Current AFR Readings ...?!? Not what I expected ..

[Puma_TBR]

So out of curiosity I went for a drive with a AEM Afr gauge and wideband sensor a couple of days ago I was suprised at the readings.

2002 1.7
421 manifold - Hoffman race tube - sportex backbox
Custom ram airbox with ramair* come filter
Tape ECU fitted
STD cams

Idle (lean)17’s
Progressive pull (pretty good) 13-15
Hard acceleration (rich) 10’s!!!
Overrun (very lean) 20+

So definitely some performance to be gained by a decent map.
But this makes me wonder just how much fueling adjustment would actually be needed to run a low pressure turbo

Now I am actually in the process of getting the bits together and building a blown motor but was very surprised at these reading on a stock Tape ECU

On a second note... Turbos

What size/model are people running on the 1.7 ?
As well as PSI and decompression plates if needed and at what PSI

What will the internals take?


Please move if this would be better suited in a different area of the forum.

Many thanks
Tom

 

[Wild E. Coyote]

I would advise as a very good starting point to check Errolls thread: https://www.projectpuma.com/viewtopic.php?t=10961
You will find very useful info there should you pursue the idea of turboing 1.7.
Mind you, the weak link are conrods

 

[grogee]

The AFR ratios are what I'd expect from my limited experience. Engines can and do run rich as a strategy to prevent overheat/detonation. This is definitely true for turbo engines, Ford 2.0 GTDi is known for it. I am not as certain about N/A engines, although I would expect very lean for overrun.

Interested in the conrods comment. Every engine has its weak spot I suppose. Are there any options available as alternatives to standard, eg forged?

 

[Wild E. Coyote]

No, not really. It is a very small volume engine. PEC used to have them in offering, but that has dissapeared now, AFAIK. The conrods from Fiat 1.4 T-JET engine are close fit. The big end is the same 42/45 mm ID so you would need to make piston fit on that. And if you make a bespoke piston, than you can adjust the CR as suited

 

[Puma_TBR]

I agree, the richness I would expect from a turbocharged engine too. That’s why I was suprised and curious on the comments. Thank you for your replies