S/Cing & "Effective" compression:

[BillyGman]

The "effective" compression ratio is arrived at by using the Naturally apsirated compression ratio of the engine in question, and the desired amount of boost pressure that the S/Cer in question will provide. there's a specific formula to plug these number into which will then give you an answer in the form of the "effective" compression. The link below will bring you to a calculator that does the work for you. All as you need to do is to punch in the naturally aspirated compression ratio, and the expected boost pressure. According to what I've read in the supercharger books that I've purchased, the best combination of power and engine longevity will be provided by keeping the "effective" compression between 16 and 18.

For instance, the supercharger set-up on the standard Trilogy S/Cer kit produces 9.5 lbs of boost pressure. And with the Marauder engine which has an exact N/A compression ratio of 9.8:1, having a boost pressure of 9.5 PSI will yield an "effective" compression of 16.13, which is comfortably on the conservative side of the 16-18 guidline.

If you use the link below, you'll find those numbers to be accurate. But if you type in 13.5 PSI of bbost, you'll find that with an N/A compression ratio of 9.8:1, that this brings your "effective" compression past the 16-18 guidline at exactly 18.8 this is precisely why I've chosen to remain content with using the 9.5 PSI pulley that the Trilogy kit comes with. But go ahead and use the calculator to punch in different #'s......

http://www.supermotors.org/resources/calculators/index.php#total_effective_engi ne_compression

[MARAUDER S/C #5]

Nice info Billy, thanks for sharing. I'm glad to know I am comfortably on the conservative side. :up:

[martyo]

I'm glad to know I am comfortably on the conservative side. :up:

Yep, that's you, a comfortably conservative...MENACE!

How's your wife by the way? When are you coming to visit "the" City again?

[Joe Walsh]

http://www.supermotors.org/resources/calculators/index.php#total_effective_engi ne_compression

Good information and very useful calculators....I just added that page to my "favorites" list.
Thanks Billy!

[Deebar]

Conservative, conshmervative, I dont give a damn. The MARAUDER appeals to me, which probably means somewhere in my subconscious I really want to hurt people. Being "conservative" runs contrary to my underlying objective. Therefore, I shall remain on the relatively dangerous side of performance untill my check book is once again called upon to grant me the power of chaos and destruction! :fire:

[merc406]

Conservative, conshmervative, I dont give a damn. The MARAUDER appeals to me, which probably means somewhere in my subconscious I really want to hurt people. Being "conservative" runs contrary to my underlying objective. Therefore, I shall remain on the relatively dangerous side of performance untill my check book is once again called upon to grant me the power of chaos and destruction! :fire:



Looks like NO fund raiser for YOU........... :lol:

[David Morton]

Nice. Only one thing is missing from this 16-18 effective compression ratio reccomendation, final charge temperature. Let's forget about how our cool running aluminum heads keep that charge cool for a minute and discuss ways we can contribute to extra timing and control of the combustion process. :grad:

Boyles Law states that when we compress a gas it heats up. Pre-ignition occurs when the intake charge reaches the temperature of spontaneous combustion, that is to say it ignites before the spark plug sparks. Detonation can be caused by pre-ignition but it also occurs when the spark plug sparks, but the charge is so volatile that it actually burns too fast and kicks the piston hard before it gets far enough past TDC, hence the "pinging". This is the sound of the wrist pins and rod bearings making metal-to-metal contact. Most experts agree that is a bad thing. :nono:

Higher octane fuels have a higher temperature point of spontaneous combustion, and if we cool the gas before we compress it, we can compress it more, before it heats up to this point where detonation occurs, as well. This is why most blower and turbo setups use intercoolers. :2thumbs:

There's also other ways to cool off that final intake charge before we close the valve and start final compression. We can put a water tank on the car and add water (vapor) to the air/fuel mixture, but this is an extra fueling requirement, nitrous oxide cools it off too but the extra oxygen defeats that purpose many times over, requireing the addition of the last and most commonly used air charge cooler, way too much fuel! :rock:

Lots of tuners use this old standby to keep the engine together, some would say it's not fuel efficient, but the numbers say otherwise. Why that is, is because the extra gobs of torque get the vehicle moving a lot easier, so the driver winds up using a lot less pedal to get the car moving and once it is, your just idling along and not using boost anyways. Some applications see an increase in gas mileage. :high5:

