Lets talk compression!

[Red97Eclipseboy]

you could probably run that tune on pump gas.. of course you're not getting any knock with e85, e85 is very knock resistant and that's fairly conservative

Right on. I know that E85 is very knock resistant. I love the stuff.

running a 190lph isnt going to get you far with e85 though..

I understand you there. The thing is, though, I'm not about power... persay. With the extra power/timing I got with just the E85 on my setup/tune, it is a perfect amount of power (to me) for road racing my FF. Which I'll be doing next season. I used to hook in second, no problem. With my E85 tune, I was blowing the tires in second away! Which I don't want. So now a dual-stage MBC/EBC is in order. My third and fourth pull so much harder now. So after I get a wide-band and do the line/filter coversion, I think I'll fine-tune the current setup and leave it.

Does that sound legit?

 

[Bud92gsx]

Please dont post anymore if you're going to spread more misinformation. this post is borderline retarded.

I thought this thread was about tossing ideas and learning from each other, not telling me I'm retarted. I get that enough from my better half, don't need it from you guys too..

 

[Bud92gsx]

There is one guy that I met that was running stock compression on E85 in a 1G. But he had cams, an safc, 950's, a walboro, and an eprom ECU. You shouldn't have to run higher compression because of detonation. Also E85 burns hotter than regular pump gas, so why would you want to run higher compression and have a chance of detonation while your burning hotter than stock? You could use colder plugs, but would only help to an extent.

Till this day I didn't know that E85 was more resistant to detonation, I probly should have thought this one through.
When the ethonol does detonate, is it a better idea to run colder plugs, or hotter??

 

[JusMX141]

Ethanol burns COLDER than pump gas, hence the higher octane rating....the same as race fuel.

This allows you to run more boost, more aggressive timing, and higher compression than pump gas without detonating.

Most guys step to a colder plug once they reach a certain point with pump gas, and from what I've seen with Ethanol you do not have to do this. My buddy's only seeing EGT's around 1450*f on a very good tune with Ethanol and 6ES plugs where he was at 1550*f+ with 93 pump gas and 7ES plugs. His fuel mileage did decrease drastically from around 20mpg with pump gas to 14mpg with Ethanol.

 

[Hazard]

Right on. I know that E85 is very knock resistant. I love the stuff.





I understand you there. The thing is, though, I'm not about power... persay. With the extra power/timing I got with just the E85 on my setup/tune, it is a perfect amount of power (to me) for road racing my FF. Which I'll be doing next season. I used to hook in second, no problem. With my E85 tune, I was blowing the tires in second away! Which I don't want. So now a dual-stage MBC/EBC is in order. My third and fourth pull so much harder now. So after I get a wide-band and do the line/filter coversion, I think I'll fine-tune the current setup and leave it.

Does that sound legit?

It sounds good, just change your fuel filter almost as often as you change your oil and rock out. Not everyone has huge power in mind. although your setup has a lot more easy power to make with a few minor changes if you want another tune for when you're feeling randy and want to push things

 

[Hazard]

Till this day I didn't know that E85 was more resistant to detonation, I probly should have thought this one through.
When the ethonol does detonate, is it a better idea to run colder plugs, or hotter??

That's the thing, good luck getting knock out of straight e85.. it is better at resisting knock than most race gasses.

Of course you can step to a colder plug at some point, but 7's will get you pretty far. I'm guessing bpr8es + e85 wouldnt be too fun where i live in the winter ....

 

[Bud92gsx]

Yeah It gets pretty cold here in the winter too. And your saying it wouldn't be fun since better gas = more power, and would be too hard to keep under control. Let me rephrase that, it would be less fun to keep under control..

 

[Kevin Jewer]

E85 should burn cleaner than E10, so colder plugs may last just fine. My EVO can run 8s all summer, but after about a month in the winter I get a little cold idle misfire. I would think 8s would be fine on E85, but I've never run the stuff, just speculating.

