Bigger pistons and cylinders

[pnikas]

Hello everybody, I was thinking of someday upgrading to 103-105mm pistons from the stock 94 ones I have at the moment , ignorer to achieve maximum torque and longevity . I use the 914 heads (42/36) halves . I was horrified by finding out the sealing problems type 4s have with bigger pistons and cylinders. The cam is rather big since the engine is arround the 140hp mark at the moment. I would like more bottom end torque without giving up the high end, and bigger cc's are a solution to anything . So by using the same cam/heads it should have some improvement in horsepower , but much more torque . Do you guys recommend combinations like the one I have in my mind ? Should it be converted to 5 or 6 studs inn-order to avoid head flex and sealing problems ?

[GARRICK.CLARK1]

Good question about the 103-105's. The heads do seam to be the problem. I have thought of stitch welding the outer fins of the head together, 1 stitch in each corner, This might help a little bit in stopping head flex.
The big bore guys on here will no.
I'm only at 96mm at the moment.

[wreck]

A stroker crank is a good option with 96mm bore . With the 103 plus size bores , Jakob from " Get Back on Track" face book page also has an option of deutz cylinders with Gas ring type gaskets which he has developed for big bore sealing issues .

I'm using 1mm copper head gaskets and will see how well they have sealed in the next month or so when I strip the engine to fix a few oil leaks and a cam upgrade .

[GARRICK.CLARK1]

Roger that.
Looks like The 96's are here to stay on my next build. I no that 78 -80 will be relatively straight forward but I do like to test things .Like If its possible then I wanna build it.
Wreck. Looking back would you have gone bigger on the crank or bought a different rod/rod length etc.

[wreck]

I actually planned a smaller 76mm crank to run 2500cc but with a mix up with the supplier I ended up with the 78mm. An issue with bigger engines is getting valves large enough to flow at higher RPM . On a 2600cc engine my 47mm intake valves "choke" around 6200rpm ,So you lose volumetric efficiency .With a scat C55 ( 265 degrees @ .050 and 0.535" lift) the engine has peak HP at just over 6000. With a smaller motor that peak HP would be higher , trade off is more power at lower revs .

Some of the top nascar engine builders (pinnacle of 2 valve pushrod engines IMHO) have stated the first thing in choosing a rod length is one that gets the piston to the right spot in the cylinder , second is rod/crank ratio . If you look at some popular V8 engines ,the rod ratios are a lot lower than type4 s.

[GARRICK.CLARK1]

Valve size might not matter with a turbo as the air will blast past the valve head , could be wrong.
The 42x36's are a good size for the 96's plus the 42 inlet is probably max I'd go on 96 jugs as 1 side of the valve is fairly close to the chamber wall already. All this info is still leading me towards 96mm stroker pistons, maybe 80 mm crank ,quality rods, web turbo grind cam, longer tubes.

[wreck]

Yeah boosted is a hole different game with VE /valve sizes . I've an eaton M90 that may end up on this engine at some stage.
I'm running a 78mm stroke with 5.325 rods . JE 103mm pistons with 30.08mm pin height . 0.043" deck . I just get way with stock pushrod tubes .

[pnikas]

So you generally don't recommend 42/36 with the 105mm pistons ?
Do you generally recommend the 105mm je pistons ? Will I need extra studs ?

[wreck]

with a 71x105 and a 42mm intake the intake will be a restriction (choke) above 5200rpm . just remember this is peak HP not maximum RPM . My engine peaks at 6000 but I've a rev limiter at 7200 .
https://www.gregraven.org/hotwater/calc ... izing.html

I think you can get away with big cylinders NA with soft copper head gaskets or gas ring type gaskets . Both Walter's "Wally's" build threads on the Type4rum and Boosted forum have a stack of good information .

[pnikas]

Its easy to add 44mm intake valves on the Porsche heads I think, do you recommend that ?

[pnikas]

with a 71x105 and a 42mm intake the intake will be a restriction (choke) above 5200rpm . just remember this is peak HP not maximum RPM . My engine peaks at 6000 but I've a rev limiter at 7200 .
https://www.gregraven.org/hotwater/calc ... izing.html

I think you can get away with big cylinders NA with soft copper head gaskets or gas ring type gaskets . Both Walter's "Wally's" build threads on the Type4rum and Boosted forum have a stack of good information .

Now at 6000 rpm the engine does a kind of roar sound and doesn't seem to be able to climb more ar the rpm range (single hd springs)
Its also kind of low at bottom end torque (big cam ) could this be kind of a mismatch that would be corrected with more displacement ?
I don't want to rev up to 7000 rpm, I want ro be able to climb to about 6000 with nice torque all the way. If I recall correctly I have an 87c cam that is kind of aggrieve .

[wreck]

What are the specifications for the rest of the engine ?

[pnikas]

What are the specifications for the rest of the engine ?

914 heads with 42/36 valves
Dellorto 40drla carbs
009 distributor fitted with electronic ignition
Bas Ahnendorp exhaust system

[wreck]

71mm crank ? Compression?,what size venturi’s ? The 86c is a big cam and won’t work below 3500-4000rpm on that size engine but will rev to 8000 . I’m guessing the noise is valve bounce ,a set of beehive springs from AC Parts net will extend the revs but doubles maybe needed . A either a stroker crank /big bore or smaller cam is the only way to get more bottom end .If you only want to rev to 6k then a smaller cam is really needed .

[pnikas]

71mm crank ? Compression?,what size venturi’s ? The 86c is a big cam and won’t work below 3500-4000rpm on that size engine but will rev to 8000 . I’m guessing the noise is valve bounce ,a set of beehive springs from AC Parts net will extend the revs but doubles maybe needed . A either a stroker crank /big bore or smaller cam is the only way to get more bottom end .If you only want to rev to 6k then a smaller cam is really needed .

I must check on the vents, compression is arround the 9.5:1 mark. ( I didn't build the engine )
If I istall 104mm cylinders and better springs do you think I will make a nice combo ?
It does sound like valve float at 6000