Upgrading Standard Throttle Body 1.9 Gti

[joni 0]

Just finished porting a head and planning on getting a 60 thou head skim.

 

Tried to think what else could be done to improve power and thought upgrading the throttle body might be an option?

 

The engine is going in a 205 road rally car. I want to stick to 1.9 8v with injectors but am looking for power/torque increase throughout the rev range. i am also adding a piper 270 cam with vernier pulley and a K&N and i don't want to change the exhaust system.

 

Is it possible to get a larger diameter throttle body or a butterfly to fit a modified standard 1.9 205 gti one.

 

IS this mod worth doing? I hear that it is possible to wind up (?) AFM's so that they tell the ECU to add more fuel into the engine at the same time. Can somebody explain?

 

Any other suggestions to improve the engines performance would be appreciated.

Thanks

[DamirGTI 325]

Hello !

 

Try this :

 

http://www.guy-croft.com/viewtopic.php?f=1...butterfly#p5527

 

I've done that on my engine ...

 

Did you match the inlet manifold to the head port/entry shape ?

 

Rgs !

Damir

[pug_ham 240 3 Cars]

Mattsav (QEP) used to sell 55mm bored out standard tb's for the XU9 inlet iirc.

 

NickR fitted one to his car.

 

Graham.

[GLPoomobile 958]

Isn't the AFM going to be the limiting factor in the inlet tract? Is there any point bothering with the TB if the AFM is strangling flow?

 

Take what you will from this (my disclaimer as not sure how relevant it is ) but when someone modified an Mi to use a VAG TB it did give some improvements, but the apparently it seemed to be flowing too much at the top end and seemed as if it was leaning out as a result.

 

Search Damir's posts on guidance for altering the mixture on the AFM. Very easy to do, but best done on a rolling road to get it right.

[pug_ham 240 3 Cars]

Isn't the AFM going to be the limiting factor in the inlet tract? Is there any point bothering with the TB if the AFM is strangling flow?

IIRC NickR did quite a lot of research into this & the AFM had plenty more flow ability than the standard & 55mm TB.

 

I'll check thorugh his posts sometime.

 

Graham.

[joni 0]

Hello !

 

Try this :

 

http://www.guy-croft.com/viewtopic.php?f=1...butterfly#p5527

 

I've done that on my engine ...

 

Did you match the inlet manifold to the head port/entry shape ?

 

Rgs !

Damir

 

Thanks Damir, I've had a look at your link. Guy doesn't seem to think any mods are required to the throttle body then?

 

Didn't match the inlet manifold to the head port exactly as is was pretty close. Just took out the sharp edges in the head, any casting marks, removed the part of the valve guides which protrudes into the ports and DIY modified the valves / valve seats.

 

Yet to see what effect it has had. How much did you skim your head? Dropping mine off for a skim tomorrow. Was going to go for 60 thou but the bloke doing it recommended going for 40 thou in case it had had a skim in the past.

[joni 0]

IIRC NickR did quite a lot of research into this & the AFM had plenty more flow ability than the standard & 55mm TB.

 

I'll check thorugh his posts sometime.

 

Graham.

 

hmmm... 55mm. what is the standard diameter? Any ideas on prices?

[DamirGTI 325]

Thanks Damir, I've had a look at your link. Guy doesn't seem to think any mods are required to the throttle body then?

 

Didn't match the inlet manifold to the head port exactly as is was pretty close. Just took out the sharp edges in the head, any casting marks, removed the part of the valve guides which protrudes into the ports and DIY modified the valves / valve seats.

 

Yet to see what effect it has had. How much did you skim your head? Dropping mine off for a skim tomorrow. Was going to go for 60 thou but the bloke doing it recommended going for 40 thou in case it had had a skim in the past.

 

Hi !

 

Yes he said that but surely a little bit of tiding inside the TB can't do no harm does it ...and it's not so hard/delicate/time consuming job compared to the head porting ..

Anyway i did remove/eliminate all the sharp edges inside the inlet tract - inlet manifold and throttle body as far as i could reach cos me thinks that it's the same as when you're modifying the head - you really do not want any sharp edges or weird shapes where the air enters inside the engine/cylinders starting from the inlet pipework to the throttle body , inlet manifold , inlet port entry , inlet port shapes , valve seats , valves etc. etc.

 

Matching the inlet manifold to the head port entry shapes is an essential thing ! and you really must do that even if you didn't enlarge or reshape the inlet port entry's on the head , as because there is already a "mismatch" from standard , from factory production .

Look on Guy Croft's website and you'll find he's comments regarding this - the inlet manifold to the inlet port mismatch on these XU9 heads is cutting a good bit of the air flow down because of the weird manifold exit and head port entry shape ...so it must be done/matched exactly to the head port entry's (or as near/accurate as you can) .. look for my old post regarding head porting here on the forum there you'll find pictures of the reshaped inlet manifold exit runners at the end of the thread , also the pictures of the reshaped inlet port entry's on the head .. If you're unsure which area you need to modify , if you need more info regarding this , feel free to ask and i'll explain more detail what you need to do in order to match the manifold to the head ..

 

I didn't skim the head , i've raise the CR with the pistons from the 1.9 DFZ engine .

 

One more and very important thing (highly recommended !) , if you didn't do that yet - cut multi angle seats , 3 angle or more if you can/if you like .. i can give you valve seat deg. values if you wish for this head based on the Guy Croft's recommendations .

 

Regards !

Damir

Edited April 1, 2008 by DamirGTI