924Board.org

[Mike77]

I used a timing light on my engine today. The Hayne's manual says 10 degrees ATDC, and that there are 3 marks l+ 0 l- From what I can tell in the manual, 10 ATDC is the line with the "minus" beside it. I guess my assumption would have been that the + went with "after top dead center" and the "minus" was before. According to the book, my reasoning is backwards. Anyhow, my car seems to run best at just before the l+ mark. Is this about 8 degrees BTDC? What do the rest of you guys find is the best setting for best running/performance. I don't have to pass any emissions tests.
Thank

[924RACR]

My cars have run best with 6 deg BTDC - corresponds to the 0 deg mark at the top of the timing window. Sounds about where you have it?

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Joes924]

Thanks for the good info Mike 77, Vaughnn.

[Benski]

Mike, I get confused every time, too. There needs to be some easy to remember mantra for this. Running more degrees ATDC is retarding the timing (plug fires later). Running more degrees BTDC is advancing the timing. This explains the +/- signs.

How to set the timing: Advance it until it starts pinging slightly up a high in high gear, then back it off little by little until it goes away. More advance = more power (up to a point! dont go beyond maybe 12 degrees BTDC).

[924RACR]

I arrived on that setting experimentally in my '77.5, just advancing it until there wasn't any more power being added. I couldn't feel anything more after 6 degrees. Yeah, the more advance you run, the hotter it'll run and the more likely to detonate.

I tested this again last spring on the racetrack, and again found no improvement beyond 6 deg.

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[-nick]

i believe this is from the chilton's manual. it may be a little different if you're non-stock:

Degrees BTDC
Pwr Increase Plug Temp Increase
(increases in %)
2 around 1.70 around 3.70
4 around 1.90 around 4.70
6 around 2.10 around 6.70
8 around 2.15 around 8.70
10 around 2.00 around 10.70
12 around 1.80 around 12.35

US Spec Engine HP increases
100HP 115HP 150HP
"" '77 924 '77.5+ 924 79-80 931
2 1.70 1.96 2.55
4 1.90 2.19 2.85
6 2.10 2.42 3.15
8 2.15 2.47 3.23

10 2.00 2.30 3.00

12 1.80 2.07 2.70

156 HP 150HP 160HP
81-82 931 87 924s 88 924s
2 2.65 2.55 2.72
4 2.96 2.85 3.04
6 3.28 3.15 3.36
8 3.35 3.23 3.44
10 3.12 3.00 3.20
12 2.81 2.70 2.88

i always found this interesting. easiest horsepower you can get. ~6* is the way to go, 8* is marginally the most power but it heats up the plugs much more.

-nick

sorry the numbers are squished together.

[ This Message was edited by: -nick on 2002-04-08 02:10 ]