Ok, done many searches and even re-read the FAQ....

I know it is all a balence of total cylinder pressure, heat, octane, and timing....
someone tell me about the trade off's....
particularly between static compression and boost pressure.

I know you can run more boost on lower octane with lower compression.... BUT what are the trade off's?
What do you sacrifice when you lower cylinder pressure? Why doesnt everyone just run 8:1 when they turbo?

when do you need 8:1 compression? how much boost could you run at 10:1?

say you had to run 93octane gas.... how much boost could you typically run at what static compression?

somewhere i found an example breakdown for a generic engine... explaining how each change MIGHT effect the engine... "every pound of boost might add 10hp, every degree of timing might add 5hp, every point of static compression might add 10hp..." and then the tell you to play with the figures like a scale.... "by dropping one point of compression you can add 7psi... so you loose 10hp from the piston change, but gain 60 from the boost increase"

that is the sort of info i am looking for here.... but applied more to our engines....

and then factors like out-of-boost performance... if i drop to 8:1 compression is my car going to be a total dog until i hit 25mph?

perhaps a nice boost calculator that works for our engines...

there is no real exact science

you want to be able to run the most timing and boost , and lowest octane gas you can get away with and not have any knock

ken soggs wrote:Ok, done many searches and even re-read the FAQ....

I know it is all a balence of total cylinder pressure, heat, octane, and timing....
someone tell me about the trade off's....
particularly between static compression and boost pressure.

I know you can run more boost on lower octane with lower compression.... BUT what are the trade off's?
What do you sacrifice when you lower cylinder pressure? Why doesnt everyone just run 8:1 when they turbo?

when do you need 8:1 compression? how much boost could you run at 10:1?

say you had to run 93octane gas.... how much boost could you typically run at what static compression?

somewhere i found an example breakdown for a generic engine... explaining how each change MIGHT effect the engine... "every pound of boost might add 10hp, every degree of timing might add 5hp, every point of static compression might add 10hp..." and then the tell you to play with the figures like a scale.... "by dropping one point of compression you can add 7psi... so you loose 10hp from the piston change, but gain 60 from the boost increase"

that is the sort of info i am looking for here.... but applied more to our engines....

and then factors like out-of-boost performance... if i drop to 8:1 compression is my car going to be a total dog until i hit 25mph?

perhaps a nice boost calculator that works for our engines...

its easy. cuz most people usually can only get 92-93 octane at the pump. so lower compression is used on a STREET car. motor will ping and miss if you try to run boost with a 11:1+ compression. If you have access to a high octane (100+) then yeah you can run the higher compression. a turbo will make more power on a higher compression engine. but as far as psi goes.. thats hard to answer as every single turbo is different with psi and cfm. 12psi on a GT45R could be in the 400+ hp area, while 12psi on a T-25 might be in the low to mid 200hp area

eric is right, most timing and most boost will make the most power. Cant have your cake and eat it. The trade off of running a higher CR on pump gas, is your limited to a lower boost level and lower amount of timing.

trade off with a low compression is you have to run more boost to make up for the lack of timing and octane

6 one way, half dozen another



12.5@116 2.0 60ft

I assume you are going to stay with the Gm charger on your motor build? If so I would not change your compression from stock. You are not going to get alot of boost out of the M45 so lowering the compression is not really needed.



FU Tuning

[quote=97cavie24ls(™)]there is no real exact science

you want to be able to run the most timing and boost , and lowest octane gas you can get away with and not have any knock

That much i knew... but was hoping for some more figures..... as to like what outweighs what... how much better is one than the other....
where do you stand to gain the most performance...

John Higgins wrote:I assume you are going to stay with the Gm charger on your motor build? If so I would not change your compression from stock. You are not going to get alot of boost out of the M45 so lowering the compression is not really needed.

