9:1 compression + high boost

[quake]

So after a fresh rebuild done by me with all machine work done by a local machine shop. I decided to go with the wiseco pistons set proper piston to wall clearence and set my sights on 600-650rwhp. Specs on motor are cometic gasket custom, all arp hardware, micropolished crank, all parts balanced, precision intercooler, precision injectors dual walbro, vpc afc, msd dis-4, v-8 b&m oil cooler, koyo radiator, aeromotive fpr, 275 35 18, fresh paint, full titan turbo back, new oil squirters, gonna use the precision 71mm turbo .69ar ex housing. what do you think questions comments welcome

[upgradedsupra]

Welcome Quake :) You already know what I think.

Duane

[quake]

Welcome Quake :) You already know what I think.

Duane
you crazy bastard 800rwhp lol id be in jail the same week i put it on the street lol :naughty:

[Doward]

Don't look at it as 'High boost'

If you are running over 20psi, imho, you have plenty of room to increase the airflow through the engine.

Boost = resistance to flow.

Flow = power.

Let it sink in for a bit ;)

[figgie]

9:1 comp ratio is what I run. Been running for 2 years going on three. But don't listen to me. I run E85 which is basically race fuel anyway ;)

[gilberjj]

since our engines don't rev as high as a lot of turbo motors, would the engine benefit from the higher compression? Are smaller AR houseings a compliment to higher compression? thanks in advance, I can't decide whether i want to go 9:1 or keep stock compression ratio... also, i don't rmember seeing, Quake, are you running stock rods?

[Halsupramk3]

i am running a sp61 with aem and i dont have it completely tuned yet. i have gotten it at 9 psi to 290 rwhp on a dyno dynamic dyno but i have been back to turn up the boost. i have been regularly to 10 psi at 10.5 to 12 a/f and no problems. the timing is a little conservative.

i dont know what your timing will be with that piggy back stuff and running higher boost than 10 psi. the stock ecu will keep the same timing at your higher boost. you may need to set your base timing at 9* or even 8* at first to make sure you dont get any knock.

i also coated my piston tops and chambers to help keep temps down and detonation away. cant wait till i go back to the dyno and turn up the boost and then put in some race gas. i have had some trouble getting the wastegate to go over 9 psi but will have that fixed shortly.

[Tun_x]

I run 11:1 with GT74

[drjonez]

Don't look at it as 'High boost'

If you are running over 20psi, imho, you have plenty of room to increase the airflow through the engine.

Boost = resistance to flow.

Flow = power.

Let it sink in for a bit ;)

that's probably the best post i have seen here on SM in a LONG time....if only people would get it....

[bountykilla0118]

Don't look at it as 'High boost'

If you are running over 20psi, imho, you have plenty of room to increase the airflow through the engine.

Boost = resistance to flow.

Flow = power.

Let it sink in for a bit ;)
So what are you advising him to do to take full advantage of this room to make more power? I assume you mean to port out the head and add bigger valves etc. to increase flow........

Can you clearify or dumb down that post so people like myself who arent really "overstanding" what you are saying can make good use of this

[quake]

that's probably the best post i have seen here on SM in a LONG time....if only people would get it....
i get it i know the engine is just a big air pumpl lol what i meant was for my ebc settings on race fuel.

[quake]

since our engines don't rev as high as a lot of turbo motors, would the engine benefit from the higher compression? Are smaller AR houseings a compliment to higher compression? thanks in advance, I can't decide whether i want to go 9:1 or keep stock compression ratio... also, i don't rmember seeing, Quake, are you running stock rods?
stock rods with arp bolts

[quake]

before this car i had a maxima compression was 9:1 and i had it tuned to run 16psi on pump and 25 on race fuel. That was a fun car got sick of spinning tires though lol

[quake]

I run 11:1 with GT74
what are u reving to?

[suprarich]

Don't look at it as 'High boost'

If you are running over 20psi, imho, you have plenty of room to increase the airflow through the engine.

Boost = resistance to flow.

Flow = power.

Let it sink in for a bit ;)

What he means is too many people relate the pressure to the amount of power achieved. Not the case, 18 psi on a stock ct is no where in the same ballpark as 18 psi on gt4067R. Need to think in terms of lbs/min instead of lbs/sq inch

[gilberjj]

i understand the fact that the bigger turbo will "flow" more air than a smaller turbo at the same psi, but it still doesn't click for me completely. isn't 18 psi, 18 psi? if my piping is holding 18 psi wouldn't that take the exact same amount of air regardless of turbo sizing. i know it isn't this simple, but i was just trying to get this figured out...... in my head, i think 18 pounds per square inch in my intercooler piping is the same amount of air no matter the size of the hairdryer.

