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Hopefully, there's somebody on this board with experience running higher compression on "pump" gas. I've read of a few tricks worth mentioning to withstand higher compression on cat-piss gas. We're really only talking about 93. It'll always get that. considering the ford zetec runs these things, it should work for ours. Those get away with 11:1 with less than this.

-shape a clover leaf combustion chamber, via creative welding and grinding. (almost-kinda sorta feasible)

-a smaller volume combustion chamber to lower the compression and increase quench. (???)

-wider cam lobe separation. It's something larger displacement engines like to make more torque at lower rpm. v8's run 106 on a tight cam. 112-114 is usually a good cruiser/RV cam. I've heard of closer to 102 being used for race engines. But, you can go as far out as 120 (HOT ROD '97)

-a cooler engine (excuse for a better radiator and cooling enhancements. ;))

-thermal coatings, cryo-treating.

-oil spray piston mod.

-better breathing capability in the first place. Breathing mods alone can let you get away with running more compression, but not much more. (1/2 pt.-ish)

There's a lot of tricks to get this to work. All of this costs money, but what will I gain because of it? Now that the impreza is parked, I can ponder some of these finer details that are supposedly required for a good n/a engine to run really well. None of it's a black art, really. It IS about what you can pay for, and how much you can do yourself. Then pilot it, fix it when it breaks, trailer it occasionally, and basically cater to it :p. There's plenty of opportunities to make it work, though.
 

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The only secrets to running questionable octane fuel (<93) are 1) Modify the fuel....MMO is a good choice 4 to 8 oz per 10 to 12 gals of fuel can slow the burn rate to a usable rate for 10.5+:1 CRs. 2)Keeping the intake air cold and the engine HOT (only works well if not predetonating..ie slow burn rate!) 3) More Spark energy (better wires & better plugs...avoid gimmicks) 4) Water injection!

No other hardware mods will help if you're limited to just pump fuel......mod the fuel ....control the burn...these tricks work with CRs up to 13:1 ...beyond that......MONEY and lots of it 106+ octane fuel!

:sunny:
 
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-a smaller volume combustion chamber to lower the compression and increase quench. (???)
If you shrink the combustion chamber and you don't decrease the stroke, I really don't think you're going to decrease the compression ratio. Won't you actually increase the c/r? Let's say you shave 10 cc's off the chamber on a car that was 10:1
uhhh.

let's see if I'm anywhere near correct.

used to be: 1000cc volume w/piston down, 100cc volume w/piston up.
now : 990cc and 90cc

Yeah. You just bumped the c/r up to 11:1

But I'm just a lay person and I could be wrong. :)
 

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I'm not sure what he was getting either....but if you mill down the face of the head you can reduce the size of the combustion chamber....increasing the CR...if you remove material from inside the combustion chamber...from the cavity in the head or from the top of the piston..you increase the size of the combustion chamber...decreasing the CR.

:sunny:
 

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Good fuel and timing managmet go a long way... as well as a properly designed combustion chamber. I used to run 93 in my bike, with over 13:1 compression, no problems.
 

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Discussion Starter #6
smaller combustion chamber = higher compression...that's what I meant. I wanted to pump it up right to 12:1 and still run a 100+ shot of nitrous. not on pump gas, tho. Thank god I can get 100 octane a few miles from here :).
 

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Discussion Starter #8
heavens no!

I get it from an Amoco mom and pop station that has it at the pump. Every racer and biker in town gets gas from that station. Boy, does my impreza love it, too :).

About your bike, yama, how much of the timing did you have to retard to make it run right? Was a it a ducati w/ fuel injection :cool:? You also had weight on your side

One of the drawbacks of higher compression is the heat it produces. There's an advantage with not having much rotational friction/force from the parts on your bike, relative to the engine size, driveline, and chassis. that's less heat back into your engine, too. The coatings and stuff that are available now make a lot of this stuff possible, too. But I want those advantages, plus fuel management. Honda 1.6's run up to 12:1 compression...and I still think a Subaru can do just the same if not better :p :devil:.
What would a 2.5-3.0 litre :devil: boxer engine do spinning just as high if not higher than some hondas. I've heard one story of aguy spinning a turbo sube to 14k rpm. It broke a dog box. Old school subies have been spun to 10k, and vw's have been spun to 10k and up to 12. Revability of a well tuned boxer seems to have been a well kept secret. Good torque is only half the story.

Crankshaft acceleration has been a weird phenomena to experience with a n/a motor. It just winds up and keeps on going.
If it could spin to 10k rpm with a linear powerband, then you've got it made...to a point. things spinning at 10k rpm don't usually last long. Oh wel...off to bed.
 