I remember in the '70s we used to run 12.5:1 compression on 91 octane by jetting the carburetor rich as hell. Man, you could smell the thing a mile away after it passed, and I would back straight out of a drive-thru if I happened to pull up behind one. :eek:

Nowadays we don't have to worry about that. The catalytic convertor will burn that exess fuel right off, just don't park it over a pile of hay right after running it hard. The cat's will be very hot and you might catch the hay and then the car on fire! :bigcry:

Just a little FYI from your local ASE Master. :D

[BillyGman]

Just FYI, the the reason I'm bringing up a conservative approach in tuning here, is merely because of the S/Ced engines we'ver heard of as of late that have bit the dust. And make no mistake about it, it has been more than one. One of which might have had to do with the extreme boost pressure being used on an engine with a relatively high compression ratio for pump gas use.

[TechHeavy]

The "effective" compression ratio is arrived at by using the Naturally apsirated compression ratio of the engine in question, and the desired amount of boost pressure that the S/Cer in question will provide. there's a specific formula to plug these number into which will then give you an answer in the form of the "effective" compression. The link below will bring you to a calculator that does the work for you. All as you need to do is to punch in the naturally aspirated compression ratio, and the expected boost pressure. According to what I've read in the supercharger books that I've purchased, the best combination of power and engine longevity will be provided by keeping the "effective" compression between 16 and 18.

For instance, the supercharger set-up on the standard Trilogy S/Cer kit produces 9.5 lbs of boost pressure. And with the Marauder engine which has an exact N/A compression ratio of 9.8:1, having a boost pressure of 9.5 PSI will yield an "effective" compression of 16.13, which is comfortably on the conservative side of the 16-18 guidline.

If you use the link below, you'll find those numbers to be accurate. But if you type in 13.5 PSI of bbost, you'll find that with an N/A compression ratio of 9.8:1, that this brings your "effective" compression past the 16-18 guidline at exactly 18.8 this is precisely why I've chosen to remain content with using the 9.5 PSI pulley that the Trilogy kit comes with. But go ahead and use the calculator to punch in different #'s......

http://www.supermotors.org/resources/calculators/index.php#total_effective_engi ne_compression
Hey Billy. Sweet link! According to the calculator I'm still in the comfort zone. Again, (according to the calculator) I'm at 17.8 with 12lbs of boost. Maybe the 3.0 pulley is the way to go??

[BillyGman]

Hmmm, sounds good Dave. Please let me point out to everyone here that my intention for this thread is just to offer some food for thought, and some additional information for those who are interested in street supercharging. I'm not trying to say that anyone person is right or wrong in what they did, or didn't do with there supercharger set-up. I'm just sharing with everyone one of the things that has influenced my choices as far as boost pressure for my Marauder.

Perhaps later on, when I get a chance, I'll supply you with a quote from a book on supercharging for the street that directly applies to this topic/

[Constable]

Good info Billy.

[Joe Walsh]

Nice. Only one thing is missing from this 16-18 effective compression ratio reccomendation, final charge temperature. Let's forget about how our cool running aluminum heads keep that charge cool for a minute and discuss ways we can contribute to extra timing and control of the combustion process. :grad:

Boyles Law states that when we compress a gas it heats up. Pre-ignition occurs when the intake charge reaches the temperature of spontaneous combustion, that is to say it ignites before the spark plug sparks. Detonation can be caused by pre-ignition but it also occurs when the spark plug sparks, but the charge is so volatile that it actually burns too fast and kicks the piston hard before it gets far enough past TDC, hence the "pinging". This is the sound of the wrist pins and rod bearings making metal-to-metal contact. Most experts agree that is a bad thing. :nono:

Higher octane fuels have a higher temperature point of spontaneous combustion, and if we cool the gas before we compress it, we can compress it more, before it heats up to this point where detonation occurs, as well. This is why most blower and turbo setups use intercoolers. :2thumbs:

