High Compression VS Low Compression Opinions

[Mike T]

External gate with good controller would Be my first investment


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On the wish list......have to let my wallet cool off


I've never openly stated my goal but to crack the 9's would make me smile.

 

[RICHIE HIGH PSI]

Great to have you chime in Richie! I have heard a lot of second hand information on your car (not CR) and it's truly amazing what you have accomplished.
Most guys in your position treat this stuff like it's "top secret" and I would like to that you for sharing this for the sake of discussion.

Nothing top secret here.
I like to keep the build simple.
Parts are much easier to come by "off the shelf"

 

[fastblackracing]

Not many takers on the low compression side.....thought there may be a couple of 3HP per cube (or more) guys out there.

This keeps taking me back to a conversation with Ricardo La Costa 10 plus years ago where he said "They think I'm crazy but I love compression". For those that don't know him he was going 8.30 a long time ago....stage stuff of course.

More compression will let the power happen somewhat easier and with some positive side effects as already stated....
The gap will widen some as you push the turbo harder and approach the limits of the turbo/ compressor and turbine side limitations and efficencies....think less charge air temp from a lesser boost number and lower IAT,s that come along with it for free.....and possibly less turbine drive pressure since you are at a lesser manifold pressure for the same or more wheel power numbers.......Also the ability to use a bigger exhaust housing without killing the spool.....and converter selection can be tighter as well.

Cylinder pressure and the length of the pressure wave in the cylinder make engine torque and the way
that the pressure is generated makes a difference.....
25# boost with 10-1 may make the same cylinder pressure as 35# with 7.5-1.. which one makes more power will revolve around the air temps,drive pressures cam timing and so on and if you take advantage of the beni's that the higher CR can give you....

Supposedly turbo engines benefit from their expansion characteristics in the cylinder by having a somewhat higher
cylinder pressure at the tail end of the Useful part of the downward stroke meaning they can produce useable cylinder pressure for a few more crank degrees.... The deal is pretty much done by 70 Degrees ATDC.
Nitrous and NA engines build the pressure a little bit different than the boosted engines......why do you think the blower cars are so damn loud at the track?? Cause when the exhaust valve cracks open their is way more cylinder pressure than a NA car but the pressure is down to a point it does not produce much usable work on the crank so they begin to empty the cylinder early......

The N2O engine we are building which is a serious but not all out race piece will have the exhaust valve Open
.085" at 95* ATDC on the power stroke.....When the piston is only half way down.....the reason I bring this up is a higher compression lower boost engine may benefit from the exhaust opening event begining a few degrees earlier
since their is less total air in the cylinder to expand and drive the piston down than a low CR Turbo engine......we are talking small changes here but if you are purpose building a high compression turbo engine why not go for all you can get?

But if you are going to be more of lesser boost say 17 to 22 pound kind of deal you can pretty much make up the power difference with some extra manifold pressure to make the power but you lose out on the other free benefits.

With that said my 8.2-1 CR 233 inch with an 18 blade ptc on a 94 degree day spooled my 71HPQ BB very fast And launching at 5# boost was at 30# boost in 5-7 tenths of a second. [.5 - .7 ]......I used a TA 3 1/2" pipe with a 1.00 inch hole in the housing a High pressure actutor and a Perrin adjustable controller and had great boost control...+ or - one-half pound.

My next engine will have more Squeeze and be much more purpose built But unless you want to scrape up an extra grand for new pistons and fitment you can get along with what you have except maybe that 17 blade. FBR

 

[Mike T]

More compression will let the power happen somewhat easier and with some positive side effects as already stated....
The gap will widen some as you push the turbo harder and approach the limits of the turbo/ compressor and turbine side limitations and efficencies....think less charge air temp from a lesser boost number and lower IAT,s that come along with it for free.....and possibly less turbine drive pressure since you are at a lesser manifold pressure for the same or more wheel power numbers.......Also the ability to use a bigger exhaust housing without killing the spool.....and converter selection can be tighter as well.

Cylinder pressure and the length of the pressure wave in the cylinder make engine torque and the way
that the pressure is generated makes a difference.....
25# boost with 10-1 may make the same cylinder pressure as 35# with 7.5-1.. which one makes more power will revolve around the air temps,drive pressures cam timing and so on and if you take advantage of the beni's that the higher CR can give you....

