Highest compression ratio on street gas?

[scorch70]

Hi guys, as some of you know, I am having work done on a spare head/cams right now by a local engine builder (paeco.com). Anyway, I am trying to figure out what the highest compression is that I can run in a daily driven 2.0L, with street gas (93 octane)? The compression ratio I want in the end will determine the grind of the cams, so it is an important question. The engine builder is pushing for 11:1, but I am thinking 12:1. I want 200 crank hp in the end, and dont think I can get there at 11:1.

What do you guys think?

EDIT: I know Install Shield 2 is running 12:1 in his test bed engine, but I'm just wondering how drive-able that would be in the real world. Cooling issues? Etc.

TIA,
scorch70

 

[RyanJayG]

if you are planning on getting a tuner for timing controll then you should be able to run 12:1.... tuning makes up for a LOT.... but if you stay on the stock ecu I wound't go over the comp ratio of the FS-ZE engine... ( and honestly this would be a good option if you could get a thin headgasket )

oh, btw, fs-ze pistons are setup for 10.4:1

 

[RyanJayG]

oh yeah, they are relatively cheap as well http://www.corksport.com/main.php3?primNavIndex=0&mainURL=/store/index.php3?cat=220746 at $185

 

[twilightprotege]

i'll eventually go for 10.9:1 - that's the 10.4:1 pistons + the 0.021" thick gasket (normally 0.040"). with tuning it should be no worries on 93 fuel

 

[scorch70]

i'll eventually go for 10.9:1 - that's the 10.4:1 pistons + the 0.021" thick gasket (normally 0.040"). with tuning it should be no worries on 93 fuel

Twilight, do you think you can make 175 whp with that compression ratio? I mean, the Japanese version runs 10.4:1, and they are only making ~168 crank hp, correct? Thats the only reason I figured I might have to go 12:1.


scorch70

 

[p5sundevil]

well since your planning on all that headwork we talked about in the other thread then I would assume engine management is in your plans, if so I would go with the 12:1 since with management you will relize much more in gains and so forth this way. Also this way you can go forged...

yah i think you could reach your goal with 11:1 but if your going engine management, besides price there is no reason not to go forged custom.

 

[scorch70]

well since your planning on all that headwork we talked about in the other thread then I would assume engine management is in your plans, if so I would go with the 12:1 since with management you will relize much more in gains and so forth this way. Also this way you can go forged...

yah i think you could reach your goal with 11:1 but if your going engine management, besides price there is no reason not to go forged custom.

Not to thread jack my own thread, but yeah, engine management is the part of this build that bothers me the most. I am down south, and all the Mazda engine tuners seem to be up in the Northeast. But, MPI is looking good for this. Also, I am hoping Twilight pays a visit to Haltech soon, and gets that ball rolling. hint, hint


scorch70

 

[MacProtege5]

compression

i have the Japanese spec intake and exhaust cams, along with 10.7:1 compression and the car runs great. with all of my mods i get a consistent 28-30mpg city or highway mileage. i have not gotten it tuned yet do to funds, but eventually it will come along. also i have had my head shaved twice (not sure how much) and have had a three angle valve job

 

[scorch70]

i have the Japanese spec intake and exhaust cams, along with 10.7:1 compression and the car runs great. with all of my mods i get a consistent 28-30mpg city or highway mileage. i have not gotten it tuned yet do to funds, but eventually it will come along. also i have had my head shaved twice (not sure how much) and have had a three angle valve job

God, I wonder what compression you're really running. 12:1? Maybe higher? Have you ever done a dyno or 1/4 mile run? Just curious where you are at.


thanks,
scorch70

 

[Installshield 2]

The quality of gas needed comes in to be a function of how well the engine is tuned...Not only with engine management, but also with intake charge temps, and engine cooling efficiency...

For the FS you could probably approach 13:1, or even a little over (mostly due to its low TDC dwell time) on street gas...assuming you have some aluminum internals, at least for the pistons...with a lower specific heat capacity, they tend to absorb far less amounts of heat...so piston heat soak is much less...which helps to prevent detonation...

The stock cooling system would need to be monitered too for hot days when the car is run hard...I haven't probed our stock radiator much yet, but it definately gets fed plenty of fresh cool air...so it may only need a slightly more water biased coolant mixture to keep it safe...

But it all dials in with the engine controller...You can make 10.1:1 CR's terribly unreliable if you want...and you can also make 13:1 very reliable...just can't skimp on the controller...

 

[mp3moose]

10.7:1 runs like stock on street gas.

 

[twilightprotege]

scorch - yeah i reckon on goal is within reach with that CR...it's all about tuning!

 

[scorch70]

scorch - yeah i reckon on goal is within reach with that CR...it's all about tuning!

Well, I emailed my engine builder, and he thinks we can make 200 hp at 11:1. I sent him the specs on the FS-ZE, and that didnt change his mind. So we will see. I am skeptical, but hey, he is the expert, and I am paying him very well, so I will stick with his recommendation.


scorch70

 

[Gen1GT]

The quality of gas needed comes in to be a function of how well the engine is tuned...Not only with engine management, but also with intake charge temps, and engine cooling efficiency...

For the FS you could probably approach 13:1, or even a little over (mostly due to its low TDC dwell time) on street gas...assuming you have some aluminum internals, at least for the pistons...with a lower specific heat capacity, they tend to absorb far less amounts of heat...so piston heat soak is much less...which helps to prevent detonation...

The stock cooling system would need to be monitered too for hot days when the car is run hard...I haven't probed our stock radiator much yet, but it definately gets fed plenty of fresh cool air...so it may only need a slightly more water biased coolant mixture to keep it safe...

But it all dials in with the engine controller...You can make 10.1:1 CR's terribly unreliable if you want...and you can also make 13:1 very reliable...just can't skimp on the controller...

Yep, what he said.

Don't forget David, dynamic compression ratio matters more than static compression ratio. The longer your valves are open, the more compression you NEED to make power. So if you have some big-assed, lumpy cams(which you damn well better, to take advantage of your crazy Paeco valvetrain), you can EASILY run 12:1 with aluminum pistons. If you're having heat problems, install a good oil cooler and some Redline Water Wetter. I doubt you would anyways, with the aluminum pistons and oil squirters.

I'm gonna run 12:1 without looking back, and Jamie's already shown it'll do it without problems. Kyle, what are your running in your new engine?

 

[scorch70]

Yep, what he said.

Don't forget David, dynamic compression ratio matters more than static compression ratio. The longer your valves are open, the more compression you NEED to make power. So if you have some big-assed, lumpy cams(which you damn well better, to take advantage of your crazy Paeco valvetrain), you can EASILY run 12:1 with aluminum pistons. If you're having heat problems, install a good oil cooler and some Redline Water Wetter. I doubt you would anyways, with the aluminum pistons and oil squirters.

I'm gonna run 12:1 without looking back, and Jamie's already shown it'll do it without problems. Kyle, what are your running in your new engine?

Dynamic you want between 8.1:1 and 8.5:1, correct? Think I read that somewhere.


scorch70

 

[Gen1GT]

Ya, that's about right.