Yes, i am going to stay with the GM charger, it is currently running 7psi across the entire range. I am told by many reputable folks that i should go 10:1 for the GM charger...
But i am wishing she had a little more up top.... and since i am rebuilding the motor and ordering custom pistons for her anyway.... figured i would get ones to fit my needs exactly. So since i have already pushed my poor blower to near its limits, i need to figure out another way to make my top end power... Enter the turbo.
No i am not replacing the blower, i am augmenting it. Dual Charging.
Much like on a twin turbo... you have a lil fast spooling turbo to get ya moving.... then a biger turbo to spin up and launch ya across the finish line. But my supercharger will be the "small turbo"

so i am looking into a turbo that isnt exactly fast spooling, but will have all the top end i need.

I am just trying to figure out how to build my engine to take advantage of this. if i stick with the 10:1 that works best for my blower, i will be severly crippling my future-turbo. If i drop way low on compression to help the turbo out, i will be hurting the low-mid range punch of the blower...

So thought about going somewhere in the middle... but where.... trying to decide where i would be happiest.
I have HP tuners and a wideband, so i can play with the timing and the fuel plenty....

I just would like a better understanding of what helps the most... would i be better with 9.5:1 but only 10psi... or 9:1 with 15psi? or 8:1 with 20psi?

As much as i love big numbers up top, i actually prefer the kick and pull of the low-mid rpms that my blower gives me... so i dont want to sacrifice too much down low just to gain a bit up top.

John H [CavalierKid wrote:]its easy. cuz most people usually can only get 92-93 octane at the pump. so lower compression is used on a STREET car. motor will ping and miss if you try to run boost with a 11:1+ compression. If you have access to a high octane (100+) then yeah you can run the higher compression. a turbo will make more power on a higher compression engine. but as far as psi goes.. thats hard to answer as every single turbo is different with psi and cfm. 12psi on a GT45R could be in the 400+ hp area, while 12psi on a T-25 might be in the low to mid 200hp area
eric is right, most timing and most boost will make the most power. Cant have your cake and eat it. The trade off of running a higher CR on pump gas, is your limited to a lower boost level and lower amount of timing.
trade off with a low compression is you have to run more boost to make up for the lack of timing and octane
6 one way, half dozen another

i am confused as to how the HP figures can vary so much with similar pressure(unless your talking about different turbos on different engines, but on the same engine how can 12psi give different power? the engine doesnt know what turbo is pushing the air. all it knows is the amount of air you feed it. 12psi should be 12psi) I know a higher flowing engine will have less pressure but more power.... but how can 2 turbos have the same psi but different hp?

Hey Ken, this is what i know about boost. a normally aspirated engine will be runing atmospheric pressure (14.79) at all times, Boost is simply back pressure in the intake manifold, being forced in. When you double the atmospheric pressure of an engine, most of the time the power output will double as long as you have a power adder big enough to flow double the output of that engine. As far as your question goes about 12 PSI being 12 PSI, that is easy to answer. Since boost is back pressure, 12 PSI of boost will always be 12 PSI. But when a T25 is using 12PSI, it is only flowing what it can at 12 psi before the waste gate opens, and lets out anything more than 12 PSI. What the turbo can flow at 12 PSI is the difference, say John H is right, at 12PSI a GT25 is making 230HP. And at 12 PSI, the GT45 is making 400HP. The difference is that even at the same 12 PSI, the GT45R is designed to flow almost triple what a T25 can flow, and at each given PSI can nearly double the amount of air going into the engine. Im not saying all this is true, so no accusations, please. Thats the easiest way i can explain. bigger turbo means more flow, more flow =more power, too much flow= ENGINE BOOM! Tuning is more critical in my opinion.

ah, ok.... i guess that makes sence.... I am still thinking in terms of superchargers... with those 12psi is 12 psi... there is no wastegate or anything, just a bypass, but that is controlled by vacuum.

anyway.... I am aware that you need to compensate for added air with added fuel and added/retarded timing....

but i am just trying to find out where is the best static compression for across the board power at 93 octane.

am i better going lower to run more boost.... or going higher to take advantage of my low range power of the SC.

i know 10:1 is best for my 7psi... but what kinda pressure should i expect with a turbo, and what kinda static compression would i need to run that on pump gas?

are there any calculators out there for this sort of thing?

