Highest compression for boost?

[SlowSVT]

An 03/04 engine with 12psi will make at least 50rw less than a flat top pistoned engine. I know as I've had experience with both.

And to run that boost level on a flat top piston you need race gas

An 03/04 on race gas can be boosted to 22+ psi FTW :banana:

One more time: if you want to make max hp on an FI motor you go low compression and boost the snot out of it.

If you wanna make max hp on a high compression FI motor you put low compression pistons in it :-D

I know this is painful for some people to accept :nonono:

op:

 

[99cobra09]

My previous motor was on flat tops with stock 99/01 heads and a baby Procharger at 12lbs. On 91 octane it made 570rwhp was fine no problem till a piston let go.

 

[procharged 99]

And to run that boost level on a flat top piston you need race gas

An 03/04 on race gas can be boosted to 22+ psi FTW :banana:

One more time: if you want to make max hp on an FI motor you go low compression and boost the snot out of it.

If you wanna make max hp on a high compression FI motor you put low compression pistons in it :-D

I know this is painful for some people to accept :nonono:

op:

You have no idea what you are talking about you need to do some more reading. Have you ever heard of e-85.

 

[SlowSVT]

You have no idea what you are talking about you need to do some more reading. Have you ever heard of e-85.

Cool, now I can boost the 03/04 engine close to 30 psi :banana:

 

[na svt]

And to run that boost level on a flat top piston you need race gas

An 03/04 on race gas can be boosted to 22+ psi FTW :banana:

One more time: if you want to make max hp on an FI motor you go low compression and boost the snot out of it.

If you wanna make max hp on a high compression FI motor you put low compression pistons in it :-D

I know this is painful for some people to accept :nonono:

op:

Flat tops do not need race gas and not everyone wants to make "max" power.

 

[SlowSVT]

Flat tops do not need race gas and not everyone wants to make "max" power.

Even some dished piston engines require race gas when they are packing big boost why would a flat tops be any different?

I think some people are overlooking something here that goes way beyond compression. It's "charge volume".

That diagram I posted illustrated this but I think a few have either not made the connection of refuse to acknowledge it :nonono: Here is an other way of looking at it. A flat top piston mod motor chamber volume not including deck height and head gasket thickness is 52 cc's, A dished Terminator slug adds another 17 cc of charge volume to the chamber which is a 30% increase. That translates directly on how much fuel the engine process before the point of detonation with most of the added energy going directly to the crack shaft. The laws of physics comes into play here and to argue otherwise is going to be an uphill battle. Under no circumstances would I choose to use flat top pistons in a blown application (with the exception of E85) and to do so you are leaving hp on the table.

As stated, a 99 Cobra engine with a forged bottom end and a PD blower will hit a brick wall around 425 hp on pump gas where an 03/04 can get close to 600 idea: Hay! that's about a 30% power advantage imagine that) Switch both engines to race gas and that gap will still be there. What ever combo you can come up with that 30% charge volume disadvantage thing will be literarily impossible to overcome.

For a centrifugal or turbo bumping the compression will help reduce the effect of lag and a poor throttle response which is a good idea plus the fact they make mad hp "on top" to begin with but the more you add the less potential the motor will have not being able to pack more boost into the engine. 9:1 tops for me. A PD blown car works great at 8.5:1 and to raise it is pointless and detrimental.

 

[snakeraper11b]

Even some dished piston engines require race gas when they are packing big boost why would a flat tops be any different?

I think some people are overlooking something here that goes way beyond compression. It's "charge volume".

That diagram I posted illustrated this but I think a few have either not made the connection of refuse to acknowledge it :nonono: Here is an other way of looking at it. A flat top piston mod motor chamber volume not including deck height and head gasket thickness is 52 cc's, A dished Terminator slug adds another 17 cc of charge volume to the chamber which is a 30% increase. That translates directly on how much fuel the engine process before the point of detonation with most of the added energy going directly to the crack shaft. The laws of physics comes into play here and to argue otherwise is going to be an uphill battle. Under no circumstances would I choose to use flat top pistons in a blown application (with the exception of E85) and to do so you are leaving hp on the table.

As stated, a 99 Cobra engine with a forged bottom end and a PD blower will hit a brick wall around 425 hp on pump gas where an 03/04 can get close to 600 idea: Hay! that's about a 30% power advantage imagine that) Switch both engines to race gas and that gap will still be there. What ever combo you can come up with that 30% charge volume disadvantage thing will be literarily impossible to overcome.

For a centrifugal or turbo bumping the compression will help reduce the effect of lag and a poor throttle response which is a good idea plus the fact they make mad hp "on top" to begin with but the more you add the less potential the motor will have not being able to pack more boost into the engine. 9:1 tops for me. A PD blown car works great at 8.5:1 and to raise it is pointless and detrimental.

Your comprehension of the topic is so vague it's hilarious. You sound like a forum bench racer that only regurgitates what he reads. There are so many other factors that need to be taken into account when talking about compression and boost. You should just let this thread die, it's getting embarrassing to read.

