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> Questions on Big Bore Kits on a 1.8
Beamer13
post Nov 20 2007, 12:45 AM
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Ok, so I'm considering (since I have to drop the engine anyway) going to a big bore kit (96mm) What exactly should I know, or what will I need to do??? I am new to Porsche and 914. If there is another thread somewhere on this, by all means please direct me to the right thread. Thanks, in advance, for everyone's help on this forum!! You've been great!!!
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Beamer13
post Nov 20 2007, 01:27 AM
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Twystd1
post Nov 20 2007, 02:04 AM
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You don't want to know... really.....
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Do you want to keep your stock fuel injection?

Or are you willing to go to carbs or aftermarket fuel injection?

The answer to that will dictate most of the answers to follow.

Cheers,

Clayton



PS: DO IT. More Torque and HP in a teener makes em FUN....!!!!!!

More is gudder.
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johannes
post Nov 20 2007, 02:42 AM
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Stroke will give you torque ... Go 2056

BTW there is another post about the same question here
http://www.914world.com/bbs2/index.php?showtopic=78297
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lotus_65
post Nov 20 2007, 05:24 AM
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raby's sites
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type47
post Nov 20 2007, 07:04 AM
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big bore kits (96mm pistons and cylinders) for 2.0 and 1.8 are different due, i think, to the wrist pin height or something like that. the difference is why you see 2 kits offered. big bore kit is bolt in.
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Joe Ricard
post Nov 20 2007, 08:08 AM
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All of it is bolt in once you spit the case.
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Beamer13
post Nov 20 2007, 08:15 AM
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So basically what you are saying is that I can just use it with my stock L-Jet and it just bolts on, so there shouldn't be much of anything else that I would need to do? Right??
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type47
post Nov 20 2007, 08:59 AM
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QUOTE(Beamer13 @ Nov 20 2007, 06:15 AM) *

So basically what you are saying is that I can just use it with my stock L-Jet and it just bolts on, so there shouldn't be much of anything else that I would need to do? Right??


right. 1.8 bore is 93mm and big bore kit is 96mm. if there is not too much increase, the stock FI system can be maintained. i think i remember that D-jet can still be used for big bore but when the increase is alot (98-105mm), they don't work correctly. there are alot of if's, ands and buts to this but that's not the answer here to your question (L-jet on a 96mm motor). does that make the motor a 1911cc?

i will admit on this board that i did not split the case on my 1.8 when i got it running. a previous poster referenced splitting the case and the majority here would probably recommend to split the case when getting the engine running. it's not that much more work and you then know the condition of the bottom end. that said, i wanted to get my 1.8 on the road to drive it and the bottom end only had 60k miles and the next motor to go into the car would be a 2L or a 2.056L anyway, so i had the cylinders honed and the pistons cleaned and put it together with new rings and installed the motor.

flame on, Cap'n


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Beamer13
post Nov 20 2007, 09:13 AM
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Very cool!! Thanks much!
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Cap'n Krusty
post Nov 20 2007, 09:38 AM
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Upping the bore from 93 to 96mm will raise your compression. This will require shims under the barrels, and the exact thickness must be calculated. Otherwise, you may be running premium fuel and still have detonation. The Cap'n
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Beamer13
post Nov 20 2007, 09:40 AM
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Thanks!! Good info! I can tell that this is going to be quite a learning experience to say the least!!
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blitZ
post Nov 20 2007, 09:43 AM
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Increasing displacement is a plus. However, getting the proper cam in your engine will really bring you car to life.
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Beamer13
post Nov 20 2007, 09:58 AM
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Ok, a friend of mine just brought me back down to Earth:-) He said to get it running first then worry about mods. So I guess it's back to looking for the ECU and harness and such for my L-Jet..... But I'm pretty sure that this is going to happen soon!!!
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Beamer13
post Nov 20 2007, 11:46 AM
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Big bore that is :-) Hopefully will have engine out shortly after Holiday. Will keep you all posted
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type47
post Nov 20 2007, 11:50 AM
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QUOTE(Cap'n Krusty @ Nov 20 2007, 07:38 AM) *

Upping the bore from 93 to 96mm will raise your compression. This will require shims under the barrels, and the exact thickness must be calculated. Otherwise, you may be running premium fuel and still have detonation. The Cap'n


why does this happen (not a wise ass question, just curious)?
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Twystd1
post Nov 21 2007, 01:22 AM
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Jim,

The answer is pretty simple.

When the diameter of the piston increases and the combustion chamber stays the same size. This larger piston is now bringing MORE air and fuel into the cylinder as it goes down the bore. Then when the piston starts to rise to TDC (or close to it) There is more air / fuel in the cylinder. That means the static compression ratio will go up. (Man I suck at explaining this...

Lets try this. Imagine you have lawn mower engine with a 3 inch across piston.

Now lets say you bore out that cylinder and stick in a 10 inch piston. Imagine how much more air it would compress on the combustion stroke.

A bunch. Hence upping the static CR.

OK.. I give up. I suck at explaining stuff.....

Cheers,

Clayton
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