[figgie]

i understand the fact that the bigger turbo will "flow" more air than a smaller turbo at the same psi, but it still doesn't click for me completely. isn't 18 psi, 18 psi? if my piping is holding 18 psi wouldn't that take the exact same amount of air regardless of turbo sizing. i know it isn't this simple, but i was just trying to get this figured out...... in my head, i think 18 pounds per square inch in my intercooler piping is the same amount of air no matter the size of the hairdryer.

it IS

the problem is that you are thinking RESITANCE.

That pressure is a resistance to FLOW.

That just means that there is that much resisitance for the amount of flow going from the turbo.

18 psi is not the same amount of air. As a matter of fact it is NOT amount of air. it is the force that is RESISTING the air from moving inside the intake system (ie valve closing, throtlle bottle closing, turbulant air flow in the system etc).

In english

as resistance goes up, flow MUST go down. Regardless if it is 20 lbs/ft^3 or 6000 lbs/ft^3. But if you have 18 lbs/in^2 of resitance against 20lbs/ft^3 or 6000 lbs/ft^3 which one do you think will be affected more (answer the smaller value of the two) ;)

and to borrow what Bernoulli created with his equation

The pressure in a fluid decreases as its velocity increases or said another way.
The pressure in the fluid INCREASES as its velocity DECREASES.

[gilberjj]

But if you have 18 lbs/in^2 of resitance against 20lbs/ft^3 or 6000 lbs/ft^3 which one do you think will be affected more (answer the smaller value of the two) ;)


what do you mean "affected?"

thanks...... i think we are making headway. eventually i will understand this. also, does a t-66 flow more air into an engine at 10 pounds of resistance than my ct-26 would flow at 10 pounds of resistance? this is confusing, because i would think that resistance would be completely up to how well your engine can flow air, not the turbo. ex. bigger valves, and a p&p head will FLOW more than a stock head, so it allows more air to be flowed into the combustion chamber before the valve shuts, therefore the turbo is actually spinning faster to achieve the same 10 pounds of resistance because the engine can now ingest more air....... thats what would make sense to me! i still don't see what the compressor size (or turbo size and capability) has to do with flowing!

is it the fact that the bigger turbine wheel creates less back pressure and allows more air to be flowed into the engine? wow....... im all over the place, but thanks for helping me understand. im trying!!!!

[Doward]

I love you guys. :D

You've got a lot more factors at play, than just the psi you are seeing on your gauge.

Everything else equal, 10psi from a T66 is going to create more power than 10psi on a CT26, because the 10psi from the T66 is more efficiently compressed. When you compress air, you heat it up. The efficiency of your turbo is a measure of how much more it heats it up than necessary. A CT26 is NOT efficient over about 13psi. It heats up the air to insane temps.

The T66, on the other hand is barely working to compress the air @ 13psi - so your temps are not increasing much over what the Ideal Gas Laws state it should.

Hot air = less dense. Cold air = more dense. The denser the air, the more power you make per volume of air. That's why we run intercoolers, as well.

Now that's just turbo sizing!

Suppose we now take two cars - one a T66 on a log manifold, stock everything else, and run 10psi.

Car #2 has one of Ron's FFIM and tubular header, as well as a set of those 272 cams. Still 10psi.

Car #2 is going to make a little more power than car #1. Possibly in the order of 20-30rwhp, but I would not expect much, at this low volume of airflow.

Now take both cars, and run 20psi. Car #2 is now going to make a LOT more power than Car #1 - why? Airflow. Car #1 is making 20psi, but the air is having to fight its way into the engine, and back out.

Car #2, on the other hand, is having no such problems - the air is easily entering the engine, flowing through it, and leaving the engine. That also means that T66 is being much more efficiently utilized ;)

To specifically answer your questions -

#1) Yes, the T66 is flowing more MASS of air, due to higher density (colder air charge)
#2) The compressor sizing is actually a slightly different part of this equation, due to what I wrote up above - You've got to take into account how dense your air is, and then how well it will flow through the engine. 2 seperate things, working together for more power :)
#3) The turbine wheel is the exhaust wheel - don't get that confused with the compressor wheel ;) A larger exhaust wheel allows more air to exit the engine, easier.

