I know, wide subject, but............For a 9.0 to 9.5 to 1 SBE engine what is the consensus for safe timing at different boost levels with a safe AFR (11.5) ? I have mine set up to take 1.5* out per psi of boost, starting at 31* at 100 kpa. So, 1 psi is 29*5, 5 psi is 23.5*, 8 psi is 19*, 10 psi is 16*, 12 psi is 13*. Am I being too aggressive with a stock bottom end 9.2 to 1 engine at 11.5 afr ?
So far , I have only mustered 6.7 psi from this setup due to other issues. Those issues are soon to be fixed. I plan to go to 12 psi max and I would really appreciate some input from those that have done this before.

 

19.5 boost, 26 deg timing, oxygenated race gas. Tighten up the hose clamps and fkn hold on to something!

 

there is a lot of things that can effect it but you should be safe if your intercooler works good. I never got above 11.5 degrees at 10# boost on mine but it ran 10.50s there so I left it until I went e85.

 

Give it what the engine wants and still remain safe and ensure there are no signs of detonation.

Not what someone on the internet who is nowhere near your engine thinks it might be ok with.

 

I tend to run higher timing, just left over from the small/big block days, lol
Around 12-13 PSI I run 16, prob could run higher, #7 plugs-when I ran a blowthru carb and Procharger, @ 12 PSI the plug reading (#6 plugs) liked 22
degs
The plugs will tell you what they want, but really its not always easy or convenient to make a blast and pull a plug, and 16 degs has been kind of proven as a ballpark starting point.
Kind of the same deal with AFR's, a buddy had a small block that dyno'ed
over 1200 HP by Steve Morris, was happy at 12.3 AFR, go figure, lol

 

Dont think there'd be too many highish CR pump fuel cars running those AFR's at that level.
And if it was, you'd need to be monitoring all cylinders all the time as it would be right on the edge.

 

That's like saying "skying is easy, just go down the hill and when something gets in your way, turn."

In other words, not very helpful. A lot of the combinations are fairly similar, so having some guidance from people that have had success, is not crazy talk...

Andrew

 

And telling someone at random miles away to do something totally unchecked and not monitored who has no experience.....can easily end up things going bang.

 

I think your underestimating me just a little there, Stevo. I can data log through 2 different devices that are part of my build and I have a very good understanding of AFR and spark timing. Been building stuff longer than a lot of people here have been breathing. Its just my first forced inducted rodeo. All I asked was to verify what I already studied and had downloaded to the MSD 6012 box. I got that answered and I appreciate all who gave their input.

 

If you know how to tune, then tune it. Dont take other peoples word for what they think should be in someone elses engine they are not tuning themselves.

And if you are attempting to copy others....play even safer than they suggest for all the reasons already mentioned

 

New, did you verify mechanical TDC matches 0 programmed? Start safe and sneak up on it. Plugs don't lie. The BIG unknown - what are your IATs like?

 

I have not verified TDC, but Ive been running the box on that car for 3 years with an NA setup that had 226 psi for cranking compression on pure pump 93 and had no issues, but I will check for safety sake. As far as IATs go, the FiTech shows IATS on its dashboard if I set it up that way, so no issues keeping a close eye on that either. So far I havent stayed in it long enough to glance at the IATs, LOL.

 

On any engine, you have to have a STARTING POINT to go by. I will tune it with the plugs after I get it building boost . I have checked them after a couple mid 6s psi runs and its a touch fat and the heat ring is maybe a 5th up the ground strap, but until I get to the boost range I plan to run (12 psi ), I wont be doing any adjustments.
I started this thread when TruckDoug spooked me with a comment to another thread about 16* being too high at 8-9 psi and I am at 17.5 at 9psi. Just made me want to verify my beginning timing again, thats all.

 

Yes and that starting point comes from tuning experience.

I would never give out suggestions, simply because I've no idea what the person is doing at the other end, what their setup is really like, what their fuel is really like etc etc.
It's just risky.

You'll rarely ever harm an engine by starting very safe and working up.

 

Here is a pump gas (91 octane) tune I did for someone with a 10:1 370 running a s480 on 15 psi.

 

^ that looks pretty money. is he spraying any water/meth?

 

Nope just our straight 91 **** pump gas. He has q16 for higher boost.

 

383, Looks good. Very Safe.

72, Software says 17.5 although could be 14 or 20 when verified. Many don't check so be careful following unchecked practices/parameters.

