Squish and rpm

[theKbStockpiler]

The Squish Effect ,squeezes the air/fuel mixture at TDC and pushes it out to the center of the cylinder. This mixes the air with the fuel. Race cars don't need this because at high RPMs the air/fuel is mixed good enough from the velocity of the air/fuel.
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[volksnhousin]

My thoughts: If you are ok with how it is currently, don't change a thing. If you want a change, use the smaller deck and a mild performance cam.

As mentioned, doing the performance cam and smaller deck together probably is the way to go. Just doing one thing or the other will make it not as good.

Search “dynamic compression” on the internet. A bigger cam “bleeds” off compression pressure. You can adjust the compression you run at with a cam... You won't need to carve up your chambers and pistons as much if you use the right performance cam with your smaller deck.

[dawie]

Also keep in mind that, being in the UK, octane rating of fuel is much higher.
Lowest octane standard fuel 95ron- (91 US?), and super around 98ron. So compression ratio can be higher.

Knock sensitivity depends on chamber efficiency/squish as well. Tight squish can be critical, especially with that large bore.

Web 73 will tolerate higher compression.

Ideally, twin plugs should allow another point of compression, be more fuel efficient, and run cooler.

[Zed999]

[nextgen]

Zed,
You mentioned you wish you found this NG sooner. Recently I have been getting more inquires from Denmark, Germany, Israel, Sardinia, UK and Malta - - not only for Upright conversion but just T-4 questions in general. Was there any Magazine articles. Or are the prices of buses skyrocketing over there, like here in the U.S. and maybe guys are thinking fixing one up is money in the bank ???
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[mark tucker]

[theKbStockpiler]

I thought that all of the open chamber/hemi designs took the squish area out in favor of high RPM flow.

For a second,marc , I almost used my spell checker.
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My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[Zed999]

[Alstrup]

The reason that "I" would never build a big bore bus engine is that it - is - a recipe for disaster in the long run. Big bore cylinders just cannot keep sealed against the heads over time. Super low CR do help and choking the engine so that it can´t make more than X power helps too.
"our" 2165 bus engine pulls better torque and better hp than that 2,4, and will last about 100.000 km. before it needs any significant service. It is also somewhat more expensive to build.

With squish.
- In your case I suspect that you have a serius amount of deck height to keep the static compression down. My quess is around 3,5 to 4 mm. If I´m right I´d say when you have the engine you have, keep the deck there. Reason is, with that much deck height the chamber in total reacts more like a hemi head than a conventional squish type head. This means that the engine most likely wants something like 35-36 degrees BTDC to pull good and make - reasonably - decent numbers out of the exhaust.
Again, if I´m right then what you want is a very good and fat spark so that you can get the burn started and get the flame propagandation accellerated as fast as possible to get a complet burn soon enough to exploit it before the piston is too far down the powerstroke.
apart from upgrtading the ignition there is one thing I would definitely do too, and that was to replace thstock muffler with a freer flowing unit. VS has some nice ones for the type 2/4 bus. Turbo Thomas has too I think. By doing that you take some heat out of the cylinderheads when the engine is working hard and you release a few ponies too in terms of less restriction in the muffler.

If you decide to do this be aware that you need to rejet as this will make some change in the burn and breathing capacity.

WRT your comment on type one´s not capable of doing 70 mph all day in a loaded bus. - Well, sounds like you need to do a reality check. Even our 100 hp 1835 thickwall Kadron carbed engine or the 100 hp 1955 cc. std plus engine will do that with ease, and they will most likely still outlast a big bore type 4
Wrt longlivety. A 120ish hp 2110 or 2165 type 4 powerstroke bus engine is about the best you can build if you want some good power and want a lot of trouble free miles. These engines do pretty good with fuel efficiency too. About 25 - 26 mpg (US) on 65 mph cruise is quite common in Westfalia Bay window busses

T

[Zed999]

Thanks Alstrup.
Well yes, it might need rebuilding but rebuilding doesn't phase me too much, I'm looking at doing so after 12,000 miles just for the fun of changing it a bit after all.

But those pistons and cylinders are large and I take your point about sealing. It does occur to me that most people with these kind od CC's are most likely to be in persuit of lots of power so maybe yes there are big problems for them that my mild-for-it's-size engine would have more chance of escaping? I don't have a problem so far is all I can say. Maybe the wise thing to do to it would be nothing at all.

Thanks for the large deck/hemi analogy, that's very interesting. If I give it more than 29degs it pinks under severe load, by which I mean a hill it will barely accelerate up, hard to find but there's one I use 10 miles away for testing. It's steep! Someone random came up to me in a car park earlier in the year and said "I followed you up Parbold hill a few weeks ago in my car. I couldn't keep up. That must be some engine in their, well done!". Very British. Lol

Hmm. Maybe I really should just leave it, it does what I want really, maybe I'm just itching to do something "engine". It's been a few years and it's an enjoyable hobby.

[mark tucker]

no they didnt mr plier, many/most hemis do have squish areas.and many have pistons that acheve this. squish does not have to be in a flat serface of the chamber like on vw's.

[theKbStockpiler]

I got it!
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My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[bugguy1967]

Already mentioned this. Squish the damn thing, and stop asking over and over again. Are you just looking for the answer you want to hear?
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[jeffrey8164]

Forgive my ignorance but, what in the world is squish?

[nsracing]

Power falls off after 4K rpm? what is that a diesel?

That is one lazy motor if it is gas. Depends what octane fuels available you can put in the tank to decide how much compression you can run. If all you got is 87 octane available, raising the CR is not the way to go.

Here in the USA 91 octane is about the highest in some states. 93 octane in my area but go out of the way some and it is 91 oct...that can tolerate close to 9 to 1 but no more.

For a heavy bus, that can be tricky. I like stock bores 94mm max on busses. Increase stroke here and there but I like Mahle 94s. Anything bigger and it will be some kind of buggy.

[Danwvw]

"Jeffrey 8164" Somebody, I think it was one of these guys explained that to me once, It's kind of like what it sounds like. It's about that flat area outside the combustion chamber between the head and the piston at TDC. It needs to be so so not more. What 35 thousandths.

But all this aside, I remember reading an article about type 4 engines back 20 some years ago in one of the VW magazines. It talks about how they could not get the engines to rev above 4000 like the 914 Porsche engine could. Turns out they realized the Porsche combustion chamber was different and the spark plug location was different in the Porsche's head. So they relocated the VW plug and Walla it would rev...
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[bugguy1967]

[mark tucker]

it also helps cool the head&piston better as well as more compleate cleaner burn and a lot less unburnt residue in the chamber/on piston top , as well as reducing the chance of detonation/pree ignition.

[Type 5 Joe]

If your going to re-use your cylinders... Remove barrel spacers or have them machined.

Be aware that the top ring may have started establishing a step (ridge).

That will have to be carefully inspected and possibly honed out. Either that or replace the cylinders if its excessive.

The compression ring seal is most important at this location. Not where you want to have an inconsistent surface / finish.
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[Zed999]