There's also other ways to cool off that final intake charge before we close the valve and start final compression. We can put a water tank on the car and add water (vapor) to the air/fuel mixture, but this is an extra fueling requirement, nitrous oxide cools it off too but the extra oxygen defeats that purpose many times over, requireing the addition of the last and most commonly used air charge cooler, way too much fuel! :rock:

Lots of tuners use this old standby to keep the engine together, some would say it's not fuel efficient, but the numbers say otherwise. Why that is, is because the extra gobs of torque get the vehicle moving a lot easier, so the driver winds up using a lot less pedal to get the car moving and once it is, your just idling along and not using boost anyways. Some applications see an increase in gas mileage. :high5:

I remember in the '70s we used to run 12.5:1 compression on 91 octane by jetting the carburetor rich as hell. Man, you could smell the thing a mile away after it passed, and I would back straight out of a drive-thru if I happened to pull up behind one. :eek:

Nowadays we don't have to worry about that. The catalytic convertor will burn that exess fuel right off, just don't park it over a pile of hay right after running it hard. The cat's will be very hot and you might catch the hay and then the car on fire! :bigcry:

Just a little FYI from your local ASE Master. :D

Interesting....Does anyone know what the final charge temperature is assumed to be when using the 16 - 18 'effective compression ratio'?

Does this mean that with a lowered (intercooled) final charge temperature the "safe" effective compression ratio is higher?....Say 18 - 20???

Also, isn't a very rich fuel mixture kind of a 'band-aid' approach to avoiding detonation?

[MARAUDER S/C #5]

Yep, that's you, a comfortably conservative...MENACE!

How's your wife by the way? When are you coming to visit "the" City again?Thanks Marty :coolman: , Mrs. Menace is doing fine. She says to say hello to you, Terry and the dogs. I would love to come visit again. Lets make plans to meet late spring/early summer at that place we went to eat during the blizzard. What was the name of that place?
I will also bring the dog along to reunite with Jay and Marie.:banana::banana: :dogrun:

And if the conditions are right I will even bring Marauder S/C #5 :P
And of course this meet would be open to anyone here that would like to join us.

Billy, I'm sorry we took this thread :Offtopic: . If we have this meet I hope you will join us and I will start a new thread

PM me Marty.

[David Morton]

Interesting....Does anyone know what the final charge temperature is assumed to be when using the 16 - 18 'effective compression ratio'?

Does this mean that with a lowered (intercooled) final charge temperature the "safe" effective compression ratio is higher?....Say 18 - 20???

Also, isn't a very rich fuel mixture kind of a 'band-aid' approach to avoiding detonation?My guess is they're saying 16-18 from experience, hard won and many thrown rods and holey pistons to prove it. Outside air temps can vary so much as well as humidity and these things have to be factored into making the whole system operate under all conditions, so by no means am I suggesting 18-20 is OK if you've got a water intercooler and are using dry ice to cool it.

What I want to do is prepare the machinery with the best available intercooling for all-around driving conditions. I think air-to-air is probably best for a real autocross type flogger, over-the-road truckers have been using them for years, because you don't have a tank of water that's getting hotter and hotter, however let's not throw out water intercooling altogether because it is more thermodynamically efficient. Perhaps the system could use a thermostat to control and keep the water below a maximum allowable limit so fuel tuning could be counting on a guaranteed maximum air/fuel charge temperature.

Extra fuel is not a band aid at all, it's very effective as long as it isn't so much as to melt the cats. They will run a lot hotter. BTW we can thank the oil industry for rooting out and eliminating the sulphur laden fuels we used to get back in the 80's and early 90's. We got a lot of "rotten egg smell" complaints from the people that used to run with their foot in it a lot. It's just the knowledge that if we do our best to keep the temperatures down reliably, then we won't have to use as much fuel to achieve the desired goal, as much horsepower and useable torque as possible without throwing rods and burning holes in pistons.

[BillyGman]

Also, isn't a very rich fuel mixture kind of a 'band-aid' approach to avoiding detonation? No. Because the air/fuel ratio isn't the only thing that is changed in an engine tune for supercharging. The ignition timing advance is decreased also, and that's more critical than the air/fuel ratio is, in the prevention of detonation in the supercharged engine.

