Race prepped opposed twin build thread

[RED-Z06 2,118]

40 minutes ago, Pullstart said:

 

Is that a gasoline calculation?  Diesel must be a much different animal..

Diesel is tested the same, generally making high torque at a low rpm and falling off as rpms increase...with hp and torque crossing at 5252rpms.

[Snoopy11 5,713]

1 hour ago, Pullstart said:

Is that a gasoline calculation?

 

AND I repeat... Emphasis added: (approximate)... certainly not (accurate)...

 

Don

[Wheelhorse#1 1,445]

I had a dream my WH had headers and a turbo charger ,then I woke up😆

This ought to be good !

[Snoopy11 5,713]

5 minutes ago, Wheelhorse#1 said:

turbo charger

Easier to use a AMR500 supercharger... (it is v-belt driven...)

 

Just got to find a way to get enough fuel in it...

 

Don

[WheelhorseBob 1,548]

Subscribed!

[Greentored 3,201]

Now things are getting even sillier. Before the V twins, opposed twins were a hot item with the roundy round racers, but heres the problem- racers spend countless hours trying to squeeze an edge on their competition, and they're not going to share those secrets. Ive even tried to squeeze some info out of folks since its not a common class anymore, with very little help.

Time to figure it out myself- I built a flow bench.  Yes its simple and crude, and I cant calculate an actual number- but it IS repeatable, and will tell me whether I gained or lost airflow, a rough idea how much, and at what valve lift I see those changes.

Starting with an old, bone stock block and a couple hours of tinkering, I've already found some interesting things on the intake side:

1. the stock port 'stalls' at just .200 valve lift (no additional air flow no matter how high I open the valve)

2. some very mild port cleanup helps, but not as much as expected

3. 'laying back' the eyebrow helps very little, but fully relieving the area between the valve and cylinder does- about as much as the light port cleanup

4. Cutting a 45 degree angle on the valve seat below the 30 degree factory seat angle, and back cutting the valve in the same spot makes a BIG difference up to .150 lift- actually three times more gain that either porting or relieving. Low lift gains are what will start that cylinder filling quickly, and that makes torque!

5. Folks talk about NOT milling oppy heads- it squeezes the 'transfer' area between the head and block and the loss of air flow hurts more than the gains in compression. In 100% stock form, removing the head gasket (mimicking a .045 head milling) indeed hurt max lift air flow a bit, but once all the other work was done, it made zero difference.

At this point, I am seeing air flow gains across the board, and no more port 'stall' at .200, although the increase in flow beyond .200 are slow, steady climbs. 

Stay tuned, the next round I will be getting into much more serious work using real porting tools instead of all I had on hand at the time- a round file

 

[ebinmaine 63,114]

VERY cool stuff Scott. Thanks for taking the time to write it out and post publicly.

 

Keeping in mind that I'm not familiar with the physical aspects of the shape of the block or head on singles or flat twins...

Why do you suppose there's a lack of airflow after shaving the head? Are the combustion chambers that much different in shape?

 

[Greentored 3,201]

The flattys are actually a terrible, inefficient design, and is exactly why an OHV engine came about and makes so much more power. I found this drawing on the interwebs and circled the transfer area. When milling a head, this area gets smaller, and restricts the air flow.  The 'air flow vs compression' argument is as strong as an oil debate, but overall it does seem like the guys building high rpm screamers argue airflow, while low rpm workers argue compression. There is definitely a balance and tradeoff.

[ebinmaine 63,114]

4 minutes ago, Greentored said:

it does seem like the guys building high rpm screamers argue airflow, while low rpm workers argue compression. There is definitely a balance and tradeoff

Understandable. 

 

So given that I'll be looking for more torque grunt from a single flathead K341...

 

If I mill a head to get more squeeze should I also consider enlarging the flow area?

[Greentored 3,201]

41 minutes ago, ebinmaine said:

Understandable. 

 

So given that I'll be looking for more torque grunt from a single flathead K341...

 

If I mill a head to get more squeeze should I also consider enlarging the flow area?

Thinking this airflow thing may not be as critical on the big Kohlers. Heck, the pullers been milling the snot out of them for years, they cant ALL be wrong

I have a K241 block and a couple old K heads, gonna make an adapter and try those too.

Think the way I did the head on Hoss might be the ticket- mill the snot out of it and open up the area around the valves.

[Snoopy11 5,713]

5 hours ago, Greentored said:

Ive even tried to squeeze some info out of folks since its not a common class anymore, with very little help

Have... you called ARC?

 

AND... have you thought about going with an E-turbo for more ooomph?

 

Don

[RED-Z06 2,118]

10 hours ago, Greentored said:

The flattys are actually a terrible, inefficient design, and is exactly why an OHV engine came about and makes so much more power. I found this drawing on the interwebs and circled the transfer area. When milling a head, this area gets smaller, and restricts the air flow.  The 'air flow vs compression' argument is as strong as an oil debate, but overall it does seem like the guys building high rpm screamers argue airflow, while low rpm workers argue compression. There is definitely a balance and tradeoff.

You can also clearance the brow between the cylinder and valves down  to just above the compression ring, costs a bit of chamber volume but you do gain flow.  

