5 GT Turbo Performance tuning Renault 18 turbo

[andyturbo2]

I am modifying an 18 turbo, I have read lots about carb mods on 5 gtt but there is very little on the 18 turbo version of the 32 DIS carb

I have also read about the group "A" mods to the carb on the R11 and there seem to be mixed opinions

The 18 turbo has a 24mm venturi, 1.1mm main jet and 1.35mm air corrector as standard and 3 stage enrichment

I have fitted a 270 degree cam, ported the cylinder head, fitted slightly larger exhaust valves. And fitted a GT 17 turbo in place of the original T3 running 7psi boost to start with but then aiming at around 1 bar when run in, aiming for 200bhp when finished.

I am considering boring out the venturi to 27.5mm and fitting a larger main jet to compensate for the extra air flow ( 1.4mm would seem to be a good starting point) and drilling out the fixed enrichment jet to 1.1mm

Obviously the car will need to go on a rolling road to make sure it's setup but wondering if anyone has any opinions on if this is a decent way forward

Would also be interested if anyone has information on at what boost pressure each stage of enrichment controls as this will help fine tune the fuelling

 

[Big Steve - Raider]

Paging @sparkie & @Brigsy

 

[sparkie]

I'd be uprating your fuel pump if you're aiming for 200 bhp. The 1.6 turbo lump is not a high revving engine from memory , it's quite torquey though. I have parts for the fuego/r18 turbo carb and I remember that the enrichment circuits don't work quite the same as the gtt version. I'm pretty sure the Haynes carb book shows the r18 version of the enrichment circuit. I've never seen any data on the opening of the various circuits unfortunately. Do not drill out the venturi. Fit your own AFR meter. Try a 1.25 air corrector and enlarge the main jet to a 1.2, then think about enlarging the enricher jet slightly. The 24mm venturi will still be OK for 200bhp. Either that or fit a gtt carb and use the tried and trusted jet sizes.

 

[Mark]

Guy, on the Fuego forum is going down the injection route, just a thought......

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[Adey]

870cc injectors, wtf

 

[andyturbo2]

I'd be uprating your fuel pump if you're aiming for 200 bhp. The 1.6 turbo lump is not a high revving engine from memory , it's quite torquey though. I have parts for the fuego/r18 turbo carb and I remember that the enrichment circuits don't work quite the same as the gtt version. I'm pretty sure the Haynes carb book shows the r18 version of the enrichment circuit. I've never seen any data on the opening of the various circuits unfortunately. Do not drill out the venturi. Fit your own AFR meter. Try a 1.25 air corrector and enlarge the main jet to a 1.2, then think about enlarging the enricher jet slightly. The 24mm venturi will still be OK for 200bhp. Either that or fit a gtt carb and use the tried and trusted jet sizes.

Thanks for the information the fuel pump and the AFR gauge are already in hand, I will have a look for the haynes book and have a read

Can I ask why the advice is not to bore out the choke, I'm intrigued, my reasoning behind the modification was thar if the 1397cc 5GTT used a 24mm venturi then the 1565cc engine, being 12% larger in capacity would need 12% more choke area to produce the power (I know that would mean the venturi should be 26.9mm) and that the engine would still have enough draw over the carb at low revs to not have any hesitation. Plus the GT17 turbo should be on boost by 1500rpm.

When people have tried it on 5 what has been the downside?

Andy

 

[andyturbo2]

Guy, on the Fuego forum is going down the injection route, just a thought......

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I had considered the injection route, also the Twin dellorto blow through carb route used by the Lotus Esprit Turbo, but designing and making a suitable air box that flows evenly to all 4 trumpets and doesn't produce any stagnant air around the trumpets and is a suitable size is no easy task in the confines of a standard engine bay.

 

[sparkie]

Thanks for the information the fuel pump and the AFR gauge are already in hand, I will have a look for the haynes book and have a read

Can I ask why the advice is not to bore out the choke, I'm intrigued, my reasoning behind the modification was thar if the 1397cc 5GTT used a 24mm venturi then the 1565cc engine, being 12% larger in capacity would need 12% more choke area to produce the power (I know that would mean the venturi should be 26.9mm) and that the engine would still have enough draw over the carb at low revs to not have any hesitation. Plus the GT17 turbo should be on boost by 1500rpm.

When people have tried it on 5 what has been the downside?

Andy

Boring it out ruins the profile of the venturi. The 25mm venturi in a gt turbo can easily handle well over 200bhp, the limiting factor is the float chamber jet which tops out at about 20psi, depending on which cam you use. The 24mm venturi will still handle 200 bhp and it'll feel a nicer drive than if you bored it out.

 

[DaveL485]

After careful consideration and poking about with carbs over the years I decided to EFI mine (R9 Turbo). It's just all positive/benefits save for retaining originality (which isnt an issue for me) and cost.