Making a good thing better - and using the hot rod....
Sunday lunchtime sitting in front of the fire post,
RecycledRS - yes here you bring up one of the burning spots, as I was writing before: the clearance is one thing, shape and form makes the next difference.
1. There are calculation basics that i found to be used in full out race engines to define the squish area in relation to the bore.
2. Yes I use both, I machine the outer diameter area parallel and then open it in different angles depending on the complete setup, sometimes on bores up to 94 mm I keep it parallel all over.
3. If you are not a friend of the last detail go with all done parallel instead of risking to use the wrong angle....since this blows it all.
4. Machining the end of the squish too round and smooth will also blow the magic by a huge factor...better keep it edged, whatever they tell you in any book.
5. To take care of what is happening please hold in mind that you have to overcompensate the squish work - so go get the effect by the minimum possible losses.
6. Squish work is living from and at below 1,5 mm...
7. To make it tighter and tighter will not be of direct linear effect - this is the next step where you see if someone knows what he is doing or not. On a high or even just good performing engine the squish must be a part of the concept and / or corresponding to all what you do. How far are you willing to go ? When will it be ok for you ? Or are you looking for perfection anyhow ? Answer this before you start doing it yourself ! Below 0,75 mm you will find no effects that are worth being discussed in any case.....this is just valid for our 2V BMW engine !
Here are some more questions / comments to give you the most possible complete picture -
To give a useful advice please tell me:
What bore diameter below what exact cylinderhead are you using ?
What is the piston to cylinder clearance ? Steel liner or alu Nikasilcylinders ?
What camshaft will be used ?
What conrod length are you about to use ?
The last question is underestimated or even missunderstood most times.
It comes from the fact that the kinematic effects of the conrods are misinterpreted very often. If you try to calculate what is the outcome of a longer conrod in relation to the latheral forces from piston to cylinder you will find out that it is in our case not worth talking about it. All started for me when I was building the first complete self engineered engine using the 97 mm Mahle cylinders that where available and common that times. It was my intention to fabricate a very light and small two ring piston that was leading me to a conrod that has to be 13mm longer then the std. one. So in 1993 I ordered 148 mm conrods from Carrillo - and this was against all trends and all what the well known tuners that times, even the woks bmw people where doing. They all reduced the conrod length to 125 mm using very light titanium conrods....
Ok on the dyno we could not believe the effect - it was the first ever build two valve bmw engine pulling veritable and often measured by different magazines 100 plus HP. This is not questioning what Udo Gietl did in the 70's but as the time went by I got all engines from all mentionable tuners on my own dyno and I can tell you by 100% safety the strongest one was the engine of my first ever race engine customer European Champion Mr. Julius Ilmberger who delivered an engine to me prepared from the works tuning guru Mr. Otto Lantenhammer in Munich. After I was overtaking him with my bike on a straight at Dahlemer Binz which was a famous airfield race that times he came to me saying: whoever was building the engine in your bike will build engines for me from now on.
This Lantenhammer engine has already a 100 mm bore and an output of 92 HP - all others where below that figure...!
Ok we did longer conrods, other pistons, new heads with std. port angle instead of the straight ones an other cam and generated close to 110 HP with 45 mm
Bing slide carbs. Julius Ilmberger and his team mate where then classic bears champions using Edelweiss Motorsport engines and parts.
The longer conrod has a great influence because it makes the piston stay longer at TDC and when it is there it is part of the porting.
So as a side hint: try to understand the system and make your piston dome flowing....
However the longer conrod is also supporting the exhaust side and was at one time resulting me to develop and use asymmetrical cams.
Try to think around the next corner and you will see quite clear that conrod length has to fit the squish.
Carl - thanks for the tip !!! now try to find Sade Adu on youtube singing charish the day on her lovers life tour 2001...what grace and beauty combined with a package of coolness and sex, wow this is breathtaking !
Alternative from Sweden and a total different direction - band junip - song: line of fire
Keep on rocking in a free world....yours,
Edelweiss-Motorsport screwed with this post 02-24-2013 at 08:01 AM