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Didn't have to retard the timing at all. Actually that's not quite true, I did remove the timing advance kit (offset woodruf key) and went back to stock timing. It was a carbed Yamaha (hence the Yamarocket name) All I had to do was richen the mixture a bit. It did have more power on 108 race fuel, (about 5-6 more according to the dyno) but it ran quite good on 93 and that's what I almost always ran, 108 was just too expensive.

Youre right about the heat, I had to run a larger radiator, it would overheat riding it hard in hot weather. It also ate exhaust valves on a semi-regular basis, even stainless race valves, but then again, the exhuast stream was hot enough to turn stainless free-flowing headers blue. What do you expect when you take an engine that made 72 HP stock and push it over 100?:yikes:
 

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Discussion Starter #10
Did that blue header have any coatings on it, yama? I'd like to run on pump gas and not sacrifice the engine to do it. The less time spent under a hood working on it is a sign of better tuning. I've heard that pump gas can do that on a high compression engine in the first place. That heat is a bitch to fight.

Heat is one thing that has been on my mind with this stuff. I'm raising compression and efficiency through mechanical means. I've read about boost increasing volumetric efficiency, and raised compression boosting thermal efficiency. Both actually create more heat, and both increase volumetric efficiency (duh!). The power from an n/a motor is always on because of certain static variables regarding compression. There's no variable torque output because of artficially induced compression. Is a high compression engine putting out the same amount of heat, if not more, than a low compression turbo at full boost? If so, what can be done to combat that heat, and raise the thermal efficiency even more?

The air is going to be getting in and out as fast as possible. There's no turbo to collect heat and stay in one spot. It's one less rotating, heat producing thing under that hood, too. I'm increasing compression mechanically instead of artifcially with boost. Geometry is making more compression ;).

I was once told that making more power was never really the whole story with an engine. It's about who can accelerate faster; getting that crank to spin up quicker. ME, VE, and TE all play into it. Too many turbo fans talk about Volumetric this and that, but there's still more. Mechanical efficiency can be increased with less total restrictions on crank rotation (lightening crank, rods, flyhweel, pistons, etc. Thermal efficiency is how much of that explosion is used, vs. wasted as heat. Bad TE can be a pandora's box. Heat affects everything....ME efficiency decreases as rpms increase, and there's less TE because of it. More of VE that's used well decreases TE, too. (Get visions of slopes, lines and graphs going in your head :).) I'm trying to get a hold of good formulae for this stuff. It's the only thing that's making N/A engines run as good as they are in import drag racing.

Ya think that new Chalak synchroset might hold up to 10k rpm launches and insane crank acceleration? :devil: :happynow:
 

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No coatings on that header, it just fot really friggin hot. A N/A motor that's built to produce 250 hp for example should run temp wise about the same as the same motor that's all stock turboed and producing 250, because the same amount of air and fuel is being used to produce that power. A FI motor uses mechanical means to force more air into the engine, a built N/A motor uses the atmosphere and it's own efficiency to coerce that air into the engine.

But keep in mind that all other things being equal, ie number of cylinders, total frictional and rotating losses inside the engine etc, if both engines are producing the same HP and torque numbers, they are consuming the same amount of air and fuel, and therefore should be producing similar amounts of heat.

There really is no way to make an engine able to deal with extreme heat without redesigning the whole cooling system. However, the cooling system is designed to be able to keep your engine cool under some pretty harsh envirroments, like Death Valley at 80 mph with the air on and 4 passengers with their luggage. There is usually some "reserve" built into it's capacity as well. The real issue is keeping the temperatures high and stable in and around the combustion chambers. Lower temp thermostats for more power are a myth. With a properly tuned ECU, you get more power with higher temps, but you have to be carefull to not overheat things of course.

But I think your real question is whether an EJ25 can take the heat produced with extreme N/A building, and the short answer is yes. The real issue will be geting the bottom end, trans etc able to deal with the power and torque.
Here's a liny you might find interesting.
http://www.mivec.co.uk/performancedata/index.htm
Scroll down a bit till you find the discussion of HP vs Torque.
 

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Discussion Starter #12
Hmm..cool...

I understand what you're saying by the same amount of fuel and air and such. But, I guess it's coimmon sense that I'd be making more heat if I had to do it at 8k rpm instead of 6k ish with boost. Thermal efficiency is worse up there. But, I know what you mean about heat in the right spots. Everything up to the intake valve needs to be as cool as possible, and everything on hte other side of the exhaust valve at a hot enough temp for a decent period. But, what about hotter more consistent temps in the combustion chamber? Eliminating sharper areas in the combustion chamber is one way of deterring hotspots. A flat top piston is more ideal with a smaller combustion chamber, and a steeper valve angle. This phase 2 has all of those! There's always room for improvement, though.