 

[SlowSVT]

Your comprehension of the topic is so vague it's hilarious. You sound like a forum bench racer that only regurgitates what he reads. There are so many other factors that need to be taken into account when talking about compression and boost. You should just let this thread die, it's getting embarrassing to read.

"Forum Bench Racers" that's funny. Now your embarrassing yourself. People who know me and have seen my work would be snickering at this post. You are more than welcome to come see what I'm up to and when you do it will be a very humbling experience. That you can count on :coolman:

Sounds like you taken this rather personally. Rather than just making some vague statements and not resorting to personal attacks why don't you explain in detail why I am wrong. Perhaps I overlooked something.

 

[snakeraper11b]

"Forum Bench Racers" that's funny. Now your embarrassing yourself. People who know me and have seen my work would be snickering at this post. You are more than welcome to come see what I'm up to and when you do it will be a very humbling experience. That you can count on :coolman:

Sounds like you taken this rather personally. Rather than just making some vague statements and not resorting to personal attacks why don't you explain in detail why I am wrong. Perhaps I overlooked something.

I'm not taking it personally, I just hate when some people get so fixated on something they are not willing to open their minds to new ideas. If you're so progressive in your ideas and developments as you say, I feel like you would be willing to lay down your defenses and actually explore the ideas of others. When talking about compression, and boost, it seems like the only thing people give thought to is the basics. Did you know an engine running 9:1 and 10.5:1 can have similar dynamic compression ratios? Did you know that an engine running low compression, can have an unnecessarily large quench area, thus making it extremely prone to detonation? Far more so than a properly designed high compression engine. Simply stating that an engine with low compression is better for boost because of it's basic static numbers is ridiculous. The engine I'm designing right now will have a static compression of 10.51 and a dynamic compression of 9.05 with quench area of .035". Your average terminator is around .46"-.50". This small quench area acts as a mechanical octane, and increases the efficiency of the burn. It actually allows you to run more compression or boost than at the same octane. Flat top pistons also allow for a better flame path across the piston as well, staving off detonation and again making the burn more complete and efficient. Not an option with dished pistons. I don't like arguing for the sake of arguing. We obviously have different knowledge and different opinions, and there's nothing wrong with that. We're obviously both very passionate about or cars and our beliefs. Only one way to settle this....lets run 'um in a few months when my build is done?!

 

[SlowSVT]

I'm not taking it personally, I just hate when some people get so fixated on something they are not willing to open their minds to new ideas. If you're so progressive in your ideas and developments as you say, I feel like you would be willing to lay down your defenses and actually explore the ideas of others. When talking about compression, and boost, it seems like the only thing people give thought to is the basics. Did you know an engine running 9:1 and 10.5:1 can have similar dynamic compression ratios? Did you know that an engine running low compression, can have an unnecessarily large quench area, thus making it extremely prone to detonation? Far more so than a properly designed high compression engine. Simply stating that an engine with low compression is better for boost because of it's basic static numbers is ridiculous. The engine I'm designing right now will have a static compression of 10.51 and a dynamic compression of 9.05 with quench area of .035". Your average terminator is around .46"-.50". This small quench area acts as a mechanical octane, and increases the efficiency of the burn. It actually allows you to run more compression or boost than at the same octane. Flat top pistons also allow for a better flame path across the piston as well, staving off detonation and again making the burn more complete and efficient. Not an option with dished pistons. I don't like arguing for the sake of arguing. We obviously have different knowledge and different opinions, and there's nothing wrong with that. We're obviously both very passionate about or cars and our beliefs. Only one way to settle this....lets run 'um in a few months when my build is done?!

This is a debate not an argument.

Quench area, now that's a first. While they are a nice feature they will not make much difference especially in a pent roof combustion chamber with tiny pads such as ours. All they do is promote turbulence at TDC but not much more (like that's really needed in an engine seeing 2 atmospheres). Lots of engine run open chambers which do have their advantages.

What is the set-up of your new engine build?

 

[snakeraper11b]

This is a debate not an argument.

Quench area, now that's a first. While they are a nice feature they will not make much difference especially in a pent roof combustion chamber with tiny pads such as ours. All they do is promote turbulence at TDC but not much more (like that's really needed in an engine seeing 2 atmospheres). Lots of engine run open chambers which do have their advantages.

What is the set-up of your new engine build?

4.6 teksid .020", +.001" deck but it will depend on the final machining, Diamond flat tops 30013's, .036"x 3.622" head gaskets", 52 cc heads, 10620 cams installed at 108 ICL 114 ECL, 10.5" PSR, ARH long tubes, Bassani 2.5" SS CB, Cobra R hydroboost pulley and alternator pulley, stewart H20 pump, HOB 4VR 8 rib braket holding an F1A at 15 PSI.

 

[na svt]

High boost should get lower compression but even then not all should get 8.5:1. The CR, like the cams, and every other component should be spec'd to meet the goals in the most efficient manner. With that, if the boost is no higher than 12psi an 8.5:1 CR will result in a lot less average hp/tq than with a flat top or even a stock piston..50rwhp/tq If the planned boost is 20psi then of course the compression should be lower, especially if it's going to be run on pump gas.