[BillyGman]

Conservative, conshmervative, I dont give a damn. The MARAUDER appeals to me, which probably means somewhere in my subconscious I really want to hurt people. Being "conservative" runs contrary to my underlying objective. Therefore, I shall remain on the relatively dangerous side of performance untill my check book is once again called upon to grant me the power of chaos and destruction! :fire:I originally overlooked this above post^because I considered it off-topic, and irrelavent. However, there are those on this board who I believe can be confused by these set of comments even though I'm sure that it wasn't the intention of "Deebar" to cause confusion. So I feel compelled to reply for the sake of some others here......

There are undoubtedly a number of board members here who may be interested in S/Cing their street vehicle (be they Marauders or not) but who also may not realize one critical fact about supercharging (or about any means of forced induction for that matter). And that is, that the number one cause of any forced induction (including supercharging) destroying an engine in a street driven vehicle is detonation (ie. spark knock, pinging).

And the number one way to successfully prevent pinging of a supercharged engine is obtaining a CONSERVATIVE engine tune via richening the fuel/air ratio, and backing off the ignition timing advance (the latter is more important, but both are needed). An aggressive tune is fine for topfuel dragsters and funny cars that only see 9 or 10 quartermile runs at the very most before having the engines rebuilt, but for a street driven vehicle (especially if it's your daily driver as my Marauder is) an aggressive tune would be careless, and undesireable to say the least. That is, if you expect your daily driver to last atleast 60,000 or 70,000 miles if not more.

Anyone can come up with a real fast car by means of forced induction, but if you're intending your fast car to last awhile, and also provide some dependable transportation with excellent driveability charactersitics for a good length of time, then you need to realize that only a responsible conservative engine tune will make those expectations realistic when using any means of forced induction be it SuperCharging, Nitrous oxide injection, or turbocharging. And this is exactly the reason that I've started this thread to pass along this info. An overly aggressive engine tune on an engine using forced induction will either melt or crack the pistons, or blow the head gaskets (or both) in relatively short order.

Reaching for that extra 20 or 30 HP out of a S/Ced or sprayed engine through an overly aggressive engine tune just isn't worth blowing it up unless the car in question is an all out drag racing car that you fully intend to rebuild the engine in atleast several times per year anyway. And I doubt that this is the case with any Marauders. What good is your Marauder being faster than any other cars on or off the track if the engine won't hold together longer than a few weeks? That wouldn't be very impressive nor favorable. Would it?

My Marauder has a very conservative engine tune (thanks to Lidio, and to Trilogy Motprsports) and is running a relatively conservative amount of boost pressure (9.5 PSI). And the car puts 400 HP to the rear wheels (which is about 480 HP at the engine) and runs 12.0 quartermile ET's. How much more do you want out of a 4,200 LB tank of a car that's also a very manageable daily driver? What times is your Marauder turning? The point being that we all need to consider realistic choices for our street cars if we expect them to last any length of time. And having an aggressive tune on a S/Ced engine that sits under the hood of a daily driven street vehicle would NOT be realistic.You don't need that to have a real fast car. That's one of the reasons why I wouldn't let anyone dyno tune my Marauder. Not all engine tuners are concerned about your daily driver's longevity. And BTW, whether you realize it or not, if you're using the chip that came with your Trilogy S/Cer kit, or you've had your engine tuned at a later date by Lidio of Alternative Automotive, then I know for a fact that you ARE running a conservative engine tune on your Marauder already. And of that's the case, then I don't see what your argument is. Because in that case, you haven't any argument.

[jstevens]

Billy,

Yours and others wisdom here cease to amaze me.
I'm still working on s/c'ing and when I do, I expect 150,000 miles out of her based on the $ needed.

[Deebar]

No confusion intended Billy. I was simply refering to boost pressure in my off color post. :) Not to be confused with a concervative "tune" as highlighted above. In fact, I dont think the word "tune" was even used in your original post. My post was only meant to express my (however rediculous) direction with my car. You see my Marauder is purely recreational, which means It needs to be exactly what I WANT it to be. Not necessarily what It SHOULD be in regards to longevity. Besides, Lideo tuned my marauder also, which is probably why Im so confortable running insane boost pressure in the first place. ;)