# A/f question

Discussion in 'Technical' started by Hetzen, Mar 29, 2006.

1. #1
Does a sudden drop in a/f cause a drop in power?

2. #2
yes, because you'd be running too rich.

3. #3
??? if you fatten up the AFR you run more power. ie running rich, it will cause more carbon deposits on the pistons and valves, but you make more power. running lean ( higher than 14.7 A/f Ratio " in theory" makes less power, running more fuel than 14.7 AFR ( rich) makes more power)

4. #4
No.

5. #5
no. running richer is just a buffer, because running lean can cause alot of problums. for FI cars, (like hetzen's) its a bit different, although the same basic rule applies.

6. #6
No to get more power you just need to burn more fuel, which releases more energy to be used to drive the crank, but to burn that fuel you need the air. So from a power point of view there is no point in injecting more fuel if you dont have the air to burn it! Having the air fuel ratio at stoichametric (my all time favourite engineering word) will allow all the fuel that is injected to be burnt.

Obviously this is a massively simplified situation as the engine design, ignition characteristics and many other factors will influence the effect the a/f ratio will have on power.

7. #7
Last edited by a moderator: Apr 25, 2016
8. #8
Lambda for maximum power is with gasoline about .85, richer than that will only decrease power output. With for example alcohols it can be a bit richer than that, about .78 for ethanol and .62 with methanol.

9. #9
Hetzen do you have a VAGCOM or did you actually go all out and get a wideband a/f meter?

10. #10
thanks for making an attempt to explain it.

11. #11
and BTW 14.7 isnt the best a car can run it is running richer at 13:1 or so will make optimum power, It depends on the engine and how well it can burn during combustion.

12. #12
Both. Wideband is getting put in tonight.

And I want to know if a sharp drop from "lean" to "rich" will make the power drop. Like 2 points on the af scale.

13. #13
I can't believe you are getting a wideband. You better be putting on a very big turbo.

14. #14

15. #15
I'm going in the other direction I think.

Mk2 GTi 1.8T (K03 maxed out). It should be fun, but I have to wait until I graduate.

16. #16
A local guy has a really clean one. He almost bought a user APR stg. III for it. There is also an MkII Jetta 5 min from my house with a 1.8T.

17. #17
Im pretty sure it will make the power drop, but it shouldnt be too much.

18. #18
Yes. gerbel01 is right. But, the duration of the fuel spike may not make any noticeable difference in what you feel of the powerband. If you look at the dyno charts you posted, you'll notice how wavy the power curves are. You don't actually feel those fluctuations like that while you are driving, right? Even the smoothest engines on the market will have a wavy power/torque curve, your body just isn't sensitive enough to notice.

19. #19
You can buy a good wideband for \$400. Its well worth the investment if your doing your own tuning.

20. #20
I don't plan on replacing my K03, so I'll be fine, thanks.