Race prepped opposed twin build thread

[RED-Z06 2,118]

The big challenge for L Heads is the constant battle between compression and airflow.

[Snoopy11 5,713]

What width head gaskets are you planning on running there, @Greentored...

 

That piston looks +++ zero deck...

 

 

Don

[ebinmaine 63,149]

@Greentored

Nice Starrett Tool there. 

I was born and raised in their hometown.  

[Snoopy11 5,713]

6 minutes ago, ebinmaine said:

@Greentored

Nice Starrett Tool there. 

I was born and raised in their hometown.  

I have a Proform deck bridge... but somehow... the dial indicator seems to get separated from the bridge... and I can't ever find either piece...

 

Don

[Jeff-C175 7,195]

It's BLEEDING!  ha ha ha

 

 

1 hour ago, Greentored said:

Pics are a pain for me to get from phone to computer to page

 

If you use Google Photos, within a few seconds the pics you take on your phone are already on the computer.  Then you can open them in Google Photos and use "Snipping Tool" on the computer to copy and paste into your posts,

(Assuming an Android phone, not sure if it works with others)

 

 

[Wheelhorse#1 1,445]

5 hours ago, Greentored said:

Guess I oughtta update more often eh?  Pics are a pain for me to get from phone to computer to page, reading is a pain on the phone ha. Anyhow.....

This project took a big turn when I acquired a junk 18hp block, built a simple flow bench (manometer for 'comparison') and started playing. Learned an awful lot by doing this and applied it to the big 20.5 block.

Here's some random photos from the last month or so.....

Hope you are all doing well!

 

 

 

Ok I’m new to the rebuilding thing….what am I looking at here.Assuming some type of cylinder test or someone cut off a finger ? 

Edited April 13, 2022 by Wheelhorse#1

[Greentored 3,201]

On 4/13/2022 at 2:27 PM, Snoopy11 said:

What width head gaskets are you planning on running there, @Greentored...

 

That piston looks +++ zero deck...

 

 

Don

Theyre up just a hair haha.  .022-.023 pop up, and running .063 copper gaskets

[Greentored 3,201]

On 4/13/2022 at 7:50 PM, Wheelhorse#1 said:

 

Ok I’m new to the rebuilding thing….what am I looking at here.Assuming some type of cylinder test or someone cut off a finger ? 

 

I got the paint cans out to 'see' where the 'fuel' was going. Pretty wild results!

Then I put the intake on and did it again and everything was completely different.  There is NO doubt the porting style would change drastically depending on what intake someone might run.

Edited May 3, 2022 by Greentored

[Greentored 3,201]

On 4/13/2022 at 2:16 PM, RED-Z06 said:

The big challenge for L Heads is the constant battle between compression and airflow.

I did a TON of experimenting and flowing in this area, from no head gasket and 42ci head, to 4 gaskets and 46ci head, then did it all over again after working the ports. I found a 42ci head and no gasket definitely hurt, and adding more than 2 gaskets to a 42ci head or 1 to a 46ci head netted minimal gains.

A few things come to mind here though: 

1. Who knows how 'fast' my shop vac is moving air and at what RPM is the engine at which matches it?

2. Pullers almost always mill their heads and dont talk much about flow. They want big grunt.

3. Roundy round guys seem to concentrate on flow and dont worry much about compression. They want it off the corners and pulling hard at high rpm.

The big question is, at what RPM does that flow vs compression tradeoff 'kick in'?  I found an old ford flatty article where they dyno'd 7-8-9:1. The higher the compression the more power up to about 4500, above that the lower compression ones ran stronger. Strangely, the worst overall performer was the 9:1 engine.

In my case, we spend 90% of our time from off idle-3000 or so, and the other 10% screaming the guts out of em on a mud run or hill bomb- Im erring a bit on the side of compression and not too worried if I lose a bit at 6 grand.  Does that make sense?

[RED-Z06 2,118]

You would want higher compression to offset a more aggressive cam grind, simply adding static compression nets little in a workable powerband, but going with more lift and duration can bleed off dynamic compression...but it moves your power band.

 

Its like modding a chainsaw..you can pull the gasket..compression jumps 10 points, it feels snappier but you've cost yourself high end power, change the port timing just a few degrees and you've drastically changed the demeanor of the saw.

Edited May 3, 2022 by RED-Z06

[Snoopy11 5,713]

36 minutes ago, Greentored said:

Im erring a bit on the side of compression and not too worried if I lose a bit at 6 grand

The meager amounts that you will lose at 6 grand will not be noticeable to you, in my opinion. When you say minimal gains, you hit the nail on the head.

 

39 minutes ago, Greentored said:

Pullers almost always mill their heads and dont talk much about flow. They want big grunt.

Roundy round guys seem to concentrate on flow and dont worry much about compression. They want it off the corners and pulling hard at high rpm.

Here is the conclusion that I have come to. I run up to 8,500 with my Tillotson 212R that I recently built. I run 7,650 (could run more, but choose not to) on my Duromax 457. I have various other examples, but what I have found with them is:

 

What is going to benefit you more than anything else here when you talk about pulling hard at high rpm is getting a cam with more lift and duration for that rpm. I look at it in a plain sense. The most good that you are going to get out of this engine is in how well you can pull air in, and push air out...