Supposedly turbo engines benefit from their expansion characteristics in the cylinder by having a somewhat higher
cylinder pressure at the tail end of the Useful part of the downward stroke meaning they can produce useable cylinder pressure for a few more crank degrees.... The deal is pretty much done by 70 Degrees ATDC.
Nitrous and NA engines build the pressure a little bit different than the boosted engines......why do you think the blower cars are so damn loud at the track?? Cause when the exhaust valve cracks open their is way more cylinder pressure than a NA car but the pressure is down to a point it does not produce much usable work on the crank so they begin to empty the cylinder early......

The N2O engine we are building which is a serious but not all out race piece will have the exhaust valve Open
.085" at 95* ATDC on the power stroke.....When the piston is only half way down.....the reason I bring this up is a higher compression lower boost engine may benefit from the exhaust opening event begining a few degrees earlier
since their is less total air in the cylinder to expand and drive the piston down than a low CR Turbo engine......we are talking small changes here but if you are purpose building a high compression turbo engine why not go for all you can get?

But if you are going to be more of lesser boost say 17 to 22 pound kind of deal you can pretty much make up the power difference with some extra manifold pressure to make the power but you lose out on the other free benefits.

With that said my 8.2-1 CR 233 inch with an 18 blade ptc on a 94 degree day spooled my 71HPQ BB very fast And launching at 5# boost was at 30# boost in 5-7 tenths of a second. [.5 - .7 ]......I used a TA 3 1/2" pipe with a 1.00 inch hole in the housing a High pressure actutor and a Perrin adjustable controller and had great boost control...+ or - one-half pound.

My next engine will have more Squeeze and be much more purpose built But unless you want to scrape up an extra grand for new pistons and fitment you can get along with what you have except maybe that 17 blade. FBR

Mannie I'm always blown away by your attention to detail and overall knowledge. I also have noticed how fair and balanced all of your responses are, IE getting your point across without belittling others opinions.....very diplomatic for a lack of a better term.

I doubt you have the time for it but there is a request for additional moderators on this board and I for one believe you would be an excellent addition.

 

[Mr.Spool]

Open to scrutiny.....

Ok my thought,too low on compression with a cast 70gt and q trim turbo and big ex housing with a low rpm window.converter needs to be real loose in that one to get the response.

 

[Mr.Spool]

Low compression here...
8.5

Ok I will bite,why?you have a fast buick no doubt but I have seen alot of fast stuff and builds usually have more compression even the nitrous v8 stuff .I understand if you don't want to go into detail.

 

[turbobuick]

Excellent thread and input Thanks Mannie and Bison.

I love high CR, my TSO motor was well north of 11:1 and boost in the 35-40 range.

 

[Mike T]

Couple of things to add here....

It's ironic that so many smart guys agree (even on other forums as it turns out) that more compression is better yet the fastest 109 out there is stock stroke low compression motor. From my perspective it seems that Richie has taken his car to what has to be getting close to the mechanical limits of a 109........What more could anyone ask for?

Looking at his combo in particular.....no doubt it works. He's at another level and maybe there are dynamics taking place that haven't been considered before. Or maybe It's the K.I.S.S. method



Back to higher compression.

Since higher compression seems be more popular these days do you guys see the dish piston going away or the dish becoming minimal in size?






.

 

[rag231]

This is a very interesting read, but if you go back to conventional wisdom that was spread in the late nineties about high compression and turbo motors didnt mix. Looking at turbo recipies ( I used to print every one of them, pre-site crash ) that we used to post on this board back in the day, no one ever posted anything greater than 9:1. I always wanted to take a Busch motor as is, just change the cam, add meth and see what would happen. I came real close, never could get the electronics to work 100% of the time. We really just didnt know what we were doing. I sold a ton of stage 2 motors to Kent Rudbeck and Lawerence Conley, they both had advised to go 9:1 max . Jason Carter that has the really quick twin turbo Malibu @ MandM Transmissions was into stage 2 stuff back in the day, 9:1 motor. Sean Lilly twin turbo GN in the 7's. All were in favor of the lower compression motors. I now that Sean and Jason moved on to bigger turbo motors and I am sure that there CR jumped up also in the pursuit of more power. I have a motor that is about to be dissassembled and rebuilt ( with a little help) and I would like to go into the higher compression direction to see what will happen.

 

[bison]

More compression will let the power happen somewhat easier and with some positive side effects as already stated....
The gap will widen some as you push the turbo harder and approach the limits of the turbo/ compressor and turbine side limitations and efficencies....think less charge air temp from a lesser boost number and lower IAT,s that come along with it for free.....and possibly less turbine drive pressure since you are at a lesser manifold pressure for the same or more wheel power numbers.......Also the ability to use a bigger exhaust housing without killing the spool.....and converter selection can be tighter as well.

