike a regular carb.

[Skib]

With a pressurized box blow through system the bowl vent(s) cannot come outside the box. If they do boost pressure will blow out. Capping them should work if nothing goes wrong. If the float sticks and it over fills the carb will flood and run lean. Proper float level is essential to having an SU run properly, unlike a regular carb.

 

 

yup, thus arises our various problems and contradictions :lol:

[sinner720st]

i have the solution to your problem. Dont know what the overflow looks like on SU, but if you run it to the intake manifold you would kill two birds with one stone. i will explain.

 

problem 1) float bowl overflowing.

- now it overflows into the intake, it just makes it more rich, i see no problem with that if it only happens once in a burple moon.

 

problem 2) you need to have equal pressure to both sides of your jets, if your pushing 3psi boost and your float bowl does not have that much psi, then your fuel will travel back into the bowl, dont think it matters if there is a strong venturi or not.

-now you have the same pressure in the float bowl as you have in the intake manifold

 

the only thing is you might want to hook up in front of the carb, before the natural pressure drop. do this in order to have slightly more pressure in the float bowl than the manifold so that fuel is helped... i would say try both ways during tuning to see

 

also the best book i know for this is the HP turbochargers book. i bought it and read half of it in one sitting. talks alot about boostin carbs and blowthrough setup, and turbo sizing

 

hp 49 - turbochargers

 

[sinner720st]

1. Air valve suction (bell) chamber

2. Air valve (piston)

3. Air valve (piston) spring

4. Air chamber to manifold vacuum connection (air less than atmospheric pressure)

5. Suction chamber air inlet (air at atmospheric pressure)

6. Dashpot

7. Dashpot piston damper assembly

8. Fuel needle

9. Jet

10. Jet retaining nut

11. Fuel bowl

12. Carburettor body

13. Throttle butterfly

14. Throttle lever (not shown)

15. Fuel float & fuel supply regulating needle (not shown)

16. Idle speed adjusting screw (not shown)

17. Choke cable (not shown)

18. Choke lever lowers jet to enrich mixture (not shown)

19. Choke cam - slightly opens throttle butterfly so not to starve engine of air when choke is used (not shown)

20. Choke return spring - ensures jet remains in the normal running position – choke is inactivate when engine is warm (not shown).

[datzenmike]

I've seen gas overflow out the vent from a sunken float. It's like taking a piss. You wouldn't want that much in the intake.

[sinner720st]

well either way, you need your float bowl pressurized... just hope your floats dont drown ... with a closed cell foam plastic float, they would never sink

 

Now what about the other main issue, getting the slide to rise while boosting (not saying the float issue is over yet)

[erichwaslike]

isnt it the same as any other boosted motor, just vacuum right? in front of the turbo or on the side of the housing?

[Skib]

SU's are tricky to blow thru, thats why you dont really see it done.

 

 

every single one of the old school Z car blow thru turbo kits are for Webbers/Solex/Mikuni type carbs which operate differently than the SU's

 

 

its not really a practical set up. but we knew that before we started out little discussion (see my first post)