 

[Black_Bullet]

I have been considering tossing together a higher compression motor as well. If you're running E85 all the time and have a solid tune, there is nothing wrong with high compression. People are laying down upwards of 500whp on stock K20a2 honda engines, which are ####ing 11:1.

if your goal is 500whp or less and you can run e85, id say go for some compression.. why the hell not? Just how much is up to you, but in a street car, everything will be more fun. everything is about having a setup that goes well together, from where the intake starts to where the exhaust exits.

Id still like to know whats the highest people have gone on these motors?
11:1 maybe???

Hey if the E85 kills my gas mileage, at least Id know I get some of that mpg back with the high compression motor!

 

[dsm-onster]

I think it is the piston top/dish design that affects allowable compression. A good "fast burn" motor has high compression and actually resists detonation because of it. It has a large squish/quench area. The closer the gas particles in the air/fuel mix are at the onset of the flame kernal, the more likely it will be burned before it recondenses to a fuel droplet. Fuel droplets in the combustion chamber instantly (relatively) explode, or cause detonation. If you can burn the fuel before it condenses then you have pushed off a cause for detonation. This is why fuel injected motors can tolerate more boost than carbureted motors. V8 Blower guys like running drawthrough carb setups because the blower forces the fuel into finer droplets.

Honda has done alot of work with "fast burn" chambers, this is why you see high compression hondas work well with boost. But the 4g63 head has a great combustion chamber. There's plenty of quench pad on the head to make a great fastburn chamber. But look at the stock pistons. There's hardly any shape matching the flat portions of the chamber on the piston top. A good piston top is a mirror image of the combustion chamber. There will be higher compression which leads to more power from better thermal efficiency. And there will be one or more large quench zones that insure the fuel stays close to the sparkplug to burn before 'de-atomizing'. A high compression forged piston does this well enough.

If you're burning the fuel faster via fast burn chamber that allows higher compression, then you need to start the fire later. You don't NEED as much timing advance. Getting power from timing is not about more timing, it's about literally timing. Timing it right. MBT is the term used. Mean best timing is the best timing for the motor at specific conditions. 3000rpms typically needs LESS timing than 7000rpms because firing off the fuel earlier will cause it to burn up before the piston/rod combo can get to put the most torque on the crank after top dead center. The piston is moving slower. Adding boost, heat, and compression means that the fuel will burn even faster. Hence, turbo motors have lots of timing retard. That doesn't mean that they are losing power from timing retard. That just means that the airfuel mixture is burning faster than it's non-turbo counterpart.

A fast burn chamber changes MBT for your motor. If you have to run lower timing because you increased compression and did it right (with a well made piston and found the best timing curve for your engine conditions), then you may THINK you're losing power because the timing curve is lower. But you're actually gaining power. Because you still found MBT with your tune and you added the higher thermal efficiency of higher compression.

 

[Black_Bullet]

^ Awesome post, very informative, makes perfect sense, and was explained in a way everyone should be able to understand!

Hmm, so now I am considering running the Magnus 10.0:1 pistons (Magnus Motorsports - DSM/Mitsu Engines) over the Wiseco's, cost is about the same.

For either sets of pistons it would be a cake walk for them to handle the power I want to put down, but I know it also comes down to which would be better for detonation control and longevity and lots of mileage on the street!

 

[dsm-onster]

Hense why I showed the Magnus pistons . I really REALLY want a set for my long rod stroker build. . . Look at the quench area!

 

[tkelly27]

One other point of quench that I've read is that the gas mixture in direct contact with the walls of the cylinder, piston, and head can't ignite because it's required that it will be the same temperature as those pieces. The more you get away from those and into the pocket area the more you can ignite. Maybe I misinterpreted that, or it's not the main function of quench?

Autoignition temperature - Wikipedia, the free encyclopedia
"The temperature at which a chemical will ignite decreases as the pressure increases or oxygen concentration increases."
That is what we're trying to fight here, right? We're increasing the pressure and we don't want to decrease oxygen concentration, so that requires lowering the temperature.

Ethanol also has a higher specific heat than gasoline and a higher density. So you are putting more of it in, and it weighs more, so the energy required to evaporate it (it must evaporate to burn) is much higher.