Cylinder pressure and the length of the pressure wave in the cylinder make engine torque and the way
that the pressure is generated makes a difference.....
25# boost with 10-1 may make the same cylinder pressure as 35# with 7.5-1.. which one makes more power will revolve around the air temps,drive pressures cam timing and so on and if you take advantage of the beni's that the higher CR can give you....

Supposedly turbo engines benefit from their expansion characteristics in the cylinder by having a somewhat higher
cylinder pressure at the tail end of the Useful part of the downward stroke meaning they can produce useable cylinder pressure for a few more crank degrees.... The deal is pretty much done by 70 Degrees ATDC.
Nitrous and NA engines build the pressure a little bit different than the boosted engines......why do you think the blower cars are so damn loud at the track?? Cause when the exhaust valve cracks open their is way more cylinder pressure than a NA car but the pressure is down to a point it does not produce much usable work on the crank so they begin to empty the cylinder early......

The N2O engine we are building which is a serious but not all out race piece will have the exhaust valve Open
.085" at 95* ATDC on the power stroke.....When the piston is only half way down.....the reason I bring this up is a higher compression lower boost engine may benefit from the exhaust opening event begining a few degrees earlier
since their is less total air in the cylinder to expand and drive the piston down than a low CR Turbo engine......we are talking small changes here but if you are purpose building a high compression turbo engine why not go for all you can get?

But if you are going to be more of lesser boost say 17 to 22 pound kind of deal you can pretty much make up the power difference with some extra manifold pressure to make the power but you lose out on the other free benefits.

With that said my 8.2-1 CR 233 inch with an 18 blade ptc on a 94 degree day spooled my 71HPQ BB very fast And launching at 5# boost was at 30# boost in 5-7 tenths of a second. [.5 - .7 ]......I used a TA 3 1/2" pipe with a 1.00 inch hole in the housing a High pressure actutor and a Perrin adjustable controller and had great boost control...+ or - one-half pound.

My next engine will have more Squeeze and be much more purpose built But unless you want to scrape up an extra grand for new pistons and fitment you can get along with what you have except maybe that 17 blade. FBR

Drive pressures increase with no other change when increasing CR. But so does VE, mass flow, and rpm (if not out of turbo). Cylinder pressure should not be thought of as relative to manifold pressure. This is why so many run so slow because they fear the boost. It's possible to have less cylinder pressure at 35psi than 25. We see guys tearing up stock block engines and lifting heads at 25psi and some are able to run 35-40psi without this problem and there's only so much you can do with the block/fastening itself to make it resilient to cylinder pressure when you have 4 fasteners around each hole. The rest is through controlling cylinder pressure directly with the tune.


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[bison]

This is a very interesting read, but if you go back to conventional wisdom that was spread in the late nineties about high compression and turbo motors didnt mix. Looking at turbo recipies ( I used to print every one of them, pre-site crash ) that we used to post on this board back in the day, no one ever posted anything greater than 9:1. I always wanted to take a Busch motor as is, just change the cam, add meth and see what would happen. I came real close, never could get the electronics to work 100% of the time. We really just didnt know what we were doing. I sold a ton of stage 2 motors to Kent Rudbeck and Lawerence Conley, they both had advised to go 9:1 max . Jason Carter that has the really quick twin turbo Malibu @ MandM Transmissions was into stage 2 stuff back in the day, 9:1 motor. Sean Lilly twin turbo GN in the 7's. All were in favor of the lower compression motors. I now that Sean and Jason moved on to bigger turbo motors and I am sure that there CR jumped up also in the pursuit of more power. I have a motor that is about to be dissassembled and rebuilt ( with a little help) and I would like to go into the higher compression direction to see what will happen.

There were some 10:1 engines in the 90's. EFI tuning and pursuit of performance has come a real long way since then. A few years back I went and raced with a 60-1 on a 7.5:1 engine and went 10.61. 60' wasn't that good either. 10 years earlier guys struggled to run 10's with that. I'm sure I could have whittled down to 10.35-10.40 too. Raise CR to 10:1, change converter, cam, and gearing drop a little weight and you're knocking on 9's. mid 90's people were getting excited about a 9.9x and they had stage 2 engines with a bunch of exotic crap bolted to them. Big turbos, custom headers and a bunch of other crap that has been long superseded with what you see today.


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[TTipe]

More compression will let the power happen somewhat easier and with some positive side effects as already stated....
The gap will widen some as you push the turbo harder and approach the limits of the turbo/ compressor and turbine side limitations and efficencies....think less charge air temp from a lesser boost number and lower IAT,s that come along with it for free.....and possibly less turbine drive pressure since you are at a lesser manifold pressure for the same or more wheel power numbers.......Also the ability to use a bigger exhaust housing without killing the spool.....and converter selection can be tighter as well.

Cylinder pressure and the length of the pressure wave in the cylinder make engine torque and the way
that the pressure is generated makes a difference.....
25# boost with 10-1 may make the same cylinder pressure as 35# with 7.5-1.. which one makes more power will revolve around the air temps,drive pressures cam timing and so on and if you take advantage of the beni's that the higher CR can give you....

Supposedly turbo engines benefit from their expansion characteristics in the cylinder by having a somewhat higher
cylinder pressure at the tail end of the Useful part of the downward stroke meaning they can produce useable cylinder pressure for a few more crank degrees.... The deal is pretty much done by 70 Degrees ATDC.
Nitrous and NA engines build the pressure a little bit different than the boosted engines......why do you think the blower cars are so damn loud at the track?? Cause when the exhaust valve cracks open their is way more cylinder pressure than a NA car but the pressure is down to a point it does not produce much usable work on the crank so they begin to empty the cylinder early......

The N2O engine we are building which is a serious but not all out race piece will have the exhaust valve Open
.085" at 95* ATDC on the power stroke.....When the piston is only half way down.....the reason I bring this up is a higher compression lower boost engine may benefit from the exhaust opening event begining a few degrees earlier
since their is less total air in the cylinder to expand and drive the piston down than a low CR Turbo engine......we are talking small changes here but if you are purpose building a high compression turbo engine why not go for all you can get?

But if you are going to be more of lesser boost say 17 to 22 pound kind of deal you can pretty much make up the power difference with some extra manifold pressure to make the power but you lose out on the other free benefits.

With that said my 8.2-1 CR 233 inch with an 18 blade ptc on a 94 degree day spooled my 71HPQ BB very fast And launching at 5# boost was at 30# boost in 5-7 tenths of a second. [.5 - .7 ]......I used a TA 3 1/2" pipe with a 1.00 inch hole in the housing a High pressure actutor and a Perrin adjustable controller and had great boost control...+ or - one-half pound.

My next engine will have more Squeeze and be much more purpose built But unless you want to scrape up an extra grand for new pistons and fitment you can get along with what you have except maybe that 17 blade. FBR

You are referencing the differences between an "Atkinson & Miller " cycle engine. Why have cylinder pressures fighting each other rather than camming for an earlier exhaust event.

 

[No disintegrations]

It would be fun to see the relationship in compression pressure on these different scenarios. Meaning what is the mixture pressurized to after boost is built and just prior to ignition.
I remember a single cylinder non-turbo diesel I worked on needed about 450psi cranking to start up. It had no glow plug iirc.

 

[TTipe]

A certain "player" in the Buick community and I went tooling around in his T Type on "auto ignition".

 

[Mr.Spool]

It's ironic that so many smart guys agree (even on other forums as it turns out) that more compression is better yet the fastest 109 out there is stock stroke low compression motor. From my perspective it seems that Richie has taken his car to what has to be getting close to the mechanical limits of a 109........What more could anyone ask for?

that's why I asked I have driven lots of different combos and the compression wakes them up quite a bit.consider what the buick 109 has,no cubes,limited rpm range,the heads suck.getting them to run fast is not easy and costs a lot more.im really surprised anyone can run that fast with the rules of that division especially on low compression.i will say I'm more in the street world currently and the low compression stuff is far behind unless the car is using nitrous.

 

[Mr.Spool]

mid 90's people were getting excited about a 9.9x and they had stage 2 engines with a bunch of exotic crap bolted to them.

that's the truth right there.i remember stage stuff running 10s and guys were happy.

 

[earlbrown]

Back to higher compression.

Since higher compression seems be more popular these days do you guys see the dish piston going away or the dish becoming minimal in size?

.

I made my inverted domes smaller to make it easier to raise compression without machining and still be able to have some quench most of the time.

 

[20psiofevil]

For what it's worth I'll throw my hat into the ring. 8.5:1 here also. I choose the lower cr for a bigger tuning window.

Also great thread!

 

[Mike T]

For what it's worth I'll throw my hat into the ring. 8.5:1 here also. I choose the lower cr for a bigger tuning window.

Also great thread!

Found mine to be very forgiving.

 

[Mike T]

I made my inverted domes smaller to make it easier to raise compression without machining and still be able to have some quench most of the time.

What's the CC Earl?