I think dual charging is over your tuning ablities at this time. If you want more top end just go turbo. If you set it up correctly lag is not a issue. I think for you and your tuning ablities lower compression is best.



FU Tuning

You really have to forget psi and start thinking about cfm...the reason every turbo is diff at a given psi is cause the cfm is diffrent..

well do a perfect equation, thats hwo to get the most power. More boost does not always mean less timing. You have to get the right Air/fuel ratio, and the best amount of timing for that ratio. If you are going to run the supercharger, stock compression is fine as it's not going over 7PSI. If you turbo your car, you will want compression more in the safe zone as I call it at Around 8.5-9.5:1. Then get that baby to a professional who works with this daily, and get them to tune the air fuel ratio and set the timing as the engine needs it. They will draw a base map up upon what size turbo/ supercharger used, then either add or lean the fuel, and advance or retard timing as needed. This way you're car will be tuned for w-air/fuel ratio, x- timing, y- boost pressure, giving you z-which would be the finished tune. Tuning is not only one thing or the other, its the combination of the whole thing that makes or breaks a performance vehicle. And John is right again, boost is not just PSI, the CFM going through the engine is what determines if power is being made. I recommend a book that you can buy from barnes and noble, i think its called "how to build turbo systems or high performance forced induction", its something to that nature and its a great book. That way you will learn how to read a turbos flow chart or graph, and it explains how the A/F ratio, Boost, Cubic Feet Per Minute(CFM) and timing of an engine works with each other. Its a good book and I've learned from it. Im not making fun of you, so don't take it like I am. Im here to help, and I have read the book about 3 times myself, just to get a better understanding of how forced induction works.

John Higgins wrote:I think dual charging is over your tuning ablities at this time. If you want more top end just go turbo. If you set it up correctly lag is not a issue. I think for you and your tuning ablities lower compression is best.

Hey now... come on..... just because i blew up my engine doesnt mean i cant tune.

I am pretty sure it had something to do with the rod bearing that i convinced myself was only a lifter tick... that and pushing my engine to 7000rpm with only stock oiling....

i think i did a pretty good job on my tuning considering the phantom knock i had to deal with

Philly D wrote:You really have to forget psi and start thinking about cfm...the reason every turbo is diff at a given psi is cause the cfm is diffrent..

I am new to the turbo thing.... it is a hair different than superchargers....

but i know that PSI is the resistance to flow.... and is only a side effect of high flow, and not a good gauge of flow.

but the thing is there is no good, or easy way to measure CFM... PSI is easy to gauge.

jd soza wrote:well do a perfect equation, thats hwo to get the most power. More boost does not always mean less timing. You have to get the right Air/fuel ratio, and the best amount of timing for that ratio. If you are going to run the supercharger, stock compression is fine as it's not going over 7PSI. If you turbo your car, you will want compression more in the safe zone as I call it at Around 8.5-9.5:1. Then get that baby to a professional who works with this daily, and get them to tune the air fuel ratio and set the timing as the engine needs it. They will draw a base map up upon what size turbo/ supercharger used, then either add or lean the fuel, and advance or retard timing as needed. This way you're car will be tuned for w-air/fuel ratio, x- timing, y- boost pressure, giving you z-which would be the finished tune. Tuning is not only one thing or the other, its the combination of the whole thing that makes or breaks a performance vehicle. And John is right again, boost is not just PSI, the CFM going through the engine is what determines if power is being made. I recommend a book that you can buy from barnes and noble, i think its called "how to build turbo systems or high performance forced induction", its something to that nature and its a great book. That way you will learn how to read a turbos flow chart or graph, and it explains how the A/F ratio, Boost, Cubic Feet Per Minute(CFM) and timing of an engine works with each other. Its a good book and I've learned from it. Im not making fun of you, so don't take it like I am. Im here to help, and I have read the book about 3 times myself, just to get a better understanding of how forced induction works.

no no no not at all... i never got the impression you were making fun of me. Trust me, i have read many books on superchargers... but i always skipped over the ones that talked about turbo alot, cuz i LOVE my blower.
but since everyone is slacking on making a intake for a bigger blower, my only choice is to get a little help from the dark side and get a turbo....

so suddenly all the info i had no interest in before is suddenly of interest. So i will definately look into that book. I have learned alot from books.... but printed pages dont always equal real world answers.... to give some examples....

one book i read talking about ignition... it said that spark gap is relative to an engine... that the manufacturers gap is just a starting point... that the bigger the gap the better.... until you start to misfire... then scale the gap down a bit. the largest gap without misfire will yield the best combustion. well... um... i managed to get 70 gap on a car that is only supposed to have 30.... and still only misfired under very heavy load. Car still ran on that gap... but my MPG and power went to poop. needless to say that book can suck my big toe.

and then my EFI and tuning book... it said "get your VE tables right, adjust for WOT and cruise, once VE is where you want it then move on to timing... slowly add timing in 2 degree increments untill you notice signs of knock, or knock senor signal, then back off a few degrees and that should yield the best timing."
well the only knock sensor reading i got were a few random peaks here and there.... but nothing consistent... and then when i actually got to where i could hear pinging, the knock sensor showed no know at all.... so wasnt real happy with that book either (the book or my knock sensor.)

But i am always open to learnign new things and trying new things. So i will check out your book. already been spending all my free time reading website and other forums about turbos, trying to get up to speed.

here's a calculator for getting the effective compression with boost when you know your static compression http://www.dragsource.com/index.php?navselect=calculators&calctoview=3




14.82 @ 97 mph

ken soggs wrote:

Philly D wrote:You really have to forget psi and start thinking about cfm...the reason every turbo is diff at a given psi is cause the cfm is diffrent..

I am new to the turbo thing.... it is a hair different than superchargers....

but i know that PSI is the resistance to flow.... and is only a side effect of high flow, and not a good gauge of flow.

but the thing is there is no good, or easy way to measure CFM... PSI is easy to gauge.

Ok but 8psi out of a t4 will have a higher cfm and higher power output then a t25 at 8psi since it has a much lower cfm......so that same psi will yeild diffrent hp ratings which will need a completly diffrent tune due to the higher cfm cramming more air at lower psi....same thing with chargers..its all cfm based in terms of what power will be made out of a given psi

psi vs cfm....

think of a house ceiling fan spinning at say 1,000 times a minute and the airflow it will make.

now think of a windmill in a field spinning at 1,000 times a minute. both spinning the same amount and working as hard, but which one will make more air?

turbos are no different. compression is just another way to make power. as long as the timing AND octane is there... with one of those out of the picture, the other has to be compinsated.



12.5@116 2.0 60ft

Ok, well now that i have done a bite more research and understand things a little better here..... I realize we are all right, and all wrong at the same time....

Turbos and Superchargers all work on the same math... it is just different in how it gets there.
As far as the whole CFM / PSI debate... it is the same across the board... it is all about the basic priciples of hydraulics.
pressure is the resistance to flow. the more you flow the lower your pressure.... less you flow the more pressure.

So when you compare one turbo to another like you all were above... you really arent being fair.... The turbo itself is only one leg of a bar stool...
YES at 12PSI a GT25 might make 230HP. And at 12 PSI a GT45 might make 400HP.... but that totally depends on what is it bolted to.
If you put both turbos on a V8... then yes... the HP figures might be right... But i would bet my granny that the GT25 wont make 12PSI on a V8.
if you put both on a 2.4L LD9.... you get the same... the 12psi and 230hp might be accurate for the GT25.... but a GT45 on an LD9 would more than likely be WAAAY above 12psi.

