Reduce Compression to Increase HP?
TECH Resident
Joined: Aug 2008
Posts: 910
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From: Dubai
First I'd like to say... I respect Martin and everything he's done for this community very much! If I wanted a cam he's the guy I'd ask. No disrespect or "bashing" intended. Just friendly discussion going on here. 
Boost is more efficient than compression at making power, period.
The reason the "racers" are using higher compression is because all the classes are turbo size limited. If the goal was peak power output and racers were all limited to the same cubic inches, you would see low compression, huge turbo setups dominating. Of course your customers aren't concerned with that, they want fast quarter mile times in class limited setups. Obviously you know your stuff and are providing them with great results the most efficient way possible for their specific goals.
I believe the most power per cubic inch ever recorded on a gas engine (nitro excluded) was produced by the 7:1 compression 1.5liter F1 turbo cars. Some drivers claimed over 80psi of manifold pressure during qualifying. They made close to 16hp per cubic inch, thats efficiency! That would be the equivalent of a 5600hp LS1. They could not have accomplished this with 12:1 static compression!
Boost is more efficient than compression at making power, period.
The reason the "racers" are using higher compression is because all the classes are turbo size limited. If the goal was peak power output and racers were all limited to the same cubic inches, you would see low compression, huge turbo setups dominating. Of course your customers aren't concerned with that, they want fast quarter mile times in class limited setups. Obviously you know your stuff and are providing them with great results the most efficient way possible for their specific goals.
I believe the most power per cubic inch ever recorded on a gas engine (nitro excluded) was produced by the 7:1 compression 1.5liter F1 turbo cars. Some drivers claimed over 80psi of manifold pressure during qualifying. They made close to 16hp per cubic inch, thats efficiency! That would be the equivalent of a 5600hp LS1. They could not have accomplished this with 12:1 static compression!
Like i said in my first post, I made alot of horsepower using a very low static and dynamic compression ratio motor and a blower. Made 930rwhp with a slipping clutch at 600feet elevation (not sure of DA). I know this car will make closer to 1000rwhp when I tune it here in Dubai all on straight pump gas. Set-up was a 427 and 17.5psi of boost and 16degrees of timing, I know it will do about 18-19 psi of boost here at sea level all on 93 octane gas and quite a bit of safety margin left in there. To put things in perspective, this is about 1350bhp at the crank if you assume blower parasitic loss of 150hp (conservative) and drivetrain loss of 15%.
how can you make this much power with high compression on 93 octane?
First result on google:
http://www.convertunits.com/from/hor...les+per+second
Boost is more efficient than compression at making power, period.
The reason the "racers" are using higher compression is because all the classes are turbo size limited. If the goal was peak power output and racers were all limited to the same cubic inches, you would see low compression, huge turbo setups dominating.
The reason the "racers" are using higher compression is because all the classes are turbo size limited. If the goal was peak power output and racers were all limited to the same cubic inches, you would see low compression, huge turbo setups dominating.
One other thing I'd like to say, is the words high boost and low boost are oxymoron's.
What one engine moves for air mass that registers 15psi of pressure above atmospheric and what another engine moves for air mass that registers 30psi of pressure above atmospheric are actually identical amounts of air mass, but one engine is much larger in comparison OR smaller and more volumetric efficient over the other due to compression and induction. Thus they register different pressures in the intake.
They both need the same fuel requirements and they both have the same end cylinder pressure. This is due to mass of the air being consumed and compressed in the cylinder.
I have a pretty good pulse on what the fastest guys at the track in the heads up radial classes are utilizing to go faster than the other guy. Not one of them, at least that I know are using low compression like is being mentioned in this thread and more boost. They are all high compression motors.
What one engine moves for air mass that registers 15psi of pressure above atmospheric and what another engine moves for air mass that registers 30psi of pressure above atmospheric are actually identical amounts of air mass, but one engine is much larger in comparison OR smaller and more volumetric efficient over the other due to compression and induction. Thus they register different pressures in the intake.
They both need the same fuel requirements and they both have the same end cylinder pressure. This is due to mass of the air being consumed and compressed in the cylinder.
I have a pretty good pulse on what the fastest guys at the track in the heads up radial classes are utilizing to go faster than the other guy. Not one of them, at least that I know are using low compression like is being mentioned in this thread and more boost. They are all high compression motors.
