Let’s talk SOI with a PD blower cam
 

Hey fellas,

So I’m stuck between a couple of smart tuners who have drastically different thoughts about where my SOI timing should be…

#1. Thinks that as your cam gets bigger than OEM, you need to trim SOI back. So 340-350 stock depending on OEM LT1/LT4 cam, and my cam is 229/245 so he has me at 330 SOI. Made the power and time slip in my signature. He thinks Tuner #2’s idea would simply shoot fuel out the exhaust because of the long exhaust duration.
#2. This guy thinks tuner #1 is leaving a ton of power on the table, likely 30-40 WHP and is hurting my injector head room by not giving the mixture enough time to burn. More burn time equals a richer mixture without actually adding any more fuel. Says he saw a car go from .84 lambda to .82 just by increasing SOI timing. He says all the 8 second AMP and Crawford cars are running 360-370 SOI. He feels my car is a solid half second slower than it should be…

Given that most PD blower cams (mine included) have virtually zero overlap, I’m wondering if #2 is right…. So what are you guys running for SOI in your cammed PD car? And why? Thanks! :happy0180:

Most PD cam cars run 370-380 that I have seen. We are running 380 on my Brother's C7Z that has a Cordes stage 2.

Higgs Boson claims to set the entire SOI table to 280 and let the ECU adjust it as needed. I haven't tried it yet but I plan on experimenting with that at some point.

So I would agree with tuner 2 for the most part.

Please post what You find with setting them to 280. I'm very curious if Higgs Boson is onto something. TIA

What it sounds like more than anything else is that each tuner is telling you what they are comfortable tuning with. If you go with the suggestions from tuner 1, then make sure he is tuning the vehicle. Likewise with tuner 2. Take both of their suggestions along with what you are comfortable with and go from there.

The goal is the best performance and optimization of a very expensive fuel system. This SOI will have a correct number based on your cam card, so leaving it incorrect means a loss of a lot of power and excessive IPW. Given that I have a hand in all the tuning that goes into my rig, I’m definitely going to get some dyno time and exclusively focus on nailing down the correct answer on this SOI question. It’ll be probably be spring unfortunately though.

Let me start off by saying this is not an attack or a disrespect it is joining the conversation to help.

Focusing on your cars stated RWHP and performance.

I agree, your car is very slow for the RWHP, we went 9.46 - 146 mph with 150 less RWHP and an heavier car with 2 less gears driving to and from the track.

146 mph on a 4000 lb. car shows 950 CRANK HP. or about 800 RWHP.

146 mph on a 4000 lb. car is also good for 9.25 et, so there is some chassis work to do.

I understand your searching for answers, but I don't think SOI is the problem.

The SOI is a math calc, a simple one, and has to be pretty far off to hurt power when you have larger than stock injectors where the opening time is less than 6 ms.

If you are trying to run 7 ms then it becomes more critical.

Respectfully

Ted.

inject as late as possible that still allows a complete injection.

if the MAF and VE aren't exactly correct in all cells then observing a change in AFR after a change in SOI is just garbage in/garbage out.

Thanks for checking in Higgs, always enjoy your posts on HPT Forum. Ben Charles (who you know is on the ball) did my VVE, VT and MAF and I’ve verified those locally as well. No issue there.

I’ll be spending some time on this topic this spring when my car comes out of hibernation. My local tuner wants to work on SOI specifically and we’ll be re-dynoing my car, only changing SOI while documenting everything else. But other tuners from the HP Tuners Forum have reached out to me privately and they think my very conservative SOI table is costing me a lot of power and hurting my IPW. We’ll see…I’m not interested in guessing. :) I’ll be happy to post up the results.

Hi Ted,

Appreciate the reply. I agree that my car traps slower than it should. My IPW is under 6 ms as I do not believe 7 is a good idea…. Another tuner on the HP Tuners Forum found 39 WHP going from 340 SOI to 372 on a similar PD blower Camaro … that’s not chump change. Given that my cams exhaust valve is closed at 2.2 degrees BTDC (with no overlap), I think my 330 SOI is WAY off. Some time on the dyno will prove this out one way or another.

Josh

an advanced SOI can help if it's needed. what does needed mean is the question. if you can get a better mixture from an earlier SOI then 280 wouldn't make sense. so many people are advancing SOI for no reason and the ECM will advance on it's own when needed in most cases.

too late of an SOI can for sure hurt.

My car is over 870 rwhp on e (has hit 880 on dyno) and it won't trap 146 but its in the tune as it lays over every time I shift. Its not as bad without rev match on but with rev match on its horrible. Its also very unpredictable to drive as you don't know if you are going to get the monster or the lame duck so you need to be prepared for the monster at all times and are very disappointed when you get the lame duck.
2018 camaro ss 1le

Hey Josh good to have you back in the conversation.

I won't run anything over 6 ms.

I agree SOI is very important but I was looking at the math of MPH vs HP.

At 330 I would agree some improvement as well from moving it toward 350s

In the grand scheme (Way off) might be a stretch, About 1-2% power.

But I will certainly take what ever we can get.

Ted.

It is actually in the operating system and will be addressed in the next round of tuning.

Ted.

Hi Ted

I had my tune tweaked by Ben Charles off HPT Forum *after* my dyno session. Ben really cleaned up how the car ran in terms of around town drivability, shifting, etc but I’m beginning to suspect my 9.6@146 run was made with a good bit less than 927 WHP I originally had. I didn’t re-dyno after those tune changes and I probably should have. Once the car is out of hibernation I will do a full experiment focusing on SOI and will report back how it affects power. But I appreciate your comment on power vs time slip…it confirms that I’m down vs what I know the car can do. :happy0180: