I know this isn't technically the right place to ask these question, but you guys are the people who's opinions I'd like (in particular DB). But I will take the car down the quarter, so maybe it is?

I am building an unusual engine combo a 1791(85.5X78) and I'm not sure on a couple of things.

The reasons for this engine are that I want relaxed power, not an angry beast. Something withe HEAPS of torque that still revs freely.

I'm looking at a soft limit of about 5500 RPM and a hard limit of 7K.

I am using Street eliminators with 40 and 35.5mm valves, and I was thinking of using a Webcam 118 cam (.402 lift, 283 duration) will this be a good match? and what head work should I get done to compliment? I plan to run 1.25:1 rockers are these a good match?

Rod length, should I use a standard length rod or something longer? will this put my RPM range where I want it?

And what about rotating mass? should I aim to keep it down? 12lb flywheel?

Let me know what you think...

"Am building" or "want to build"?

have about half the stuff needed...

The Webcam 110 will limit your usable power to about 5500-6000rpm, and it will only get that far if the heads are ported as well.

I'd definatly get some 87mm mahle forged pistons in it too. Not for the displacement, but for the piston strength. I cringe at the though of a cast stock piston swinging 7000 rpm. I ran the 87's in my 1641 turbo motor to 7000 no problems though.

I'd change the cam to a web 110 which will give you a tad more duration for more top end rpm (probably 6500). A web 109 will get you to 7000 no problems.

Then use webber 40 or 44 idf's with 28 mm ventiri's and a 1 1/2 inch head for driving on the street. Use a nice restrictive 1.75-2" baffeled muffler and it will be pretty tame and still have good torque because of the stroke on the crank.

When you go racing you could switch to 32 or 36mm venturies, and change muffler to something thats 2.5" straight through, and re-jet of course.

Use stock lenght rods too. Your lift at the valive is 0.456" with the 1.25:1 rockers too.

Hope that helps...

Cheers,
Ian

I would keep the rods stock length.(shame you cant buy shorter ones).
I would agree with most that Ian has shared,
but would go for a smaller 1.375" exhaust and high quality muffler.

The cylinder heads is where your limitations will be
unless they have had some work done to them.

Street Eliminators can be made to flow very well with excellent velocity...just what you want!

Unfortunately the small bore will limit your power and head flow,
but after seeing Col's 1600 run in the 14's I think you can build what you want and be happy.

So in summary, do some port and chamber work,
the Webcam110 looks good (lose the ratio rockers unless the cam is designed for them),
1 3/8" exhaust,
tight deck height,
and
it would be nice if you are going to rev to 7000 to have quality pistons.
(you WILL want good dual springs)

...oh yes, no lighter than that 12lb FW if you want nice drivability.

thanks guys, great info...

the heads came assembled, with dual springs, will these do or should I have them replaced when I get them ported?

I am trying to hunt down some 85.5B's next week, apparently Century make some? Mahle describes both the 85.5's and 87's as forged, but it says on Cip1 that both are actually cast? any light on this one?

thanks again.

There are cast 85.5's and then there is Mahle "forged" which are spun cast. THe mahle's are good for about 7200 from what i've read. Personally i've reved them to 7000, and they look fine.

Real forged pistons are a entirely diferent ball game. Wiseco, JE or CP are the main manufacturers that make VW pistons. They start at 90.5 with wiseco's, and JE and CP will make anything you want to order.

My new custom CP's are costing me $675 USD for a set of 4 94's with big dishes. Every CP piston is made to order so the prices are generally the same. Easily good for 9000 RPM as are most real forged pistons.

Last time i checked, the 85.5 was a stock size barrel. Why are you trying to source centurary barrels when stock would suit your needs, or instead go for mahle 87's?

[ Edited on 20-5-2007 by 2443TT ]

110 sounds good ,but for your exhaust i would have to go against some of guy's and say 1 1/2 inside diametre for the extractors, so 1 5/8 pipe due to the fact of the higher rev's.smaller sizes are good for lower rev's.
2 to 2 1/4 for your exhaust.
if the gas can't get out it can't get in so muffler choice is very important.try a straight through ofset centre with perforated tube as apossed to fluted.
combo sound's like fun....

There is quite a few topics of discussion about square engines on http://www.shoptalkforums.com.  The general concensis is why bother, when you can go larger if you want too. I suspect it is some cross over information from the EJ20T subaru and SR20DET nissan people infecting the VW croud with their theories. VW engines have WAY more potential for the modifier than these import engines. By that I mean, lets see either of those engine put on an extra 800-1000cc in capacity.

Also, Rod Penrose can probably help you out with the cylinders as well. Centurary/Jaycee etc are all the same as i understand it. I don't have his number but its here on the forum somewhere.

Cheers,

ian is right about the sqaure bore.most of these engines are produce with max torque at as low a rpm as possible.but because of the variable cam timing that these cars have ,they can also rev them quiet high.some of these cams have as much as 11 mm lift standard.440'
i wouldn't be chasing a square bore if you want to rev the snot out of it.
vw's don't have the main bearing strength of the new motors.
for eg
f1 100mm piston 45 stroke and rev to about 19,000 rpm
nothing sqaure about that.
long rods ,big piston's ,short stoke = rpm

Hot Vws are in the middle of a buildup of a square b/s high milage engine at the mo. So that might be fueling some of the interest too.

Out of interest, in the bore V stroke theory, why is it that people only go up to a 94mm big bore? Surely you could go bigger. Is there a good reason, beyond the strength of the case? Coz the ali cases are alot stronger aren't they?

Larger than 94 isnt a strength issue anymore with the release of alloy cases with no head studs that can be purchased with extra deck material, and heads that can be purchased without head stud holes drilled. Its more of a pricing factor for most I suspect.

To step up to 96 bore on a stock case can be done, but its better done on a blank alloy case so you can re-locate the studs without compromising the case strength. You can buy CB Comp eliminators without head stud holes drilled, so you can then custom drill them for a 96mm bore cylinder as well. The studs must be moved further outwards, as the holes for a 94mm bore would overlap on the cylinder sealing surface of the 96's. Now these are the cheap option....

To get really big you need autocraft 910's and can go up to 105mm or 4" bore and beyond in some cases. At that level your playing with heads that are normally used on 8-9 second drag cars, so streetability becomes a concern too.

[ Edited on 24-5-2007 by 2443TT ]

Or you go type 4 case as they can handle a set of 105mm bores and you can machine stock type 4 heads to use 105 as well. but you usually set them up not to be huge rpm pullers but to use the V8 style grunt they can produce.


big block volkswagens we call em... LOL

fair enough, I knew there was a good reason.

Bores above 96mm require 6 studding to stop cylinder leaks as well.