Squish and rpm

[Zed999]

I'm in the process of planning to reorganise my low revving 2.4l type-4 camper engine. It has a large deck and it would be a bit of a game to get it stock and retain it's stock cam CR.

The engine falls off a cliff at 4000rpm which is fine with me as it has bags of low rev torque. It has been suggested to me that the higher the revs, the more gain from squish and that at the revs my engine operates at I'd have to be very perceptive to notice a difference and would be better off turning a blind eye to the deck and simply changing the cam for one with more exhaust duration.

Any comments?

[nextgen]

Well, your reorganizing plan, is another way of you want to rebuild your engine.

Right off I will tell you, what ever your plan is forget keeping the stock cam.


Right off it should be removed due to being inefficient and has a history of wearing out .

On my 914 which was a 1.7 I used the stock heads, made the engine a 2.0. stock stroke. Also added a cam. Amazing difference.

Your bus is a stock 2.0 you have 71mm stroke stock. You are already ahead in the game in the torque dept.. Get advise what cam to use.
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[sled]

[theKbStockpiler]

Squish is all about low RPMs.
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[Zed999]

Nextgen : It's 2.4l - 104 x 71

Generally, well the cam is original and hasn't worn in 40 years but yes I accept that I should have changed it when the motor was built.

Changing just the cam would be very quick and easy and it's an attractive proposition.

Changing just the deck to restore squish would be cheap but take more organising. The attraction is leaving the bottom end in one piece.

I hope to gather info to help me make up my mind. I now have one chap who has done a LOT of experimental racing mods to a/c VW engines saying squish is more and more important as revs rise and Stockpiler saying exactly the opposite!

I'm not short of torque, 180ft/lbs at the flywheel. It's a camper, I'd like the engine stay mild and low revving for touring and engine life. Stock 2l is done at 5,000rpm, my 2.4 is done at 4,000. That kind of makes sense. A bit of cam might take it back to 5,000rpm but the question still remains re revs/squish.

It's true that I would like to do as little as possible to the engine, I don't have the facilities for starters, don't have the budget and don't have any other vehicles which is why I'm trying to side step dealing with the deck height. Just changing the cam sounds like a lazy weekend even in a car park.

[Zed999]

[slalombuggy]

The reason your power falls off a cliff is because you have a great big lazy burn making it very inefficient. Closing up your deck will make your engine much more efficient, get you better mileage and probably run cooler since combustion will take place in the head, not in the tops of the cylinders.

What is going to make is so much work to change the deck height on your engine?

brad

[nextgen]

Zed, I agree with your builder 100% we are talking about, most likely the least aerodynamic vehicle on the planet.

Keep in mind when you change the cam you will be doing the rings also , most likely in a T-4 engine the bearing will be fine but in a bus you never know.

2.4 cam and heads, Don't worry about RPM's , It will last and the torque is the best feeling.

I have 71 mm stroke in my bug, Love it. I was told the 66mm revs faster but I don't know if the bug is faster, same engine.
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[Zed999]

[Zed999]

[slalombuggy]

I have a friend getting 27mpg with a 2.3 in a 2300kg Westphalia towing a small trailer.

brad

[Brian_e]

21mpg with that much low end, and no need to rev it isn't great.

.040" deck, 8.3+cr, and a Web 73 or 86 cam.

Just do it all, so then you know its correct instead of wondering "what if". It will it make a far more efficient, higher revving, cleaner burning, and easier to tune. The added throttle response and more power are added benefits.

It must have a pile of spacer right now to get the compression that low. Shouldn't be too tough to pull some out and get it closer. Dish the pistons before you go carving the heads out, especially the non-plug side.

Brian

[nextgen]

Zed had no idea you did that much to the engine. But Brian has some good numbers. Your builder sounds like he has a good background, so just run the numbers by him.

Here is a great post on T-4 Cam.

Alstrup is quite knowledgeable on T-4's Your side of the Pond.

https://www.thesamba.com/vw/forum/viewtopic.php?t=567668
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[Zed999]

[Zed999]

[Splitdog]

On my type-1 bug motor (turbo) I wanted at the most .060" DH. With a 7.1 CR, it necessitated a 78cc chamber. 68 in the heads, 10 in the pistons. There is no squish. Semi-hemi was the only way to get this much volume. Runs fantastic on or off boost.
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#notacallooker

[sled]

apparently no one who has chimed in as of yet on the benefits of a tight deck is to be believed? maybe waiting for one of the samba performance aficionados to chime in

here is a tidbit I pulled from an outside source but applies to our engines just the same, might clarify a couple things.