With that, if there are no plans to add more than 12psi, the compression level is absolutely safe with flat tops and the power made will be 50rwhp/50rqtq higher than a similar 8.5:1 combo. I've seen a few unhappy people after they replaced their stock shortblocks with one that has a 8.5:1 CR...none were happy about making less power with the new engine.

When I talk about pump gas I'm thinking of 93 octane, not the 91 that sold in some areas.

 

[SlowSVT]

4.6 teksid .020", +.001" deck but it will depend on the final machining, Diamond flat tops 30013's, .036"x 3.622" head gaskets", 52 cc heads, 10620 cams installed at 108 ICL 114 ECL, 10.5" PSR, ARH long tubes, Bassani 2.5" SS CB, Cobra R hydroboost pulley and alternator pulley, stewart H20 pump, HOB 4VR 8 rib braket holding an F1A at 15 PSI.

15 psi on a centriffy that car is going to pull revs like a kawi H2R tripe :uh oh:

E85 or race gas ?

 

[snakeraper11b]

15 psi on a centriffy that car is going to pull revs like a kawi H2R tripe :uh oh:

E85 or race gas ?

That's the plan! 7,200 redline and I'm sure it'll still pull like a raped ape until I let out. It'll eat a full tank of 91 and 32 ounces of torco accelerator. Should be around 98 octane, plenty for 15 psi. I don't like the loss of miles per tank and the crazy pumps and injectors required for E85. It's not easily accessible in LA either. The torco would add another $20 to each fill up, but that is still cheaper than E85 when you factor in the decrease in fuel economy. It'll be a hassle I guess, but that's just the price of having an awesome car.

 

[03Steve]

It's a short trip from Pasadena to Ontario. Go to Accufab, buy a t-shirt, and debate with some of the folks there why a high boost/low compression 4.6L will outpeform a high boosted flat top 4.6L.

 

[IUP99snake]

I have a 10.5:1 motor and 12LBS of boost via Procharger. The motor doesn't even have forged internals. I'd rather have better throttle response and low end power that I'm actually going to use on the street instead of all out peak HP at the top of the RPM range.

Lots of people probably have more powerful combinations than I do. Lots of sacrifices are usually made in the process. I feel like I have a good combination for the street.

I'd rather use timing to manage detonation instead of the compression. You can change the timing for free based on the combination. You can't change the compression once you build it.

I had a forged 8.5:1 combination once. This motor lasted the least amount of time compared to any other combination of mine. It made great peak HP, but it ran like a dog on the street.

 

[na svt]

I have a 10.5:1 motor and 12LBS of boost via Procharger.

For the 20th time you have a 10:1 engine.

I'd rather use timing to manage detonation instead of the compression. You can change the timing for free based on the combination. You can't change the compression once you build it.

I had a forged 8.5:1 combination once. This motor lasted the least amount of time compared to any other combination of mine. It made great peak HP, but it ran like a dog on the street.

:rockon:

 

[SlowSVT]

That's the plan! 7,200 redline and I'm sure it'll still pull like a raped ape until I let out. It'll eat a full tank of 91 and 32 ounces of torco accelerator. Should be around 98 octane, plenty for 15 psi. I don't like the loss of miles per tank and the crazy pumps and injectors required for E85. It's not easily accessible in LA either. The torco would add another $20 to each fill up, but that is still cheaper than E85 when you factor in the decrease in fuel economy. It'll be a hassle I guess, but that's just the price of having an awesome car.

E85 chages the equation quite a bit but the availability, what it does to your fuel mileage makes it a bit out of reach for most and may not be practicle for most people. I remember way back when filling my tank with $6.00 a gallon 100 octane and realizing much of the benefit was wasted idling at a light or part time cruising which accounted for 95% of the diving was just spewing that expensive fuel out the tail pipes. For me it wasn't worth it on a street car but that's just me.

You car is going to be a monster with that set-up. If you can run it on E85 I think that is the direction you should take Plus you get super cooling with E85..........just don't plan on any cross country trips :nonono:

 

[procharged 99]

E85 chages the equation quite a bit but the availability, what it does to your fuel mileage makes it a bit out of reach for most and may not be practicle for most people. I remember way back when filling my tank with $6.00 a gallon 100 octane and realizing much of the benefit was wasted idling at a light or part time cruising which accounted for 95% of the diving was just spewing that expensive fuel out the tail pipes. For me it wasn't worth it on a street car but that's just me.

You car is going to be a monster with that set-up. If you can run it on E85 I think that is the direction you should take Plus you get super cooling with E85..........just don't plan on any cross country trips :nonono:

If your building a engine like he is I am pretty sure he can handle the price of $3.60 a gallon for e85. I don't think most of us is worried about gas mileage.

 

[snakeraper11b]

If your building a engine like he is I am pretty sure he can handle the price of $3.60 a gallon for e85. I don't think most of us is worried about gas mileage.

I'm actually only 24 and about to be at the end of my military contract, so I'm about to be broke. Fortunately my deployment is right up until 90 days before I ETS. Just dumping 10 months of deployment pay on a 9 year dream before it's unobtainable again :beer: Fueling this thing will be quite a concern actually haha.