High Boost vs Timing @ high RPM

[rb25drag]

Guys I wanna see what kind of Timing you are running in your Rb25's

Tell me what kind of Boost you are running and the timing at High RPM say 6000+

Im currently Running 15PSI and 25.5 Degree's timing up top 6000-7500rpm. The car feels like it wants more. But im not going to change it until I get some Dyno time to see the results. But are you guys running any more timing than that on gas?

I know Propane Likes alot of timing compaired to Gas. Just curious to what numbers you guys are running so I have something to compair to.

[virus77]

Before I got to the propane part i was thinkg "god damn, runnin 25 degrees and he wants more" hahaha Cant help you there buddy, Mr. conservative here running 17 degrees at 14psi

edit: Just wanted to add im running 91 octane piss for gas
Modified by virus77 at 7:31 PM 6/16/2009

[Darius]

The IGN map that the PFC comes with from the factory for the RB25 has fairly aggressive timing especially up top (~25*). I have my map trimmed back about -5* to -8* from that and am running at 17 psi. I'm hoping to keep the same timing and creep the boost up to around 25 psi. We will see if it begins to knock. If it does, I'll just pull some more timing to compensate.

[240z4u]

I added a degree or two across the whole stock PFC map and run 23-25psi. Turns out that is more aggressive than I thought it was LOL.

[Carl H]

trick here is egts, ramp timing until egts peak smoothly (and slowly) with a max of no more than 850*c.i run 24* @ 14psi and taper down to 22* at 22psi, no knock at all and controlled egts.its a ballance for sure, too little timing and it will be a slug and egts will skyrocket...too much and it will be fast as hell with horrific egts for about 5 minutes.

delicate ballance for sure...all in the tuners touch we all have different methods for the madness.

[WhatsADSM]

I always wanted to get a thread together with people who are willing, to put their timing maps up. Glad we have at least some version of that!

Timing is EXTREMELY dependent on the burn rate of the fuel you are using. So to be honest with you, us telling you our timing numbers on gas (and/or gas mixtures) really won't do you much good on propane. You will need to go to a dyno along with a known working DET monitor and tune for MBT under low load and a few degrees before knock under high load.

In truth timing is a mix of TONS of variables. Under low load it is pretty easy to get right by using MBT. Under WOT it is a function of fuel properties, KNOCK (most engines die from this NOT AFR/EGT like many think), flow rate, RPM, IATs, brake torque, AFRs, EGTs, and engine stength/desired duty... Not really a simple run XX timing for XX boost.

FWIW, I personally don't like to push the tuning envelope too much on a stock motor being worked hard, and basically s*** for monitoring knock. On e85 (considerably slower burn than 93oct) with I'm guessing somewhere in the low 600bhp @ 20psi, at the top of the gear I am at ~22.5*. I just tuned for a bit more boost (since my fuel will allow that), and at 24psi I have it ~18* at the top. But that is getting awfully close to the limits of the stock engine. For a daily cruise/drag car I am comfortable with that. When I take it road racing, I take a few degrees out and the boost comes down to wastegate pressure (~17-18psi).

Hopefully I can get some more quantified data together once I get some time to finish my knock monitor.
Modified by WhatsADSM at 8:52 AM 6/16/2009

[Carl H]

^ what he said.another thing to consider is the static CR of the engine, an engine with a 9:1 cr vs 8.5:1 will need less timing overall to make the same power as the lower compression engine.with my setup i found that for whatever reason the 20 loves timing, i started out low around 18* at 14psi and it was a DOG to drive and egts were retarded high, slowly added timing back to where i am now and it works well.been running this way for over 2 years now...

another thing to consider (and this might not apply to propane) is your injector lag time, the wrong lag time will yeild a poor tune and possibly erratic flame front which can cause knock.

so many variables in the equn. that it isnt even funny.

[WhatsADSM]

^ what he said.another thing to consider is the static CR of the engine, an engine with a 9:1 cr vs 8.5:1 will need less timing overall to make the same power as the lower compression engine.with my setup i found that for whatever reason the 20 loves timing, i started out low around 18* at 14psi and it was a DOG to drive and egts were retarded high, slowly added timing back to where i am now and it works well.been running this way for over 2 years now...

another thing to consider (and this might not apply to propane) is your injector lag time, the wrong lag time will yeild a poor tune and possibly erratic flame front which can cause knock.

so many variables in the equn. that it isnt even funny.

Yup there really is a lot to it. Dunno how I missed CR... That is a HUGE factor.

But yea too much timing is very bad. People also don't realize to little will hurt the motor over time as well due to consistently high EGTs. The "too little" timing isn't nearly as detrimental as too much timing but none-the-less as Carl said there really is a "sweet spot".

In terms of the OP, IIRC he is running a carb setup for propane, and has the ignition computer controlled. So at least the injector dead time is out of the equation.

[neo240sx]

Hey I didnt know they made carb setups for rb25's?!! I wonder how that fits under the 240 hood?

I just rebuilt my neo because I melted the corner edge of the piston and was looking for some tuning answers. I think its was the crappy injectors I bought but I'm not 100% that its all of the problems.