You are correct. They were limited to 102 RON fuel. They ran an 84:16 toluene/heptane mix. Basically ran straight toluene and dumbed it down to meet the 102/RON requirements. (I was basically excluding nitro with that comment) Todays race fuels had much more octane than the F1 toluene mix. No ones coming close to 16hp per cubic inch with it either.
TECH Resident
Joined: Aug 2008
Posts: 910
Likes: 0
From: Dubai
As I explained to you on facebook, not quite.
First result on google:
http://www.convertunits.com/from/hor...les+per+second
I guess I could have replied with this, but I went too 'newtonian'. I don't have thousands of customers, what could I possibly know? After all, we know that running a business automatically makes you correct.
First result on google:
http://www.convertunits.com/from/hor...les+per+second
I guess I could have replied with this, but I went too 'newtonian'. I don't have thousands of customers, what could I possibly know? After all, we know that running a business automatically makes you correct.
"Horsepower" is the unit of energy needed to lift 550 pounds the distance of 1 foot in 1 second. Near the end of the 18th century the Scottish engineer James Watt (1736-1819) made improvements in the steam engine and wished to determine how its rate of pumping water out of coal mines compared with that of horses, which had previously been used to operate the pumps. In order to define a horsepower, he tested horses and concluded that a strong horse could lift 150 pounds 220 feet in 1 minute. Therefore, 1 horsepower was equal to 150 x 220/1 or 33,000 foot pounds per minute (also expressed as 745.2 joules per second, 7,452 million ergs per second, or 745.2 watts).
Yes, horsepower is a unit as well. I was using joules/sec to explain how it is also a rate. Neither of us are wrong. What are you getting at?
This is where I struggle with you sometimes....you leave out the pertinent details as brought out by ForceFed86 such as compressor limits and octane. I agree that the smaller motor has a higher VE when making the same power, how else would a smaller motor make equal power. We went from talking about purely street setup's on pump gas for the OP who is getting his feet wet with boost, to talking about max effort drag cars. Ayousef's setup is exactly a case in point with lower compression and more boost. Hey as long as your customers are happy that's all that matters, but for someone just getting his feet wet in boost, there are distinct advantages going with a lower CR for a purely street car.
You stated pump gas street car.
His question was simply, "reduce compression to increase hp." Right?
I have a customer who races Outlaw Drag Radial. He can run whatever turbo he wants. Any turbo. Biggest one he wants and can afford. Problem is, he is already running the biggest single turbo he can possibly buy. Of course he could buy twins, but he is at the point where he has no more boost to make. Tapped out. Only way to increase power in his case is by increasing VE.
I also agree 100% that boost is much more efficient in adding power than compression. When you're tapped out though, and you need a little more, or you're looking to really optimize a set-up...you don't have to run low compression and "high boost".
Before I posted in this thread it was shaping up to basically come to the conclusion that, "you have to run low compression and high boost to make good power". I just wanted to interject that you did not have to do so to make good power.
Last edited by Sales@Tick; Aug 7, 2013 at 07:59 PM.
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Verdad Gallardo TECH Resident
Joined: Aug 2008
Posts: 910
Likes: 0
From: Dubai
The OP never said he was limited to pump gas. In fact, he never once mentioned octane or any limitations at all.
You stated pump gas street car.
His question was simply, "reduce compression to increase hp." Right?
I have a customer who races Outlaw Drag Radial. He can run whatever turbo he wants. Any turbo. Biggest one he wants and can afford. Problem is, he is already running the biggest single turbo he can possibly buy. Of course he could buy twins, but he is at the point where he has no more boost to make. Tapped out. Only way to increase power in his case is by increasing VE.
I also agree 100% that boost is much more efficient in adding power than compression. When you're tapped out though, and you need a little more, or you're looking to really optimize a set-up...you don't have to run low compression and "high boost".
Before I posted in this thread it was shaping up to basically come to the conclusion that, "you have to run low compression and high boost to make good power". I just wanted to interject that you did not have to do so to make good power.
You stated pump gas street car.
His question was simply, "reduce compression to increase hp." Right?
I have a customer who races Outlaw Drag Radial. He can run whatever turbo he wants. Any turbo. Biggest one he wants and can afford. Problem is, he is already running the biggest single turbo he can possibly buy. Of course he could buy twins, but he is at the point where he has no more boost to make. Tapped out. Only way to increase power in his case is by increasing VE.