Turbine sizing is ALWAYS a trade off between maximizing power, and minimizing lag.

[quake]

thats why i went with a 71mm will help me get away with more power when i use pump gas:icon_bigg

[Doward]

Everything with a turbo is trade off - that's why the very first question I ask, when someone's asking 'What do you think of this turbo?' is

"What are your goals?"

Be sure not to go too big ;)

[MRSUPRA]

Please do not try to make 600-650rwhp on pump gas, especially with a stock ECU. On race gas with the 71, not a problem..even with the 9.1 compression.

[upgradedsupra]

If you go with a meth kit then yeah...pump gas would be ok but other than that I wouldn't take a chance.

My .02
Duane

[quake]

Please do not try to make 600-650rwhp on pump gas, especially with a stock ECU. On race gas with the 71, not a problem..even with the 9.1 compression.
those numbers are resurved for the c16

[gilberjj]

I love you guys. :D

You've got a lot more factors at play, than just the psi you are seeing on your gauge.

Everything else equal, 10psi from a T66 is going to create more power than 10psi on a CT26, because the 10psi from the T66 is more efficiently compressed. When you compress air, you heat it up. The efficiency of your turbo is a measure of how much more it heats it up than necessary. A CT26 is NOT efficient over about 13psi. It heats up the air to insane temps.

The T66, on the other hand is barely working to compress the air @ 13psi - so your temps are not increasing much over what the Ideal Gas Laws state it should.

Hot air = less dense. Cold air = more dense. The denser the air, the more power you make per volume of air. That's why we run intercoolers, as well.

Now that's just turbo sizing!

Suppose we now take two cars - one a T66 on a log manifold, stock everything else, and run 10psi.

Car #2 has one of Ron's FFIM and tubular header, as well as a set of those 272 cams. Still 10psi.

Car #2 is going to make a little more power than car #1. Possibly in the order of 20-30rwhp, but I would not expect much, at this low volume of airflow.

Now take both cars, and run 20psi. Car #2 is now going to make a LOT more power than Car #1 - why? Airflow. Car #1 is making 20psi, but the air is having to fight its way into the engine, and back out.

Car #2, on the other hand, is having no such problems - the air is easily entering the engine, flowing through it, and leaving the engine. That also means that T66 is being much more efficiently utilized ;)

To specifically answer your questions -

#1) Yes, the T66 is flowing more MASS of air, due to higher density (colder air charge)
#2) The compressor sizing is actually a slightly different part of this equation, due to what I wrote up above - You've got to take into account how dense your air is, and then how well it will flow through the engine. 2 seperate things, working together for more power :)
#3) The turbine wheel is the exhaust wheel - don't get that confused with the compressor wheel ;) A larger exhaust wheel allows more air to exit the engine, easier.

Turbine sizing is ALWAYS a trade off between maximizing power, and minimizing lag.

thanks for your help, and yes i knew that the turbine wheels is the exhaust wheel.

[bigboost7m]

I wouldnt even think about going past 8.5:1. The turbo is already forcing air into the cylinder, you dont need that extra pressure (high compression). Yeah, your motor may live, but its getting beat to hell on the inside, bearings especialy, if you do a couple full dyno pulls after that build with that compression, and you pull those upper rod bearings out (considering you have all your clearences correct) you might as well junk them because that babbit material will get worn of so quickly its not even funny. If you do go through with this build at that compression, i reccomend doing some dyno or street pulls, drain the oil while its hot and cut the oil filter open, then you'll see the bearing material that im talking about. That was a half a-sleep explanation, but for further info contact Bill Miller Engineering at 775-887-1299, and they will be glad to guide you in the right direction.

[drjonez]

you're kidding, right?

[MRSUPRA]

:icon_conf

[Doward]

bigboost7m - only if you are detonating like crazy - that's not a matter of compression, that's a matter of tuning.

