How much Boost?

[tjav8b]

What is the maximum boost S65's are running on the stock rods/bolts? At about what power output can one expect failure?

[Patrón]

Originally Posted by tjav8b

What is the maximum boost S65's are running on the stock rods/bolts? At about what power output can one expect failure?

What fuel/octane?

[tjav8b]

93 octane.

[Longboarder]

Member Bihn runs 10psi on an ESS kit with an upgraded intercooler system. He trapped 134.X in the quarter mile. Record for a stock motor. 93 octane.

I don't think that's a long term solution though. Too much boost for too long and maybe a bad batch of gas and BOOM.

For the long term around 7.5 psi is consider the max from a longevity standpoint.

[R_lara]

Originally Posted by Longboarder

Member Bihn runs 10psi on an ESS kit with an upgraded intercooler system. He trapped 134.X in the quarter mile. Record for a stock motor. 93 octane.

I don't think that's a long term solution though. Too much boost for too long and maybe a bad batch of gas and BOOM.

For the long term around 7.5 psi is consider the max from a longevity standpoint.

Agreed, my P3 gauge reading 7.9-8.1 with a 3.7 inch pulley on my S/C anybody with this pulley.

I think we should do a pulley size boost result thread.

[Patrón]

Originally Posted by R_lara

Agreed, my P3 gauge reading 7.9-8.1 with a 3.7 inch pulley on my S/C anybody with this pulley.

I think we should do a pulley size boost result thread.

that is a good idea, but the variance factor is also going to be the temps at time of reading. i got some really high readings when it was humid and cold, ten degrees hotter on another day and diff humidity and i'm one psi or more lower. i didn't think the humidity and temps would affect it that much but it does. i am not running my car hard until ambient temps are below 75 again.

[R_lara]

What is the variance give of take with temp and humidity? Also clean or dirty filters will affect I assume and boost gauge used.

But we can gather enough data to average out.

[Patrón]

Originally Posted by R_lara

What is the variance give of take with temp and humidity? Also clean or dirty filters will affect I assume and boost gauge used.

But we can gather enough data to average out.

i am going off of data on my p3, which is tapped into the line very near the BPV line connection.

i was reading 8-8.4 one evening when it was 65-60deg. with humidity in the 40-50% range. low 70s and similar humidity and the psi dropped. 80s and it dropped more. i will have to redo some samples in different tempatures and log my readings. i'll do it again in September when the tempatures drop. it is in the mid 80s now with 80% humidity. i don't push my car hard in hot tempatures. never have because it seems above 77 degrees or so and the car (even in N/A form) drove very differently.

[R_lara]

Hmmm where I live we rarely see any temps under 80 degrees.

[tjav8b]

I recently de-catted my headers and think I have a slight boost loss due to the increased flow. I run the 3.55" pulley now and my gauge shows a maximum of 6psi. AJ told me I could go down to the next size pulley of 3.25" "at my own risk". He said the software would support the smaller pulley but at these power levels the rods/bearings could fail.

I come to this board a lot for answers because there are not a lot of supercharged S85 engines running around that frequent the boards. Since S65/S85 engines are mostly the same, my engine should be able to handle more boost right? What do you guys think? Does AJ tell everyone "at your own risk" but its really ok or will I end up blowing my engine?

Thanks guys.

[sales@ESSTuning]

Right around 8 psi on 93+ octane fuel is max boost we like to run the S65.

[Disturbed]

Originally Posted by Roman@ESS

Right around 8 psi on 93+ octane fuel is max boost we like to run the S65.

Seems pretty low. You should have no issue running 14psi-16psi on 93. Even on many other platforms that's pretty normal limit on 93 as far as boost. Is it due to compression ratio? If so, why not use a bit thicker head gasket to drop the cr and easily make up the extra power by adding more boost for even more power on pump gas. These cars could easily make 650rwhp on 93 with the rpms they run.

I admit this S65 and the low power output in the aftermarket baffles me.

With the bore/stroke these cars run why hasn't a street car been running 9,500rpm?

[pbonsalb]

Seriously? With 12.0:1 CR people run 14-16 psi on 93 pump? Who?

[regular guy]

Originally Posted by Disturbed

Seems pretty low. You should have no issue running 14psi-16psi on 93. Even on many other platforms that's pretty normal limit on 93 as far as boost. Is it due to compression ratio? If so, why not use a bit thicker head gasket to drop the cr and easily make up the extra power by adding more boost for even more power on pump gas. These cars could easily make 650rwhp on 93 with the rpms they run.

