High Compression VS Low Compression Opinions

[Mike T]

Mine made 450 to the ground on straight 93 @22 psi. At the time it had a small flat tappet (that I later found out was going away), Cheap converter and a right out of the box tune. By out of the box I mean no changes through the translator pro.

 

[bison]

Did the math on the .027s too . Looks like your block has been decked and for the pistons to still be .010 in the hole you must have change the CH as well?

Blocks are squared to the mains and deck height measured then pistons ordered that's why the full custom. Too many changes and different compression height. Also I like the more spherical dish with less aggressive reliefs


Sent from my iPhone using Tapatalk

 

[earlbrown]

What's the CC Earl?

22cc, any OD, any CH.


Keep in mind there's more to it than just the CCs. As the bore goes up, so does the compression. A stroker crank will run it up too.

I don't have my notes in front of me but I'm a little over 9:1 static with right at .060" quench on my .032" over 4.1 with a stock stroke.


Dynamic is what really matters though.

 

[Mike T]

22cc, any OD, any CH.


Keep in mind there's more to it than just the CCs. As the bore goes up, so does the compression. A stroker crank will run it up too.

I don't have my notes in front of me but I'm a little over 9:1 static with right at .060" quench on my .032" over 4.1 with a stock stroke.


Dynamic is what really matters though.

Great point Earl.
Working with the CR calculator a couple of days ago using a 4 inch bore and 3.625 stroke found that my heads (larger chamber than normal 53CC) would come in around 10.0:1 using your pistons, a .000 deck and .040 HG

On my stock stroke 3.820 bore this same combo works out to 8.7:1

Here is a link to a simple CR calculator that you guys can play around with to get a better understanding of how much little things affect CR.

http://www.csgnetwork.com/compcalc.html

 

[earlbrown]

^and this is the one that you use to show how the biggest cam you can buy usually isn't the right one....

http://www.wallaceracing.com/dynamic-cr.php

 

[Wahoo]

This is a cool thread. Any one recently build a high compression motor. How do you like it?

 

[TTipe]

Static compression ratio is only one player in this thread. Dynamic compression ratio (driven by cam profile/overlap,boost, fuel displacement in the chamber) does a lot to change what the combustion charge and the power cylinder actually sees & reacts to.

 

[750H.P.V6]

This is a cool thread. Any one recently build a high compression motor. How do you like it?

I'm currently working on one with a target compression ratio of 11 to 1. I'll keep you posted.

Neal

 

[earlbrown]

^normally aspirated?

 

[jasjamz]

^normally aspirated?

Lol! He's got my attention on that one.

 

[marleyskater420]

Static compression ratio is only one player in this thread. Dynamic compression ratio (driven by cam profile/overlap,boost, fuel displacement in the chamber) does a lot to change what the combustion charge and the power cylinder actually sees & reacts to.

I was just thinking about this..

How does the combustion chamber volume along with the fuel type/volume (let's assume e85 for this question) in the cylinder have an affect on the performance/ VE/ MAP of the motor in relation to the CR?

Would you look for a larger CC chamber as you increase in CR, pending on fuel type (E85 for this question) and ignition type (lets assume the TR-6 since most have that) ?

How does the higher CR affect the choice of where to open the exhaust valve after BDC on the compression stroke? If a higher CR motor with larger chambers can burn the fuel and essentially finish the "power" well before BDC on the compression stroke, would that allow us to open the exhaust valves much earlier ABDC, providing we still keep a good amount of LSA so as to not have much overlap?

Or am I starting to ask the type of questions that, essentially up to this point, no one has really wanted to explain to me because it falls under the whole "trade secrets" area and their ideas on the matter are what make them as fast as they are? (Can you start to see how it becomes hard to learn about cams?...)

 

[Reggie West]

Neal are trying to spin that big turbo you have a little harder??

 

[No disintegrations]

I was just thinking about this..

How does the combustion chamber volume along with the fuel type/volume (let's assume e85 for this question) in the cylinder have an affect on the performance/ VE/ MAP of the motor in relation to the CR?

Would you look for a larger CC chamber as you increase in CR, pending on fuel type (E85 for this question) and ignition type (lets assume the TR-6 since most have that) ?

How does the higher CR affect the choice of where to open the exhaust valve after BDC on the compression stroke? If a higher CR motor with larger chambers can burn the fuel and essentially finish the "power" well before BDC on the compression stroke, would that allow us to open the exhaust valves much earlier ABDC, providing we still keep a good amount of LSA so as to not have much overlap?

Or am I starting to ask the type of questions that, essentially up to this point, no one has really wanted to explain to me because it falls under the whole "trade secrets" area and their ideas on the matter are what make them as fast as they are? (Can you start to see how it becomes hard to learn about cams?...)

Fastblackracing had a nice post on page 3. post #43. Lots of knowledge there to absorb.

 

[750H.P.V6]

^normally aspirated?

I run E85. I decided to step up the static compression from 9.5 to 1 to something higher.

