Performance Boats Forum banner

1 - 20 of 315 Posts

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #1 · (Edited)
Head Flow - Boost- Dynamic Compression

I've been thinking about this for a while and I didnt want to cloud up EdonShanno's blown 588 thread. Its winter, I'm bored, so here we go.
For this discusion lets leave compressor efficiency & intake temps out of the equasion for the time being.
Lets use EdonShanno's blown 588 for a starting example here. He made 1100hp on pump gas at 7psi of boost. You have to get X-amount of fuel & air into that engine to accomplish this, that fuel & air is converted to a dynamic cylinder pressure to achieve the resulting 1000ftlb & 1100hp. A fuel can only stand so much dynamic compression ratio- cylinder pressure before it will detonate. Here comes the big question, you ready for it :happy:
If you were to put a very small set of heads on that same engine and crank up the boost till you had the exact same tq & hp numbers, wouldnt that indicate the same dynamic comp - cylinder pressure and wouldnt you be able to still get away with the same fuel no matter what the boost guage in the manifold ended up reading?

imagesCAX2JSH7.jpg
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #2 · (Edited)
Next question,
An engine with great cylinder head flow actually gets more -boost- into the cylinder which is why they make great power at a low boost number. For this reason do you think that an engine with great heads will find detonation at a lower boost number than the same engine with small heads that would actually get less into the cylinder for compression? Talking about pump gas here.
 

·
Distinguished Member
Joined
·
5,782 Posts
This could get good. If you get the same HP/Tq, in a basic sense, you're reacting the same amount of fuel. The problem I see is by cranking up the boost, you're also increasing the heat into the charge, so it will be more prone to detonation. Better heads with the proper cam, should fill the cylinder at lower boost. Better heads are never a bad idea, but a blower can definitely make power with "wrong" heads.
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #5 · (Edited)
This could get good. If you get the same HP/Tq, in a basic sense, you're reacting the same amount of fuel. The problem I see is by cranking up the boost, you're also increasing the heat into the charge, so it will be more prone to detonation. Better heads with the proper cam, should fill the cylinder at lower boost. Better heads are never a bad idea, but a blower can definitely make power with "wrong" heads.
Thats why I wanted to leave the intake temp and compressor efficiency out of the equasion, because there are certainly more efficient ways of aquiring boost than what they used. And I know that his big billet blower was pretty efficient at those #'s.
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #6 · (Edited)
This could get good. If you get the same HP/Tq, in a basic sense, you're reacting the same amount of fuel. The problem I see is by cranking up the boost, you're also increasing the heat into the charge, so it will be more prone to detonation. Better heads with the proper cam, should fill the cylinder at lower boost. Better heads are never a bad idea, but a blower can definitely make power with "wrong" heads.
What if you put a set of peanut port heads on there and ended up at 21psi in the manifold to make the same 1000ftlb & 1100hp? Could you still use pump gas "if" the intake temps remained the same ? Wouldnt that indicate the same amount of fuel/air being burned as well as the same cylinder pressures?:)hand
 

·
Distinguished Member
Joined
·
5,782 Posts
Thats why I wanted to leave the intake temp and compressor efficiency out of the equasion, because there are certainly more efficient ways of aquiring boost than what they used.
At first I thought "how can you leave intake temp and efficiency out of the equasion (sic)....." :duh: until I realized this is a clever attempt at another "turbos are better" thread. :rolleyes: You guys have fun, I'm out :)hand
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #8 · (Edited)
At first I thought "how can you leave intake temp and efficiency out of the equasion (sic)....." :duh: until I realized this is a clever attempt at another "turbos are better" thread. :rolleyes: You guys have fun, I'm out :)hand
Once again, NO. thats why I wanted to leave that out. I'm just talking Head Flow-Boost- Dynamic compression here. I dont give a damn were the boost comes from. I'm just talking about what ends up in the cylinder.

Here is a neat little dynamic comp. calculator to play with. It doesnt figure cylinder head flow into the equasion at all.:))ThumbsDwn
Wallace Racing: Dynamic Compression Ratio Calculator
 

·
Or Seth, either one
Joined
·
3,270 Posts
I've been thinking about this for a while and I didnt want to cloud up EdonShanno's blown 588 thread. Its winter, I'm bored, so here we go.
For this discusion lets leave compressor efficiency & intake temps out of the equasion for the time being.
Lets use EdonShanno's blown 588 for a starting example here. He made 1100hp on pump gas at 7psi of boost. You have to get X-amount of fuel & air into that engine to accomplish this, that fuel & air is converted to a dynamic cylinder pressure to achieve the resulting 1000ftlb & 1100hp. A fuel can only stand so much dynamic compression ratio- cylinder pressure before it will detonate. Here comes the big question, you ready for it :happy:
If you were to put a very small set of heads on that same engine and crank up the boost till you had the exact same tq & hp numbers, wouldnt that indicate the same dynamic comp - cylinder pressure and wouldnt you be able to still get away with the same fuel no matter what the boost guage in the manifold ended up reading?

