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limited bore engine discussion (85.5-86mm 87s 88s)
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ralf
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PostPosted: Mon May 03, 2010 5:28 am    Post subject: limited bore engine discussion (85.5-86mm 87s 88s) Reply with quote

good day guys,

(while i wait for my parts for the 1679 and 1800cc motor) an unusual tech/theoretical discussion sounds good
seeing seasoned veterans in racing and building and machining here,
and i know ive learned my fair share also.. (from here)
guys like Modok,John at acnet, NSR nick , and a few more


lets say we are limited to 85.5mm piston bore (seeing sum1 do custom pistons in 86mm bore and bore/honing the 1600 barrels to be used)
so lets say we are limited to 85.5 - 86mm bore

goal is to make the most (realistic) power off those bore size, with the displacement unlimited
could stroke it 74,76,78,82 heck even 84 (i think)

point of discussion is - stroke size - head size (due to the limited bore) - cam choice - rod length choice
what would work for power and what wouldnt

lets say piston pin height / comp height we have the choice of 39.6 (A) , 34 (B) and shorter 30mm respectively


and to simplify a rather widespectrum of choice, lets limit carb size to the ff:
Weber 44 or 48 IDFs (or dells respectively) and or 48IDA's
-----------------
*how would you configure your limited bore/ unlimited displacement engine
(hope this is as interesting of a topic as it is to me.. for everyonehehe)

"throwing a wrench into the fan" gas limit lets put at 96+ron or , 91premium in the u.s
reliability should be no lesser than the common "internet" configuration engine i.e. 1776,1914,2110-2276 motors
use: streetable / strip motor
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ralf
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PostPosted: Mon May 03, 2010 5:30 am    Post subject: Reply with quote

i understand we could go bigger bore etc for the same cost.. or actually spend less and make more proven power.. but lets not debate or discuss that.. there is an obvious answer to that...

im more interested in the discussion of.. making power around the given mechanical efficiency or defficiency of a said configuration...


hope to hear some ideas and opinions Very Happy
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AlteWagen
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PostPosted: Mon May 03, 2010 12:02 pm    Post subject: Reply with quote

There were a few considerations for me when building my 1699cc.

Application
Proven reliability of parts
Cost

Specs:
New AS41 Brazil case
New 043 Heads with step
New 74mm cast crank
New Mahle 85.5 A forged pistons/cylinders
New Engle 110 cam
NOS german lifters
Rimco Super Stroker rods
German lightened flywheel
36mm DRLA
S&S 1 1/2 merged header/turbo muffler
9:1 compression with "0" deck



Original application was for use in a bus, so "extreme duty" was the plan.

Almost all of the parts used were OEM (except for the crank, pushrods and cam). My reasoning behind that is the fact most reproduction parts are questionable so peace of mind won out over "more power". I used a brand new stock Brazil case so I could not bring myself to machine for bigger pistons or do extensive work to it. I wanted more meat on the heads and case for strength given the intended punishment. I figured that when the time comes to rebuild it, a line bore and bore would come next.

I found I could build a mini stroker for the same cost as a standard 1584 rebuild. More power with a counterweight crank was definitely a bonus.

I also thought of breaking down somewhere out in the middle of nowhere. I figured it would be easier to find "stock" components vs. a modified performance part.

The only limiting factor for the bore size is going to be valve size. 40x37.5 would be the biggest I would go before valve shrouding would cause problems with flow. Given that a 40mm valve can flow pretty well with the proper port job, getting the flow numbers needed for a 84mm crank would be a challenge.

If I were to do it again today I would use a forged 4130 78.5 crank, 85.5 B pistons, and 5.5 h beam rods so that shimming would not be an issue and that cast crank would not give me nightmares. It would add another $500 or so to the build cost but still have the strongest components possible.
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nsracing Premium Member
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PostPosted: Mon May 03, 2010 1:10 pm    Post subject: Reply with quote

This looks like a cooking lesson. Very Happy

"What one has conceived, one can achieve".... Albert E.

Come on, Ralf. The engine does not know what parts it has.

If you find a suitable cylinder (talking custom cut) and a piston to stick in there, the rest is just inserting the proper lower end. It is all machining challenge. You can move holes where you like it.

Valve size is limited by bore size taking the valve unshrouding into consideration. There was topic on this before.

You can stroke until you cannot find the proper length of rods and piston skirt clearance.

You can cam this engine to its intended purpose. Is it gonna climb a pole? or going down the straight?

This is the beauty of pushrod horizontally opposed engines. YOu get to do what you like. Not limited by deck height so on.

If you notice, the VW aircooled has so many combinations your get dizzy just from the possibilities. That is why I love the VW so much. YOu can make it do anything.

Now, if you can figure out how to stick Chevy or Ford transmission gears into the VW, I would love to see that. Laughing
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ralf
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PostPosted: Mon May 03, 2010 1:35 pm    Post subject: Reply with quote

hahaha nick... thanks for the input..

and word for word are taken into account...


everyone and u and i both know the near endless configuration our beloved T1 has and t4's too...

but i was more interested on the discussion of why "some1" would go for this.., and their reason... vs how the other would do that and his reason...


not to talk on who can piss farthest...

but more like... lets talk about how many ways we can skin a cat..

much like why im waiting on parts for my 88x74 and 88x69 builds,
some reasons i liked on it.. and some i find enticing for me..

though we all know i could have done a 1776 and 1914 and have a bigger motor with more potential... yup... but im building what i find enjoyable..

