What compression ratio would you run for 40psi on gas. Is 9.0:1 doable, or do I need to drop it down into the 8.5:1 range?

Getting Custom CP pistons made soon and just wanted to work out this detail. Cort, Geoff & others, what do you run?

Regards,
Justin

 

Wow, want to know too...

i quess 9:1 is possible on race gas maybe... but it would be hard on the limit of gasoline...i remember jeff said something about it.

Best regards
Malte

 

Why 40psi..

 

Only reason I can think of is to use two cheaper staged turbos to eclipse the power potential of a single more expensive unit.

Charge temps would be a nightmare in that case, really would be volatile unless you dropped CR more. On gas as in pump gas ??? Given a stupid wild *** guess as to the power potential of 40 psi... 6.5:1??


If this is an attempt at a practical question, you might want to check out boostfed's recent 700+ whp build in the high 20's boost numbers. Notice how they got huge numbers in the low 20's and minimal gains at higher boost. See how things changed with larger charge pipe, etc. The system dynamics have increased an order of magnitude in complexity, and looking at CR with relationship to 40 psi boost pressure (devoid of power output) doesn't even scratch the iceberg.

There is NO real way to answer your question. Sorry.

 

isnt terry running something like 7.8?? on his GT4088R (haha i forget the exact number, correct me if im wrong)... you should ask him about it

 

I have a gt4202R and it is a serious question. I will be running C16.

Here is the compressor map for the GT4088R. There is a reason Terry didn't gain a lot of power at higher pressure ratios. The gt4088R just isn't efficient the higher pressure ratios:



Check out the map for the gt4202R that I have. Very efficient at higher pressure ratios like 40psi or 3.72 Bar.

 

Do you have a power goal or do you just want to run 40 psi and see what it makes. I think you would get a better answer if you layed out how much power you want on C16 regardless of boost level.

 

Kind of a side question, whats after c16?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote"> Given a stupid wild *** guess as to the power potential of 40 psi... 6.5:1??
</TD></TR></TABLE>

You have to keep in mind that there is a minimum CR to get combustion....isn't it like 7.0:1? I can't remember exactly what it is, but I remember it being in the 7.0 range.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by andysila &raquo;</TD></TR><TR><TD CLASS="quote">Kind of a side question, whats after c16?</TD></TR></TABLE>
Methanol

 

Hot digity dogg!

whats after meth.??

 

nitromethanol

 

HAHAHAHAHAHAHAHAAHAHAHAHA!!!! The reason why we didn't gain as much power when we turned it up IS we HAD TWO MAJOR EXHUAST/BOOST LEAKS before the turbo, one bolt completely came out of the turbo to mani and one was LOOOOOOSE! So we noticed the boost was very laggy after the first night. Also I run 9.2:1CR not 7's or even 8.x:1 lol I have made some changes and one is the turbine will be a 1.06 A/R not .95 A/R, we shall see how that helps power now. My end dyno numbers truly are INCONCLUSIVE until we finish the tune up to 40psi


Edit:Also I don't think going down to say 8.5 - 8.8:1 CR is gonna be too bad for that much boost, it all comes down to the particular engine and head and combustion chamber design. How efficient etc etc etc Justin you dont have a Honda right? On my set up I think 8.5-8.8:1 CR would be perfect too

 

I posted this in the drag race topic but.

9.0:1 -10.0:1 will be fine. If you want to keep the thermal efficeincy higher then do 10.0:1. Also make sure you prep the crowns of the pistons to remove and chance of pre-ignition.

Here is a good article to do so.
http://www.theoldone.com/artic....html

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by uglyasscivic &raquo;</TD></TR><TR><TD CLASS="quote">I posted this in the drag race topic but.

9.0:1 -10.0:1 will be fine. If you want to keep the thermal efficeincy higher then do 10.0:1. Also make sure you prep the crowns of the pistons to remove and chance of pre-ignition.

Here is a good article to do so.
http://www.theoldone.com/artic....html

</TD></TR></TABLE>

That link is dead Cort

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dunc &raquo;</TD></TR><TR><TD CLASS="quote">

You have to keep in mind that there is a minimum CR to get combustion....isn't it like 7.0:1? I can't remember exactly what it is, but I remember it being in the 7.0 range.</TD></TR></TABLE>


My bike is running 6.5:1 compression

 

Here's the link he was trying to post:

http://www.theoldone.com/articles/en...ppistons1.html

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dunc &raquo;</TD></TR><TR><TD CLASS="quote">You have to keep in mind that there is a minimum CR to get combustion....isn't it like 7.0:1? I can't remember exactly what it is, but I remember it being in the 7.0 range.</TD></TR></TABLE>

In the early days of the turbocharger with shitty materials, poor machining, and almost total lack of theory or fuel control, 7:1 CR was how you made great power for two minutes before melting holes in your piston. I have lit-er-ah-CHOOR here that mentions 4.75:1 CR as working well and not being at all volatile. Super low CR just gets hard to start when cold, but a jot of ether gets things warmed up and going.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">nitromethanol </TD></TR></TABLE>

Either you have aluminum rods, or prepare for rod bearing failure. That, and with how nitro's specific gravity wanders all over the place as temps change, and $15/gal priced that like 1.2:1 AFRs for 100% and 2.6:1 AFRs for 50% mixed with methanol.... it's a big fat pain in the ***.

I say go for it


Modified by J. Davis at 9:50 PM 1/10/2006

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by andysila &raquo;</TD></TR><TR><TD CLASS="quote">Kind of a side question, whats after c16?</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TrueNorthStar &raquo;</TD></TR><TR><TD CLASS="quote">Methanol </TD></TR></TABLE>

its goes... c16, then VP Import (120 motor octane, vs c16's 116) then Ethanol, Methanol, Nitromethane. I will probably look into ethanol to use as a daily... its basically methanol but with lubricating properties

 

has anyone ever ran anything else but methanol on their drag cars?( like nitromethane)

did you sleep good hahah

 

we made over 800 whp w/ less than 40 psi on 9:1 and it was still on gas.

but i doubt id run it often like that...

if you're seriously trying to make that much and run it more than just to prove a point. run meth

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase &raquo;</TD></TR><TR><TD CLASS="quote"> run meth</TD></TR></TABLE>

and pick up 8 - 1 million cc injectors

if you run meth you need all braided lines and you get to change your oil every 20 seconds....it will also corrode the **** out of everything it touches including sleeves pistons valves, valve seals fuel lines...ect....

im guessing this is why it says on gas in the top of the post....