"The Squish Effect
Since wedge-style combustion chambers rely on the squish or quench area to create turbulence in the combustion chamber, an intriguing effect occurs in the combustion process. To better understand this process, imagine that the intake valve opens and a rush of air mixed with fuel enters the combustion chamber area. The piston comes screaming up toward TDC at 5,000 rpm (almost 3,000 feet per minute) as the intake valve closes. As the piston reaches TDC, a virtual hurricane of fuel and air is squished out into the chamber from this tight area between the piston and the head. While this turbulence sounds bad, the opposite is true. This turbulence has the effect of more thoroughly mixing the air and fuel into a much more homogenous mixture that tends to burn much more quickly and efficiently.
One way to produce maximum power from an engine is to use the least amount of fuel necessary to create maximum power while attempting to burn all of it. Given this, if you can evenly mix the air and fuel into a homogenous mixture with an extremely fine mist of fuel, you will make outstanding power.
Unfortunately, the opposite is also true—varying pockets of lean and rich mixtures within the cylinder when the spark plug fires will cost power and the combustion process will not be as smooth. Excessively lean or rich pockets within the chamber directly affect the rate of combustion and the amount of pressure applied to the piston. Rich mixtures tend to burn slower, while lean mixtures generally burn at a faster rate than a “proper” air-fuel mixture. If modifications to the chamber or piston affect these rates, the ignition timing will also need to be changed to optimize power.
What is the proper air/fuel mixture? In the last few years, the answer has been changing as the area between the combustion chamber and the top of the piston becomes more efficient. For example, the classic air/fuel ratio has always been 12.5:1, meaning 12.5 parts of air for every one part of fuel. But many race and properly designed street engines can make best power with air/fuel ratios now approaching 12.8 to 13:1.
So now let’s introduce a tighter quench space into this equation. All of the respected engine builders who we’ve talked to are firm believers in minimizing the quench clearance. According to Ken Duttweiler, the tightest quench he recommends is around 0.050-inch. He has built engines with far tighter clearances than this, but much of this depends on the piston-to-wall clearance. All pistons tend to rock slightly as they transition through TDC and this rocking motion reduces the piston-to-head clearance. Smaller-diameter pistons with tight piston-to-wall clearances don’t rock nearly as much in the cylinder bore compared to larger-bore pistons with wider piston-to-wall clearances.
Since piston clearance plays such a big part in piston-to-head clearance, it is possible to run a piston-to-head clearance tighter than 0.040-inch if you feel brave. Noted horsepower hero John Lingenfelter says that clearances of 0.037 to 0.040 inch are possible, but you must know what you’re doing. The late Smokey Yunick also recommended a quench clearance of 0.040 inch as a safe but critical clearance.
Advantages
So what are the benefits of all this squishing and quenching? The benefits are small, but >> often important. Pump-gas engines that run on the ragged edge of detonation, for example, can greatly benefit from a tighter piston-to-head clearance to reduce rattle. That sounds contradictory since increasing compression should lead to increased detonation. All the engine builders we spoke to mentioned that tightening the quench (reducing the piston-to-head clearance) to get it under 0.050 inch will increase the static-compression ratio, but this tighter clearance also creates a more powerful squish effect. This additional turbulence creates a more homogenous “soup” in the chamber, reducing the harmful effects of lean air/fuel ratio pockets. With all other variables being equal, this contributes to creating an engine that is less prone to detonation.
We tried this on a recent dyno flog of a 383ci small-block. To keep the compression at around 9.5:1, we used a set of 0.050-inch head gaskets that created a wide piston-to-head clearance of around 0.060 inch. CHP engine flogger Ed Taylor swapped in a set of 0.040-inch Fel-Pro head gaskets and then tested the engine again. We witnessed only a marginal gain of around 2 to 3 hp (less than 1 percent), but it’s doubtful that the marginal increase in compression was responsible. Clearly, tightening quench with a thinner gasket had something to do with the increase in power. Tightening the quench area often results in the reduction of ignition timing requirements. This can then lead to a reduction in negative work (the cylinder pressure rising while the piston is still approaching TDC). This often is evidenced by a gain in low- and mid-range torque.
There is plenty of discussion about the net effect of squish and quench. While it’s doubtful that this will ever amount to more than a few horsepower in any street application, it does offer some distinct advantages when it comes to increased engine efficiency, better fuel mileage, and driveability. If you’ve ever wondered why certain engines run better than others, this could be one reason why."





you're leaving a lot on the table (not just simple horsepower) that could be fixed relatively easily.

if you have 3.5mm deck then bringing that down closer to 1.3mm is going to be a huge improvement.


this is what you need

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[Splitdog]

I agree. Less deck is best. For a lot of reasons.
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#notacallooker

[sled]

[mark tucker]

squish helps everywhere, especialy at lower rpm applications.