It is indeed about CFM.... the VOLUME/MASS of air that is being moved.... air mass determines horsepower. if you have X amount of air... you can squirt X amount of gas, and make X amount of power.

So you decide how much power you WANT... then you can tell how much air you need.
then you find a turbo that can flow that CFM....

AND THEN you get to the compressor maps and your engine....

i am just making some figures up off the top of my head here..... but just for example....

say i want to make 400hp with my LD9.... that requires 200cfm lets say....
well if i have a completely stock car... it might be quite a chore cramming 200CFM through it. you might be talking 20-30psi... (due to the restictive flow of the stock parts)
mind you it is still the same AMOUNT of air... but the restrictions of the engine would be like putting your thumb over the tip of a garden hose. water still comes out.... but with alot more speed and pressure.
Say we spend some money and get the engine breathing... port the head, valve work, good intake manifold, etc etc... now that 200cfm moves thru it better... so that same 200 CFM now only makes 15psi....

So you look at the compressor map.... your peak horsepower goal would be plotted along the bottom left to right.... based on air needs... but then the pressure (based on cramming that much mass into your engine) is shown up and down...

so if you wanted to make 400hp peak... lets say it puts you SMACK center of the map... (right to left center) but then you need to plot your up and down based on your engines flow. so a better flowing engine will sit lower on the map.... a more restrictive one will sit higher...

This is all just talking about peak HP now.... just a single point on the map. well you want to pick a compressor who can make that CFM at that PSI the most effectively.... so you look at your "point" on several different maps till you find one that has a good efficiency island right where you want to be....

then you plot some other points for your engine... since you cant ALWAYS make peak HP, and you dont always drive at redline... so you draw a line to represent your engines air curve.... and then look at more maps to see if there is one that keeps pretty efficient thru most of your engines path...

if you go too far in one direction you get increased heat and IATs... which kill performance... go too far the other way and you risk damage to the turbo itself.




Think of it like traffic....
the road is the engine. the city is your air demand. each car is a air molecule.

if you have some little hick village of a town... you only need a little 1 lane dirt road to get the 20 farmers from work to the bar. (normally aspirated small displacement engine running 100hp @ 0 psi)

if you have New York City, you best have a superhighway infrasctructure ready to get the people home before they start a riot. (2000hp twin turbo V8 big block @60psi)

the more cars you can get home before dinner the better your "city" is. if no one makes it home for dinner... then all the wives bitch, and the next day everyone is crabby and the whole place goes to hell..

You want to get the people all home on time... the bigger the road the better... but you only have so much room to widen a road... yeah everyone would love a 8 lane highway to everywhere they wanted to travel... but no one wants to live by a 8 lane freeway.... or have to loose their backyard to build one.

so you make the road a lil wider... but then have to get creative.... cramming more cars onto the road makes everything tighter (more PSI). lots of psi is fine... until things get packed so tight that people start hitting eachother... then every accident causes further backups. too tight makes things real touchy....

a big turbo is just like adding more people to the city's work force... it is just that many more cars to get home... if you dont improve the roads to handle the higher trafic demands you will only hurt matters.

so to say "a gt45 makes 400hp at 12PSI" is like saying "i took me 5 hours to get home"

get home from where? how were you driving? what roads did you take? yeah to get from new york to pitsburg might take 5 hours... no shock there... or to walk from your house to the mall might take 5 hours...



so anyway... sorry for the novel... but needed to get this out of my head and in writting... so someone tell me if i am wrong here... this is what i have come up with from my research...

You are correct to a extent...a little of the explanation goes way off in left feild..you do have to fit the turbo to your needs and engine..yes...to large a turbo will be a bad thing...but it is still related to cfm..psi isnt really much of a factor in determining total power output...look at it this way..
Turbo 1>>>>300cfm at 15psi....roughly what the saab setup is at......will put you in the 250 hp range...

