lowering compression

[ISBjornen]

Hello.

im thinking about lowering the compression,

1/ but wath is the advantagers whit it?

Im running whit a 12mm injector head and a schwitzer turbo at 1,5bar boost.

[Benjamin]

offtopic   : great to hear you again    do you have any new spec from your engine?
whats happened after your broken bearing from a previous engine you had?

CR (compression ratio) is only needed to make much heat to be able to start up the engine, you have to much heat when running, so you can lower it. Another instrested fact is that you can put a little bit more hp on the crank while there is not more power on the pistons/conrods.

this one is also very intresting, its about lowering the compression, but not in the way to have a bigger headgasket but bigger prechambers
http://vwdiesel.net/phpBB/viewtopic.php?t=2329&start=0

Greetz, Benjamin

[ISBjornen]

nothing new has been don to the enigen. i have just taken a new block and top and put it together. fore the moment am saving mony to get a reinforsed one so I can have 2,5bar instedd.

This weekend the (rem) thing that conects the cam and the crank jumped off. it happened becus the bult in the wheel tha keeps it stretched got broken. the valves seems to have made it but it vont start again.

the compression is 18, 20, 18, 18 whit a cold enigen.

Im going to drag it after a nother car today to se if it starts. it worked the last time.

mor uppdate on that later tonight.(my night)

[ISBjornen]

i grages after my outer car and after 50m it started. is runs very hard but its just e ignition that has to be adjusted. i Will do that tomorow.

Last time i drove it i only hade 0,5bar bost and it smokes a lot.

tomorow im hopping to have 1,5 or something i wrong.

[ISBjornen]

now i have 1,5bar boost, it smokes just o litel.

It takes same time to get the boost but it runs like hell.

[Audi80]

Did you lower your compression?

[ISBjornen]

not yet. the enigen has crashed. i trying to fix money to by a new one.

[VentoTD]

I'm also planning on lowering compression. Why? Because I want to reduce  stress on engine internals. I've got a fairly high power goal, and some stuff to get me there. But I dont think the crank/rods can handle 2 bars of boost in the long run. So how low can I set the cr? standard AAZ is 22,5:1 right? At say 17:1, would it still start? Probably not in cold weather, but who cares?

I'm thinking volume/cylinder~500cc.

500/22,5=22,2.

500/17=29,4.

It seems like a starting value in material removing from piston top would be 29,4-22,2=7,2cc.

I know its not a good thing to do this, but I just hate rebuilding my engine every month.

I have been thinking about another thing, is it possible to use a gasser gti camshaft? (is there any cam that fits in the head?) If you get some more space under the valves so they wont hit the pistons.... Seems to me a gti camshaft would do wonders for breathing at higher rpms...

[ISBjornen]

a friend of mine did try to lower his compression whit 2 gaskets. hit gott 12,3 and it did start. it was not god but it worked.

[Northboundtrain]

I've been thinking of lowering the CR in my naturally aspirated engine, because I read in the original SAE paper on the 1.5L that a lower compression ratio would improve engine efficiency.  I calculated that by shortening the rods by 0.024 in (0.61 mm) I could change the CR from 23:1 to 20:1.  The SAE paper states that CR below 20:1 would have difficulty starting.  I'm pretty sure my machinist can shorten a rod by relocating the hole that connects it to the crank.  

Alternatively I could take down the top of the piston by the same amount.  Any suggestions as to which would be the better method?

[Audi80]

Both are bad. I tried 5-layer steel gasket, got ~18,5:1. Took 2 gaskets and removed top layer from other. But this is not any better, easier though...

[VentoTD]

I dont think you should try to shorten the rods. Removing 0,64mm of the pistontop isnt all that bad. You loose the coating but that shouldn't be a big issue.

I'm going to remove about 2mm of the pistontop. Unless you guys here can convince me not to. Hoping this will give about 17:1 cr.

I'm pretty sure double gaskets is a bad thing, they will fail eventually.

[Sierra94]

I run 35 psi of max boost (and atleast 20 during regular driving) and my engine works just fine. I have driven it almost 10000 km now without any problems at all. And the engine had 180000 KM on the clock before the turbo conversion.

The water/methanol injection works just fine to. It begins to spray at 20+ psi and lowers the EGT almost 140 degress celsius. From 850 to 710 which is superb.

I don´t know if I have a sample "blessed" from the guy upstairs or one that just seems to work well. But theese small diesels seem to handle almost any abuse put into to them.

[HarryMann]

Sierra, where are you njecting that water methanol and what ratio water to methanol..

That is a good EGT result!

[Sierra94]

Take a look at my pictures in posts here http://www.vwdiesel.net/phpBB/viewtopic.php?t=10150&postdays=0&postorder=asc&start=15

I´m currently using a water/meth% ratio of 60/40. And the nozzle I use right now injects 5 gallons/hour at 100 psi. I´ll try the 7 gph nozzle soon just to see if I get any gains.