304 Power Curve

[Grim304]

14-61 WOT run with ignition-Fuel.JPG

[Holden202T]

do you have a wideband on this ?

4.11 ... no question

[Grim304]

I bought the car as is, so assumed it was stock, whys that?

4.1 eh, that was my initial thought everyone else was saying 3.9

[v6bucket]

I 2nd the 4.1 diff gears.

[Holden202T]

the reason I ask about the wideband is because you really need one to be able to safely tune the car properly when racing, otherwise you really need to do it on a dyno. see the monitor above, at the start your o2 millivolts are over 900, this is really rich!

the only reason you'd want a 3.9 is if you wanted to drive it daily and fuel consumption was an issue.

lets say you had say 4.11 and a T350 behind this motor and found you were getting to 3/4 track and running out of gears, that's when you'd want a 3.9 or similar.

my Gemini used to have a 3 speed auto, 4.11 diff and slicks with similar rolling diameter as standard commodore wheels, and that car did a 12.78 over the 1/4 and was on about 5500rpm across the line. the whole idea of it is to get the most out of the take off you get from a 4.11 while making sure you have the legs to get across the line. in your car, your car needs to accelerate a lot faster to reach that 12.78 time where your getting closer to needing a different diff ratio.

the same engine mentioned above (202) is now in my brothers vs commodore, with T700 and 4.11 diff with slightly taller slicks, and it does 14.1 I think it was over the 1/4.

[Dylan]

900mv what ratio would you think that would be? 12-1?

[Helical]

I'm toying with what ratio I'm going to go for, but I'm putting a T56 in. I made this spread sheet to see what RPM the motor would be doing for each gear and speed. Might be of use to you, it's still a rough work in progress but if you change any of the values in coloured boxes it will update the tables.

Troy

[Holden202T]

900mv what ratio would you think that would be? 12-1?

well at that point in the range its not real accurate but i'd be saying 11's probably, I reckon the plugs are fairly dark coloured if not black

I've in the past used narrowbands to roughly tune a car when there was no other option and aimed for 830-850 but like I said, its really not that accurate, that's why you need a wideband!

[Grim304]

Remembering this is my daily driver and will be the tow car for my 202 powered chevette.
The good thing is that as it is my tow car lowering the gearing is probably not that bad.

I actually turned up the fuel to it compared to the day before to try and boost the power as the day before I could only manage 14.8@93mph although it may have been counter productive as I also added some timing and it's likely the timing gave me power not the fuel.

Seat of the pants told me it was too rich but I wanted your guys opinion so i can learn from what i do, I am still farkn busy with other stuff going on here and I haven't been able to catchup to spend more time on other stuff. I will set it back, just got back from watching Classic Car racing and doing the pics now before I go out for the evening.

[Holden202T]

202 chevette

pics ?