Cams closing later in the upward portion of the piston travel can bleed off pressure lowering the dynamic compression ratio.

The more I learn about compression ratio the less I know which I want.

 

[Black_Bullet]

Hense why I showed the Magnus pistons . I really REALLY want a set for my long rod stroker build. . . Look at the quench area!

But then again Wiseco specializes in pistons and I normally buy accordingly.

Do the Wiseco pistons emphasis on the quench area the same as these "deep dish" Magnus?

Im sure either would be great, but I am not as well read up as you are on these things...

 

[dsm-onster]

Cams closing later in the upward portion of the piston travel can bleed off pressure lowering the dynamic compression ratio.

The more I learn about compression ratio the less I know which I want.

One thing to think about with dynamic compression. . . A cylinder with the properly chosen cam will be at about 100% VE for 2-3000rpms. 100% VE is 100% of the volume of the cylinder. Dynamic compression is equal to the static compression.

Black_Bullet, I don't know much about wiseco pistons, other than the fact that they are proven. I have never held one in my hand so I can't say how large the quench pads are. Marco Passante specializes in the 4g63. And has used his talents in other engine platforms afterwards.

 

[TunaTalon]

Dynamic compression is equal to the static compression.

I believe when tkelly27 used the term “dynamic compression” he was referring to “effective compression ratio” which involves the timing of closing the intake valve and does not change dynamically with engine conditions.

The effective compression ratio will always be lower than the static compressison ratio.

From page 31 of http://www.kidzuku.com/StrokeOrNot.pdf.

The compression ratio that is normally used discussing 4G63 specifications is the (30) Static Compression Ratio (SCR). SCR is simply the sum of displacement and head volume divided by head volume. SCR is a useful number because it doesn’t change with the camshaft profile. However in any real 4G63 version, the intake valve doesn’t close until several degrees after BDC. The delay in closing the intake valve allows the ram effect in the intake air stream to continue flowing air into the cylinder even while the piston is going up. (There’s that velocity effect again). The delay allows more air in the cylinder but compression can’t start until the intake valve closes. In any 4G63 version there will be some uncompressed volume because the piston is not at the bottom of the stroke when compression starts. The term Dynamic Compression Ratio (5) is often used for the compression that happens from the time the intake valve closes to piston TDC.
However piston position at the valve closing event does not change with engine operating conditions so this paper will use the less popular term of Effective Compression Ratio (ECR). ECR is affected by the cam profile and the rod ratio. At lower RPM’s air is forced back up the intake tract through the open intake valve as the piston moves up. At higher RPM’s the velocity of the intake stream still has air going into the cylinder as the intake valve closes. Peak torque occurs about the point where the air stream is just stopping as the intake valve closes. At higher RPM’s the volumetric efficiency starts to drop off as the cylinder does not get the full charge of air.

 

[SBstar]

This is great stuff, just the information I've been looking into.

 

[dsm-onster]

Yep. And effective compression ratio is at it's highest point at about torque peak. This is where VE as at it's peak and where the most cylinder pressure is seen. Where VE is 100%, it is safe to say that effective compression ratio is the same as static CR, right? This is the point in the rpm range where knock is most likely to occur. So a cam that comes on later will make the peak torque higher and also make the onset of detonation occur later in the rpm range. But it won't prevent it, unless you bought a cam profile that doesn't peak in VE until after your revlimit. . . I could be completeling not understanding tkelly27's point.

 

[TunaTalon]

I think we need a new term for what you are describing as where the most air enters the cylinder.

Yes peak torque is about where the most air enters the cylinder. That will be the point of maximum cylinder pressure at ignition and maximum VE. And that point is dynamic and varies with boost and RPM. That's why I don't like the term Dynamic used to describe the effective compression ratio (ECR) which is fixed by engine geometry.

Static compression ratio (SCR) and ECR can be calculated from bore, stroke, head volume, and degrees after bottom dead center when the intake valve closes. In any real engine SCR will be higher than ECR. They could be the same only if the intake valves closes at BDC.

 

[dsm-onster]

Ching! I see what you are saying now.