View attachment 194514
Next question,
An engine with great cylinder head flow actually gets more -boost- into the cylinder which is why they make great power at a low boost number. For this reason do you think that an engine with great heads will find detonation at a lower boost number than the same engine with small heads that would actually get less into the cylinder for compression? Talking about pump gas here.
It's difficult to speak of detonation and ignore inlet temp. I get the basis of your scenario, and on the whole you're accurate that if the same amount of air/fuel is burned, the same dynamic cylinder pressure will be achieved, identical torque.

Taking the theory a step further... If an intercooler is used in both scenarios, and if we don't ignore inlet temps and look at what may occur if we run smaller ports and higher boost to get the number, the restriction may allow more dynamic cylinder pressure/torque to be made overall without detonation.

I know, makes very little sense. Hold on a sec, let me explain.

Without going into all the science of why/how, because I'm pretty sure all/most of us ore up to speed in that... As air is compressed it gets hot. Compress it more it gets hotter, more, hotter, and so on. That's what causes detonation, it's compressed to a point which the air is hot enough to ignite the fuel.

So, anyway... Let's say, hypothetically, you put small port heads on and due to the restriction you had to create twice the boost to get the same number. The intake air temp will roughly double (not taking into account any mechanically added by turbo/blower) before the intercooler. The hotter the charge, the more heat energy the intercooler is able to remove.

Similar to the way refrigeration works, if the ports were a restriction the air entering the cylinder would contain less heat energy with higher boost and could therefore create more dynamic compression without detonation... More dynamic cylinder pressure... More torque... More Power.

Anyway, I'm bored too. Just a theory that's been rolling around in my head for a few days.

Whacha think? Make any sense at all?
 

·
Or Seth, either one
Joined
·
3,270 Posts
Another way to look at it:

What if you put a restriction in-line post intercooler and pre throttle body/carburetor? Say a plate with a hole drilled in it... And raised the boost (measured at compressor/ outlet) until performance was identical...

In my theory, manifold boost pressure that would previously cause detonation should be able to be met without detonation, as more heat has been removed by the intercooler.
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #11 · (Edited)
It's difficult to speak of detonation and ignore inlet temp. I get the basis of your scenario, and on the whole you're accurate that if the same amount of air/fuel is burned, the same dynamic cylinder pressure will be achieved, identical torque.

Taking the theory a step further... If an intercooler is used in both scenarios, and if we don't ignore inlet temps and look at what may occur if we run smaller ports and higher boost to get the number, the restriction may allow more dynamic cylinder pressure/torque to be made overall without detonation.

I know, makes very little sense. Hold on a sec, let me explain.

Without going into all the science of why/how, because I'm pretty sure all/most of us ore up to speed in that... As air is compressed it gets hot. Compress it more it gets hotter, more, hotter, and so on. That's what causes detonation, it's compressed to a point which the air is hot enough to ignite the fuel.

So, anyway... Let's say, hypothetically, you put small port heads on and due to the restriction you had to create twice the boost to get the same number. The intake air temp will roughly double (not taking into account any mechanically added by turbo/blower) before the intercooler. The hotter the charge, the more heat energy the intercooler is able to remove.

Similar to the way refrigeration works, if the ports were a restriction the air entering the cylinder would contain less heat energy with higher boost and could therefore create more dynamic compression without detonation... More dynamic cylinder pressure... More torque... More Power.

Anyway, I'm bored too. Just a theory that's been rolling around in my head for a few days.

Whacha think? Make any sense at all?
I'm trying very hard to leave that part out of the equasion. It is possible to reach a relatively high boost number and keep the intake temps very low if the correct components are used. But once again, lets just say that its possible (because it is) and figure that the intake temp remains constant.
Kind of wanting to take the direction of comparing boost numbers on pump gas with Big-expensive heads compared to stock low performance heads. Is the boost # in the manifold really that important? Or should we actually have some form of pressure transducer to log actual dynamic cylinder pressures so we would be able to walk right out to the edge on pump gas? Could you get very close to the same pump gas results with both sets of heads if we did this?:hmmm:
 

·
Or Seth, either one
Joined
·
3,270 Posts
I'm trying very hard to leave that part out of the equasion. It is possible to reach a relatively high boost number and keep the intake temps very low if the correct components are used. But once again, lets just say that its possible (because it is) and figure that the intake temp remains constant.
Kind of wanting to take the direction of comparing boost numbers on pump gas with Big-expensive heads compared to stock low performance heads. Is the boost # really that important? Should we actually have some form of pressure transducer to log actual dynamic cylinder pressures so we would be able to walk right out to the edge on pump gas? Could you get very close to the same pump gas results with both sets of heads if we did this?:hmmm:
Even without intercooling, higher boost will still contain the same heat as lower boost per given volume... and in this case volume in the cylinder is identical. Even if the air temp in the manifold is significantly higher. Interesting thought pattern.

Good thread. Interesting.
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #14 ·
Even without intercooling, higher boost will still contain the same heat as lower boost per given volume... and in this case volume in the cylinder is identical. Even if the air temp in the manifold is significantly higher. Interesting thought pattern.