I have personally run 16psi from a T61 on 9.6:1 compression aluminum headed GM 3100 V6, with ZERO detonation (on pump gas)

[bountykilla0118]

I wouldnt even think about going past 8.5:1. The turbo is already forcing air into the cylinder, you dont need that extra pressure (high compression). Yeah, your motor may live, but its getting beat to hell on the inside, bearings especialy, if you do a couple full dyno pulls after that build with that compression, and you pull those upper rod bearings out (considering you have all your clearences correct) you might as well junk them because that babbit material will get worn of so quickly its not even funny. If you do go through with this build at that compression, i reccomend doing some dyno or street pulls, drain the oil while its hot and cut the oil filter open, then you'll see the bearing material that im talking about. That was a half a-sleep explanation, but for further info contact Bill Miller Engineering at 775-887-1299, and they will be glad to guide you in the right direction.
:nono: So in other words someone else told you all that bla bla bla ...... That motor you are referring to was detonating. Granted higher compression increasing your chance of detonation. But like Doward has said if tune it right you can pretty much run anything you want. Not to stray to far from the topic but this kinda reminds me of all the negative talk about the factory head gasket..... I had my block and head machined and a year and 7 months ago and i have been running 14-15psi since and she is holding up just fine mind you i drive really hard most of the time. I also have a pretty good tune of 291rwhp and 336lbs of tq with A/F ratio of 11.5 using SAFC II, with my factory 440 injectors, pump, AFM and a holy accordian hose.

It has been, still is , and will be all about the tune

[suprarich]

I wouldnt even think about going past 8.5:1. The turbo is already forcing air into the cylinder, you dont need that extra pressure (high compression). Yeah, your motor may live, but its getting beat to hell on the inside, bearings especialy, if you do a couple full dyno pulls after that build with that compression, and you pull those upper rod bearings out (considering you have all your clearences correct) you might as well junk them because that babbit material will get worn of so quickly its not even funny. If you do go through with this build at that compression, i reccomend doing some dyno or street pulls, drain the oil while its hot and cut the oil filter open, then you'll see the bearing material that im talking about. That was a half a-sleep explanation, but for further info contact Bill Miller Engineering at 775-887-1299, and they will be glad to guide you in the right direction.

Crap! I guess I need to return the custom 10.5:1 7m cp pistons I ordered...

[foreverpsycotic]

i would not concider 9:1 high compression, its all in the tune and fuel (notice i didnt say gasoline) that you are running. i know of someone with a MONSTER turbo AND high compression (over 11:1), but they are on standalone with a sick tune running strait meth

[Halsupramk3]

remember 9.5:1 is very different from 9.0:1. doesnt sound like a much but it is inapplication. so comparing CR of 10:1 to 9:1 is quite a different engine. as long as your octane can be compressed in that 9:1 cylinder without igniting you can run it. watch that timing.

to help keep detonation or autoignition away on my 9:1 cr i had the tops of the pistons coated and also the chambers. also the exhaust ports. that way i will keep heat out of the engine to help keep detonation away. at least thats my theory.

unfortunately i have not gotten boost control to work yet so i have not gone over 12psi on my engine yet. sp61gt. only been on pump gas 93 so far. of course i dont buy off brand cheap gas.

[IJ.]

It makes for a very responsive snappy motor but leaves NO ROOM for error 1 tank of crap gas WILL ruin your day if you don't have a strategy in place to deal with detonation.

Just not worth the risk for me.

[NeatOman]

Theres a drain plug on the tank LOL

[IJ.]

Theres a drain plug on the tank LOL
So you can drain the fuel and replace it AFTER the motor rebuild? ;)

[Kai]

With a turbo build, i know you can use high compression ratio's, but....i'd rather stick to the safe side and not go over 8.8:1....unless your tune is perfect and you know the fuel going in the other end is also perfect, you could end up with a very expensive rebuild...

[MRSUPRA]

I have owned a 1st gen eclipse turbo which comes with a 7.8:1 compression and a 2nd gen eclipse turbo with a 8.5:1 compression. The off boost response is clearly better in the 2nd gen eclipse due to the higher compression. (Of course it has smaller intake ports for higher velocity air intake to also help low RPM drovability)

I purposly bumped up my compression to about 9.0:1 in my new 7M for improved response and drivability at low RPM. The pig can use it too.

[zbaVR4]

one thing not mentioned is that higher compression helps spool-up :)

[bigaaron]

Another thing not mentioned is the you can make more power on pump gas with lower compression. What kind of gas are you going to run 99% of the time?

[IJ.]

one thing not mentioned is that higher compression helps spool-up :)

It makes for a very responsive snappy motor but leaves NO ROOM for error 1 tank of crap gas WILL ruin your day if you don't have a strategy in place to deal with detonation.

Just not worth the risk for me.
It wasn't?

[MRSUPRA]

Another thing not mentioned since we are going over un-mentioned things: Most new turbocharged cars use a much higher compression in there engines. The reason: Again, drivability. And of course better technology like Direct injection for better cylinder cooling allows a lower detanation threshhold.

