Built KA

[Structure240sx]

Im leaning towards turboing the KA now b/c of its low end torque. my plan is first to install the Npsort stage 1 be happy with the 240hp then within a year later build a spare KA with forged internals. my goal with the built engine is about 350rwhp. my question is (couldn't find the answer i wanted) would i need to go with low compression for that much power. this car would still be daily driven. forget for driveablitly off boost with low compression. jsut would it be neccessary to go low compression for that. from what i've read searching it seems that stock c/r with forged internals will be fine with enough fuel of course.

[I am Technoman]

Just use a 2 mill steel head gasket if you’re worried about compression. A 2 mill head gasket will lower stock compression to 8.5.01 don’t boost over 12 psi with out 550cc injectors and an meth injector to run 15psi . and maybe your motor will last a wile just stay at 12 and you will be fine…

[I am Technoman]

Boostin on stock compression is fine for a wile but you will pinch a ring at some point….

[Top Speed Coupe]

I seen a KA with close to 500RWHP on stock internals. Custom intake and exhaust manifolds, big turbo, FMIC, Big Injectors and a Stand Alone n some more goodies.

[I am Technoman]

I seen a KA with close to 500RWHP on stock internals. Custom intake and exhaust manifolds, big turbo, FMIC, Big Injectors and a Stand Alone n some more goodies.

But was it stock compression? Im sure they lowered it with a gasket.

[Tony Starks]

I'd go low compression for efficiency purposes if I go anywhere above 350bhp let alone 500.

[gyfer]

Structure240sx: forget for driveablitly off boost with low compressionGo with lower compression then.

Instead of going lower compression, I would go HIGHER compression running at 7psi. Nahhh... no time and money for new piston. Stock internal is good for 350whp if you get it right. ( very right )

Lower comperssion is just a "safer method" if you went something wrong. There is NOTHING directly related high compression = engine go bye-bye.

[WDRacing]

Structure240sx: forget for driveablitly off boost with low compressionGo with lower compression then.

Instead of going lower compression, I would go HIGHER compression running at 7psi. Nahhh... no time and money for new piston. Stock internal is good for 350whp if you get it right. ( very right )

Lower comperssion is just a "safer method" if you went something wrong. There is NOTHING directly related high compression = engine go bye-bye.

A lower CR motor on boost will ALWAYS produce more power then a high CR motor. That is what I was taught and what I have read from people such as KenneBelle.

WD

[ADAMHU]

that does not make sense...why is that?

i would think that as long as you control detonation and preignition with the fuel octane..the higher compression motor with the same amount of boost will produce more power...

[C-Kwik]

A lower CR motor on boost will ALWAYS produce more power then a high CR motor. That is what I was taught and what I have read from people such as KenneBelle.

WD

Not true. Given the same boost, timing and fuel the higher compression motor will be faster. But the higher compression motor will be prone to knocking. The Lower compression motor can see more boost before this occurs and typically will have the potential to make more power given the same kind of fuel.

[S13Ka24e]

Basicly if you run lower compression you can run more boost and produce more power, but I would think that if you keep the boost the same the higher compression engine would make more power.

[C-Kwik]

Basicly if you run lower compression you can run more boost and produce more power, but I would think that if you keep the boost the same the higher compression engine would make more power.

Correct, provided you don't detonate and blow the motor up, and you don't blow out the spark.

[C-Kwik]

Boostin on stock compression is fine for a wile but you will pinch a ring at some point….

Technoman,You say this over and over again. I still can't figure out how you come to this conclusion. Consider that the combustion process starts at the spark and works outward. The last bit of fuel is generally burned at the outer edges of the piston, while the piston is most of the way down the stroke. Yet the peak cylinder pressures will occur in the first 45 degrees of crank movement from TDC. Now consider detonation usually occurs in the last place fuel is burned. That would put it quite close to the ring lands if you ask me. If you've seen or heard experiences of pinched rings, you may want to consider that detonation was the cause. I've seen effects of detonation in motors even as robust as a Supra, where pieces of the piston were missing. All the damage I've seen have all been at the edges of the piston.

[WDRacing]

What parameters determine how much boost an engine can run on 92 octane? Good question. 2 of the most commonly asked.

COMPRESSION RATIO - Lowering the compression ratio allows the engine to run more boost with the same octane. For example, 8.0:1 vs 9.5:1 can tolerate another 3 psi. 3 psi gives 38HP. The 1.5 lower CR loses 3% (2% per point) or around 9HP in a 300HP engine. That nets 29HP (38-9=29). Now you know why OEM's use low compression ratios on supercharged engines.

BOOST - Both higher compression ratios and boost increase cylinder pressure and demand higher octane fuels to eliminate detonation. Fuel octane is a major player in the amount of boost an engine will accept. One octane will support one psi of boost. Example: If fuel octane is 94 or you add a can of NOS Octane Booster you can typically run 1-2 more psi then if you were using just 92 octane.