I admit this S65 and the low power output in the aftermarket baffles me.

With the bore/stroke these cars run why hasn't a street car been running 9,500rpm?

I don't think a thicker head gasket will drop the compression ratio as much as you think. If you double the thickness of the head gasket, the compression ratio drops from 12.0:1 to 11.15:1. If you triple the thickness, the compression ratio will drop to 9.7:1. The thickest head gasket I've ever seen on this engine is 0.089 mm. That would make 11.5:1 compression ratio.

[Disturbed]

Originally Posted by regular guy

I don't think a thicker head gasket will drop the compression ratio as much as you think. If you double the thickness of the head gasket, the compression ratio drops from 12.0:1 to 11.15:1. If you triple the thickness, the compression ratio will drop to 9.7:1. The thickest head gasket I've ever seen on this engine is 0.089 mm. That would make 11.5:1 compression ratio.

9.7:1 would work nicely. I was running 9.5:1 on my Talon and pushed 16psi without issue...that was back in the late 90's/early 2000's.

[8k3]

Originally Posted by regular guy

I don't think a thicker head gasket will drop the compression ratio as much as you think. If you double the thickness of the head gasket, the compression ratio drops from 12.0:1 to 11.15:1. If you triple the thickness, the compression ratio will drop to 9.7:1. The thickest head gasket I've ever seen on this engine is 0.089 mm. That would make 11.5:1 compression ratio.

And do you really want to rely on a head gasket mod to drop compression... I don't

[tjav8b]

Originally Posted by Roman@ESS

Right around 8 psi on 93+ octane fuel is max boost we like to run the S65.

Roman...What about the S85?

[regular guy]

Originally Posted by 8k3

And do you really want to rely on a head gasket mod to drop compression... I don't

No of course not...it's pure insanity to do that. But apparently, it doesn't bother some people.

[pbonsalb]

On some motors, the thicker HG or spacer plus HG works fine, is reliable and allows big power. Like the S52 used in the E36 M3.

Much more work on a V8 with dual vanos heads.

Of course an expensive built motor with low compression pistons would be more desirable but not everyone has the big bucks.

[regular guy]

Originally Posted by pbonsalb

On some motors, the thicker HG or spacer plus HG works fine, is reliable and allows big power. Like the S52 used in the E36 M3.

Much more work on a V8 with dual vanos heads.

Of course an expensive built motor with low compression pistons would be more desirable but not everyone has the big bucks.

But would you go 3x the factory head gasket thickness on this engine (specifically on this engine)?

[pbonsalb]

Typically double thickness is what you see, meaning you are starting with less compression. The thicker HG also reduces squish, which can make combustion less efficient (though on the S52, it seemed to have little to no effect according to tuners). For a triple thickness, I would use an annealed copper spacer with stock gasket rather than a triple thickness gasket.

But given the work to do this on an S65, I would just build the engine. Besides, if you are lowering CR to make more power than you could with stock CR, you are likely at the limits of the stock rods on the S65 (I made 520 lbs rwtq on S52 rods with compression lowering headgasket, but it does not appear the S65 rods have the same overhead).

If rods were not a limiting factor, those living in E85 areas could run E85 since it will allow substantially more boost on the same CR. We may see some such cars soon. But given the inconsistency of E85, I would want a flex fuel sensor and tuning that accommodates it or a failsafe of some kind. Nearest E85 is about an hour away for me so I have never looked seriously into it, but I have been running meth/water on my n/a 08M3 for 3 years.

[Spoolin1]

Originally Posted by Disturbed

9.7:1 would work nicely. I was running 9.5:1 on my Talon and pushed 16psi without issue...that was back in the late 90's/early 2000's.

I ran my S2000 F20c in stock block form at 11:1 CR and pushed 34 psi to it making over 800 whp and spinning it up to 9500 rpm. Not one issue and held the stock block record for years but of course the F20c comes with forged internals from factory.

Also, lowering compression with a thicker gasket or spacer is only asking for trouble. We have tried this with the F20c motor before and because the piston comes out of the deck some, all of the combustion happens on that gasket/spacer and in time they blow from the weakened thicker gasket/spacer area, even when running strong H11 headstuds. I'm not sure if the S65 pistons come out of the deck some but I would assume so with 12:1 CR.