I have always heard that you have to pull a lot of timing to run High Compression on pump gas (Example. 13.5 compression on 93 pump). How do one knows how much timing to pull? i'm sure some most tuners probably dont have knock ears or detonation detectors.

So lets say i take a 13.5 comression on 93 pump to tune, i would assume the tuner would start with retard gnition timing and slowly advanced it. How would he know when to stop advancing? Spark plug reading? MBT? Or would doing MBT be too risky?

 

yes, you really do/should have a form of detonation detection. on the street you can rely on it and they verify with checking spark plugs. (see my thread in the stickies about that its very useful).

on the dyno its about mbt and plug checks. id say that the hardest part of it to tune wont be wot, it will be moderate load from 2000-4000 rpm.
now going 13:1 on pump lets say could run into an issue where you have to retard timing so much that you start to balloon your egt's. somewhere in there you may hit the point of diminishing returns where you loose power because you have to much timing pulled you'd be better off with a little less compression and a little more timing.

to my understanding it really doesnt matter what your static is nearly as much as the dynamic which i think you want to shoot for something in the mid 10's if my memory serves me right

 

whats the point in running that much compression for a street car only to run pump gas (non e85)?

you pretty much get to a point to where ramping in ignition timing to MBT becomes much like a turbo engine and your power suffers because of it. You will never get the full effectiveness out of your engine because the compression choice and use of pump gas was not a wise choice.

the detonation to be concerned with is not the detonation you hear (which is easily rectified) but the detonation that is unheard and only seen on the spark plug. The other concern is tuning this kind of engine on a dyno that is unloaded or one that cannot simulate an every day load. This will drastically change how the ignition timing curve needs to be done as the higher load on the street vs. the dyno will put more stress on the engine, thus require a lower ignition value. Then lets not forget the variances in knock defense from tank to tank when you fill up at different stations.

 

Thanks for the reply fellas.

What would you guys recommend as a rule of thumb for tuning a High compression NA regarding Ignition retarding per compression ratio?

Would it be like retard 1.5 degree's for every 1 compression over stock?

 

there is no rule of thumb. the rule is know what you are doing.

 

Also is it possible to start detonating before you reach MBT?

 

low RPM, high load is the most prone area of detonation. Once you reach MBT, the ignition timing flattens out

 

Thanks for the reply. I have seen/read several thread with your responses and feedbacks from years ago.

How would you start/attack tuning a b20v with 12.8 compression w/sk2 pro2's on pump 93? Let's say the motor is newly built. (Assuming everything is set to oem specs ignition timing, fuel pressure, etc) During start up and after adjusting idle to 14.7 afr, would you then retard several degree ignition timing from the right of idle coloum (Coloum 3-10) through out the entire map before start moving car and tune since compression is pretty high?

 

I'm assuming that's a yes. So watch out/keep ear out for detonation @ wot. I have just started tuning and haven't mess with ignition yet cuz it's street tune atm. Thanks.

 

It really just depends on what the engine wants. You need to start out with a map that has already been cleaned up (none of the stock basemap crap).

If you contact Xenocron, phearable.net or HAmotorsports they can provide you a basemap likely from a car with the exact setup they previously tuned for a small amount of money in comparison to building your own map and risking damaging your engine from running the engine too "hot"

Is this setup going to be your first time tuning?

 

I would highly recommend paying a professional to tune the car the first time so you can watch what they do and sometimes your tuner won't mind you asking questions. If you go into the appointment with the tuner knowing you are wanting to learn, they will be more willing to tell you what they are doing. This way you will ALWAYS have a map to revert back to when you get in a pinch.

I was lucky enough to know John from phearable a long time ago who coached me a bit when he tuned my car the first time many moons ago. It was a blessing because I was learning and made plenty of mistakes that if I wouldn't have had his map, I wouldn't have made it to work or school. I also started learning with a stock engine would paid out dividends in the end

 

No, that setup is not going to be my first tune. That setup is what I'm going to try to tune in the future. I have to degree in the cam first and check clearances as the motor piece together already.

I have a basic bolt on's GSR teg w/Blox cams i got street tuned by someone. Got it dynoed later and made 190whp with me playing with camgear settings. So i have got to seen some street tuning.