[Snoopy11 5,713]

6 minutes ago, RED-Z06 said:

costs a bit of chamber volume

Wouldn't be worth it then... would it? That would actually decrease power...?

 

Don

[ebinmaine 63,114]

Just now, Snoopy11 said:

Wouldn't be worth it then... would it? That would actually decrease power...?

 

Don

Not necessarily. 

In every engine there's a line to be drawn between getting squeezed and moving the air.  

 

[Snoopy11 5,713]

1 minute ago, ebinmaine said:

Not necessarily. 

In every engine there's a line to be drawn between getting squeezed and moving the air.  

 

I'm not much into the grinding stuff... just not my thing. I certainly am not opposed to getting more educated about it... but I can make more than enough power in other ways...

 

Don

[RED-Z06 2,118]

3 minutes ago, Snoopy11 said:

Wouldn't be worth it then... would it? That would actually decrease power...?

 

Don

Depends on how its built, the ability to draw in more air can result in higher dynamic compression

[Snoopy11 5,713]

Just now, RED-Z06 said:

Depends on how its built, the ability to draw in more air can result in higher dynamic compression

I find it easier to "push" air in...

 

Don

[ebinmaine 63,114]

Just now, Snoopy11 said:

I find it easier to "push" air in...

 

Don

I can understand the logic there. 

I find the challenges of creating a normally aspirated engine fascinating.  

 

Of course there's always a nice big giant roots type supercharger too.  

Nothing quite like a 6 foot tall engine too say "power". 

[Snoopy11 5,713]

1 minute ago, ebinmaine said:

I can understand the logic there. 

I find the challenges of creating a normally aspirated engine fascinating.  

 

Of course there's always a nice big giant roots type supercharger too.  

Nothing quite like a 6 foot tall engine too say "power". 

Absolutely!

 

My 457 is N/A... and while I could go the route of forced induction... quite easily... the power of N/A is MORE than sufficient.

 

Don

[RED-Z06 2,118]

The bottom line is...air in..air out, the more air you can get in, the more fuel you can add, results in a more violent explosion, you can supplement an inefficient engine by bumping compression but you creep up on the detonation line which is where you pass the point of no longer gaining anything..and power plummets.

 

You can add an oxygenizer like Nitrous, its not flammable but under combustion the 2 oxygen molecules break apart from NO² to NO and O, this free oxygen molecule allows you to add more fuel without going rich...instant dynamic compression boost.

 

Or you can add air under pressure with a supercharger or turbocharger, this forces more air in which allows you to add fuel.

[Snoopy11 5,713]

1 minute ago, RED-Z06 said:

The bottom line is...air in..air out, the more air you can get in, the more fuel you can add, results in a more violent explosion, you can supplement an inefficient engine by bumping compression but you creep up on the detonation line which is where you pass the point of no longer gaining anything..and power plummets.

 

You can add an oxygenizer like Nitrous, its not flammable but under combustion the 2 oxygen molecules break apart from NO² to NO and O, this free oxygen molecule allows you to add more fuel without going rich...instant dynamic compression boost.

 

Or you can add air under pressure with a supercharger or turbocharger, this forces more air in which allows you to add fuel.

I have a tiny bit of experience with methanol... which changes that fuel/air mixture... definitely helps make more power. Just a... pretty expensive way of doing it...

 

Don

[RED-Z06 2,118]

Boosting is cool.  My car makes 425 at the crank, 385 at the tires, runs the standing 1/4 in 11.9@127, i could strap a bottle in...a button, some lines and a solenoid...and spray my way into a 10.9 pass easily...never hurt an LS with a 125 shot...

 

But...why risk it

[RED-Z06 2,118]

1 minute ago, Snoopy11 said:

I have a tiny bit of experience with methanol... which changes that fuel/air mixture... definitely helps make more power. Just a... pretty expensive way of doing it...

 

Don

You can do it that way too...you just need a ton of fuel and the stuff hates to sit.  Ran it in a built open mod gx200 Honda, 24hrs ruined the fuel system because we didnt flush it...never seen such a mess.

[Snoopy11 5,713]

2 minutes ago, RED-Z06 said:

Boosting is cool.  My car makes 425 at the crank, 385 at the tires, runs the standing 1/4 in 11.9@127, i could strap a bottle in...a button, some lines and a solenoid...and spray my way into a 10.9 pass easily...never hurt an LS with a 125 shot...

 

But...why risk it

The difference with the automotive world is... you have to know what the flip you are doing... tuning-wise.

 

Any grease monkey can throw boost around... but can you make it run with boost over a long term... reliably.

 

Small engines... you do testing and mostly go by ear, along with temperatures.

 

Don

[RED-Z06 2,118]

1 minute ago, Snoopy11 said:

The difference with the automotive world is... you have to know what the flip you are doing... tuning-wise.

 

Any grease monkey can throw boost around... but can you make it run with boost over a long term... reliably.

 

Small engines... you do testing and mostly go by ear, along with temperatures.

 

Don

You just keep adding timing and boost until the piston crown comes out the breather...then you know, 1⁰ less timing and 1psi less boost.