Boost and a C4 Auto

[Anonymous]

Hi Guys,
Im almost done fitting a turbo to my "Log head" 250.
Im running a C4 Auto with kick-Down cable, How do you guys get your auto's to change gears at the right time? Say for street use. Do you still run the vac line? , Bleed valve?.

Thanks for any advise.

 

[xctasy]

Cool!!!!

Do a google search for the Mustang Carbed Turbo forum. Those guys will know.

I'm not sure how to do this.


I can tell you what doesn't work. Vaccum cansiters from a large capacity can

I used a Mustang based C4 which was used in all the early Britsh V6's before the C3 came out. Both transmissions have the same kind of modulator, and I used a Ford Prefect vaccum canister on Pommy Cortina 2.3 V6. I tried an IHI turbo on it for a while. Full throttle up shifting doesn't work unless you run the vaccum out of the carb. The old 9 ball plasitc XF vac cans (found under the window wiper grille) don't work either because they don't sense the fine movement of the accelerator.



How I think it is done is you have to boost reference the modulator.

The modulator may be easy to boost reference, I'm not sure. I've never done it.

Basically,the 100 buck replacement cost modulator valve controls clutch load on shifting by ported vac , and if the right signal is not being feed to the modulator correctly, upshifts will be too light. A turbo engine on a stock set of slipping clutches will burn the pack out eventially.

You tap the body and add an extra line to the modulator housing. Same way as when you booster preference the carb or the machanical fuel pump.

This applies pressure from the manifold above the carb. That means it still sees the ported vacuum, but it works normally.

Back in the 70's and 80's, when people used turbo Cortinas and Pintos, they used heavyist clutch pack, and forget about the modulator.

One a good turbo 200, 221 or 250 a stock C4 would be wrecked.

 

[rbohm]

8) how you run a vacuum line to your modulator depends on whether you are using a draw through or blow through system. if a draw through, then take the feed from just below the carb before the turbo. if using a blow through system, then you need a check valve in the system that prevents naything but vacuum to the modulator.

 

[Anonymous]

Awsome, Thanks for the info. Ill beef up the C4 after I see how the thing goes. Im using LPG (Propane). If it's good it stays with a new C4 or AOD, If it's crap the turbo comes off.

Cheers

 

[addo]

If you use an adjustable modulator, it shouldn't be too hard to dial in.

Full manual valve body would be the other option.

 

[Anonymous]

You can anctually buy the vacuum modulators with two nipples on them. I am going to try one to see if xecute's idea works.

Right now, I use the "check valve and bleed orifice" trick. The orifice is a little too large, and the upshifts come in pretty late while driving normally (something I don't do much)

I have stock valve body, stock mudulator and pretty much stock everything else in my trans. I upshift manually with my shifter at 5500. Shifts nice and hard.

 

[Fingers]

The orifice is a little too large, and the upshifts come in pretty late while driving normally (something I don't do much)

.

It all depends on what you call driving normally.... :roll:

 

[Anonymous]

It all depends on what you call driving normally.... :roll:

It's not really debatable, it's just that the shifts come in a lot later than MOST people would like them too. it's kind of annoying driving around the neighborhood at 2500 RPM waiting for the trans to shift, ya know???

I need to make the orifice smaller, and I am going to get a double-inlet modulator and play with it, too.

 

[Fingers]

Just having a bit of fun...
It's just when I drive "normally", it's a heap different to what somebody like my grandmother call "driving normal"

 

[rbohm]

8) linc, before you start changing the size of the vacuum orifice, try adjusting the modulator first. the single nipple modulators are adjustable, the farther in the screw, the later the shift points. i found this out when changing the modulator on my grand marquis. start by setting the screw about half way in, that should get you close for a start.