Turbo2>>>>750cfm at 15psi....roughly what the hahn with 20g upgrade is will put you in the 325 hp range..


These are very very rough numbers but its to show you that the cfm is the determining factor in how much power you will end up making......You are correct though..slapping a huge asst4 that is capable of huge cfm wont garentee you making more power..possibly more peak power but its only good for dyno queens....Thats where sizing the turbo and your wants and needs becomes so important...luckly most of us use the same kinda setup..

Philly D wrote:
Turbo 1>>>>300cfm at 15psi....roughly what the saab setup is at......will put you in the 250 hp range...

Turbo2>>>>750cfm at 15psi....roughly what the hahn with 20g upgrade is will put you in the 325 hp range..

Yes, but my point is that given the SAME engine... the above figures wont work....

if you take the engine from bob's cavalier... and slap on TURBO 1 yes you might get 15psi... and make 250hp... but that is due to the CFM....

but if you take off turbo 1 and bolt turbo 2 onto that EXACT same engine... you WILL NOT be able to get 15PSI at 750cfm.... it is IMPOSSIBLE given the same engine.


the engine itself is the "pipeline" which the air moves through.... if the pipeline stays constant... and you change the volume of air... you are going to see the pressure change.

if you get 15psi pumping 300cfm thru an engine.... and you double the CFM... it is IMPOSSIBLE to keep the PSI the same.

you can flow a million CFM at 15psi if ya want... but it would need the alaskan pipeline to do it...

you need to talk about all the variables and constants....

if you change any one variable... the others change to compensate....

if you increase CFM, but keep resisitance the same... PRESSURE will go up.

if you keep CFM the same, and lower resistance.... pressure goes down.


pressure is directly linked to resistance, and both are linked to flow.

3 + 3 + 3 = 9

3 + 3 + three = 9

3 + 3 + 3 = 9

you can say it anyway you like.... it is all the same....

unless you are a magician... there is no way you can double the volume of air thru a fixed pipe without doubling the PSI.


the only way you can get 2x the flow at the same PSI is if you cut the restriction in half. (thus hook the huge turbo to a 8cylinder as opposed to a 4cyl)


if you want to run the "turbo 2" and make your 325hp... you can do it... but you wont be able to do it at 15psi. not without opening your engine up.

actually im using numbers based loosly off a eco....same engine....thats where .ar numbers come in ..

Also i said these were made up somewhat numbers..just a generalization....you are right...you prolly wont have to hit 15psi to get 750 cfm....it will more tn likely hit that at a lower psi..

Same engine same everything...a small turbo will NOT out out the same hp as a larger turbo(properly sized) on the same engine at the same psi...it will not no matter no how..reason why...CFM...

Otherwise why would we all not just put t25's on our cars?? cause a t3/t4 puts out more cfm and is a better fitting turbo.

Hmm..

ok well here is another idea....in terms of the original question....a larger turbo will put out more cfm at a lower psi so.....the larger turbo will put out alot less heat which means you will have alot less chance of detonation....


The smaller turbo will have to run at a higher psi to make the same power as the larger turbo and with that comes more heat..more heat is bad as we know..

So in terms of octane and such always run the highest you can get...92 or 94 and run a properly sized turbo for your power goals and needs...keeo in the turbos efficnecy range and youll be golden!

Philly D wrote:
The smaller turbo will have to run at a higher psi to make the same power as the larger turbo and with that comes more heat..more heat is bad as we know..

No. no no no.... that is exactly my point... CFM is provided by the turbo. A big turbo provides more CFM. The PSI is 100% based on and DIRECTLY related to engine flow.

A small turbo will have to run at a higher SPEED to make the same CFM/PSI... that extra speed creates more heat (running outside the efficiency range) which makes more heat which make the same volume of air less usefull.

my point is that no matter which turbo, and how efficient, the CFM and PSI should be directly linked to one another based on your engines flow.

making numbers up here... but....

