Squish trouble?

[Chip M]

I got my squish test done today hope you guys have some input for me. I was not getting the power I think I should have after rebuild but the shee is new to me so I have nothing to compare to. The leakdown test was great, I lost no pressure. I did the compression test and had 165 one side, 162 in the other. The squish test showed .044. I cannot find the numbers on the domes so I have no idea what size they are. How can I check them? Is the bowl shape suppose to hold the amount of liquid in cc's? If that is true,I assume you just fill the bowl shape, not the squish band area to check true size of domes?. Whatever the case, can someone explain to me(or direct me to link) how the squish/compression/octane go together. I would really like to understand the differences or advantage/disadvantage of this part of my build. If I am missing some information that you need to make sense of this to me, please let me know. Thanks

 

 

96 Banshee-64.75 mm bore

V Force Reeds/Cages

ProDesign Cool Head

FMF Gold Series Fatty's- Powercore 2 Silencers

K&N Air Filter-stock box w/lid-no snorkel

Timing +4

Presently 300 main jets-27.5 pilots

93 octane

@ sea level-80 deg. F

Hard trail / MX style riding

[Glamis321]

Your compression is borderline high for running pump gas. If I remember right, at 160ish you want to run race fuel to prevent it from detonating on you. Or you can drop your compression by going a size bigger on your domes.

 

Here's a thread on measuring your dome size if they aren't stamped.

 

http://bansheehq.com/forums/index.php?showtopic=148752&st=0&p=1283665&hl=+measure%20+dome&fromsearch=1entry1283665

[Chip M]

Your compression is borderline high for running pump gas. If I remember right, at 160ish you want to run race fuel to prevent it from detonating on you. Or you can drop your compression by going a size bigger on your domes.

 

Here's a thread on measuring your dome size if they aren't stamped.

 

http://bansheehq.com...1

 

Great!!..So it is the entire dome including squish band area. Helps me out alot. We have a Sunoco that sells 100 octane race fuel from a pump. It says up to 10% ethanol. Would I be safe to run it straight? or should I mix with my 93 octane. I have also heard of a shop that sells 110 octane, would that be better for my motor?

[Nightmare]

straight 101

[Coupelx]

Great!!..So it is the entire dome including squish band area. Helps me out alot. We have a Sunoco that sells 100 octane race fuel from a pump. It says up to 10% ethanol. Would I be safe to run it straight? or should I mix with my 93 octane. I have also heard of a shop that sells 110 octane, would that be better for my motor?

 

 

Its not 'supposed' to include the volume of the squish band from what ive read. the flat plate method like sprinklerman posted in that thread will give you an idea though.

[Wildcardracing]

First of all, yes the cc of the dome includes the squish area as all of this is calculated into your compression ratio. Only exception being stroker domes where the piston will take up some of this volume at tdc. As for your comp test, 162/165 tells me the engine is still healthy in both cylinders. I would have recommended doing an other leak down test before teardown when you had problems as it may have shown your cooling system leak which has been discussed in your piston pics thread. However the cooling system may only leak at much higher preasures than the leakdown test. As I stated in the other thread do a cooling system pressure test after it goes back together. As for your questions on squish, here is the best quick explanation I can give. MSV=maximum squish velocity, all fuels have a safe MSV range they can be used in. MSV, trapped compression ratio and uncorrected compression raio (UCCR) are all used in determining the appropriate fuel for a given engine. The use of the engine will dictate dome design. All three of these variable affect each other as do other engine parameters. Decreasing squish clearance, tightening the squish angle (which should always remain divergent=open up toward the center of the bore), decreasing trapped compression ratio (bigger dome or higher exhaust port) or widening the squish band width will all increase your MSV. Opposite changes will decrease your MSV. Shelf domes (PD, Noss ect.) are typically designed with a conservative MSV when used with an engine with stock ports and appropriate octane fuel. Custom domes could be anywhere in the spectrum depending on what the builder was trying to accomplish. As for your fuel choice, you can either mix 93/110 50% of each or buy the 101 whichever is most economical. Just be aware that oxygenated fuels while having good power potential will affect the jetting of your bike. Which BTW is very rich by the looks of your plugs.

 

-Brandon

[Chip M]

First of all, yes the cc of the dome includes the squish area as all of this is calculated into your compression ratio. Only exception being stroker domes where the piston will take up some of this volume at tdc. As for your comp test, 162/165 tells me the engine is still healthy in both cylinders. I would have recommended doing an other leak down test before teardown when you had problems as it may have shown your cooling system leak which has been discussed in your piston pics thread. However the cooling system may only leak at much higher preasures than the leakdown test. As I stated in the other thread do a cooling system pressure test after it goes back together. As for your questions on squish, here is the best quick explanation I can give. MSV=maximum squish velocity, all fuels have a safe MSV range they can be used in. MSV, trapped compression ratio and uncorrected compression raio (UCCR) are all used in determining the appropriate fuel for a given engine. The use of the engine will dictate dome design. All three of these variable affect each other as do other engine parameters. Decreasing squish clearance, tightening the squish angle (which should always remain divergent=open up toward the center of the bore), decreasing trapped compression ratio (bigger dome or higher exhaust port) or widening the squish band width will all increase your MSV. Opposite changes will decrease your MSV. Shelf domes (PD, Noss ect.) are typically designed with a conservative MSV when used with an engine with stock ports and appropriate octane fuel. Custom domes could be anywhere in the spectrum depending on what the builder was trying to accomplish. As for your fuel choice, you can either mix 93/110 50% of each or buy the 101 whichever is most economical. Just be aware that oxygenated fuels while having good power potential will affect the jetting of your bike. Which BTW is very rich by the looks of your plugs.

 

-Brandon

 

Thank you so much for all your help. The leakdown test was done just before I tore it down to find the washed piston. It held the full 6 psi for 10 minutes before I released pressure. I will check all surfaces before my assembly and do the coolant pressure test as suggested. I found the laser etched 19 on the domes. I can get the 100 octane at a local sunoco and I will try it out after I figure out my leak but I think since I only run trails and do not race I will opt for the bigger domes. I think 22 cc was a suggested place to start. The squish explanation really helps me to understand what is going on with the changes I am doing. Maybe if I find too much loss of power after trying out the 100 octane and switching to a larger dome with the 93, I will be switching back. But either way, I now know that it is not smart to run the 93 with present setup. Good luck to you................Chip

[registered user]

im not sure theres a competant engine builder in the world that uses cylinder pressure to decide what octane fuel to use. too many other important things than what a psi gauge says

 

if you want to know compression ratio forgot about messing with the head. bolt it back onto the jug and put piston at TDC and measure how much fluid you pour through the plug hole until it gets to the bottom of the threads. total cylinder volume+head volume at tdc divided by head volume at tdc= compression ratio

 

checking the method above the exh port is the same way except you calculate from the top of the port instead of BDC

Edited April 5, 2012 by registered user

[Chip M]

im not sure theres a competant engine builder in the world that uses cylinder pressure to decide what octane fuel to use. too many other important things than what a psi gauge says

 

if you want to know compression ratio forgot about messing with the head. bolt it back onto the jug and put piston at TDC and measure how much fluid you pour through the plug hole until it gets to the bottom of the threads. total cylinder volume+head volume at tdc divided by head volume at tdc= compression ratio

 

checking the method above the exh port is the same way except you calculate from the top of the port instead of BDC

 

How to say this with a little tact....let me think...........................................................................................I wish I had a flush button for some replies. I feel like someone just shit all over my post.

[registered user]

just trying to help you in simple terms. imo people get caught up too much in the psi tunell vision. honestly cranking pressure is the last thing i worry about. my honda single is 13.5:1 but only about 120psi at 6000' just because the way the engine is setup. your 165 is fine, put it together and ride

Edited April 6, 2012 by registered user

[Wildcardracing]

just trying to help you in simple terms. imo people get caught up too much in the psi tunell vision. honestly cranking pressure is the last thing i worry about. my honda single is 13.5:1 but only about 120psi at 6000' just because the way the engine is setup. your 165 is fine, put it together and ride

I agree about the cylinder pressure comment, people do in fact get too caught up over cranking psi. Cranking psi is more of a way to monitor the condition of your engine. However, the last porting of your post I have to dissagree with. 19cc domes are much to small for his engine to survive happily on pump gas at sea level.