As an aside, I've been wondering why there isn't a nitrous only class in import racing. Boost and N/A are covered, so why not n20? (I won't use the word NOS for fear of reprisal :stinky:)

For this beast of a denial of physics, I'm going to be running extra injectors. How many and where is my secret, but I think nitrous can be controlled better if used that way. The biggest thing that scares me about using it is this car's tendancy to burp once in a while. I think it can be tuned out...I hope. The thermal challenges I'm going to encounter are the whole reason I'm looking so extensively into coatings and "magic"-treatments. I was originally thinking of what I could use and couldn't, but compromises even cost you money, too. Some people run a little on the rich side to cool the motor down, but I'd prefer to avoid those kinds of shortcuts. I've even considered coating the valves.

Oh well..off to dinner
 

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hmm...I keep reading that 12:1 compression with fuel mods can run on regular gas. Beyond that is dangerous and a zone of diminshing returns. What really bugs me is that boost gets a higher compression ratio that you can really rely on compared to N/A. Believe me, I'd like to bump it up near 13:1/13.5:1 comp. Effective comp ratios in boosted apps can get higher than N/A means, can't they? I can't control this with a knob. It's a lot of precise work in the first place. I need to know if someone can get thermal exchange numbers on tungsten or molybdenum? Some of these coatings aren't necessarily thermally related, but reduce friction and then reduce heat as a byproduct. I think that's what molybdenum does.

Is there a chemist or a metallurgist in the house? :)
 

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Molybdenum as a coating has excellent wear characteristics with standard lubricants but does not reduce thermal conductivity, Tungsten is hard...very hard and great protection for extremely high temps and it does provide a small reduction in thermal conductivity...however geting it to bond to aluminum is a problem. One material to consider might be silver tungsten carbide...not as hard as pure tungsten but machinable (silver gives it the machability). It does bond to aluminum but not to stainless (wouldn't be good for valves!)....If you can find someone willing to sputter silver tungsten carbide to the top of your pistons and the inside of the head and use Tungsten (plated or sputtered) vlaves with Moly plated valve guides with a synthetic racing oil you should be able to reduce the thermal transfer ratio to keep the pistons from melting down at 13.5:1 CR.....however your exhaust gas temps will rise proportionally and you will need to handle that! No estimates as to hoe long all of this will hold together but with the boxer design....chances are it would be several thousands of hours!

:sunny:
 

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Discussion Starter #15 (Edited)
Hmm..cool...I've been wondering about the valves, too. If I should upgrade to titanium while I'm at it, or try to reuse the stockers. I posted earlier about the sodium filled exhaust valves. Valve guides hadn't crossed my mind, though. I know if you use too radical of a cam, guides get chewed to hell. It doesn't need too-radical camshafts, just something similar to cobbs spicey cams. To make more power at 10, 000 rpm, I'll need much bigger cams, but one thing at a time, 'eh :)? Still using the stock crank and possibly rods are appealing. The crank would be lightened, but not really featherweighted. Reading some builds on subies, power to 8k is certainly a possiblity. I want to spin higher than 6k and make waaayyy more power in that higher rpm. You can never tune-out the powerband of a cam, but you can smoothen the ramp to it, and make the powerband itself even more enhanced.
As my car sits now, it's barely tuned, and pulls right to redline. It doesn't get there blazingly quick, but gets there nonetheless and doesn't hesitate. That's even with stock cams.

There's other areas that could use improvement, too. Oil foaming is a problem in our blocks at hihger rpm, IIRC. What can be done inside the block, other than polishing, to the oil galleis and drainback areas? External filters have also been considered, as well as a secondary oil cooler and piston sprayers. More dowels in the block have even been considered. There's still improvement in the valvetrain area that can be had....but with more money as always... .this isn't senseless rambling, but very expensive rambling.

What is it about exhaust gas temps, though? When they rise on a turbo, it usually means it's too lean. Plus, if I'm increasing thermal efficiency in the first place, my temps should rise, but not skyrocket, shouldn't they? I still want to be able to tell the difference. Or, am I looking at 1600-1800 F temps? Exhaust temps on turbos I've ruidden in ride perfectly at 1350-1450 F. I should just be adding more fuel to keep them down just like a turbo. Keeping it closer to 12:1 or even 11.5, I can run more nitrous and still have room to spare High-dose nitrous cars actually can run very low compression. But, big dogs running brutally quick run high comp, nitrous, and then hold on for the ride. Ever wonder how far an import can go with high compression and nitrous? Some hondas run into the 11's with that combo.

eDit: gotta stop that drunken post whoring...things just keep getting more expensive :biggest: :nuetron: :p :stinky:
 

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You should consider radical changes in the bottom end as well as the top to push 8K! Titanium rods, valves and pistons (weight consideration!) multiple valve springs, harden the cams(Spicies probably won't provide the duration you will need at 8+K!)
:sunny:
 

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Discussion Starter #17
Sorry I haven't been on in a while. Work has had me very busy. I know the stock crank can handle the 8k redline, but I know it needs new pistons and possibly rods. If I found stronger units with lighter weight, I'd use them, otherwise the stock bottom end will just be cryoed with better pistons. the top end will probably retain the stock valves with better springs, retainers and cams. Even the rocker arms can be redesigned for better strength and lighter weight.

