single point injection question

[Gray6634]

hi as you prob know from now ( from all my posts !) that i have a 1.3 cl spi. i was wondering what would happen if i replaced the injector with one from a multipoint gt? maybe better fuel flow maybe an increase in power if only very small? thanks

[Aphex]

if you just replaced the throttle body nothing would happen as there are no fuel jets in the body and it wont fit to an AV manifold
.
to convert to multipoint if GT you will need

GT Ecu
inlet (gt/nz:g40) whichever
ignition rail
Throttle body
lower oil breather
Arfm
air feed
main engine loom

theres rumours that the GT dizzy may be needed to as the gt ecu controls the base timing and fuel mix (like the AAV) but i havent gone this far to know for sure. If it was a conversion from NZ then you would definately need a GT dizzy as the NZ is vacuum advanced.

There is an article on this on club polo
http://www.polo-gt.co.uk/mechanical/gtconversion.html

[amstrange1]

You do need the GT dizzy - the AAV one has different spacing on the hall sender trigger wheel. You'll also need the GT inline fuel pump too - I think I missed that off when I wrote the Club Polo article.

With that lot on it'll run, and be possible to get 40mpg if driven carefully - and around 70-75bhp from my experience. To improve things further a GT cam is a good idea (something I never got round to trying), as would be a GT gearbox - as the closer ratios make better use of the engine's new found ability to rev.

Any more questions, just give me a shout - it's a while since I did the conversion though! Oh, and without the GT cam and GT gearbox a proper GT is a fair bit nippier - food for thought...

[Gareth_GT_Hatch]

yeah A GT engine without a GT cam isnt really worth the effort. NZ injection would be a more suitable option if you cant get a gt cam as the nz engine block is the same as the AAV (same compression ratio and things like that)

[DanW]

yeah A GT engine without a GT cam isnt really worth the effort. NZ injection would be a more suitable option if you cant get a gt cam as the nz engine block is the same as the AAV (same compression ratio and things like that)

Is it? I though it was slightly less on the NZ, but I'm probably wrong...

[Gareth_GT_Hatch]

nope, both 9.5:1. has the same head and probably the same profile cam as well (but is a different part number)

Only difference is With a chip and a GT cam you can get about 80bhp out of an NZ dan. (whereas youll be lucky to get 70 with a modded aav) You can get slightly more from GT injection but with the right bits NZ works just as well.

[DanW]

nope, both 9.5:1. has the same head and probably the same profile cam as well (but is a different part number)

Only difference is With a chip and a GT cam you can get about 80bhp out of an NZ dan. (whereas youll be lucky to get 70 with a modded aav) You can get slightly more from GT injection but with the right bits NZ works just as well.

or 90.2bhp* like steve has

the cam in the NZ I knew was weak, but hey.


*or something like that wasn't it or am I going totaly bonkers today

[Aphex]

nope, both 9.5:1. has the same head and probably the same profile cam as well (but is a different part number)

Only difference is With a chip and a GT cam you can get about 80bhp out of an NZ dan. (whereas youll be lucky to get 70 with a modded aav) You can get slightly more from GT injection but with the right bits NZ works just as well.

i havent been able to find that anywhere, the haynes doesnt list the nz compression ratios. iirc optima said that the nz is less, as the nz had to be restricted to 55bhp and as it had the same exhaust as the aav there is only compression to hold it back. i could be wrong however.

what i do know though is that the nz and gt injectors are the same, its the throttle bodys that are different, The gt has a butterfly position sensor whereas the nz only has a 3 stage sender.
The GT cam is said to be an improvement over std aav but a 270 duration would be far more effective. 80 is a bit of a high claim just on a chip and 3f cam.

[Gareth_GT_Hatch]

Well Tim you could be right, Ive checked etka and the part numbers for AAV pistons and NZ pistons are different. The AAV has the same pistons as the MH and 2G incidentally.

Anyway etka doesnt supply the compression ratio for any engine. but I have this website to back me up:

http://www.carfolio.com/specifications/ ... car=101519

And also *plays hand* I have the VW brochure for the "new" polo hatchback dated november 1990 (or there abouts) wherein it lists the engine specs for the CL. with it being the first brochure it has the specs for the NZ engine (which it describes as having digijet injection) and in there it gives the compression ratio we all know and love of 9.5:1

80bhp is IMO not unreasonable. Like you said the injectors are the same, the afm is the same and the cylinder head is the same as a GT. And like dan said in an earlier post steve's NZ powered mk1 got 90bhp at the stealth racing rolling road day, 76bhp at the JBS rolling road day and 81bhp at the club polo rr day at aldon two weeks ago. His mods are; chip, GT cam and G40 exhaust. By comparison my 1.4 GT with more mods only managed 89bhp at aldon so 81bhp aint a bad achievement from NZ in my book.

The only thing about steves engine is the bottom end is from a 2G which shouldnt make any difference so long as my facts are straight.

The NZ has a VERY mild cam as standard which restricts the power immensely, a GT cam makes a huge difference, my 1.4 had 60hp with spi and now it runs nearly 90 and I bet most of that has come from the GT cam, with more to come once ive sorted the valve timing with a vernier.

[amstrange1]

80bhp is IMO not unreasonable. Like you said the injectors are the same, the afm is the same and the cylinder head is the same as a GT. And like dan said in an earlier post steve's NZ powered mk1 got 90bhp at the stealth racing rolling road day, 76bhp at the JBS rolling road day and 81bhp at the club polo rr day at aldon two weeks ago. His mods are; chip, GT cam and G40 exhaust.

Steve also has a mildly ported head don't forget.

A GT cam is likely to be a good mod to an NZ injected or GT injected motor. I think the 3F GT injection is the better system, if only because you've got mapped ignition as well as fuelling. However, that's likely to create you problems if you start to seriously mod your engine.

[Aphex]

the other bonus of the nz is the g40 inlet, this is something said to give quite a substantial amount of torque on a gt. its all a case of swings and roundabouts really, Still pleased that the nz can have the base ignition timing advanced without the ecu compensating for it.

[amstrange1]

the other bonus of the nz is the g40 inlet, this is something said to give quite a substantial amount of torque on a gt. its all a case of swings and roundabouts really, Still pleased that the nz can have the base ignition timing advanced without the ecu compensating for it.

Interesting debate about the inlet manifolds, waiting for Dom to do some more power runs now he's got his car running right with the correct ignition timing. Metz and Yoof have compared their near stock GTs to each other - both decatted I think, Metz has NZ inlet, Yoof the GT one - I think Yoof's car just had the edge, and was more noticeable top end.

Oh, and you can still advance the base ignition timing on a GT - the ECU adjustment is simply a +/- so many degrees over the base setting.

[DanW]

and you can take the vacume advance of the NZ, there a tube/connector on it somewhere.

[Aphex]

Interesting debate about the inlet manifolds, waiting for Dom to do some more power runs now he's got his car running right with the correct ignition timing. Metz and Yoof have compared their near stock GTs to each other - both decatted I think, Metz has NZ inlet, Yoof the GT one - I think Yoof's car just had the edge, and was more noticeable top end.

Oh, and you can still advance the base ignition timing on a GT - the ECU adjustment is simply a +/- so many degrees over the base setting.

The gt manifold always had the best top end doesnt it. Dunno, will have to see what happens next week when my NZ:AAV comes to life.

and you can take the vacume advance of the NZ, there a tube/connector on it somewhere.

There is but why would you want to?

[DanW]

and you can take the vacume advance of the NZ, there a tube/connector on it somewhere.

There is but why would you want to?[/quote]

I can't remember the reason now, but Dom or Steve said there was...