TheSamba.com :: View topic - Considering increasing bore during rebuild

Sun Feb 07, 2010 9:59 pm

If I were rebuilding my engine, since I'd have it out and torn down would it be a bad idea to bring the case to a machine shop to increase the bore while I'm there for a little extra power? If so, what all is involved? Obviously bigger pistons. Can I use the stock rods, crank, etc when I do this? I wouldn't have a WHOLE lot to spend in this endeavor. What effect does this have on temperatures, etc? Because I can see how it could make it run hotter, or cooler too.

I have no knowledge in this area. Is it even a good idea?

Sun Feb 07, 2010 10:58 pm

sorry i can't help but i have read other post's on here stating in some cases it can help and in other cases it makes thing worse than stock.

Sun Feb 07, 2010 11:13 pm

thegoodfight7211 wrote: If I were rebuilding my engine, since I'd have it out and torn down would it be a bad idea to bring the case to a machine shop to increase the bore while I'm there for a little extra power? If so, what all is involved? Obviously bigger pistons. Can I use the stock rods, crank, etc when I do this? I wouldn't have a WHOLE lot to spend in this endeavor. What effect does this have on temperatures, etc? Because I can see how it could make it run hotter, or cooler too.

I have no knowledge in this area. Is it even a good idea?

If you are talking about your 2.0 Westy in your sig line, I would say VW had already extracted most of what the air-cooled engine could give as far as simple bore increases. Any step up from here, will require very careful analysis and a comprehensive upgrade of all parameters of your engine, such as head work, exhaust, cam profiles, etc.
Colin

Sun Feb 07, 2010 11:30 pm

i was told that the biggest out of the box P,s & C's that will work with stock heads are 2.5..
the 356 gurus up here and ive seen one,have built a 2.9 litter type 4 fire breather.. what a monster

john

Sun Feb 07, 2010 11:40 pm

copellos wrote: i was told that the biggest out of the box P,s & C's that will work with stock heads are 2.5..
the 356 gurus up here and ive seen one,have built a 2.9 litter type 4 fire breather.. what a monster

john

Might be good in a 356 . . . a bus, on the other hand is working a lot harder just to push through the air with all of the crap you lug around. I think I have read most bus owners as wanting dependability so they can go off the beaten path or take a tour of the country and that might include summer time too.

My suggestion to the original poster stands. Be thoughtful and look at all parameters carefully. A 2.9 litter breather . . . may not be what you want in the long view.
Colin

Mon Feb 08, 2010 12:19 am

A good place to start is budget. When you say you dont want to spend too much, how much is that? Heat can be taken care of by using superior materials, i.e. Nickies (~$2500), which can take a lot more punishment and dissipate considerably more heat. You can go with a "camper special" from Jake Raby ($3500), all who went that way were happy. Or, if you have a small budget and want a little more oomph without blowing your budget then an AA 96mm p/c set (~$250-400) will make you a 2057. This will work best if you have the shop check them for height deviations and correct for them. AND, you will not have to bore your case out. They are available on Ebay. I personally would not look at anything larger than that without the Nickies. It is all in your setup and how well your cooling system, fuel system, exhaust, etc are setup. If they are in top shape, you are good to go......but it will still be a loaf of bread being propelled through the air ;)

Mon Feb 08, 2010 3:17 am

EvilWerks wrote: When you say you dont want to spend too much, how much is that?
Yeah, Camper Special's certainly not within my budget. I could only wish. Working three days a week in a sushi bar, you do the math. :lol:

Amskeptic wrote: Any step up from here, will require very careful analysis and a comprehensive upgrade of all parameters of your engine, such as head work, exhaust, cam profiles, etc.
Colin
And this was what I was afraid of myself...but after searching eBay as was suggested I found this:

http://cgi.ebay.com/ebaymotors/VW-Porsche-96mm-Big...ccessories

If I'm not mistaken, the stock 2.0L pistons are 94mm...and these are the 96s mentioned which they say will fit with no further modifications. I'm just wondering about the quality...they DO come with a warranty but other than that at the bottom it pretty much says they're not name brand. How would anyone feel about running these? The price is definitely up my alley...

Mon Feb 08, 2010 8:02 am

Quote: http://cgi.ebay.com/ebaymotors/VW-Porsche-96mm-Big...ccessories

If I'm not mistaken, the stock 2.0L pistons are 94mm...and these are the 96s mentioned which they say will fit with no further modifications. I'm just wondering about the quality...they DO come with a warranty but

those are chinese, and getting a replacement will not pay for the work it takes to fit them to the broken engine. i love ebay sellers ( :roll: ) instead of saying it is chinese he says " they are not Mahle, cofap, wiseco, JE ..." if the guy is afraid to say what they ARE but saying what they are not, you should be worried about the quality! i have yet to hear anyone say with pride "theyre chinese :D " unless they bought some jade statue :lol:

regarding the choice of bigger pistons- there are two ways to get more power from a rebuild. you can build bigger, or you can build more carefully with better parts. the latter choice will often give you the same power gain, but with better mileage.