IGNITION TIMING - Retarding ignition timing will allow the engine to run more boost but not without a penalty. 4° retard=16HP.

AIR FUEL RATIO - You can't make horsepower without fuel. Richer air fuel ratios reduce power but permit higher boost levels on a given fuel octane. Leaner ratios make more power but need lower boost so a lean mixture with high octane makes the most HP.

What causes detonation? 1. Lean fuel mixture, 2. low octane fuel, 3. excess boost, 4. lack of fuel, 5. advanced ignition timing, 6. vacuum leak, 7. "hot" spark plugs, 8. overheated engine, 9. excessive inlet temperature (underhood filter). Are just a few that come to mind.

Perhaps my earlier statement wasn't detailed enough for the more tuner minded individuals. I didn't exactly mean a low 8.1/1 CR motor running 8 psi will make more then a 9.5/1 motor running the same amount of boost. I meant the 8.1/1 will be able to run more boost then the 9.5/1 motor, which in turn allows for increased hp. Also as you add boost you'll have to do far more to a high CR motor then one with a low CR.

WD

[C-Kwik]

Perhaps my earlier statement wasn't detailed enough for the more tuner minded individuals. I didn't exactly mean a low 8.1/1 CR motor running 8 psi will make more then a 9.5/1 motor running the same amount of boost. I meant the 8.1/1 will be able to run more boost then the 9.5/1 motor, which in turn allows for increased hp. Also as you add boost you'll have to do far more to a high CR motor then one with a low CR.

WD

But that's the way it read...=)

[WDRacing]

:moon .........

[cnichols]

So....what CR are you guys planning or are already running?

It seems that for the KA, the most popular CR is 8.5:1, but I was considering anywhere from 8.0:1 - 9.0:1.

Obviously there are advantages to each and I should probably decide what kind of power and driveability I'm looking for. It will see some track time, but it will mostly be a street car.

The only thing I'm afraid of is losing too much low end....anyone out there running 8.0:1?

[WDRacing]

Actually I'm going to keep the stock CR and use alcohol on my motor.

WD

[erich]

I've got 9.0:1 on my built KA. Off bost is fine, but I have a ball bearing T3 that spools up really quick.

erich

[cnichols]

I wouldn't mind using alcohol either, but I have to admit that I'm ignorant on the subject...never read anything about it.

Do you have a separate small tank in the engine bay for alcohol and run an AIC w/ one or two injectors before the throttle body?

And....when you say alcohol....can I just go to my liquor store and buy some Everclear ? Seriously, what kind and percent are we talking about? and where do you get it?

[cnichols]

I've got 9.0:1 on my built KA. Off bost is fine, but I have a ball bearing T3 that spools up really quick.

erich

yeah, I've got a ball bearing HKS GT3037, but have yet to see what kind of spool time I'll see. I am going to be using a stock motor to learn on with my standalone....I guess I'll just see how that goes and adjust accordingly.

But, as far as other parts of the engine go, I was considering getting the intake manifold Extrude Honed, oversized valves, and porting the intake side of the head. I wonder if I would just be wasting a lot of time and money here and should concentrate more on other aspects?

[WDRacing]

I prefer Denatured alcohol. It can be purchased at any hardware store. Yes you have a small tank to hold the alky. My kit is boost activated. You can set the boost level to what psi you want the alky to come on at as well as the volume of alky coming from the pump. Just do a google search on alcohol injection. Try and learn from the GN guys. They've been using alcohol for years.

WD

[I am Technoman]

I simply want to use lower compression because the motor will last longer with the right fuel mixture. On stock internals with a steal head gasket "thick" 2 mill Ill get my 8.5.01 compression and I can run 14 psi.

[TrunkMonkey]

I simply want to use lower compression because the motor will last longer with the right fuel mixture.

a boosted engine will last at any compression with the right fuel mixture.

the days of lowering compression to run boost are about dead. the average late model automobile runs @ 10:1 compression. does that stop people from boosting? nope. look at the S2000. there are at least two bolt on supercharger systems (and one turbo?) available for it, and it has 11:1 compression.

-demetrius

[cnichols]

I simply want to use lower compression because the motor will last longer with the right fuel mixture. On stock internals with a steal head gasket "thick" 2 mill Ill get my 8.5.01 compression and I can run 14 psi.

I'm going to run 14 psi on stock internals too, but with a stock head gasket, and I wouldn't be surprised if my engine lasts longer.

[Ozone]

I simply want to use lower compression because the motor will last longer with the right fuel mixture. On stock internals with a steal head gasket "thick" 2 mill Ill get my 8.5.01 compression and I can run 14 psi.

Are you aware of what that will do to your cam timing? By 'that' I mean using a 'thick' headgasket. Do you have a source for your headgasket yet? Is it going to be a copper gasket? If so they can be tricky to seal up. Don't take my questions the wrong way, I just boucing some thought on ya.

kevin

[WDRacing]

As long as you have ajustable cam gears you'll be fine with the timing.