[NeatOman]

Also the smaller the engine (cylinder with, sorry forgot how to speel the other with) normally is more forgiving towards detonation it is.

[Doward]

Actually, with a smaller bore (not necessarily the engine) and the same style combustion chambers, you'll have less chance of detonating with the smaller bore - the quicker you get the flame front propagated, the less chance of you having combustion where you don't want it :D

[gilberjj]

there is a local dsm running (que drum roll) 30 psi on pump gas w/out meth. I kid you not. he ran an 11.1 in steet form. kinda cool i thought.

[zbaVR4]

It wasn't?


'responsive' and 'snappy' might not be as clear and concise, for others, as you might think it is. I could say my lawn mower was responsive and snappy but that doesn't describe if its turbo'd :)

[NeatOman]

Actually, with a smaller bore (not necessarily the engine) and the same style combustion chambers, you'll have less chance of detonating with the smaller bore - the quicker you get the flame front propagated, the less chance of you having combustion where you don't want it :D

U says it smrt :love:

Thats what i was trying to communicate.


there is a local dsm running (que drum roll) 30 psi on pump gas w/out meth. I kid you not. he ran an 11.1 in steet form. kinda cool i thought.

Also... 30psi! WTF... stock flow! LOL

[Nick M]

Pretty good thread, as long as you let the good info sink in.

[Doward]

Breath in the good info, breath out the bad info :D

[quake]

Another thing not mentioned is the you can make more power on pump gas with lower compression. What kind of gas are you going to run 99% of the time?
yeah your right. So i bumped the compression down a bit to 8:4:1, pulled the 71mm and put the ct back on for the mean time now looking for a 67.

[upgradedsupra]

yeah your right. So i bumped the compression down a bit to 8:4:1, pulled the 71mm and put the ct back on for the mean time now looking for a 67.

Geez....not done yet?













































:biglaugh:

[quake]

Geez....not done yet?

not fully but i drive it every day. Ended up with 400rwtq keep a lookout in your rear view. lol:biglaugh:











































:biglaugh:

[upgradedsupra]

LOL the only person in the rear view will be you :biglaugh: The only way I would be in the rear view is if I already had hit the brakes and you did the ricer fly bye LOL

[quake]

LOL the only person in the rear view will be you :biglaugh: The only way I would be in the rear view is if I already had hit the brakes and you did the ricer fly bye LOL
lol

[upgradedsupra]

lol


So any updates?

[quake]

So any updates?
not yet been lazy this week messing around with a msd dis-4 right now.

[ozworldwide]

Hi our current WRC engines run at 11 to 1 compression ratio on 2 bar boost
runing WRF fuel witch is around 100 octain.

[drjonez]

yeah, comparing modern WRC engines to 25 yr old passenger car engines is a great idea....

[ozworldwide]

Sorry but an engine is a engine just some are more efficant as a std engine before serious mods.
Think its just a fancy air pump

[drjonez]

i disagree.

the other thing you're ignoring is engine management....

[bountykilla0118]

DrJ..... FTW

[ozworldwide]

Yes totally understand about your ECU management reply but going fast reliably does cost some money unless you have full access or piggyback the std ecu .
Look forward to your reply.

[gilberjj]

im going to get custom 3:1 compression pistons and run 80 psi....... on pump gas ;)

[IJ.]

I used to run 30 psi in my old 4v Toyota V8 with 6.5:1 forged Mahle pistons on pump back in the day :)

[gilberjj]

I used to run 30 psi in my old 4v Toyota V8 with 6.5:1 forged Mahle pistons on pump back in the day :)

haha....... awesome! after driving my car with the new turbo, i have no complaints about spool time. im considering getting a bigger exhaust ar housing just to give a little more top end and pull to redline. ij, if you could, plz post on my thread here. id like to hear your input!

http://www.supramania.com/forums/showthread.php?t=54084

thanks

[Dirgle]

I used to run 30 psi in my old 4v Toyota V8 with 6.5:1 forged Mahle pistons on pump back in the day :)

Holy hell, what was that thing like off boost?

[IJ.]

Gilb: No probs will have a look.

Dirgle: 1100kg car wet with 3.4L V8 and low Diff gears it was pretty good off boost :)

[88guy]

I know this is a VERY old post but..... I would just like to say thank you to everyone that posted on this topic. Ive learned more about airflow, turbos, boost, psi in the past half hour of reading then i did in 3 years of HS auto. Thanks you everyone i really feel like i learned something today :)