Bore Size & Reliability

[Paul Illick]

Good question. I'm to the point where I'm deciding which pieces to use and I'm tempted to put a welded 78mm crank together with stock 96mm pistons. Longer stroke means more torque and a lower cost than just bigger liners. Or no? Sure bigger is better when it comes to total performance, but are there any of those 'sweet' combinations like you see in the Type 1's?

[Joe Del]

I'm familiar with performance Type 1 engines, but have a few questions regarding the bore size of performance Type 4 engines. For example, I know the 90.5 P/C (1776) is a good choice for the Type 1 and the 88 P/C "slip-ins" (1679) should be avoided.

What about Type 4 P/C kits? I'm looking for a good balance between performance and reliability. The 96 and 103 kits seem to be the most popular. Since most of us are building Type 4 engines for a lighter Type 1 Beetle/Ghia, is bore size, cooling efficiency even an issue?

[This message has been edited by Joe Del (edited 08-02-2000).]

[JohnConnolly]

96s for 1700s should be avoided. 96s for 1800 and 2000s are very good. 103s are good provided you 5th stud (or 5/6) the heads and cylinders. Any engine with 103s that makes RESPECTABLE power will leak at the head/cylinder junction if this isn't done.

Once you hit 78/80 stroke, you should to have a clearanced cam (smaller base circle) if the cam is on the large side. Use type 1 rods to get rid of the boat anchor type 4 rods (too heavy).

[[email protected]]

This is simply information I have collected, I haven't ran any of these combinations yet.

96 sets for the 1.8/2.0 work well, like John said. They would provide a decent bang for the buck.
103s are more more complex. The heads need to be very stiff, probably welded top and bottom, and 6th studded or 5th studded. The heads I am buying are welded around the intake and exhaust port, welded around the plug hole, 6th studded, the chamber reworked, 48x40 valves, and other tricks. $1500 for a set of heads is expensive, but that is what it takes to make 103s work.
If you can't budget for super strong heads to use with 103s I would do a 78x96 combo. And buy stroker 96 pistons, the install would be very easy.
I have been told 15,000 is the max life you'll get out of 103s between hone jobs and possible reringing. This is fine for me 200 street horsepower has its prices to pay!

If you are going to look into a 78 or 80 stroke crank talk to John Connolly. I bought a crank with type 1 rod journals, counterweighted, and offset ground to 78mm stroke. This lets me use regular old Scat 4340 H beam rods in a 5.4" length, and type 1 22mm wrist pins. The 22mm pin instead of a Type IV 24mm pin saves a gob of weight on each piston. I think my 103 JE pistons weigh less than a Cima 94
By the same token, you can run light weight Cima Type 1 94mm pistons in a 2.0 barrel with the special crankshaft and be in business.
Steve Arndt


Steve Arndt

[Slugmika]

my engine has 103s and 84mm stroker. i use this engíne for circuit racing. heads are scat splitports and i only use 4stud, no leaks. i am planning to built another engine and it would be something like 78/80 stroke and 103s. if i use vw heads i will get those 5or6 studded. shorter stroke makes it possible to use wilder cam so i can get more lift.
problem with my current stroker is that i have to special order my cam, and lift is quite mild. bytheway those cams are made of 1.7 t4 original cam.
i use porsche 11 blade fan and big Riechert Tuning oil cooler and i havent had any problems with cooling.
And yes like Jacob said you really dont need first gear if you are using stroker.

Mika