what you should do is balance the moving parts, buy a Raby cam and lifter set, and match all your chamber sizes with a CC plate and burette (syringes are imprecise). when one is on a supertight budget, but must have some gains, the Raby cam is the best way to get it.

connecting rods count for some power too- dont have a local shop just replace your bushings. when the bushings arent bored square before honing, you lose power to poor ring seal. so buy your rods from a source that can verify over the phone that the rod bushings are both bored and honed. ask Jake Raby. i imagine he does them that way.

as an example of what you can get out of an stock engine that was built with care, i got a 40% improvement in my 0-60 time as compared with the factory 0-60 spec. part of that power gain was found in the single to dual carb swap on my 1600cc type 1, but the new carbs are only 32s, (smaller than the single 34) and the heads remained stock. at least half the power gain was found thru rod choice, balancing, matching chambers, and lining up the manifold port to the head carefully. there was no CR increase- in fact, my CR is less than stock at 7.1. whats more, i am running a 009! :oops:

Mon Feb 08, 2010 11:36 am

I would ask if those p/c are AA. AA are good sets, better than the Chinese stuff. Any set you get is going to have to be inspected and trimmed to fit. Even the AA cylinders can have a slight deviation in length that would need to be fixed so that the deck heights end up correctly. Jake sells that AA sets as well, but I am pretty sure he has them perfect and at a comparable cost for the work to do such.

Mon Feb 08, 2010 12:52 pm

How big?
Consider the fact that during the development of the CS engine I did a lot of experimenting with larger than 94mm bores. Time and time again the engines with larger than 94mm bores made LESS power when at temperature than the smaller bored engines that ran cooler and lost less power to expansion.

The issues with larger than 94mm bores are extensive in a bus, primarily the cylinders don't stay straight or round for very long and the pistons are always flat topped, making for exceptionally tall deck heights to attain compression ratios of 8:1 or less that are necessary for a bus.

I have had success with one 96mm combination in a Bus that has been on the road for over 3 years in testing. This engine resides in the weekender of one of my employees and we call it the "CS Lite". If it continues to provide solid cool running service I may make it into a kit in 2012.

This combination uses a custom dished 96mm piston, bored OEM cylinders with cryo and altered skirt clearances.

I have already proven that a stock 2.0 71X94mm engine with less than 8:1 CR can make over 100HP with 130 lb/ft of torque and do so at below 5,000 RPM with a torque curve that is outstanding.. Its easy to go too big and its even easier to become part of "the bigger is better crowd".

Mon Feb 08, 2010 1:14 pm

while everything jake says is right, I think you should consider staying stock displacement just because of something you said earlier along the lines of "budget". If yours is tight, spend it where it counts, get a QUALITY cam and lifter set, from the same mfr. I would strongly reccomend you just call jake and have him set you up on that part. Then spend the money you would have spent on jugs on exhaust instead.
so my answer is no, on a tight budget rebuild, big bore 96 p/cs on a 2.0 are not worth it. would require cutting too many other important corners to pull it off.

Mon Feb 08, 2010 3:26 pm

Great. These are the things I wanted to know. This isn't an ambitious mission to squeeze more power out of my engine...I just didn't know if it was a matter of "hey, may as well while I'm here". It definitely sounds like more than I'll have the time and $$$ to get into.

I've seen plenty of good words about the Raby cam upgrades, and I think I'm certainly going to investigate that possibility within the next month or so.

So on the subject of "may as well while I'm here"...is there anything I should definitely address while I have it all torn down that would suck to replace later? For example, I'm considering clutch. Mine shows no problems as of now but a new one's cheap for the peace of mind it would give me and again, it's better to do it then instead of pulling the engine JUST to do a clutch in the event it does go out.

Mon Feb 08, 2010 3:39 pm

Engine balancing... If you are going in, may as well balance the assembly.

Wed Feb 10, 2010 3:23 pm

I completely agree with what Jake and fusername said. Quality is always a better investment :)

Thu Feb 11, 2010 9:47 am

as for clutch, if you are really on a budget, skip the clutch for now, and spend that money on getting the whole thing balanced by jake. being able to safely rev your engine that extra thousand or so rpm (I'm sure he will reccomend a new redline) to keep up with traffic will really help. I would imagine 5k is more than safe once he has spun it.

Budget out this:
Cam kit from jake
Balance job, also jake
HEADS, done right!

see what you have left and go from there.

do you have a single thread on your engine rebuild yet, cause I am posting abou things that this thread is not about.

Thu Feb 11, 2010 1:11 pm

Interesting! That doesn't sound all THAT out of reach. And the rebuild is still in the "developmental brainstorm" stages; I'm tossing around my options and how much my wallet will be able to handle. I don't know good of rebuild I could do for $500, which was my original projection, but it seems like more in the $1000 range would be worth the investment. No telling how long it will take to save that though...I work three days a week at a sushi bar. :lol: