9:1 compression piston (Pros and Cons)

[diambo4life]

It's cause its stupid, it's a bi*** to not knock with any amount of timing and it blows shit up and you gain nothing vs a lower compression higher boost engine.

That's not true. If you tune the car accordingly, THAT will not happen. It's also "stupid" to call other people here 'stupid' beacause they do not follow your train of thought no matter how flawed it may be. There are people who prefer higher compression and others who do not. It's personal preference. Nothing "stupid" about it. You talk as if people don't blow up their cars on stock 1G compression.

 

[ekanddsm]

Here's my experience with 9:1 compression.

9:1, 25 psi, 91 octane, no problem.

9:1, 28 psi, 91 octane, now you need to have a way of adjusting timing.

On my old 8.5:1 95 piston big rod motor it didn't seem real partial to running over 23 psi, so who knows... Different motor, different turbo, different cams, different intake manifold, so comparing the two isn't apples to apples.

So 9:1 compression helps to accel the engine to get to boost faster.
But boost is harder to control in excess of 25 psi.
And I need a nice forged piston to handle the abuse of being a true dsm owner
This is what I have absorb from this forum.

 

[Black94TSI]

Here's my experience with 9:1 compression.

9:1, 25 psi, 91 octane, no problem.

9:1, 28 psi, 91 octane, now you need to have a way of adjusting timing.

On my old 8.5:1 95 piston big rod motor it didn't seem real partial to running over 23 psi, so who knows... Different motor, different turbo, different cams, different intake manifold, so comparing the two isn't apples to apples.

Holy crap, you're running 25 pounds of boost on 91 octane and 9:1 compression with no knock? How much timing are you running, what cams, what turbo?

 

[diambo4life]

So 9:1 compression helps to accel the engine to get to boost faster.
But boost is harder to control in excess of 25 psi.
And I need a nice forged piston to handle the abuse of being a true dsm owner
This is what I have absorb from this forum.

*shakes head*

 

[Mirage2LTurbo]

Holy crap, you're running 25 pounds of boost on 91 octane and 9:1 compression with no knock? How much timing are you running, what cams, what turbo?

If it sounds too good to be true, it probably is. He's eithe running no timing and getting crazy EGT's, or knocking up a frieght train, or maybe just doesn't run a knock sensor.

 

[DSMJim]

High compression on a turbo motor is so F$%#ing stupid for 99% of people here.
I wish I could lower mine to from 8.5 down to 8:1 which is near ideal for turbo cars.
As it is I have to back the timing way off to run 20psi without knock. Who cares that it has better off idle torque. Don't race at 2000rpm's, do you?. I want my old 1g motor back. 22psi with stock timing on pump gas.
You don't see domestic's putting 15psi blowers on their stock 10:1 compression v8's do you?? Want to know why? It's not cause they don't know what they are doing. It's cause its stupid, it's a bi*** to not knock with any amount of timing and it blows shit up and you gain nothing vs a lower compression higher boost engine.

Anyway all you smart guys know better, because this stupid topic comes up way too much. Go tune that 9.5:1 engine for 25psi. Let me know how long you can afford to fill up everyday on c16 or when you blow it up.

I run 23psi on pump gas with no knock on 8.5:1 compression so if you can't your doing something wrong or only have 91 octane gas. The whole point of higher compression is so you don't have to run that much boost. A typical DSM with a 50trim is having to run 23psi to make 400whp, if the compression was higher than it could be done on 20psi. It's easier to make the same HP with less boost when you have higher compression.

Nobody cares about off boost performance, I wanna make the same HP I do now with less boost on the street, and run more at the track and continue to make more HP again.

However you decide to build your motors is fine, just don't go around saying that it's stupid because others want to build their cars that way. IMO 8:1 compression is stupid for a turbo car, it's way to low and is a band-aid for people with no tuning skills.

 

[blackGSX2g]

^ well said, I agree completely

 

[crankbender]

I run 23psi on pump gas with no knock on 8.5:1 compression so if you can't your doing something wrong or only have 91 octane gas. The whole point of higher compression is so you don't have to run that much boost. A typical DSM with a 50trim is having to run 23psi to make 400whp, if the compression was higher than it could be done on 20psi. It's easier to make the same HP with less boost when you have higher compression.

Nobody cares about off boost performance, I wanna make the same HP I do now with less boost on the street, and run more at the track and continue to make more HP again.

However you decide to build your motors is fine, just don't go around saying that it's stupid because others want to build their cars that way. IMO 8:1 compression is stupid for a turbo car, it's way to low and is a band-aid for people with no tuning skills.

I have to respectfully disagree with this.

Lower compression will net you a higher maximum power. This isn't really the question that you need to ask though. What will get you the most usable power is a better question and that will vary from car to car.

Unfortunately I am having a crappy couple of weeks here so I can't go into it in too much depth but here are the basics of it.

As you decrease compression ratio you increase the ammount of air you can move through the engine without detonation. This increase happens at such a rate that you will make more power. However you come to a point where getting the intake to that pressure isn't realistic and you can't attain the power at usable points in the curve. This is very engine dependent.

In general you want to run as low of compression as you can so that you have boost putting you right at the edge of knock with a good tune and reasonable spool up. What this really means to your car is up to you.

Just a note most of the pros run 6-8:1 compression for drag cars. Most of the record setters that I actually know for a fact what they are running use around 7.8:1 with gasoline of some sort (nirto, meth, etc are different).

 

[DSMu4ia]

I run 23-24psi on 93/94octane at about 19degree timing. No knock. 11.2-11.6:1 AFR's. This is roughly 48lb/min via DSMlink. Barely any tuning time, just a few fuel curve tweaks to get to desired AFR.

Just to be sure I'm not getting knock, I've swapped to two different knock sensors. If I do see knock (rare), it's very very minimal. I guess that's something to be said for building a motor based on proper principles.

I'm not voting for one side of the compression argument or the other, just stating my results on 9:1. And yes, this is a TRUE 9:1, no milling to the head, degree'd cams, the whole works.

 

[sunflashx]

I'm running a 2g style knock sensor with about 5000 miles on it. Over 25 psi with no additional tuning and the knock sensor goes crazy. If I back the timing off 2-3 degrees I can push 28 psi, at least in the 30 degree weather we currently have, never tried to do it in the summer. Knock sensor is definately very active.

Timing is around 24 degrees peak (ala DSMLink) on the 24-25 psi settings. I have a 2.4L motor and according to Marco, they like more timing, so don't compare my timing directly to a 2.0L, but at the same time I'd say that it's safe to say that I'm not running excessively low timing.

Car specs are in my profile.

Another local guy is running 28 psi or so on a stock 2.0L 7 bolt and hasn't blown it up yet, so it can be done. Our setups are pretty similar, other than the motors. We seem to make about the same power (racing from a roll), I just do it on roughly 20% less boost, which should be expected.

 

[DSMJim]

Just a note most of the pros run 6-8:1 compression for drag cars. Most of the record setters that I actually know for a fact what they are running use around 7.8:1 with gasoline of some sort (nirto, meth, etc are different).

With all due respect, not the pro's I know and I have traveled the country and met them all working for a national magazine. Lets put it this way. The worlds fastest Gasoline powered Honda running 8.66@141mph is running 9.5:1 compression with 35ish psi of boost. Gary Gardella ran mid 9ish:1 compression for years while on C16 as did Chris Rado back in the day. Now these are all honda's however when your talking full race cars with fully built motors there isn't much difference between a B18 stroked to 2.2L with a fully bulit head and a 4G63 at the same level.

V8 guys have been runnign 10:1 or 11:1 on their race cars in boosted applications making 1500-2000hp for years they wonder what us import guys are doing running low compression. I heard it from one guys lips at the dyno after he maxed the dyno out at 1200hp (he said it made 1250whp, not sure how he knew...) and he was twin turbo charged 350. Another guy I know with a Cyclone truck that runs that 6 which comes in the truck runs 10:1 with boost making 850whp on pump gas which just makes me sick.

It may be the circles I run in, however I don't know anybody going low compression with lost of boost in a serious car. [shrug]

 

[Mirage2LTurbo]

I agree with ya. Your post is one of experience, the above are ones of rumor and theory.

With all due respect, not the pro's I know and I have traveled the country and met them all working for a national magazine. Lets put it this way. The worlds fastest Gasoline powered Honda running 8.66@141mph is running 9.5:1 compression with 35ish psi of boost. Gary Gardella ran mid 9ish:1 compression for years while on C16 as did Chris Rado back in the day. Now these are all honda's however when your talking full race cars with fully built motors there isn't much difference between a B18 stroked to 2.2L with a fully bulit head and a 4G63 at the same level.

V8 guys have been runnign 10:1 or 11:1 on their race cars in boosted applications making 1500-2000hp for years they wonder what us import guys are doing running low compression. I heard it from one guys lips at the dyno after he maxed the dyno out at 1200hp (he said it made 1250whp, not sure how he knew...) and he was twin turbo charged 350. Another guy I know with a Cyclone truck that runs that 6 which comes in the truck runs 10:1 with boost making 850whp on pump gas which just makes me sick.

It may be the circles I run in, however I don't know anybody going low compression with lost of boost in a serious car. [shrug]

 

[Aaron91RS]

I'll trust the 3.8 TTA/GN people who where doing this long before a DSM was ever even thought of.
Yep I'll go with those guys making 1000HP daily drivers using more boost and using 8:1 compression and able to fill up on something less then c16.

On the other hand you can trust the people here talking about dragsters that have no relation to our daily drivers. Or the ones that tell you v8's run 10:1 compression and twin turbo setups all the time.

Damn and all this time I was running my Camaro wrong.
Wait till the guys hear their LS1's can handle 15psi stock. Hell modded they go high 10's NA. Should be able to spin the world backwards on the launch when this gets out.

 

[CanadianTalon]

Another guy I know with a Cyclone truck that runs that 6 which comes in the truck runs 10:1 with boost making 850whp on pump gas which just makes me sick.

I'd like to see said 4.3 litre syclone that makes 850 WHP on pump gas with a 10:1 motor. That's 2/3rd's of a 350 chevy, and I've built numerous 350 chevy's and with a 4" bore and good aluminum heads and I know you're hard pressed to get more than 10-12 pounds of intercooled boost out of them. If you'd like to share the secret for what would essentially be a 1275 RWHP 350 chevy on pump gas, I'd love to hear it.

FWIW, basically every single Pro 5.0, SSO, or any other fast class motor is running 9:1 compression or less. A lot of the NMRA renegade guys tried to go with higher compression like 10:1, 11:1 to try and make more power since they are limited to small blowers and a serpentine drive system, but almost all of them started melting pistons like you do on nitrous cars. The only motors you're going to see there running higher compression would be the 4.6/5.4 modular motors, they use a 3.5" bore and an efficient 4V head and can run higher compression without the drawbacks you see on the big headed conventional SBF's.

 

[DSMJim]

I'd like to see said 4.3 litre syclone that makes 850 WHP on pump gas with a 10:1 motor. That's 2/3rd's of a 350 chevy, and I've built numerous 350 chevy's and with a 4" bore and good aluminum heads and I know you're hard pressed to get more than 10-12 pounds of intercooled boost out of them. If you'd like to share the secret for what would essentially be a 1275 RWHP 350 chevy on pump gas, I'd love to hear it.

FWIW, basically every single Pro 5.0, SSO, or any other fast class motor is running 9:1 compression or less. A lot of the NMRA renegade guys tried to go with higher compression like 10:1, 11:1 to try and make more power since they are limited to small blowers and a serpentine drive system, but almost all of them started melting pistons like you do on nitrous cars. The only motors you're going to see there running higher compression would be the 4.6/5.4 modular motors, they use a 3.5" bore and an efficient 4V head and can run higher compression without the drawbacks you see on the big headed conventional SBF's.

Sorry that was supposed to be race gas not pump gas, yeah I'd like to see that too. The problem with talking about high compression on V8's is there are so many different motor types and setups that were basically wasting our time talking about them. I do however know many of the import guys running fast and it's pretty split if they run high or low compression. A lot of the Honda guys are trying out high compression and are getting great results from it. Others are sticking with lower compression and still going really fast, so I all depends on what your used to or wanna do.

Damn and all this time I was running my Camaro wrong.
Wait till the guys hear their LS1's can handle 15psi stock. Hell modded they go high 10's NA. Should be able to spin the world backwards on the launch when this gets out.

Who said anything about running 15psi on a stock Camaro motor? I honestly have no idea where you were going with any of your post. You couldn't possibly be talking about what I said because nobody here said anything about a stock Camaro running boost or any other stock motor for that matter.

Honestly were getting way off course here and it's gonna be a crash course the way this is going.

 

[awdterrorpty]

Hello fellow DSM'rs...I'm from Panama City in Panama I had a 1991 TAlon TSi with JE piston 9.0:1 compression w/stock rods..What i will mlike to know is how much boost will be safe to run on 95octane gas..i'm running 15psi in low boost and 18psi in high boost on a evo3 big 16G w/ 510 injectors and 3000gt Fpump. I'm planning on running 21 psi on race gas w/ a 20G..so Is it safe..how much is safe?.
and how much Fuel pressure do I need.

 

[anconover]

Umm.. Get a logger, learn to tune, and figure it out yourself is the best advice your going to get.

 

[peregrine]

Hello fellow DSM'rs...I'm from Panama City in Panama I had a 1991 TAlon TSi with JE piston 9.0:1 compression w/stock rods..What i will mlike to know is how much boost will be safe to run on 95octane gas..i'm running 15psi in low boost and 18psi in high boost on a evo3 big 16G w/ 510 injectors and 3000gt Fpump. I'm planning on running 21 psi on race gas w/ a 20G..so Is it safe..how much is safe?.
and how much Fuel pressure do I need.

38-40 psi fuel pressure with no vaccuum attached, 21 psi on race gas is fine, i would run 25-26 psi max on that turbo.

 

[anconover]

run a base of 36-38 with no vac IMO, thats stock. And Id run as much boost on that turbo as i could untill it stopped making power.

 

[Rémy B]

I wonder if after 20 years in advancements and understanding what is needed to run pump gas on 9:1CR with a little larger turbo, the persons involved in these posts have the same opinion.

 

[biglady112]

I wonder if after 20 years in advancements and understanding what is needed to run pump gas on 9:1CR with a little larger turbo, the persons involved in these posts have the same opinion.

If anyone with half a brain when it comes to tuning, 9:1 is certainly not extreme. One could easily make 400whp easily on pump gas. After that the risk factor drastically increases.

I don’t know the compression ratio of 99% of the cars I tune. It doesn’t stop me or slow me down. I tune for what the car wants and for what it needs.

 

[jed344]

From what i have seen too the real compression ratio is rarely what the piston is rated anyway. When built you have to measure some things to get real compression ratio and most time's unless block and head have been cut quite a bit you end up lower then the piston rating anyway. I agree 100% with biglady's comment. 10:1 is a different matter but 9:1 is fine.

 

[Rémy B]

That was my point guys, seen all the comments from 20 years ago, I only could imagine they didn't had the knowledge and tech of now days.

 

[bastarddsm]

Gotta be a record! 20yr old thread revival. I don't think much has changed in understanding. Biggest things for us was getting real engine control and away from stuff like the SAFC. Not having timing control, made higher compression much harder to work with. Also E85, better intercoolers, and getting away from bolt on turbo's.

I still run 8.5:1, and I know I'm leaving power on the table, but the engine is way happy and makes power easily, and it's versatile. it'll still make close to 500whp on 87oct.

 

[Canadian_CD9A]

We have better sensors, better fuel injectors, more efficient turbochargers and far better ECU systems and tuning capabilities these days, but that just helps our safety window for tuning. The limits of pump gas are still very real and apply to the 4G63 - we would make similar peak numbers as 2004 with the same lb/min of peak airflow, but turbo technology advancements and better tuning options have created far better response and "under the curve" numbers to go with it. More advanced engines have better knock control strategies with more knock sensors and faster processing, variable cam timing with better cylinder head design and direct injection, which are actual game changers.