"Blueprinting" VW heads

if this is a street car, do not polish the intake ports. The exhaust and intake port flow should be in a certain relation to each other, for the head to work well. (Exhaust flows less, 1target is a certain percentage of intake flow, like 85% for example). If you just go to town and hog the ports out as big as you can, you will likely ruin the heads.

More flow can be found safely from a professional competition valve job. (Including but not limited to what is called "3-angle valve grind" ) The valves and seats are ground to certain progressive angles (or a controlled smooth radius), and the valve faces can be radiused too (but only on one side.The exh is ground on the piston side, while intake valves are radiused on the port side. If memory serves... ) There's more that can be done to the valves depending on their design.

Yes, do it. Some cheap aftermarket "stock heads" have an obscene amount of flash clogging up all passages.

I drill them. No shock of hammer blows.

What is the octane of your premium gas?

9.2:1 is too much for that cam, unless it's pretty darn high octane gas. Don't go over 9:1, and if you have the kind of fuel I think you do, you need to stay in the 8.7:1 neighborhood.

You will need to slightly radius all sharp edges in the combustion chamber. Also unshroud the valves in the chambers. Make chambers deep and narrow, if you need more volume. Do not widen them. You want the mixture to be concentrated in a tight, small area. It can be deep, but not any wider than it has to.

You also want to run a very tight deck height. Between 1.1 and 1.3mm, NO MORE. I'd rather try to get it closer to 1.1mm. Set that first, then figure out how big your chambers need to be, to produce the CR you want. Then work on the chambers to get there.

No personal experience. Some people say it works.

Jan

Oh yea, you can most likely run 1.25:1 rockers with that cam, for a little more lift.

Hi Jan, Thanks for the drill idea! Will look at long enough drill bits to make this happen.

As for the main question about CR: Over where I am at, it is 91 octane. My current CR is 8.2:1. I agree that a jump to 9.2:1 is steep, but I was wondering if the use of heat barrier coatings could justify that jump.

Problem is that the engine is running a bit too cool, even cooler than the stock 1600 (with the same cooling setup). I can't give any real temp numbers but only a comparative observation is based upon the use of a Berg oil dipstick temp sensor device.

-Geoffe Elias

'74 Super Beetle

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It's not just the fact they are liquid-cooled. The foundation issue is the use of a computer to control the process of combustion. Most folks start acting silly when you say things like that but it's the truth. Light the fire in ANY gasoline-fuel, spark-ignited engine and the following 'combustion event' will take something like two thousandths of a second REGARDLESS of your rpm. (There is a clue buried in there. QED and all that.) The basic combustion controller is a chip from Zilog. Pretty crude but it's cheap and has a good track record with regard to failures. AND it runs in the megahertz range, meaning you've got tons of time to do whatever needs doing before the NEXT 'combustion event' comes around.

But that's just the start of it. In a modern-day vehicle you're liable to have as many as SEVEN 'computers,' if your definition is limited to microprcessors capable of reading instructions, doing things and recording the results. The literal definition of a 'computer' is an MPU, an I/O controller, and some memory. The fact you can get all that on one chip doesn't change anything. The distinction is between 'controlling' something and controlling something on the results of a computation. What makes it tricky is when the computer in charge of combustion starts using INPUT from one or more of those other computers to determine when the engine gets another shot of fuel, how much fuel it gets and so forth.

Actually, it's rather interesting. Study of the code gives you a keen insight as to the politics behind how all that crap -- most of which is carcinogenic -- got into our motor vehicle fuel... then getting you to pay a PREMIUM for such crap. Clearly, we have the best government money can buy :-)

-Bob Hoover

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Well, we have the best Gazoline money can buy... Our politicians on the other hand you can have at a very reasonable rate. :-]

J.

the following 'combustion event' will take something like two thousandths of a second REGARDLESS of your rpm The basic combustion controller is a chip from Zilog.