100cfm = 5psi @ stock LD9
300cfm = 15psi @ stock LD9
600cfm = 30psi @ stock LD9

100cfm = 4psi @ properly modded performance LD9
300cfm = 12psi @ properly modded performance LD9
600cfm = 30psi @ properly modded performance LD9

600cfm = 10psi @ race prepped big block V8

with PSI comes heat. heat degrades the quality and usefullness of the air. Due to heat, you may only get 300hp out of your 750cfm... but if you created less heat, you would get more power from the air. You can remove heat with intercoolers, but those also restrict your flow. It is best to MAKE as little heat as possible... then you have less to take out.



Also going back to the original question... yes i know you want to run the highest PSI available.... but my question was more geared for "how much boost/pressure/cfm can i run safely on pump gas?"

I know i was plenty safe running 93 octane at 7psi with pretty high IAT's and fairly high compression (9.7:1).

But now i am at 8.5:1 and if i cooled things down a little, how far could i push the turbo?

Philly D wrote:You are correct to a extent...a little of the explanation goes way off in left feild..you do have to fit the turbo to your needs and engine..yes...to large a turbo will be a bad thing...but it is still related to cfm..psi isnt really much of a factor in determining total power output...look at it this way..
Turbo 1>>>>300cfm at 15psi....roughly what the saab setup is at......will put you in the 250 hp range...

Turbo2>>>>750cfm at 15psi....roughly what the hahn with 20g upgrade is will put you in the 325 hp range..


These are very very rough numbers but its to show you that the cfm is the determining factor in how much power you will end up making......You are correct though..slapping a huge asst4 that is capable of huge cfm wont garentee you making more power..possibly more peak power but its only good for dyno queens....Thats where sizing the turbo and your wants and needs becomes so important...luckly most of us use the same kinda setup..

i agree with this

ken...

im running 9 psi on a custom kit... t3/t4 57 trim, .63 a/r, Garrett. I'm fully spooled by 2700 rpm. now i have not yet been to the dyno so i cant even guess what I'm at for power level. i know that at 9 psi on this custom setup should put me over 250. now if i take the Saab turbo and put it in place(i know you cant due to flanges but walk with me here) i will spool super fast and max out the efficiency of that turbo and make less power due to size. as for the motor being the pipeline... i see your point but it looks like your missing a few things. a big part is fuel. my tune is set up to give more fuel per what the turbo is doing... meaning i have the car tuned for the Garrett turbo. not the Saab. more boost equals more fuel. id bet I'm using more fuel with the Garrett than i am if i had the Saab turbo on the car because im forcing more air in and increasing the volume and velocity of the air at the same time.

yeah vincent, no doubts there at all.... we havent even gotten into "tuning" yet....
at this point just talking sheer air volume....
you can pump 100000 cfm into an engine, without the proper timing and fueling, you wont make crap for power.

This is mostly theory we're talkin here... skipping over lil details like flanges and space and tuning, and such....
the more air you pump in, the more fuel you NEED unless you want to go lean and blow you engine.


But am i wrong in saying that the MASS of air will create a given pressure based on the engine it is flowing through?

it can be a T25 or a GT70.... if its on the same engine the pressure will always increase with CFM.
you cant say "but you will get more CFM at 15psi with a bigger turbo"

the only way to get more CFM at 15psi is to make your engine breathe better.

changing turbo's might get you COOLER air at 15PSI.... (cooler air is slightly denser, but not enough to worry about in this discussion)

but even a GT70 wastegated to 15psi is going to give you the same CFM as a tiny lil moped turbo at 15psi.

I'm glad I found this thread... so if I'm on stock motor with a t3-super60 turbo with a upgrated fuel pump/injector, now normally I will run 93 octane all the time, but I would like to run about 5-7 gallons of 110 octane and fill the rest up with 94.. would it be worth it to put the higher octane in?


**changes are here**