I also agree 100% that boost is much more efficient in adding power than compression. When you're tapped out though, and you need a little more, or you're looking to really optimize a set-up...you don't have to run low compression and "high boost".
Before I posted in this thread it was shaping up to basically come to the conclusion that, "you have to run low compression and high boost to make good power". I just wanted to interject that you did not have to do so to make good power.
I made good power with high compression and boost, but this was with 10.85:1 and 8.5psi of boost, and a cam with intake closing of 44 ABDC, I knew I could have run about 2 more psi safetly on straight pump gas, but that was quite at the limit. If I wanted to run more, I had to either drop DCR by means of a cam, or drop SCR or a bit of both. Of course a cam swap is much easier, but the consequences of having a very late IVC event is killing some low-end and making more top-end and usually means you have to increase overlap as well unless you try to bias as much of the additional intake duration towards the closing event.
Last edited by ayousef; Aug 7, 2013 at 08:33 PM.
Wow! this thread got crazy. I think the right answer really depends on what you are after. If you after a max effort combination, you will need to run higher compression to keep up with the big boys because thats what they are running.
For the majority of people who want to run pump gas, it is a better option to run lower compression. I will be running 9.5-1 in my new motor with around 20psi. But I'm only looking to run in the mid to high 8's. If I wanted to go faster, the combination would be different
For the majority of people who want to run pump gas, it is a better option to run lower compression. I will be running 9.5-1 in my new motor with around 20psi. But I'm only looking to run in the mid to high 8's. If I wanted to go faster, the combination would be different
TECH Resident
Joined: Aug 2008
Posts: 910
Likes: 0
From: Dubai
Wow! this thread got crazy. I think the right answer really depends on what you are after. If you after a max effort combination, you will need to run higher compression to keep up with the big boys because thats what they are running.
For the majority of people who want to run pump gas, it is a better option to run lower compression. I will be running 9.5-1 in my new motor with around 20psi. But I'm only looking to run in the mid to high 8's. If I wanted to go faster, the combination would be different
For the majority of people who want to run pump gas, it is a better option to run lower compression. I will be running 9.5-1 in my new motor with around 20psi. But I'm only looking to run in the mid to high 8's. If I wanted to go faster, the combination would be different
I may of sounded like I was challenging a few of the members in my previous posts on pages 1 and 2, but I never said anything out of line, cursed or made any personal attacks.
I would like to be treated the same way whether you may not like me personally or how I present my side of the discussion.
The whole pump gas street car was my idea though, I reason I suggested this is so we can all discuss a single class of vehicles since we cant compare compression ratio and boost used on a full out race car to a street car on pump gas etc...
I made good power with high compression and boost, but this was with 10.85:1 and 8.5psi of boost, and a cam with intake closing of 44 ABDC, I knew I could have run about 2 more psi safetly on straight pump gas, but that was quite at the limit. If I wanted to run more, I had to either drop DCR by means of a cam, or drop SCR or a bit of both. Of course a cam swap is much easier, but the consequences of having a very late IVC event is killing some low-end and making more top-end and usually means you have to increase overlap as well unless you try to bias as much of the additional intake duration towards the closing event.
I made good power with high compression and boost, but this was with 10.85:1 and 8.5psi of boost, and a cam with intake closing of 44 ABDC, I knew I could have run about 2 more psi safetly on straight pump gas, but that was quite at the limit. If I wanted to run more, I had to either drop DCR by means of a cam, or drop SCR or a bit of both. Of course a cam swap is much easier, but the consequences of having a very late IVC event is killing some low-end and making more top-end and usually means you have to increase overlap as well unless you try to bias as much of the additional intake duration towards the closing event.
PD blowers have torque for days, they don't need any help in the cam department in making more torque. Use the cams exhaust events to carry torque farther into the rpm range and not so much the IVC event.
Unless it's a 2.9-3.0 blower or larger I really keep overlap at a minimum. Even using negative valve overlap at @.050" lobe lift just to keep the blower's extreme pressure differentials across the valves from over scavenging the intake runner.
Hope this helps. It's the way I do it on my PD blower cams. Works well.
Sorry, I thought it was obvious that I was going to run pump gas. If E85 was more available in my area, I would run that. But for now it will be pump gas and meth. Hoping that will get me too my goal.
