cBigganz

Hey club,

My engine is a gt4088 turbo 6port with no 6port sleeves, ported exhaust baffles, 2 piece 2mm apex seals, and solid corner seals. Intake is custom with a 75mm TB and all restrictor plates removed.

Hot starts easily and pulls 15-16 inhg at 900rpm idle.

I've been working on improving my cold starts for months without much luck until yesterday, when I moved "crank timing" up to 25deg advance. This seemed to make it kick over and fire up quickly.

What is considered safe for "crank timing"?

Initially it was at the stock 7deg, and I had tried the teens, but still found I had cold start issues.(Crank forever and not even sputter) while hot start didnt care. No amount of prime pulse, coolant correction, or addition to base map seemed to help.

Looking forward to hearing experiences from others.

Craig

C. Ludwig

iTrader: (27)

In a practical sense, you can't really hurt the engine when cranking it. Give it what it wants. If it's trying to kick back on the starter, then you have too much timing. That said, 25* sounds pretty excessive.

cBigganz

Thanks for your input. I figured advancing until kickback occurred was best practice, but I never experienced kickback.

I think I'm starting to understand my issue. Open 6 ports is a ton of air, much more at startup than the stock system would have seen.

Last night I added a silly amount of fuel to the base map crank area and tuned it to start hot. With 1000cc injectors I'm now at 6ms in the cranking cells (-2.9inhg @ 0 & 500rpm), where as before I was at 2ms. Hoping this gets me closer to what the engine wants cold with reasonable coolant temp correction.

dguy

iTrader: (8)

I regularly run a fixed distributor setup @ 25*s of advance on e production 6 ports. With a few kicks of the accel pump in an IDA they fire up dead cold so while I agree that 25*s is a bit much for a street car, it wont hurt a thing.

cBigganz

Thanks Dguy, at least it's good to know I'm not crazy (or at least not alone).

Tried another round tonight with more fuel. Got it to start with 4ms in base map cells, and an extra 150% coolant correction. Problem with that is once it fires, it's running 10.5s or richer while smoking like crazy due to overfueling until it gets warmed up a touch to 30c.

I think I'm going to try playing more with the 25deg crank advance and see what I can do. If Dguy is getting 6 port race engines to fire quick there, my modified street engine should do it.

Will report back after another attempt.

j9fd3s

iTrader: (3)

the training manual, says it cranks at 5btdc. i find that the warmer the engine is the more advance it can use before it kicks back, doesn't seem to make much difference in starting though

for fuel, i always end up with a big primer shot, and the the cold enrichment is more for once its running.

cBigganz

How big a primer shot? My primer is at 160ms. Can't add much more before it hits limit of 200ms.

j9fd3s

iTrader: (3)

it depends, but if its almost maxed out that should be enough

cBigganz

Update after a few more cold start attempts:

Cold start has improved after discovering that the 0 second column on post-start enrich directly effects the injection time during cranking. This is essentially the cranking injection table, and post-start enrich table. I have not seen this stated anywhere before, so this discovery has helped me greatly.

Car still takes 2 cranking cycles to get started, but it starts strong after the second cycle. I think I can get this down to starting on the first try.

Changes I made are:

FUEL
Fuel Base Map 5ms @ cranking area (0rpm & 500rpm, 0.0psi & -3.0inhg)
Coolant Temp Correct 75% @ 10c (-28inhg to 0psi)
Post Start Enrich 50% @ 20c/0s, 80% @ 0c/0s
Prime Pulse 200ms@ -40c linearized to 180ms@20c

IGN
Ign Base 15deg idle range(750-1500rpm -15 to -18inhg), up to 20deg at 0rpm to prevent stalling
Crank Timing 15deg entire range
Zero Throttle Ign disabled, Ign Base map setup for idle.

Will update again after a few more attempts. Once complete, I'll post some map pics.

Hopefully this info helps another poor diy tuner someday.