Compression ratio ?

hi again everyone

So we are starting to get to point of having to decide what parts to use for my engine.

If you remember i made a post about it awhile back.

Motor is mainly goning to be built from old fuel parts as i have a friend running a TF dragster here i Europe.
I know the engine wont be top notch, but my goal is to have a good reliable motor that doesn't tear it self up all the time.

To recap this is what we plan to use so far:

TFX billet block
AJPE Stage 2 fuel heads
SSI prepped fuel blower
New fuel system
MSD 44
Endele Buzzard Square Door injector

We popped a tall fuel piston with a tall fuel rod in it the other day to figure the cr. it came out to 9.8 - 10 depending on which head gasket we use.

Will it be enough for an alcohol only engine? or will i need to get some taller pistons? If so what cr should we aim for?

Sorry for the long post and thanks for a fantastic forum!

Thanks

Sune Larsen from Denmark

 

we like to see about 12.5/1 in our roots blown alky engine,
i guess there will be many oppinions but between 12 to 12.5 will work well

 

You can run with 10 to 1, it just won't be really fast. You can still make it respectable though by taking fuel away and speeding up the blower.

 

Thank you for your responses, We have decided to run it with 10:1 for now. if it is too crappy i'll changing it later on just want to get the engine in the car and have some fun for now.

 

Are you limited on OD? A lot of the cars are limited on the air that they can make, so they have to get the efficiency of the engine up in other ways. Compression is one way, if you are not limited on OD, you can run the boost up.

 

No we can run whatever OD we want As long as we stay with roots blowers, screws are limited

 

We have run as low as 11:1 and up at 13.5:1

Higher CR means narrower tuning window

For me 12:1 - 12.5:1 is about right and what we run now

10:1 is low, what thickness head gasket you looking to run?

 

When I built Manzo's first alky motor back in 1976 1/2" stroke, 1/4' long rod,
piston out 3/4" approx. 12.4 C/R.with .045 gasket. Best to have piston super lightened.

 

Don't remember what the thickness we had in it, but it was rather thin, will of course try and bump it up by using the thinnest possible gasket.

 

Compression Ratios

It will run at 10.0-1 just fine. It just may not make a ton of power. The nicest thing about lower compression ratios is that it makes your tuning window wider. If you accidently get it a little too lean or put in a little too much timing it will be much more forgiving. Once you get the motor up into the 12.0 and greater compression ratios it wont let you lean it too much or put in too much timing without hurting itself badly. I feel 10.0-1 is a great place to start with until you feel comfortable with tuning it. Just keep in mind that as your compression ratio goes up you need less timing and more fuel to keep it from detonating and beating the bearings out of it. Once the bearings go the rods get angry and leave the block through the side. Dave Germain

 

What kind of HP will this combo make? I am also putting together a similar motor for my street car, just to have some fun. In order for me to decide where to place the engine (setback, height, angle) I will need to know approximate power levels. So, on a soft tune with a 4.25" bore X 4.50" stroke, fuel-head 172cc chamber, 14-71 std helix blower - how much power will I make? Sune - how is it working out for you?

 

Also- I'm assuming that the sleeves (KB Stage 10) Darton sleeves can be bored safely to 4.25" from 4.187" since the wall thickness is 0.224"? Resulting wall thickness is 0.161" which is close to the wall thickness on Darton's other new sleeves (0.163") as shown in the chart at the link below:

http://www.darton-international.com/sl_black.html

Thanks for any help---