-----

derluft, yeah saw ur post in the other forum too.. and here
1699cc is rather interesting.. thanks for the input.. and costwise ur right..
to counterweight and rebuild an 1585 would cost the same as ur motor if not close to it

------

id like to know other's opinion on shrouding and limited bore use..

lift to valve dia. ratio.. cam choice due to these limits.. etc


another thing Nick.. we're talkin about street motors on a beetle ,

which means ideally we cant go too wide... and it should be reliable (though thats primarily parts quality and machining quality)

hope my ramble is getting sumwer hehehe Very Happy
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vwracerdave
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PostPosted: Mon May 03, 2010 1:44 pm    Post subject: Reply with quote

If 85.5 is the limit I won't waste my time or money building anything larger then a stock 1600. If I can't go bigger pistons, I won't go larger stroke either.
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AlteWagen
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PostPosted: Mon May 03, 2010 1:56 pm    Post subject: Reply with quote

what about destroking for quicker revs? 62x88
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nsracing Premium Member
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PostPosted: Mon May 03, 2010 3:33 pm    Post subject: Reply with quote

There is only one way to skin a cat. You start w/ a blade. Laughing
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ralf
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PostPosted: Tue May 04, 2010 5:11 am    Post subject: Reply with quote

hahaha alright guys...

still find it interesting.. JPM in sweden opted to try :

JEpistons 86mm bore'd and honed barrels which made around 150ish hp i think

i think it ran below 12s, on a light body , it was an 86x69


sorry anyways... thought thinking bout sumthin diff was gona be fun LOL

Nick , im having Arias make me 86mm bore with 32mm comp height..
should be fun , (but i have to finish the 88x74 and 88x69 when it gets here)
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jamestwo
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PostPosted: Tue May 04, 2010 8:43 am    Post subject: Reply with quote

advantages to smaller bore that I can think of-

less friction

can run more Compression, because the flame front is more compact.

Lighter piston
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ralf
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PostPosted: Tue May 04, 2010 9:01 am    Post subject: Reply with quote

yeah agree..


so i wonder.. whatever stroke it is..

lets say.. a given displacement on a 40x35.5 size head, will still work with the same cam... that would on a big bore small stroke of the same displacement?
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fastinradford
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PostPosted: Tue May 04, 2010 10:04 am    Post subject: Reply with quote

vwracerdave wrote:
If 85.5 is the limit I won't waste my time or money building anything larger then a stock 1600. If I can't go bigger pistons, I won't go larger stroke either.


why?
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AlteWagen
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PostPosted: Tue May 04, 2010 11:20 am    Post subject: Reply with quote

ralf wrote:
yeah agree..


so i wonder.. whatever stroke it is..

lets say.. a given displacement on a 40x35.5 size head, will still work with the same cam... that would on a big bore small stroke of the same displacement?



On a NA engine the cylinder head/valve size/flow will be the limiting factor. If trying to compare smaller cams used regardless of displacement the outcome would be similar.

I think the best thing to do would be to have the heads ported and flow benched. With the flow data you can see what the maximized lift for the port is, then you can start making decisions on cam choice. Now that the lift is figured out now you can decide on duration as well which will determine what your dynamic compression will be.

I figure a superlight weight rotating assembly with a ton of torque from a stroker crank and a bit of compressions will be a beast!
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ralf
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PostPosted: Tue May 04, 2010 11:55 am    Post subject: Reply with quote

yes.. this is why the topic is berth'd

not cuz of cost savings.. and certainly am not interested in doing a bigger motor cuz it costs the same or gives less work...


sometimes the journy is better than the destination...


interesting discussion with lets say 86mm max bore (85.5 smallest)

valve size choice.. on the intake.. and exhaust.. with relation to cam choice

plus.. how to take advantage of short dwell time of big stroke low r/s motors vs the typical..

im sure that plays a role on combustion characteristics also
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modok
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PostPosted: Tue May 04, 2010 9:26 pm    Post subject: Reply with quote

What no 90.5? stock is only 5mm less right?
So if you were to move the intake valve 2.5 mm inward it would be just as much "unshrouded" as with 90.5 bore. Moving the valves is probably worth some hp. Shoot, I'd move the exhaust valve closer to the wall, probably not lose any real performance and makes room for even more intake valve!
Lot of work though, lots of welding to rearrange the heads this much.
I'm thinking 6 or 7mm stem intake valves, CB ls1 beehive spring kit, fancy stuff like that.
I'd run at least 78 stroke, can't think of a reason to run any less.
You know this thing's gotta turn 7k rpm to make as much power as if it had 94's though, and will need lower tranny gears too. Golly it's gonna be expensive.


Now for motivation...........
They did kick me off the company insurance due to too many tickets. Maybe I need to build a mini motor so I can still have fun but not speed so much?
Or I could just fix my bus, never got a ticket driving that.
Yeah, making the vehicle bigger is cheaper than making the engine smaller.
That's my solution, hahaha.
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ralf
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PostPosted: Wed May 05, 2010 4:22 am    Post subject: Reply with quote

maybe id like to try a
86mm bore x 82 stroke


hahaha myt be worth the giggle
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