Good thread. Interesting.
Thanks. Some of the Diesel guys are running over 55psi and well below ambient intake temps with w/a intercoolers using ice.
With us boat guys having the water to use, and its almost always below the ambient outside temp, we should be able to get some great results with the w/a intercooling.
 

·
Administrator
Joined
·
16,892 Posts
Makes my head hurt thinking about that. The fuel is the limiting factor. I don't want to play.
 

·
Or Seth, either one
Joined
·
3,270 Posts
I see. If you take compressor efficiency out of the equation, air inlet temp really doesn't matter. Even if it has to be compressed to a point that it's 500 degrees in the manifold, it's decompressed to and equal volume in the cylinder. An equal volume will contain equal heat...
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #17 · (Edited)
I see. If you take compressor efficiency out of the equation, air inlet temp really doesn't matter. Even if it has to be compressed to a point that it's 500 degrees in the manifold, it's decompressed to and equal volume in the cylinder. An equal volume will contain equal heat...
Air temp does matter, thats why I gave it as a constant. Outlet temp of the compressor is how the efficiency is rated. Still not quite getting it.
Point was if he made 1000ftlbs / 1100hp with 7psi and 85* intake temps, would the same engine, except with low performance heads with 21psi and 85* intake temp putting out the same power, same cylinder pressures still survive on pump gas?


I was expecting a reply from Steelcomp or GN7 on this eventually. After they had time to ponder it.:happy:
You know how Bob just hates the idea of just cranking the boost knob till you get the desired results.:laugh1:

I think it would be kick ass to be able to monitor actual dynamic cylinder pressures, and see what cam changes, intercooling, timing and other variables actually do. It would be a good way to wring the power out of one of these deals. If monitoring every cylinder some fail safes could be put in place, esp with efi, to get all there is out of pump gas.
 

·
Or Seth, either one
Joined
·
3,270 Posts
Air temp does matter, thats why I gave it as a constant. Outlet temp of the compressor is how the efficiency is rated. Still not quite getting it.
Point was if he made 1000ftlbs / 1100hp with 7psi and 85* intake temps, would the same engine, except with low performance heads with 21psi and 85* intake temp putting out the same power, same cylinder pressures still survive on pump gas?


I was expecting a reply from Steelcomp or GN7 on this eventually. After they had time to ponder it.:happy:
You know how Bob just hates the idea of just cranking the boost knob till you get the desired results.:laugh1:
Pretty sure I get it, however in the case you're describing with intake temps equal, the 21psi/crappy head combination has the advantage and would be able to produce more power before detonation occurred.

That's why, if you take compressor efficiency out of the equation, or just assumed they are equal in either case, 21psi would naturally be hotter in the manifold, but once the cylinder is filled with an equal volume of air... it's a wash between the two. They would have the same volume and same heat. From a technical standpoint, a complete wash.

I'm curious to hear what those two have to say on the subject too.

Your original question...
If you were to put a very small set of heads on that same engine and crank up the boost till you had the exact same tq & hp numbers, wouldnt that indicate the same dynamic comp - cylinder pressure and wouldnt you be able to still get away with the same fuel no matter what the boost guage in the manifold ended up reading?
It all makes sense in my mind that the answer is/should be YES.
 

·
Registered
Joined
·
6,287 Posts
Discussion Starter · #19 ·
Pretty sure I get it, however in the case you're describing with intake temps equal, the 21psi/crappy head combination has the advantage and would be able to produce more power before detonation occurred.

That's why, if you take compressor efficiency out of the equation, or just assumed they are equal in either case, 21psi would naturally be hotter in the manifold, but once the cylinder is filled with an equal volume of air... it's a wash between the two. They would have the same volume and same heat. From a technical standpoint, a complete wash.

I'm curious to hear what those two have to say on the subject too.

Your original question...


It all makes sense in my mind that the answer is/should be YES.
Yes and bear in mind that the 21psi was an off the wall guess. It all depends on just how crappy of heads we are talking about here. Might actually only take 14-16psi . But the point remains.
I think this is why you see some guys saying that they get away with a high boost # on pump gas. It all depends on the cam, heads, and were they are taking the reading.
If we were all looking at actual dynamic cylinder pressures then the swing wouldnt be very wide as pump gas can only take so much.
 

·
Or Seth, either one
Joined
·
3,270 Posts
I think it would be kick ass to be able to monitor actual dynamic cylinder pressures, and see what cam changes, intercooling, timing and other variables actually do. It would be a good way to wring the power out of one of these deals. If monitoring every cylinder some fail safes could be put in place, esp with efi, to get all there is out of pump gas.
Wouldn't monitoring torque be very much the same thing?

Can't you take torque and calculate cylinder pressure?

Just pulling this calculation outta my ass, but seems if you had 1000ftlbs and a 4" stroke, that pressure on the rod journal would be 3000lbs. If the cylinder has a 4" diameter, the piston face would have a surface area of 12.57 square inches... 238.66psi cylinder pressure.

Dunno. Maybe waaaaay off base, maybe right on???
 
1 - 20 of 315 Posts
Top