OK, here's the deal. I just finished my engine build and now street tuning my car.

engine:
B18C with eagle rods and 9:1 JE pistons
t3/t4 .63 turbo, custom tubular manifold
RC 750cc injectors
.5 bar turbonetics WG
Greddy Profec B II - Lo(14 psi) Hi(20 psi)

I'm using Crome Pro with Ostrich and LC-1 wideband to street tune. First, tuned the idle perfectly 1k RPM at 14.7 afr. Then, Lo boost (14 psi) at 11.5-12:1 afr up to redline. But when I try to tune Hi boost (20 psi) right around 15-16 psi, car starts to backfire, sounds like it's coming from the front, and hesitates so I let off. I'm doing a conservative tune, 1 deg/psi retard, til I have time to see the dyno. I've done tunes before but on stock motors and never over 14 psi and kinda paranoid going over 15 psi now. Any ideas would help, thanks.

 

what map sensor?

 

spark plug type/gap?

 

oops...i forgot to state is a 2.5 bar motorola map and using MSD 6A ignition with ngk plugs gapped at .035.

 

What does the a/f ratio do at that point. On my car when I had too little timing it ran ok on lower boost but as it pulled more timing for higher boost it caused it to misfire. Pull the plugs out and see what they look like. Make sure you don't have any detonation. If you don't I would try and ramp in some timing after peak torque and see how that works. If you can monitor knock somehow or get on a dyno so you can see what its doing that would be the best. Also you can lower you gap on your plugs and see if that helps. I run my gap at .028 for any boost over 14 and have great results with that. My guess though is it needs more timing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TypeR II &raquo;</TD></TR><TR><TD CLASS="quote">oops...i forgot to state is a 2.5 bar motorola map and using MSD 6A ignition with ngk plugs gapped at .035.</TD></TR></TABLE>

lower the gap size
try .030

 

cool, i'll try lowering the gap and giving it more timing. my afr was still 11.5:1 at 16 psi, i let off because it started to hesitate and backfire. thanks

 

Drop the gap it to .020 and see if it fixes the problem before adding timing. .020-.025 is where we run most of our cars running over 15lbs.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by trickeng &raquo;</TD></TR><TR><TD CLASS="quote">Drop the gap it to .020 and see if it fixes the problem before adding timing. .020-.025 is where we run most of our cars running over 15lbs. </TD></TR></TABLE>
ok, ill try it, thanks for everyones help!

 

Aside from the over-gap of the plugs. Are you really doing 1 deg/psi....ouch .

That means at around 17psi you will be at 10* timing......OUCH! If you don't know what that means, don't tune your car.

Also check if the boost conrtoller or the boost cut on the EMS is set high enough...I always get scared when I hit those in a normal session.

 

Try a colder plug.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adseguy &raquo;</TD></TR><TR><TD CLASS="quote">Aside from the over-gap of the plugs. Are you really doing 1 deg/psi....ouch .

That means at around 17psi you will be at 10* timing......OUCH! If you don't know what that means, don't tune your car.

Also check if the boost conrtoller or the boost cut on the EMS is set high enough...I always get scared when I hit those in a normal session.</TD></TR></TABLE>

well my plan was to tune the fuel maps before i hit the dyno, then tune the timing maps on the dyno. i read somewhere 1deg/psi was conservative for street tune, is that wrong? i don't wanna spend to much time on the dyno tuning both fuel and timing. what should i do?

 

if u retard the timing by too much, u will have very high egt's.

having said that, 10* at full boost is too retarded. You have a B18C so your peak TQ should be somewhere around 6k rpm. Increase timing after this rpm by a couple degrees. On my setup, (similar to yours) my timing at 20 psi is around 15*

Look up how to do a step retard. This is the best way to retard your timing without sacrificing low boost performance.

Good luck

 

i have my plugs gapped at .028. were at .035. had this same problem before. i know what you mean. also i have my timing retarded to .9*/lb boost. 7psi though. stock pistons and rods. if i remember right im around 22.5* at WOT.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by not2slo128 &raquo;</TD></TR><TR><TD CLASS="quote">if u retard the timing by too much, u will have very high egt's.

having said that, 10* at full boost is too retarded. You have a B18C so your peak TQ should be somewhere around 6k rpm. Increase timing after this rpm by a couple degrees. On my setup, (similar to yours) my timing at 20 psi is around 15*

Look up how to do a step retard. This is the best way to retard your timing without sacrificing low boost performance.

Good luck</TD></TR></TABLE>

ok great thanks for the info. just to give me an idea, how much power did you make? i'm shootin for 350 HP @ 20psi


Modified by TypeR II at 9:04 PM 12/15/2006


Modified by TypeR II at 9:08 PM 12/15/2006

 

1deg/psi is "safe" for a basic 9-10psi setup, but when you start pulling 1 deg per psi and your running it up to 20+psi the timing numbers end up waaaay too low.

Also you shouldnt have any problems hitting 350... Just last night I tuned a car that had a similar turbo to yours... it made 280hp@9.5psi on a stock block b16 with conservative timing numbers...