[rb25det250sx]

corner edge

i know your problem...your pistons are square.

[BEST1TUNING.COM]

Most people think that running excessively low timing is going to eliminate the chances of a failure, however too low timing can have very poor results.

If the mixture ignites too far ATDC the peak pressure of combustion occurs too late for the most of the heat to be absorbed through the block, water jacket etc. Like Carl H said, it will cause very high EGT's since the combustion is happening closer to the exhaust stroke.

Instead the heat is absorbed more through the exhaust valves and head which can cause overheating or a sunken valve (valve heats to temperatures which the valve warps and doesn't seat properly)

If the valve or head develops a hot spot it can pre-ignite the mixture and cause immediate damage and failure. This isn't as common due to the engine running poorly at that little timing, but valve and head damage will still occur.

So timing is your friend but it is a process to get it right. Carl H touched on most of the factors involved with correct timing.

It would be great if we were able to monitor things like cylinder pressure which max combustion pressure should occur at 14 deg. ATDC to ensure maximum efficiency. Alot of people use MBT (minimum timing best torque or minimum best timing) which is the least amount of timing which produces the best torque output, however detonation can still occur at MBT.

I could go into more since we all know there is much more info but the best way to go is getting some type of knock detection, proper heat range plugs, proper fuel and pray your technique for finding correct timing works!

[Carl H]

^ excelent advice...at a minimum you should have a wideband as well as an egt gauge...a proper knock sensor monitor can be very helpful but also keep in mind that at high rpm/high boost there can also be lots of 'engine' noise that would set the knock sensor off falsely.

[BEST1TUNING.COM]

Yeah knock is pretty tough to distinguish.

It occurs at 6-12 kilohertz but so can other noises, what matters is the durration of the noise which is consistent if it is actual knock.

[FinkenS14]

I know on my old Grand Prix GTP tuning that, stock head gaskets would start to go around 21* timing, whats the boost/timing limit on a stock RB25

[Carl H]

no real limit to how much timing...as long as you have the fuel with octane to match as well as know the limits of the motor.again key points here are detonation, as long as its not detonating 9 times out of 10 the hg wont pop...i'd expect the head to lift on stock studs before the hg blows out.I used to run 18psi on stock studs/hg and it was fine, even when later on down the line we found out it was detonating it still held up.that was long ago when i was ill informed when it came to tuning, times have changed thats for sure.

[Sil240]

About how much are knock meters (entry level)?Which ones would you reccommend??

Now after reading that I'm getting paranoid......I know I've seen a Techtom or Technosquare one, It was just a little meter with #'s.

I've also seen ones that have headphones.Which is way too overboard for the average person.

[Shocker]

From my experience RB's are notorius to knock based on their cylinder head design alone. Whats good for response, and fuel economy isnt always the best for high timing.

The quench pads in the cylinder head love to heat up when EGT's are high, and when timing is too far advanced or to retarded. They act almost like a glow plug and hold in heat more so on the intake side. When the fuel is squirted into the combustion chamber some of this air/fuel mixture can get trapped between the piston and quench pad. As this mixture is compressed when the piston is traveling upwards into the glowing hot quench pad it can be pre-ignited, this occurs right before the spark is actually fired. This small amount of pre-ignition isnt shown on an a/f meter since its getting expelled with the rest of the fuel burnt by the actual spark on the exhaust stroke. So the a/f meter might be reading pig rich when actually the engine is pre-detonating its head off.

The next issue is the fact that the quench pads take up most of the flack from this small amount of pre-det so it goes almost unseen on the spark plug readings. Therefore a good knock monitoring system should be used. I have in the past been against them, but after burning a couple of motors here due to this same pre-det issue caused by a CAS/ECU related error I have decided to go to one next time around.

If anyone cares to see what type of damage I'm talking about look for my past build thread, it shows plenty of it on the cylinder head, and pistons.

[xracerx972]

i run 24* @ 14psi and taper down to 22* at 22psi, no knock at all

What the hell are you guys talking about? My d-jetro version has my 20 load row at around 11* in full boost (24psi) or something like that. Thats the stock IGN map numbers. Im baffled to see you guys saying your stock IGN maps have numbers in the 20s for full boost..

What exactly is "no knock" by the way? something less than 10? Or literally 0? I get counts between 3 & 11.. After reading this, I feel like my timing may be too low?

I want to see if maybe my timing is way retarded and advance it some, Im just not sure how much I should rely on these old knock sensors.. I have no EGT gauge :|

[RRRRB]

Holy Thread revival!!

Timing is all relative to the setup and engine management.. 22 degrees sounds aggressive as hell on pump gas..

I was running around 17 degrees on pump gas around 20psi on my RB25

Lots of thing to consider... who knows if everyones timing is synced properly.. or there maybe a compensation in the map not set right thats pulling or adding.. could be lots of things that change from one persons setup to another..

[xracerx972]

yeah definitely an old thread.. I found it and was surprised to see that their stock maps had such high numbers for timing.

These are my stock numbers.. They look pretty low comparatively..

[Yellow4g63]

I run 26 deg max on meth injection. 19 without it.