Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

[CJH]

Ah, ok, thank you - probably rarer than the 'N' suffix in that case. But I'll add it to the search criteria.

[CJH]

Inspired by the 112i logo....



...I made my own

[itchyfeet]

112i is 112bhp injection?

whats 121p?

[bigherb]

112i is 112bhp injection?

whats 121p?

Pferd?

[CJH]

That’s the Pierburg ‘P’.

[bigherb]

Should be CAT for carb a toot

[itchyfeet]

yes but 121? I can't see 121bhp on the graphs?

[CJH]

I thought about a 'c', but there isn't a standard symbol for 'carb' I think. Anyway, it's my little 'in joke' - it doesn't need to make sense to anyone else!

121 = flywheel power = 102.7HP at the wheels plus 18.3HP in drivetrain losses. I knew my post was too long.

[itchyfeet]

So is this more than a standard 2.1 injection or are all figures published at the wheels?
If its more It can only be the cam I assume?

[CJH]

I asked about that, and he said that manufacturers quote flywheel power, so it would be directly comparable to the 112 quoted for the injection model. One way to check I guess would be to check the quoted power for the 2WD DJ versus the Syncro DJ - if they're the same then it must ignore drivetrain losses. I don't know how accurate his measurement of drive train losses was though.

The cam is one possibility, the exhaust is another, but the explanation that the fuel is better atomised by a carb than by an injector seems feasible. I know nothing about fuel injection - are the injectors near the valves or near the throttle body? One explanation I was given was that the carb drops the fuel into a long induction manifold which is under high vacuum, in an airflow that is moving very fast, and this can atomise the fuel better than an injector that sprays the fuel (in droplet form) rather than atomising it. I'm only going on what was suggested to me yesterday, but he seemed very clear that it's not uncommon for a carburettor to perform better than an injection system.

[bigbadbob76]

Thanks for posting the graphs CJH. Great to see what effects what.
The venturi diameter stuff ties in with my experiences when I did my 600cc-750cc conversion on my bike.
The original carbs from the 600cc were smaller diameter than the originals for the 750 but once properly jetted gave me better mid range response.
This made for a better ride on public roads where flat out max speed is immaterial.
Accelleration was better in the 50mph-70mph range, right where you want it for road riding.
Using the bigger diameter carbs left it a bit flat low down in the rev range.

[itchyfeet]

yes injectors right by the heads.
Very interesting Chris, of course they can't measure flywheel BHP so they estimate transmission losses on a rolling road but VW mayhave measured at the flywheel.

[CJH]

Thanks for posting the graphs CJH. Great to see what effects what.
The venturi diameter stuff ties in with my experiences when I did my 600cc-750cc conversion on my bike.
The original carbs from the 600cc were smaller diameter than the originals for the 750 but once properly jetted gave me better mid range response.
This made for a better ride on public roads where flat out max speed is immaterial.
Accelleration was better in the 50mph-70mph range, right where you want it for road riding.
Using the bigger diameter carbs left it a bit flat low down in the rev range.

A similar result then. I remember someone posting in an earlier thread about carbs that the air speed through the venturi(s) is important. I wonder if this is the key - up to a certain point the bigger venturi benefits by allowing more air in, but after a certain critical point a bigger venturi means slower air flow and less complete atomisation. It's a theory, at least.

yes injectors right by the heads.
Very interesting Chris, of course they can't measure flywheel BHP so they estimate transmission losses on a rolling road but VW mayhave measured at the flywheel.

Good point - I'm sure VW will have dyno'd the engine on the bench during development.

[kevtherev]

Brilliant work
What a bunch of awesome surprises.
Well done Chris.

[itchyfeet]

What a bunch of awesome surprises.

I seem to remember you saying carb was as good as injection before but I nerver believed it.