As far as cars boosting with high CR goes. Without race gas or alky your car is limited to a very little amount of boost or you'll suffer from detonation. The supercharger kits for the S2000 don't push more then 4-6 psi I'm sure. Anymore then that and she'll pop.

Now I've been building cars for awhile now, I don't want to hear about how you can simply add a ton of fuel to avoid detonation. Cause that makes you lose power as well.

If you are running pump gas and want to boost over 14.7 psi, the best way is to lower your CR.

Techno, I think you'll be fine with the stock internals and a good fuel system. Without having to go with a 2mm gasket. But I wouldn't play with much more then that.

WD

[TrunkMonkey]

As far as cars boosting with high CR goes. Without race gas or alky your car is limited to a very little amount of boost or you'll suffer from detonation.

but the advantage of running a higher compression ratio is so that you won't need to run high boost to make power.

The supercharger kits for the S2000 don't push more then 4-6 psi I'm sure.

they push aound 8 psi.

Anymore then that and she'll pop.

and you know this for a fact? you can still squeeze out more power. the paxton kit is non-intercooled and the vortech uses an small water to air intercooler. upgrade to a better intercooler system and fuel system and you'll make more power...on pump gas.

Now I've been building cars for awhile now, I don't want to hear about how you can simply add a ton of fuel to avoid detonation. Cause that makes you lose power as well.

no one's talking about adding a ton of fuel and running rich. keep it simple, the more air you add, the more fuel you'll need.

there are other ways to combat detonation besides fuel management, but i'm sure you know that.

-demetrius

[ADAMHU]

we are talking race machines here no? who cares what the engine does on 92 octane...why build a low compression slug anyway?

given your same train of thought....

2% more power per compression point...

one engine running 25psi at 500rwhp with 8:1 compression

the other engine running 25psi at 550rwhp with 13:1 compression....

who is going to win the race..either drag or road racing.......!!!!!

the 550rwhp car....

what you are REALLY saying is.... i am building a fast STREET car..and fuel availability and cost is an issue...so what COMPRIMISES can be made to accomodate using street fuel.......

the comprimise is...using lower compression pistons...at the loss of thermodynymic efficiency of the engine...thus...less total power being made....

What parameters determine how much boost an engine can run on 92 octane? Good question. 2 of the most commonly asked.

COMPRESSION RATIO - Lowering the compression ratio allows the engine to run more boost with the same octane. For example, 8.0:1 vs 9.5:1 can tolerate another 3 psi. 3 psi gives 38HP. The 1.5 lower CR loses 3% (2% per point) or around 9HP in a 300HP engine. That nets 29HP (38-9=29). Now you know why OEM's use low compression ratios on supercharged engines.

BOOST - Both higher compression ratios and boost increase cylinder pressure and demand higher octane fuels to eliminate detonation. Fuel octane is a major player in the amount of boost an engine will accept. One octane will support one psi of boost. Example: If fuel octane is 94 or you add a can of NOS Octane Booster you can typically run 1-2 more psi then if you were using just 92 octane.

IGNITION TIMING - Retarding ignition timing will allow the engine to run more boost but not without a penalty. 4° retard=16HP.

AIR FUEL RATIO - You can't make horsepower without fuel. Richer air fuel ratios reduce power but permit higher boost levels on a given fuel octane. Leaner ratios make more power but need lower boost so a lean mixture with high octane makes the most HP.

What causes detonation? 1. Lean fuel mixture, 2. low octane fuel, 3. excess boost, 4. lack of fuel, 5. advanced ignition timing, 6. vacuum leak, 7. "hot" spark plugs, 8. overheated engine, 9. excessive inlet temperature (underhood filter). Are just a few that come to mind.

Perhaps my earlier statement wasn't detailed enough for the more tuner minded individuals. I didn't exactly mean a low 8.1/1 CR motor running 8 psi will make more then a 9.5/1 motor running the same amount of boost. I meant the 8.1/1 will be able to run more boost then the 9.5/1 motor, which in turn allows for increased hp. Also as you add boost you'll have to do far more to a high CR motor then one with a low CR.

WD

[WDRacing]

I'm not talking about building a race engine at all. I never was...If I was then the fuel would never be an issue. I would run high CR with Methonal and a ton of boost. But then you need a fuel system 3 times the size of a motor ran on pump gas. Because Methonal runs with an A/F mix of around 6/1. You also need an ignition system that will light off that much fuel under such high pressure, not to mention the ignition temps of methonal being so high in comparison to pump gas.

But we're talking about building a street car. One that I can drive to work.

My point is this and only this, I'm done saying this over and friggin over again. If you want a high hp daily driver with boost then you should lower your CR because boost gives more power. Period, no if, ands or buts involved.

If you guys want to build your motors with high compression be my guest. I'll see you at the track and blow your doors completely off...

WD