1800cc engine compression ratio with bus

[ti-ti]

Hi
I know there are several posts related to my question but I haven't been able to find an answer to them. I am in the process of finishing reassembling my 1800cc. I replaced all the bearings, replaced the original camshaft with a WebCam 142. I have 2 new AMC heads with a 3 angle job on the valve seats. I have been a technician at Volkswagen for 10 years but I have never had the opportunity to reassemble an aircooled engine. As this is my first one that I'm putting together, I have several introgations. The engine is a 1800cc which will go into a Westfalia 77 with a 6 rib transmission.

I know that there is a tsb linked to the 2000cc to lower the compression ratio in order to reduce the temperature of the heads. Does anyone know if this is also necessary to do on an 1800cc? I did not install the plexiglass on the step cut of the head but directly on the base of the combustion chamber. I calculated that I had a 51cc combustion chamber. I calculated that I had 9cc for my pistons. I have a step cut on the head of 0.029'. So if my calculations are correct, with 93mm pistons and a stroke of 66m and a height deck of 0.06' I would have a compression ratio of 7.37:1. Can I put it at 7.5:1 or should I follow the tsb and take it all down to 7:1.

THANKS
Etienne

[ti-ti]

I forgot to specify that the engine works with the original injection. I only installed a wideband on the exhaust to adjust the AFM manually.

[Millionmph]

Fix that deck height I dont know the spec of that cam but just did a 1700 bus motor at 8.5:1 with Scat c25 and runs great! That step in the head and 060 deck height will do more to cause cylinder head heat... machine the step off and get the deck height to 045; 8-8.5 compression is totally doable and will run cooler with the right duration and deck height.

[ti-ti]

I'm not sure I understand correctly. The calculation I made for the deck height is as follows, 0.029 (step cut) + 0.03 (distance between the top of the piston and the top of the cylinder. If I remove the step cut I will have to install a shim under my cylinders thicker. It won't be the same? I don't have a flat piston, I have pistons with a 9cc dish. Having 8-8.5:1 is impossible with my pistons, I think...

[oprn]

My 1700 Bus engine with 96mm flat top pistons (1911cc), no smog step in the heads, 12* initial timing and a 86 Web cam is set up with 8.4/1 CR. It runs sweet and cool on 87 octane without even a trace of a ping. It is in a light car but I would not hesitate for a moment to put it back in a Bus.

Run all the CR you can possibly squeeze out of those smog pistons and heads.
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[Vanapplebomb]

I don’t ever “calculate” deck height, or more accurately piston to head clearance. I treat it as a fixed thing. Anywhere from 0.030 to 0.040 with stock bores is where I like to be on T4 engines. If you feel the need to lower compression, find some room in the combustion chamber (or piston crown, as long as it doesn’t cut into the quench area).

The other option is to use a little more cam…. But seeing as you have stock injection, that doesn’t really work, so you are kind of stuck with opening up the chambers in this case. But, you’re not far off.

I would shoot for 8:1 on the 142 cam… which is as close to a stock cam as you will get from the aftermarket. With a tighter deck, you can actually run a little cooler, even with slightly more compression. Recalculate compression at 0.040 piston to head clearance, and see where you land on compression.
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1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[Alstrup]

Stoop stop stop.
The 142 cam is a 914 2,0 equivallent right?
So it actually LIKES 8,3 or more CR, even/also with the old D-jet and even more with the L jet.
You have 0,029 step in the heads. OK. Then you - should - have something like 0,027" deck height without any gaskets. This gives you a total of approx 0,056" - Maybe the 0,060" you are referring to. That gives you roughly 8,25 CR which is good, but with a hair much active deck height. It will run of course, but once again, the tight deck we are preaching IS a great advantage, and especially in bus engines.
The easy way to get around the problem is to raise the cylinder to a 1 - 1,1 mm deck and machine the step away in the heads and then find 2 cc´s in the chamber. That will give you 8,4 CR which will work very well on medium grade fuel and make the engine run significantly cooler than it ever did stock.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[ti-ti]

What am I doing differently from you so as not to have the same results?

[Vanapplebomb]

The 142 is close enough to one of the 2.0 cams. Not sure we had that particular one in the USA, but they are all so close it makes darn no difference. It runs fine with the stock FI, which is not very forgiving. Heck, any of the stock cams are good to at least 8.5:1 in a passenger car with the stock lazy deck height. I think 8:1 in a bus with that cam is right on the money with a tight piston to head clearance. It’s a bit safer, but not so conservative that it makes it inefficient and run hotter.
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1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[Vanapplebomb]

[ti-ti]

It’s the original piston from the block. I will try to measure the pistons again. I used a precision balance to calculate the amount of water. Otherwise from what I understand, I will try to adjust my deck to 0.04. To increase my ratio, I think I should find flat pistons. THANKS

[Alstrup]

I never saw 93 mm dished pistons... U sure its not 94?
93´s are either flat or with a small dome (?)
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[ti-ti]

It’s 93mm with dish.

[Alstrup]

I stand corrected
Get rid of those and go with flat tops.

EDIT. I just checked... You can´t even get 93 flat tops, nor "S" pistons anymore. Youre screwed
- OK. What you can do is in the blines of what I wrote earlier.
Correct the deck height in the cylinder. Then machine the step out in the heads, + 0,9 mm. That will give you approx 46 cc chamber, plus the 9 cc dish and 1 mm deck = 8,25 - 8,3 which will be good.
You will need to shorten your pushrods, but thats not a big deal, and this will get you what you want.
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[Vanapplebomb]

[Vanapplebomb]

The picture he added is a 412/914 Ljet equipped piston, and is as close to flat top as 1.8 pistons get.

Most other 93mm pistons I have found have a shorter pin height. Chrysler Powertech pistons have the same pin diameter, but the pin height is nearly 10mm closer to the piston crown. It can be done, but it isn’t a drop in deal

What I have done is to take the 412/914 Ljet pistons and shave the top down. This reduces the dish volume a little. Then shorten the cylinders to get the piston to head clearance back down to a reasonable level. Last ones I cut 30thou off the piston crown. I was able to get the engine just above 8:1 compression with those pistons and stock heads.there is plenty of meat there to remove 30 thou off the top.
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1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[Alstrup]

Well yes, but that kinda complicated since it messes with everything. But you of course use most of the original parts.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[ti-ti]

For this summer, I think I'm going to ride it with these pistons. I've already waited too long to receive all my parts to reassemble it... I installed the heads yesterday on the block and my final compression is 7.5-7.6. Without the shims under the barrels, I have a deck height of 0.02 + 0.029 (step cut). Maybe I'll install 96mm pistons next winter when I store it!

Thank you for your help!

[Alstrup]

0,031". Thats tight Good thing it is a short stroke. But it´ll mix well even though its low compression
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[Vanapplebomb]