Neal

 

[earlbrown]

I was just thinking about this..

How does the higher CR affect the choice of where to open the exhaust valve after BDC on the compression stroke? If a higher CR motor with larger chambers can burn the fuel and essentially finish the "power" well before BDC on the compression stroke, would that allow us to open the exhaust valves much earlier ABDC, providing we still keep a good amount of LSA so as to not have much overlap?

From what I understand that's actually what Harold did when he came up with the Voodoo line of cams for N/A's. His logic was to crack the exhaust valve at the tail end of the power stroke while a slight bit of power was still made. That would effectively 'blow down' the cylinder pressure and make a serious negative pulse in the header collector. By having that, the cylinder finishing up the exhaust stroke at that time will get a good pull to clean out the burnt gasses without having a buttload of overlap (to maintain lower RPM power).


Don't beat yourself up about not knowing everything there is to know about cams and cam timing. I've been studying this stuff hard for the last few years and every time I learn something, I know even stronger that I don't know shit!

 

[1952ray]

From what I understand that's actually what Harold did when he came up with the Voodoo line of cams for N/A's. His logic was to crack the exhaust valve at the tail end of the exhaust stroke while a slight bit of power was still made. That would effectively 'blow down' the cylinder pressure and make a serious negative pulse in the header collector. By having that, the cylinder finishing up the exhaust stroke will get a good pull to clean out the burnt gasses without having a buttload of overlap (to maintain lower RPM power).


Don't beat yourself up about not knowing everything there is to know about cams and cam timing. I've been studying this stuff hard for the last few years and every time I learn something, I know even stronger that I don't know shit!

Hey skater420, if Earl Brown said he doesn't know shit about cam timing after years of study take that to your bank. I have found that Earl is damn good at this GN shit as well as anybody. Enough said

 

[marleyskater420]

From what I understand that's actually what Harold did when he came up with the Voodoo line of cams for N/A's. His logic was to crack the exhaust valve at the tail end of the exhaust stroke while a slight bit of power was still made. That would effectively 'blow down' the cylinder pressure and make a serious negative pulse in the header collector. By having that, the cylinder finishing up the exhaust stroke will get a good pull to clean out the burnt gasses without having a buttload of overlap (to maintain lower RPM power).


Don't beat yourself up about not knowing everything there is to know about cams and cam timing. I've been studying this stuff hard for the last few years and every time I learn something, I know even stronger that I don't know shit!

I appreciate the response and that does seem to make sense.

Did you mean crack the exhaust valve at the tail end of the compression stroke? Cracking at the end of the exhaust stroke while power was still being made doesn't make sense..cause I thought there isn't any power to be made on the exhaust stroke? Or am I missing something?

"Only until we admit we know nothing, can we truly know everything" - not sure who said it, but I remember reading it in Be Here Now by Ram Dass

Hey skater420, if Earl Brown said he doesn't know shit about cam timing after years of study take that to your bank. I have found that Earl is damn good at this GN shit as well as anybody. Enough said

I appreciate the heads up, truly.

I may be a young dude at 30, but I really want to try my best to learn as much as I can..... and I also need to find a way to change my screenname that I made when I first joined this forum at 17yrs old since a name like "Marleyskater420" doesn't always lend itself to thinking that person is serious in their inquiries hahahah!

 

[1952ray]

I appreciate the response and that does seem to make sense.

Did you mean crack the exhaust valve at the tail end of the compression stroke? Cracking at the end of the exhaust stroke while power was still being made doesn't make sense..cause I thought there isn't any power to be made on the exhaust stroke? Or am I missing something?

"Only until we admit we know nothing, can we truly know everything" - not sure who said it, but I remember reading it in Be Here Now by Ram Dass




I appreciate the heads up, truly.

I may be a young dude at 30, but I really want to try my best to learn as much as I can..... and I also need to find a way to change my screenname that I made when I first joined this forum at 17yrs old since a name like "Marleyskater420" doesn't always lend itself to thinking that person is serious in their inquiries hahahah!

With what you just said, I have to hand to you. You are ahead of your years. Not common, as I have seen in my life. Good luck with your build.

 

[marleyskater420]

With what you just said, I have to hand to you. You are ahead of your years. Not common, as I have seen in my life. Good luck with your build.

That means a lot to hear...really. Funny enough, my coworker said to me earlier this week that I was born about 30 years too late.

I know I lack the tests of time and in-field experience that you guys posses, but we all must start somewhere, and I hope to begin from a place of enough knowledge to at least try and stop myself before I break something

Do you know if my response to what Earlbrown wrote was correct in that he meant to say "at the tail end of the compression stroke" ? That has me scratching my head right now.

I appreciate all the kind words, and I hope to build a car that will definitely make other Buick owners proud

 

[earlbrown]

Do you know if my response to what Earlbrown wrote was correct in that he meant to say "at the tail end of the compression stroke" ? That has me scratching my head right now.

yeah, I meant power stroke but typed 'exhaust' since I was thinking about blow down.