As for coatings, I guess a molybdenum coating for the cylinder walls and rings would reduce friction. I can use ceramic coatings in creative places for cooling. What about cryo treating, though?

I also wanted to ask about VE advantages with a boxer engine. Do we have a volumetric efficiency advantage because of our mechanical layout? There's increased Mechanical advantages for the reciprocating mass because of the push-pull action of the pistons. Does this translate to better cylinder filling capability in a termendous way, or just a slight advantage?
 

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The primary advantage to the boxer design is ballance and excellent torque distribution...the latest head design adds considerable gains in VE (didn't know anyone else even knew about this!) but the intake runners and throttle body limit the production of useful power above 7K. Lightening the pistons and connecting rods will make it easier to turn those revs but only if one can get more air into it! Force feeding is one way...but to do this NA.......only breathing easier will make the difference...that will require a larger TB and polished intake runners and intake ports...a larger diameter exhaust will help a little as well as a reduced back pressure cat and muffler.

If you are still intent...good luck!

:sunny:
 

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only breathing easier will make the difference...that will require a larger TB and polished intake runners and intake ports
For all that farting around you still don't get many gains at all. Just go with individual throttle bodies.

I read the entire thread, and you never said what your purpose of this car is. From what I read, you want it to be a semi-daily driver. If that is that case, you need to concider some other things: Will you be satisfied with a 1000+ RPM idle? Huge overlap cams needed to spin the piss out of an engine do not idles well at all. The short intake velocity stacks on the individual throttle bodies will hurt lowend torque, and you will have an unresponsive engine under 5000 RPM, and it won't really do anything untill 6000 when it comes up on cam. Also, where to place the injectorsm and can your management support two sets of four injectors, and taper fueling duties from one set to the other. FOr lower RPM use, close to the valve is best, for high rpm toward the end of the intake horn is best. A good comprimise is right behind each throttle body. That placement will do fine for up to 9-10 thousand RPM. I have been investigating the possibility of a ram air system utilizing the space to place ducts in where the blinkers are next to the blinkers. THere was an engine pictured that used a large CF box under the hood scoop to feed the 4 throttle bodies that would probably be a better Idea, but it has already been done. I haven't seen blinker ram air on a Subaru yet.

Pauter makes steel rods that will be fine for 9-10,000 RPM, they also make Ti rods. A lightweight rod is not as critical as a lightweight piston is at high RPM.

DOHC heads can be used for adjustability of the cams (with vernier cam pullies) and you can have two maps, and the cams marked to run a high reving power mad, and have an every day, little more in the midrange for drivability. DOHC and use shim under bucket which is a super pain in the ass to lash, and I have been told by Cobb that this design isn't as reliable as the SOHC for spinning at high RPM. This intreauges me, as motorcycles use this same design and they rev very high with very good reliablity. Maybe Yamarocket can tell us about this.

Using a 2.5 block to spin high RPMs puts a little more side loading on the bore due the the rod stroke ratio. A piston that is fitted well, and a skirt that has been coated with a friction reducing material or process would be a good idea to reduce friction, and thuse bore wear as well as some heat.

I would like to know where you read/heard that we have a problem with foaming oil. Unlike many the V8, our crankshaft does not drag through the oil pan and churn the oil, sure it splashes, but our crank also have very small frontal area on the counterweights, unlike the heavily weighted V motors, so windage and oil parisitic losses are very small. A dry sump is a good idea on any engine, I'm not trying to talk you out of it, but I am wondering why the oil is at risk of foaming?

If you wish to run a huge shot of nitrous with a high RPM engine, you might be in for a very hairy trip. Due to the nitrous you are going to have to use pistons that have much stronger tops that a lightweight piston that would see no nitrous. This puts you in a conundrum. You want lighter pistons to be easier on the bearings and rods, but you need a heavier piston to deal with the nitrous. This is the time for titanium rods. The titanium can build a rod that is stronger and lighter as well as the atributes of Ti being that it absorbs energy. This may not be good for the effeciency of your engin (It will not be much at all), but the ability to absorb shock will help your bearings to last a lot longer.

If this car is to be a semi-daily driver you need to have a back up plan if you get a bad tank of gas, or happen to have a REALLY hot day. This can be as simple as a bottle of octain booster. If you are going to be running the ragged edge of pump gas with octain boosters, you are bucking the odds, and an engine, no matter how good the parts and build, will det itself to death if the proper octain isn't being fed to it. Something to think about.

cheeRS,

Greg
 

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This is starting to look like a forum for building a screamin' AWD dragster!

What are you going to do for a trannie, diffs and axles?

:sunny:
 
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