E85Forum.com

BlownEthanol · Joined: 08 May 2007 Posts: 43

I kow there is lots of info on this subject out there on the internet but sometimes it seems like its too much info so I wanted to see what you guys have to say about how much timing to run on a boosted application.

I know that dyno tuning is probably the only definitive way to figure this out, but I just don't have hundreds of dollars to spend all day at the dyno so I am looking for some generic, "rule of thumb" type info on where to start. I know that timing is based on the flame front and that adding boost speeds up the flame front and that timing should be lowered as boost goes up. How much should timing be lowered in general for each pound of boost? Another thing that almost contradicts this is that I have heard that generally less timing is desired at lower rpms to produce more torque. Well I see l less boost at lower rpms, so do I do more timing because of a slower flame front, or less timing because of lower rpms? Here is a chart of what my boost did in a 1/4 mile pass, I let out when it didn't want to shift and hit the rpm for fuel cutoff, hence all the KR:

Also note that I did not tune for this pass at all, I just added 30% more fuel and it was the first run on E85 ever.

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

The short answer is to use the same timing that gives good results on gasoline or +1 or +2 if you want to push it. E85 will Tolerate more timing but it is seldom an advantage.

Cranking up the timing as a crude crutch and drastically increases cylinder pressures ( read that is not kind to bearings and head gaskets or rings) for very little power increase.

You should try for minimum best torque timing. This is usually 2 -3 degrees retarded from the onset of knock. If you get on a dyno crank up the timing until you see an additional degree or two of timing does no good. When you get there you are already too far advanced, back off the timing until you can just detect a power drop and you should have a safe tune that gives you within 1 -2 % of maximum possible power.

Larry

shizon · Joined: 09 May 2007 Posts: 16 Location: Avon, IN

BlownEthanol · Joined: 08 May 2007 Posts: 43

I have HPTuners, but this is a graph from an excel file. I don't have the HPT software on my work computer so I have to convert but here is a graph with rpms/100:

The bottom numbers are just frames recorded, but the whole thing is a 1/4 mile pass start to finish. BTW this is only a ~80% throttle run so it may not be able to tell much. The car is supposed to shift at 6k but it didn't want to , I think the trans fluid is low. Then out of second it shifted at 5500 because of the low throttle angle.

Boosted3Bar · Joined: 14 Jul 2006 Posts: 50 Location: San Antonio, TX

I run between 6-8* more timing at WOT than stock. I believe stock was 16* and now I run 22-22.5* for my street tune and 24* for my race tune. My car has responded well to a flat spark table. What I mean by this is, from about 3000 rpm through 6000 rpm I'm at max timing. I used to start max timing at 2500 rpm but it would just light the tires up so I dropped the timing to drop the torque in that area.

Now one key difference between our L67's is that I have a roots blower and you have a whipple. My boost maxes out very fast, around 2500 rpm at 11 psi (I only make another .5 psi over the next 3500 rpm). Your blower continues to make more boost the faster you spin it, with this I would guess that you may have to retard the timing a bit up top when you are at 14+ psi. This is just speculation on my part, but HTH.
_________________
2003 Grand Prix GTP

http://www.cardomain.com/ride/2155875

94NDTA · Joined: 01 May 2007 Posts: 18

I thought whipples were roots style superchargers...
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1994 Trans Am GT - Stuff
1999 Regal GS - less stuff

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

BlownEthanol · Joined: 08 May 2007 Posts: 43

Okay so lets see if I am understanding this correctly:

There is a certain amount of timing that is ideal for an engine at a given rpm, this value is called minimum best timing or MBT. For most engines you want the actual flame front to hit the piston around 12* after top dead center. When tuning the car you can usually just add timing until it gets KR and then back it off a couple degrees and you are probably at mbt where you will make the most torque. We always hear on the forums that more timing is better and that is simply not true, its possible to go past mbt, not get any KR but still lose power, and this is why its best to do tuning on a dyno where you can see the actual results. The reason why its difficult to get your flame front to hit the piston right at 12* atdc is because there are factors that speed up the flame front like boost and compression. As boost increases the flame front moves faster, thus you have to run less timing to hit that 12* number. So when you put a Whipple on, being able to run 24* of timing with 16 pounds of boost is probably not helping you at all, its just as bad to go past that ideal number as it is to go before it. So even tho 24* of timing on a 7 psi M90 setup might be ideal, its in no way going to be ideal for a Whipple setup. What I was thing about doing is dropping one degree in timing for every pound of boost I add. My numbers will look something like this:

Boost - Timing
5 - 24
6 - 23
7 - 22
8 - 21
9 - 20
10 - 19
11 - 18
12 - 17
13 - 16
14 - 15
15 - 14
16 - 13

This is just a starting point that I was going to go with until I can get it on the dyno and find out for sure.

Does this sound like a good plan? Am I misunderstanding anything or forgetting something?

shizon · Joined: 09 May 2007 Posts: 16 Location: Avon, IN

I guess I always considered MBT in conjunction with flame front speed/propagation regarding the fuel being used. Since E85's burn is so much slower, you do need more timing to get to MBT.

I think we're saying the same thing anyway Smile

. I just know when I was reading, a lot of people in the LS1 world was talking about timing and E85 and that they shouldn't add timing. The dyno proved that wrong.

Good discussion.

BlownEthanol · Joined: 08 May 2007 Posts: 43

Well I got the wideband hooked up tonight and found out why I saw some KR at ~12 psi of boost, how about a 13.5+ afr on E85 at WOT Shocked

Not entirely sure why it is going so lean when I am commanding a 7:1 afr, I am still running the stock MAF tables so I can tune it out, but I think even the stock ones would be much closer than that, they usually error on the rich side anyway. I do have an intake leak, but its after the blower and if anything I would think that would make it go slightly rich. Anyway, I will get it all tuned out, no biggy there. It is however kind of interesting that I only saw 3* KR max at WOT above 12psi of boost and ~16* of timing, I'm thinking this is gonna work out REAL nice. I may be able to pulley down and get a few more pounds of boost out of this thing and I'll just keep going until I can't run anymore boost w/o KR or until the head gaskets blow at which point we'll go with some better ones. The future is bright!

Boosted3Bar · Joined: 14 Jul 2006 Posts: 50 Location: San Antonio, TX

BlownEthanol · Joined: 08 May 2007 Posts: 43

A Whipple is a twin screw which compresses the air within it, its a more efficient way of doing it than a roots like the stock Eaton M90 which simply crams air into the manifold to create boost. The Whipple is also much larger in this case and it can hanle a lot more boost, this particular blower is long-term endurance rated at 30 psi which means its capable of much more. My engine is mostly stock really, stock heads and cam, just headers and good exhaust and I can already run 16 pounds of boost non intercooled and its not even tuned yet Very Happy

I'm thinking I may be able to get 18-20 psi out of this thing non intercooled!!!!

It will be a while before I have dyno numbers but track numbers are coming this weekend.

shizon · Joined: 09 May 2007 Posts: 16 Location: Avon, IN

Sounds to me like you might be maxxing out the MAF which means your going to have to fudge your commanded AFR after the maf limit.

BlownEthanol · Joined: 08 May 2007 Posts: 43

I will have to double check that, this MAF in stock form can handle 60 lbs/min of air at 11,500 Hz, but on our V6 PCMs IIRC we can only run up to 10,500 Hz which translates to 43 lbs/min. If thats the case I may not be maxing it out yet, but probably getting really close.

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado