Team Go Dog, Go! Modified Partial Streamliners

[wobblywalrus]

Dennis, you have valid concerns.  Here is what and why I did what I did.  This might be useful for others to see.

There is a formula for the intake flow in cubic feet per minute that is needed at 28 inches H2O test pressure to produce a given horsepower as follows:  Q = intake flow at 28 inches in cubic feet per minute, HP = engine horsepower, n = number of cylinders, and Q= HP / (.26 x n)

I need at least 110 HP out of a 2 cylinder engine.  Q = 110 / (.26 x 2) = 211 cubic feet per minute

The intake flow test curve is shown.  Note at lifts up to 0.25 inches the curve is a sorta straight line.  The straight line, if extended, will give me well over 211 CFM at the over 0.40 inch lifts my new cams will have.  This indicates the valve curtain areas are OK and I do not need bigger valves.  Note how the curve flattens out.  This shows I am getting choke at lifts over 0.25 inches.  The valve curtains are getting larger and the port is not able to supply the curtains with enough flow.

Examination of the combustion chamber shows areas where the walls curve in toward the intake valve head margins at lifts over 0.25 inches.  This certainly does not help flow.  One of these areas is shown by green fingernail polish near an intake valve.  A similar situation occurs near the exhaust valves.

The metal removal is only a small amount.  Installing larger valves and seats will require cutting the chamber walls one millimeter deeper in the green areas.  This will be quite a bit more metal removed and it will drastically lower the compression ratio.  It seems to make sense to do what I did and to stay with the valve sizes I have.  The head will be sent to Kibblewhite who made the valve train.  They will put it on their flow bench and try to reshape the ports to give more flow.  They will also check to verify that the new cams and valve train are compatible and they will renew or replace worn parts.

The intake flow test graph shows that I do not need much more flow.  These little changes should get me what I require with out undesirable consequences or great expense.  The exhaust flows look OK.       

[wobblywalrus]

Dennis, you have valid concerns.  Here is what and why I did what I did.  This might be useful for others to see.

There is a formula for the intake flow in cubic feet per minute that is needed at 28 inches H2O test pressure to produce a given horsepower as follows:  Q = intake flow at 28 inches in cubic feet per minute, HP = engine horsepower, n = number of cylinders, and Q= HP / (.26 x n)

I need at least 110 HP out of a 2 cylinder engine.  Q = 110 / (.26 x 2) = 211 cubic feet per minute

The intake flow test curve is shown.  Note at lifts up to 0.25 inches the curve is a sorta straight line.  The straight line, if extended, will give me well over 211 CFM at the over 0.40 inch lifts my new cams will have.  This indicates the valve curtain areas are OK and I do not need bigger valves.  Note how the curve flattens out.  This shows I am getting choke at lifts over 0.25 inches.  The valve curtains are getting larger and the port is not able to supply the curtains with enough flow.

Examination of the combustion chamber shows areas where the walls curve in toward the intake valve head margins at lifts over 0.25 inches.  This certainly does not help flow.  One of these areas is shown by green fingernail polish near an intake valve.  A similar situation occurs near the exhaust valves.

The metal removal is only a small amount.  Installing larger valves and seats will require cutting the chamber walls one millimeter deeper in the green areas.  This will be quite a bit more metal removed and it will drastically lower the compression ratio.  It seems to make sense to do what I did and to stay with the valve sizes I have.  The head will be sent to Kibblewhite who made the valve train.  They will put it on their flow bench and try to reshape the ports to give more flow.  They will also check to verify that the new cams and valve train are compatible and they will renew or replace worn parts.

The intake flow test graph shows that I do not need much more flow.  These little changes should get me what I require with out undesirable consequences or great expense.  The exhaust flows look OK.       

[Old Scrambler]

Thanks for lesson...........I need to start a file on some of this 'stuff'

I'm guessing that Kibblewhite will remove some serious metal in the roof of the ports and possibly 'D'-shape the floor at the curve.

Tom Mellor has stated that his triple has 100-HP and he has gone 200-MPH   Besides obvious power in his motor, I think the 180-200 mph gap is helped by his ram-air system and his streamlining........his chin is almost touching his low-profile tank

I'm trying to get past 150-MPH with about 80-HP at the rear wheel.........and no streamlining.............I must be dreaming

[wobblywalrus]

This post will be in three parts.  I am having a hard time connecting to landracing.com.  It is an issue here 'cause it happens on other websites, too.