 

temp plays a role in chemical reaction rate. Combustion is a chemical reaction. As temp increases, reactions typically speed up. Compression causes temp to rise, whether the piston or turbo does it. IAT is only one side of the story, the cylinder has it's own set of temperatures (cyl head temp, piston surface temp, cyl wall temp, think of the surroundings). Knowing the temp of every item in the engine is unlikely. We can measure EGT fairly easily, location of the probe and reaction speed of the probe are two major variables so the word "EGT" is only useful when you have experience, or a book containing those experiences/experiments. I mentioned EGT because it will give us a snapshot of what the temp averages are coming off of the cylinder(s), which is what we are really concerned with. High end performance setups may have an EGT probe per cylinder. As we retard timing, the EGT typically will rise. This method may be used to find the diminishing returns point of timing, i.e. the point at which EGT begins to rise rapidly defines the lowest timing limit given the current environmental/combination variables (the current temps/pressures of all surfaces/scalar quantities combined, wherever the engine is installed). The headroom from that point, for more timing, is also variable. In fact there may be none at all; the engine might ping no matter what you do, if octane is low enough. Zero octane fuel exists, it is known as n-octane, a straight chain hydrocarbon containing 8 carbon atoms. This is measured against a 100-octane, more branched hydrocarbon chain (2,2,4-trimethylpentane) in a test engine to determine the octane/performance of other fuels before they are sold to us. The branching hinders the coordinate reaction, slowing it down, and also reduces its total energy released (since more energy is wasted in collisions between atoms that do not contribute to the chain reaction of combustion). Thus the higher octane numbers in gasoline fuel will provide reduced economy.


If you assume you have enough octane to protect the engine given the existing temperatures, you can reduce timing to find diminishing returns by watching the EGT suddenly increase as you gradually reduce timing advance. This is a sign that more fuel is burning in the exhaust system (near the probe) rather than in the combustion chamber, thus engine efficiency is reduced (economy would decrease) and torque will also decrease (because we are assuming octane is high enough to complete the reaction fully in the combustion chamber, while this is not always the case in reality). From this point, you may advance timing and watch EGT drop. The engineers who design and test OEM engines likely set the timing near this region, as EGT drops the most within the first couple of degrees you add from this point, when every engine part is beyond fully warmed up (too hot, a durability test for worst case scenarios). As temp increases in engine parts, the EGT ramp also moves. In other words, say you found that EGT suddenly jumped from 1350*F to 1600*F when you move from 10* to 5* of timing. If you increased the temperature of all engine parts an extra 50*F, you may find that EGT at 5* would fall to 1450*F from 1600*F. This is because the additional *F in the engine components increased the combustion reaction rate, as if timing were advanced. The reason there is no direct correlation between temperature and advance in degrees is because fuel octane cannot be compared to the rate of change of engine RPM and piston location vs time (the forces acting on the piston due to fuel octane has no direct, comparable connection to fuel octane). By setting the timing near the diminishing returns "ramp", you have a maximum amount of headroom for increased temperature (worst case scenario). As engine computers and sensors improved, the engineers are now able to push more advanced timing under certain allowable conditions, because they have much more observation of the variables which can harm the engine when optimal conditions are not present. In other words, lets say for a given engine with 100% VE at 4000rpm that 30 degrees is optimal if everything is perfect, maximum efficiency is achieved and minimal EGT is recorded by a probe. If temp rises 20*F and fuel octane drops 3 points, now the optimal number is 26* btdc instead. You couldn't do that with a distributor because there are no sensors present to detect suboptimal conditions, you would just need to run the 26* (or less) to ensure that when conditions are sub optimal the engine is still safe.

So lets take another look at EGT. If you note a very high, unsafe EGT at 5* of timing, and it drops significantly with 10* of timing, wouldn't 15, 20, 25, 30, etc... be even better? As you continue to advance timing, EGT will not rise again. It will continue to drop. So how do we know when too much timing is too much, if EGT is always dropping? The measurement of EGT can not be used to find optimal timing in the same way a dynometer can. It can be used to find minimal timing (because as you reduce timing you will eventually see an undesirable EGT which might melt parts). As you advance from minimal timing, a dynometer should be used in conjunction with knowledge of the vehicle's application. In other words, you add timing from the EGT ramp based on the application of the vehicle. For daily drivers, just enough timing to drop the EGT to safe region and bring torque within 10% of max is plenty. If the vehicle is a strict race car, timing is pushed farther. If the vehicle has unlimited spare engines and sponsors with unlimited funds, you can afford to run max timing and assume optimal conditions are always present, since unlimited funds not only buys unlimited engines, but also unlimited 'toys' like ice cooled intercoolers and special race fuels. The application of the vehicle will dictate how much extra timing is pushed from the EGT ramp rate. At some point while advancing timing, after it's ultimate peak, torque will drop, even while EGT is dropping or staying the same. This is bad for an engine because now pressure is spiking and a gasket or piston will have a hole blown in it, depending on what those parts are made of. In fact it was probably spiking before it's peak. This is why you want the dynometer, so you can do well to avoid the absolute peak of torque. Alternative fuels may also hinder the use of EGT as an indicator. One of the important concepts to take away from this, if anything, is that a timing which results in absolutely highest peak torque numbers is often too far advanced. Pressure spikes caused by too advanced timing often cause wavy or spiky graph outputs on the dynometer, requiring the use of smoothing. Smoothing should always be set to 0 for optimal diagnostics of dyno graphs.

An example
http://www.nsxprime.com/forum/showth...=1#post1909252

 

383, Care to share finding MBT at various rpms and loads? Dyno? Street tuning? Assume the approach is not different using 93, E85, C16?