Correct timing on 930?

[dynevahn]

Ive searched and not find exactly what Im looking for. My mechanic said my 930s timing was set too high (35 degrees at 4000 rpm) and he set it to about 30 degrees. It felt like it ran so much better at 35 degrees. He is saying that running it at 35 degrees can cause the cars engine to blow up. I need your guys input on what to do. The engine is a 87 with sc cams. Thanks

[89turbocabmike]

Your mechanic is correct. Specs are 29 degrees +/- 2 at 4K. It will feel better at 35, but once your on the boost you will have too much advance and risk serious damage. One of the vacuum canisters on the distributor is responsible for retarding the timing when you build boost. It can mechanically only do so much. This is one of the key areas that efi conversions and their accompaning programable ignition systems can optimize drivability and power safely.

[javadog]

dynevahn,

Actually, the timing is 29 +/- 1 BTDC for a Euro engine and 26 +/- 1 BTDC for a US engine, with the vacuum hose detached, at 4000rpm. You should then check it at 900rpm, with the vacuum hose connected. For a Euro, you'll want 2 +/- 2 BTDC and for a US car, 1+/- 2ATDC.

The amount of timing that you can safely use is a function of a lot of things; compression, boost level, gas octane, temperature, which intercooler you run, which cams you run, etc. With today's 91 octane gas, I have to run mine at the lower setting to avoid detonation.

Do you know what detonation sounds like?

JR

[Jerry S]

I am sorry to hijack.....

But with my setup what would you recommend


ROW 930 (stock 300 HP)

SC cams
Garretson Intrercooler
single 3" out muffler
K-27
otherwise stock motor(rebuilt + strong)




Thanks Jerry S

[javadog]

Jerry,

It's hard to say. You didn't give your boost setting or the octane rating of the gas you have available.

If you can get good gas (octane rating of 93-94 R+M/2, or 98RON) I'd suggest you stick with the stock timing for your car, which is 29. If you run a lot of boost, or plan to drive it in places where you are limited to poor gas, I'd back it off 3 or 4 degrees. Keep in mind you may not have perfectly equal fueling to all cylinders and you don't want even one of them to be lean/hot enough to cause a problem. If you hear any detonation, back off the timing. Go a few degrees back past the point that the detonation disappears.

My personal philosophy is that conservative is better; I wouldn't go looking for the last 5 or 10 hp and close to the thermal limit of the engine in doing so. It's hard to feel the difference in the seat of the pants.

I get lousy gas where I live (91 R+M/2) and both my stock Euro 930 and modified US 930 (964 cams, Garrett turbo, F Garretson intercooler, .8bar boost, modified exhaust) run around 25-26 degrees. The stock Euro car needs at least 93 to use the stock timing and it runs a fair bit richer than a US car.

JR

[dynevahn]

ok, im running 1.0 bar of boost and 100 octane.

[Jerry S]

I am running stock boost (0.8bar) and our premium fuel I believe is 91 (Canada)

[javadog]

Dynevahn,

I'd run yours at 29. You might be able to run more, on 100 octane but I don't know the upper limit where you start losing power from too much advance. More is not always better. A dyno would be helpful here.

Jerry S,

I'd run yours at 25 or 26.

JR