Dennis, the fellow at Kibblewhite said it is hard to promise anything definite about a head the at has been ported before.  He said with some work he usually finds a way to improve things.

Mr Mellor isn't the biggest guy on the salt, has a good tuck, and is a skilled rider.  That combined with a bike having a good shape and a small frontal area gives him speeds the rest of us dream about.

The British author and racer, Alan Cathcart, set an FIM record on a Hinckley Thruxton at over 150 mph.  It was a naked modified bike.  His ass was about 3 or 4 inches off of the seat, his head down, and his back level.  The engine is like mine and it likely made 100 HP and not a lot more.

   

[wobblywalrus]

Static compression ratio is calculated by the formula Ratio = (Vcc + DISP) / Vcc  where Vcc = combustion chamber volume and DISP = displacement based on bore and stroke.  The pistons come in a box that says 13:1 compression.  This is based on a standard cylinder head.  Mine has 2mm larger intake valves that were installed a few years ago.  The machining to install the seats removed enough metal to drop the compression 1 point.  The 13:1 pistons are expected to be 12:1.  This is before the metal was removed to prevent shrouding.

The compression ratio formula can be rearranged to give the combustion chamber volume as follows:  Vcc = DISP / (Ratio - 1)  Using a cylinder with DISP = 497.5cc and Ratio = 12, Vcc = 497.5 / (12 - 1) = 45.2 cc

No more than 1cc was removed from each chamber to eliminate the shrouding.  The new Vcc = 45.2 + 1.0 = 46.2 cc.  The new static compression ratio is (46.2 + 497.5) / 46.2 = 11.77:1  This makes it clear why I do not want bigger valves.  A small amount of metal removal makes a substantial drop in compression.  The much larger amount removed to put in bigger valves and seats will drop the compression ratio too much.

Vizard's chart says there is a 1.3 percent power difference between 11:1 and 12:1 static compression.  Using bonehead algebra, the power loss for a 110 engine HP motor running 11.77:1 compression is:  110 x .013 (12 - 11.77) = .33 horsepower.

The power loss due to the drop in compression from removing the shrouding is .33 engine horsepower.       

[wobblywalrus]

The shrouding removal combined with reshaping the ports is estimated to give 15 CFM, more or less.  The new flow is estimated to be 225 CFM at 28 inches of water.  Using the formula presented a few posts prior, the 210 CFM flow supports .26 x 210 x 2 = 109 HP

A flow of 225 CFM supports .26 x 225 x 2 = 117 HP  This is 8 more horsepower.  It appears I am giving up .33 of compression horsepower to gain eight potential flow horsepower.

It is doubtful the motor will have a full 117 engine horsepower.  The flow will be available to do this and it will not be a limiting factor.   

[revolutionary]

As someone who ported heads for a living for many years, I would like to drop a few hints, though your results may vary:

1. When you are flow testing you MUST place a cylinder where the engine bore is. I have seen the flow numbers by 10% just by shifting the location of that bore by .100". How close the valve is to the cylinder wall makes a big difference and you are not reading this part of the story

2. Don't go withany bigger valves than you have now. Using flat face valves as sugged earlier is a great way to pick up some compression

3. It is very important to bull nose the divider on the intake side and you can knife edge the divider on the exhaust side.  Make both sides of the divider as identical as possible

4. knocking down the guide boss can make a huge difference in flow on those heads. Get ready to be swapping out guides pretty regularly though as they will wear out quicker with less lateral support of the valves.

5. your chamber work looks good and there is not a whole lot more you can do other than smoothing all edges

6. figure out a way to add more compression back. it is not just about squeezing it tighter, when you are on the intake stroke, the pressure differential is greater with higher compression and it wants to pull more air through. At Bonneville you need all the air you can get.  I'd be happy with 15:1 but I know it is really tough with small 4v heads to get there.  The best way to get there is to dyno the engine, move the cams where they make the best power, then go back and make a chamber mold of the head and get custom pistons made with the valve notches cut for minimal clearance.

7. drink a beer, it always helps.

[fredvance]

I have wondered why you do not go with much more compression. In our 1350 we run 16-1. Since it is a 4 cylinder that is 337cc per cylinder. I am not a math guy but I have been told that you lose 1/2 point of compression for every 1000ft of altitude. So at Bonneville you will lose a little more than 2 points. So my 16-1 becomes 14-1.

[wobblywalrus]

This post will be made in two parts.  I have a hard time maintaining an internet connection for any length of time or to send large posts.

The 995cc engine has big bores in comparison to the combustion chamber.  They are over 10mm wider than the standard 790cc bores.  I am not worried about cylinder wall shrouding.  Flat faced intake valves are used and the deck to head and piston crown to head clearances are at minimum. 

[wobblywalrus]

This piston is 13:1 with a standard combustion chamber and 11.8:1, estimated, with the ones on my head.  Note the tall crown.  I did not want to go any higher so as to not interrupt the flame front during combustion.  This limited the CR.

The valve pockets are cut for 5mm larger intake and exhaust valves.  That is the typical design for these.  The compression ratio could be raised higher than I have now if I would have ordered them with standard size exhaust valve cutouts and 2mm larger intake valve pockets.  Unfortunately, I ordered a lifetime supply of pistons and have four of them and all are setup for big valves.   

[Old Scrambler]

The flat-faced valves will help..............can you reduce or eliminate the base gasket?  I found that advancing the ignition timing helps to overcome piston-crown blockage of the flame. You could also play with cam-timing.  With that amount of over-bore are you sure your getting enough air through the carbs at peak rpms?

[wobblywalrus]

The Keihin 39mm FCR carbs are marginal, sizewise.  A custom Triumph Bonneville built in Germany has a pair of 41 mm FCR's on it.  I am trying to contact the owner and get details.  The purchase is justified if I can adapt the 41mm mixers to blow-through mode for the turbo motor.   

[wobblywalrus]

On the subject of valves, there are some other calculations I did to decide to stay with the smaller valves.  There is a mach index calculator at www.rbracing-rsr.com/machcalc.html

The data for the 2mm oversize intake valves I have was entered along with an 8,400 rpm engine speed.  The mach index is .454.  That is low enough.  The valves I have are OK as per mach.

RB racing and others recommend an exhaust flow of 65 to 80 percent of the intake flow.  The exhaust valve flow is 186.6 cfm at .45 lift.  (186.6 / 80) x 100 = 233 cfm  (186.6 / 65) x 100 = 287 cfs  The exhaust valves will support 233 to 287 cfm of intake flow.

The intake flow is 210 cfm now and I might get 220 to 230 with the port work.  The exhaust valves flow plenty good.  No changes needed there. 

[wobblywalrus]

More calculations.  These are to figger out the target horsepower for the engine.  The first step is to estimate the engine RPM for the three 2104 runs.  A few glances at the tach during the timed mile tell me the engine rpm is around 7300 during the first run.  That works out to 5% wheelspin.  The pits were covered with standing water that year and the track was not very dry.  The 5% spin seems to be reasonable given the conditions.  The speeds and rpm's are listed on the chart, as follows: Run 1 is 146.45 mph at 7,300 rpm, Run 2 is 141.95 mph at 6,880 rpm, and Run 3 is 143.82 mph at 7,580 rpm.  All assume 5% wheelspin.

[Koncretekid]

Bo,
I really appreciate the attention to detail and the sharing of your build with us. I think you and I are on the same page when it comes to improving our bikes - - one step at a time and hope for best results.  I recently read two books about Burt Munro (should be required reading for those of us building special bikes) and I found out that if you compared his speed year after year, from about 1950 when he decided to dedicate the rest of his life to the "Gods of Speed" to 1972, you find that his average annual speed increase was only something like 5 mph per year.  There appears to be no magic pill to make it happen sooner.

If I can follow in his footsteps, I should be able to hit 200 mph by the time I'm 78!

As for horsepower to speed relationship, I used my existing results to program a spreadsheet based upon the rule of cubes - - that  with a known bike (coefficient of friction), you will need to cube the hp requirement for a linear increase in speed.  That is to double your speed for example, you will need 8 times as much hp.  It has proved very accurate so far.

I can probably email my spreadsheet (MS Excel) if you like.

As for solving the blow thru issue with carbs, If you figure it out, please let me know.  Not only do you have to deal with equalizing pressure in the bowl and at the vents, you have to increase fuel pressure equal to your boost.  And float valves seem to be very sensitive.

Tom