Anyways, I started using Crome about a month ago to tune my other car and I used "Xenoncron how to create a base map article" to do my first tuned. Using Crome i use the base P30 map and transfer a LS base map to the P30 base and started tuning from there. It's a basic bolt on's LS with B16 pistons and 310cc injectors. I've got it tuned pretty well i'm sure. Just havent touch Ignition Timing yet.

 

I'm going to try to retune my 190whp gsr just to get use to tunning high and low cam. Just for practice.

 

And Thanks for the tip. I guess i can get it tuned by a reputable tuner and ask more questions or get a map from places you mentioned and tuned from there. Thanks. Makes plenty sense.

 

people are always looking for an easy way to tune ignition.
I've been doing this a long time, I'm an engineer, I love math and simplifying things, but I can assure you there is no rule of thumb for this.
Even identical engines can yield remarkably different ignition needs.
Knock detection is an absolute MUST. Ears are good, but if it's your car, I'd recommend installing KnockSense.
Start with a high compression basemap, H22, CTR or ITR. reduce 10* ignition all over the map, tune to 11:1 AFR, tune ignition, lean out.
I'd highly recommend dyno tuning for high compression also. Often times you can detect potential knock zones before they happen by overlapping your last 2 pulls.

 

Yep. It goes all the way up the scale too. At the race end of the spectrum, MBT curves are developed on the dyno and from track test data. Engines are then individually (manually) trimmed out based on the weather/running conditions and to an acceptable amount of knock.

Ignition control is on of those things that is still a bit behind the times, unfortunately. Compound that with the fact that those of us in this forum are typically calibrating a 20-25 year old ecu and it gets even worse.

There are more advanced closed loop spark control systems out there, but it takes a lot of processor and/or special equipment to do. It's generally not even legal for a lot of racing yet and is pretty far off from being viable for the mass market, let alone the tuner market.

Get good at understanding what is going on now, and you'll have a leg up on understanding the good stuff if/when it comes down the pipe!

 

Yes, if the combustion chamber isn't efficient (i.e. slow burn, especially high-dome (CTR) pistons, quench area not to spec. Compare TODA high-comp pistons which are a more flattish design

Other variables that invariably come into the picture on high-comp builds:-

Also, normally high-compression builds have better headers, cold air ram intakes, oil catch cans etc, which improve VE which lowers ignition lead requirements.

How the head is ported also has a impact via "mixture motion" which also impacts ignition requirements

As a "ball park" At WOT timing on fully modded high-comp engine could be 10 degrees (or more) lower than stock - at part throttle less than that

 

I have yet to see much difference at the peak timing a high compression engine was able to achieve as long as the compression wasn't so high it was crippling the low end and the setup was relatively efficient. If your peak timing value of a stock compression engine vs the same engine with higher compression requires a 10* retard, i would imagine there to be some inefficiencies with the engines ability to breathe causing that.

For instance, my 12:1 h23vtec setup was still able to achieve peak timing of what a stock compression h22 would typically see although the timing curve and ignition ramping was much different getting there. The ramp on the 12:1 wasn't near as steep but after mbt was reached, you could continually add timing as the weight of the chassis vs. the drivetrain had already been overcome allowing you to add power back to the engine much quicker without worrying about detonation.

 

Agreed. I don't think there is a ton of value in running the sky high cr's either. A lot of people like to throw the number around, and I think it becomes falsely important... as in I see people making it a goal of their builds over displacement or even power.

Especially with as shitty as gas is these days (and make no mistake, it's only going to get worse), I can't see building anything over 11.5 or maybe 12:1 for a street car. If you focus on airflow and maximizing efficiency at a reasonable compression, the power difference from a >13:1 will be small and you will still (most likely) be able to tune it to MBT with a nice margin to the knock threshold. Beats the **** out of breaking a sweat every time you have to pull up to a halfway dodgy gas station.

 

... and fill up with E85 only to start the car and let your ethanol content sensor have the ECU do the compensation for you.

Sorry, I had to... all my modified cars get E85 except my supercharged GMC. It's still on 93, which I know that's what this thread is all about.