What compression ratios can use pump V/race

[c_williamson007]

I am slowly trying to build an R like the one I always wanted when R's ruled the track. My budget is nonexistent due to a baby coming in February.

I live in California and I'm stuck with 91 octane at the pump. I would like to push up the compression to the max for pump gas. I need to pull the top end and make some measurements befor I order any parts.

I have heard a lot about a UCCR test and measuring squish wth a piece of solder. Is there any way to select parts to achieve the desired compression without buying, bolting together with solder, measuring, then replacing the dome to get the desired compression?

Is there a tutorial of the solder thing or the UCCR test. I know I got a lot of questions hear so thanks in advance!

[Rupp250]

I think there is one on this site under the tech and how to guides.


Local race gas. ERC has 110 and Methanol.
http://www.ercracingfuels.com/ercCustomBlending.htm

And Sunol Super Stop has 100 at the pump.

[c_williamson007]

I will do more searching of the site when I get home but my first search just gave my a bunch of threads talking about doing it not how to do it.

As far as the race gas goes thanks for the info on where to get it but I am trying to accomplish a build where I don't need it. It is an additional cost I do not wish to have plus a long trip to a remote riding area will require me to bring a lot with me and if I run out getting more is not as easy as just finding any old gas station.

Once again thank you for your help

[christph]

You might consider this product: http://race-gas.com/.  I just came across it this weekend watching auto nation.  Apparently it is a real octane booster--unlike most of the crap at Autozone, etc. that just raises octane 1/10 of a point.  They say 2 ounces raises one gallon 4 points, all the way up to 105 octane.  The good thing about this additive--especially in California--is that you don't have to prove you're racing.  Check out their website.  It looks legit.

[Jerry Hall]

2 oz raises it 5 points on which scale?  The motored method or the research method?  I am very skeptical of such advertisements based upon my past experience. The motored method is the one that really means anything.  

My experience over the last 40 years on octane booster has not been good.  Any of the old boosters that raised the octane 5 to 10 points or even close to to what they advertise are now illegal and you needed to ware a Hazmat suit while handling them.  They say that handling these chemicals can cause dain bramage.:cocksure:

Those old boosters that half way worked cost as much to treat a gallon of fuel as it did to just buy race fuel.  If high octane race fuel could be made from pump fuel by adding a few ounces of the booster the race gas manufactures would also be doing it.

It is always better to use fuel that is a few octane points higher that what the engine needs because you may not always get 91 octane as graded or rated by your engine when hot and under full load, even though it is advertised as 91 octane.  I have challenged the fuel quality at .a particular gas station and days later the state will come to the station a take a sample and take it to a test lab and test it. The octane rating has always tested higher that what is posted using (R+M)/2 method.   I think that the(R+M)/2 method of rating is used so that the fuel will meet  or exceed what is advertised.

The problem with the (R+M)/2 method is R means the research test method and the M means the Motored test method.  An engine under full load agrees more with the motored method and not the research method when determining the fuels level of detonation resistance.  

Example of:  octane rating = (R+M)/2 = 90

Let R=95
     M=85    
                     octane is 90


Now let:
    R=85
    M=95
                    octane is 90

Both of the above test will meet the octane rating of 90 but when M= 85 you will have severe detonation problems because your engine thinks it is 85 octane.  When M=95 your fuel will behave in your engine (resist detonation) like you are running 95 octane fuel.

[DnB_Racing]

2 oz raises it 5 points on which scale?  The motored method or the research method?  I am very skeptical of such advertisements based upon my past experience. The motored method is the one that really means anything.  

My experience over the last 40 years on octane booster has not been good.  Any of the old boosters that raised the octane 5 to 10 points or even close to to what they advertise are now illegal and you needed to ware a Hazmat suit while handling them.  They say that handling these chemicals can cause dain bramage.:cocksure:

Those old boosters that half way worked cost as much to treat a gallon of fuel as it did to just buy race fuel.  If high octane race fuel could be made from pump fuel by adding a few ounces of the booster the race gas manufactures would also be doing it.

It is always better to use fuel that is a few octane points higher that what the engine needs because you may not always get 91 octane as graded or rated by your engine when hot and under full load, even though it is advertised as 91 octane.  I have challenged the fuel quality at .a particular gas station and days later the state will come to the station a take a sample and take it to a test lab and test it. The octane rating has always tested higher that what is posted using (R+M)/2 method.   I think that the(R+M)/2 method of rating is used so that the fuel will meet  or exceed what is advertised.

The problem with the (R+M)/2 method is R means the research test method and the M means the Motored test method.  An engine under full load agrees more with the motored method and not the research method when determining the fuels level of detonation resistance.  

Example of:  octane rating = (R+M)/2 = 90

Let R=95
     M=85    
                     octane is 90


Now let:
    R=85
    M=95
                    octane is 90

Both of the above test will meet the octane rating of 90 but when M= 85 you will have severe detonation problems because your engine thinks it is 85 octane.  When M=95 your fuel will behave in your engine (resist detonation) like you are running 95 octane fuel.

I agree with what your saying but are you sure of the formula?... the formula is R+M/2 isn't just the  the M/2  not the whole ( R+M) /2

[Jerry Hall]

I agree with what your saying but are you sure of the formula?... the formula is R+M/2 isn't just the  the M/2  not the whole ( R+M) /2

I may be wrong I will have to look at the pump next time I go to the gas station.

[Jerry Hall]

I googled octane rating and the sites I visited said it is the average of the Ron and Mon which is expressed in pure mathematical terms as:           (R+M) / 2.  Some sites expressed the equation as:  R+ M/2 but also say it is the average of the Ron and Mon.  What is important is we understand the concept of how the octane rating posted on the gas pumps is derived, not how non mathematicians may try to express their thought in mathematical terms.

I copied the following from the VP website.

1.    OCTANE: Octane is simply a rating of a fuel’s ability to resist detonation and/or preignition. It is not so much an indication of a fuel’s ability to make power, but rather a fuel’s ability to make power safely, i.e., without blowing your engine.  Octane is rated in Research Octane Numbers (RON), Motor Octane Numbers (MON) and Pump Octane Numbers (R+M/2).       A Pump Octane Number is the number you see on the yellow decal at gas stations, representing the average of the fuel’s RON and MON.       (See below for a more detailed explanation of how octane numbers are derived and what they represent.)

I am sure that Steve burns (owner of VP racing fuels) did not proof reed what one of his guys published.  I think that Steve would have put the )  bracket after the M and not after the 2:love-struck:

[wilkin250r]

On the topic of compression ratios, it's not nearly as straightforward as a 4-stroke.  This explains why you don't see too much reference to "compression ratios" and instead you'll just see references to combustion chamber volume or "dome size".

You're already familiar with the Uncorrected and Corrected compression ratios (corrected is sometimes referred to as "trapped compression ratio" or "trapped volume").  But a major factor in that whole arena is the pipe effect.  In the meat of the powerband, the returning pressure wave from the pipe can actually pressurize the cylinder higher than atmospheric pressure, essentially supercharging your engine in that small rpm range.

In simple terms, the pipe effect can actually get MORE than 250cc worth of fuel/air mixture into your 250cc engine.

The first questions that pop into your head are "how much more?".  I don't have an easy answer for you, it depends on the strength of that returning pressure wave (which depends on your pipe dimensions), it also depends on your porting, and even your carburetor size and your reeds.  I've seen people run into detonation problems without changing anything internal in the engine, but merely by changing their pipe.

In a 4-stroke, compression ratio is 95% of the equation in determining octane requirements.  In a two-stroke, it's more like 60%, and the unfortunate aspect is that I don't know of any reliable method to calculate the other 40%, it's usually figured out by trial and error.

[pinned250r]

[MENTION=460]Jerry Hall[/MENTION] will you ever quit impressing?

[udontknowme]

The first questions that pop into your head are "how much more?".  I don't have an easy answer for you, it depends on the strength of that returning pressure wave (which depends on your pipe dimensions), it also depends on your porting, and even your carburetor size and your reeds.  I've seen people run into detonation problems without changing anything internal in the engine, but merely by changing their pipe.

.

this is the main reason why i find kicking compression to be useless. sure it may 180psi when the engine isnt running but what does that meen when the engine is running ?  nothing as far as i can tell. we know its going to be higher than 180, and vary quit a bit with different pipes, cylinders, etc. im not aware of any mathematical way to figure what its going to be when the engines running, not to mention through various engine speeds. so i'd like to know how all these people can determine they need X amount of octane just from the 180psi. IMO determining octane requirment from the kicking compression is just rubbish, brought on by internet folk lore

like jerry said, i think theres alot more to it than just throwing on any random head with X amount of volume

[c_williamson007]

WOW!!! I have been working my self to death this week and have not gotten a chance to read up on this thread I started. I am blown away by the posts by wilkin250r and udontknowme. These pieces of information are extremely valuable to me as far as as 2 stroke performance and tuning. It feels like the first time I opened up an engine and saw how it worked! So thank you guys for your explinations. You confirmed one of my fears and that was I will need to build, test, tare down, inspect, change, and rebuild to get my set up right. The good news is I have learned new information about 2 stroke performance that I had previously not even considered. The other fear was I now know it is a waste of parts to stay off race gas....

[c_williamson007]

So in the effort to help me squeeze a little more juice out of my R I'm going to ask some new questions to hopefully get me going a little faster.

I have a stock 86 engine no porting and the following bolt on's Pro Circuit Platnum pipe, SA Pro silencer, Boyesen Rad Valve, stock PJ 34 carb with stock air box and uni filter.

I want to step up the compression to give me a little more juice. My thought was to start with a cool head but I would like to see what size dome other people are running with a similar set up.

[Sand_Blaster]

You could run a cr gasket to bump up comp. When I had my 87 cylinder rebuilt by Arlen he recommended the cr head gasket to raise comp.I'm not 100% sure if it will require the use of racefuel though or if you can get by with pump.

[c_williamson007]

I was reading an older post in the engine section about the CR head gasket and some people were saying that it has a problem leaking coolant. I think I am one of those people. When I bought my R the guy I bought it from said he had just done a top end on it and used a CR head gasket boasting about compression boost. After my first ride I noticed a leak and retourqued and it still leaks.

I just ordered a top end gasket set and I plan to do a flat sand on the head to tune up the surface (figure 8 motion, 400 grit paper on a piece of glass) but if I was dropping on a cool head no flat sand and I would not be throwing away a head gasket in a month.

I have also realized I can't get where I want to go with out race gas