 

Basically, you have improved airflow through the engine, which is good, butchya gotta get those valves pumpin'

 

Don

[Snoopy11 5,713]

1 hour ago, Greentored said:

Theyre up just a hair haha

Yessir... that is what I noticed!

 

Definitely don't want any... eh... impacts... at RPM...

 

Don

[Snoopy11 5,713]

7 minutes ago, RED-Z06 said:

aggressive cam grind... going with more lift and duration

RZ beat me to it...

 

Don

[Snoopy11 5,713]

One other thing that might go under the radar, but be sure to put a performance Autolite racing spark plugs in this engine... those really do make a difference at all rpm levels.

 

 

What are your plans for exhaust/air filter there @Greentored?

 

Don

[Greentored 3,201]

23 hours ago, Snoopy11 said:

 

 

 

What are your plans for exhaust/air filter there @Greentored?

 

Don

same 2:1 header I run on the current one, as well as the cleaned up 2 piece oem aluminum intake and the 27hp Kohler carb.

[Greentored 3,201]

Cam in this is a Precision 212alt, bumped one tooth- should move plenty of air and still be rock solid dependable.

[Thor27 720]

On 4/13/2022 at 11:16 AM, RED-Z06 said:

The big challenge for L Heads is the constant battle between compression and airflow.

Just spit ballin here, but I think lsa the cam is ground on would make a world of difference compared to just lift and duration, maybe even more so on a L head with no piston to valve clearance issues.. Overlap for scavenging at desired rpm range is useful to fill cylinders, especially with marginal head flow.  

 

 

[ebinmaine 63,149]

14 hours ago, Thor27 said:

Just spit ballin here, but I think lsa the cam is ground on would make a world of difference compared to just lift and duration, maybe even more so on a L head with no piston to valve clearance issues.. Overlap for scavenging at desired rpm range is useful to fill cylinders, especially with marginal head flow.  

 

 

 

Interesting point.

So for lower RPM like 2000, 3500, are we talking about a tighter LSA?

[Thor27 720]

To a point, It tends to lower the rpm of where peak horsepower is made, but also tends to raise where torque peak is and makes for a narrower concentrated power band. Moves peaks of tq/hp closer together, and makes a less efficient idle. 

 

I don't know, the cams for these are ground to start with, may be a tight lsa?  I am only familiar with carburated v8s, so apples to oranges is the basis for my incoherent ramblings. 

 

Anyhow, @greentored, I'm enjoying your build and looking forward to where it goes.

[ebinmaine 63,149]

34 minutes ago, Thor27 said:

incoherent ramblings. 

 

 

 

A sentiment I can will relate to there. 

Bench Dyno has always been interesting to me so it's fun to see what some of the answers are here back and forth. 

[RED-Z06 2,118]

I used to have a jig for twisting cams for briggs 5hp, Tecumseh Star (hm80).  Pretty cool setup, it firmly supported the cam journals so they stayed in line, then it had a wheel you put on the gear, and it locked the gear in place...and had these levers you put on the lobes...there was a center shaft support.  You used this ring torch to heat the part of the cam you wanted to alter, then used the levers to apply force.  You could go a few degrees in overall advance or retard then a few degrees on each lobe.  Never had to use it because the aftermarket had custom grinds by that time but it was a very cool piece of hardware

[ebinmaine 63,149]

1 minute ago, RED-Z06 said:

aftermarket

Is there such a thing as a readily available high torque grind for something like an older Kohler single engine ?

[Snoopy11 5,713]

42 minutes ago, ebinmaine said:

Is there such a thing as a readily available high torque grind for something like an older Kohler single engine

"Readily available"

 

My answer would be emphatically NO.

 

BUT... you can send your cam to the Dyno Cams small engine shop, and they could hook you up and give you lash specs based on science.

 

Don

[RED-Z06 2,118]

55 minutes ago, ebinmaine said:

Is there such a thing as a readily available high torque grind for something like an older Kohler single engine ?

Isky used to do custom grinds, I doubt they still do.  The market has changed.  12 to 15 years ago, your hopped up engines were..

 

5hp briggs/Blockzilla

Briggs Animal ohv

8hp tecumseh star

Kohler CH6 XKE

Tecumseh powersports 6.5

Honda gx200 small and gx390 big block

Kohler Command V Twin

Briggs vanguard v twin

Kohler K series (for pulling).

 

There was decent support for all...

 

But now...many of the hop up parts have dried up, the chinese engines are cheap to get into and usually run well enough to have fun before some quality control issues arise.  The big go-to name for K/M kohler was Kirk Engines but last i looked their offerings were 1/3 what it was years ago

[RED-Z06 2,118]

1 hour ago, ebinmaine said:

Is there such a thing as a readily available high torque grind for something like an older Kohler single engine ?

Might contact Vogel maybe they will know of someone 

 

https://vogelmanufacturing.com/garden-tractor.html?p=2