increasing ccs, need help

[CHR!S/DVK]

i recently got a pair of cylinderheads which i got machined for my cylinders and springs.
but now it the machining man tells me the volume of the chambers is just 36cc.

i want to run my engle vz-14 on my 1679(88x69) and believe i can have a CR of max 1:9.0.
by calculating i found out that i need 2.7mm deckheight for 1:9.0 CR. i thought that deckheight could only be 1.5mm max?


what should i do? can i use rings to mount between cylinder and head to win cc? are the actually rings around for my 88mm cylinders(outerdiameter 98mm)?
i can try to win some ccs by enlarging the chambers(unshrouding) but that would be a win of maximal 5-10cc.

perhaps there will be answer of changing the cam but i'd rather not change my plans at this stage..
still, all answers are welcome and helped is needed badly.

[Zach Gomulka]

That is a little cam, but if your fuel can support that relatively high (9:1) compression ratio, go for it. You can also have the pistons dished for more CC's. Are you sure it's only 36cc?? That's quite small...

[Neil Davies]

Having just run some numbers through John Maher's engine calculator (http://www.johnmaherracing.co.uk/enginecalc.htm), I reckon you need to get to 43ccs to get your compression to 9.0:1 with those heads and 0.060" (1.5mm) deck height. By increasing to 2mm (80thou) you could get away with 40cc combustion chambers.

I'd re-check the heads, then look at taking a bit out of the heads, AND a dish out of the top of the piston. A little from everywhere is better than a lot from one place!

[Diederick/DVK]

brother, i think we need to know the the maximum CR you can run on Euro 95 fuel with the VZ-14 first. if anyone could tell us, please... i know there's people here that can calculate that via a computer programme.

my bet would be around 8.5:1. but please feel free to post if you have a more profound bet

then, a deckheight of more than 1.5mm (.060") is generally not recommend for the reasons we discussed on the phone.
and unfortunately, (1) copperhead gaskets are not available for machine-in 88mm cylinders and (2) in my understanding those copperhead rings increase the deck not the chamber. am i right?

that leaves us with one option, using the engine calculation you will need to increase the CCs with 11(47cc total) to obtain 8.5:1 or for example 8(45cc) to obtain 8.9:1. all with a supposed deck of 1.5mm, since we have not gotten around to check that yet.

therefore; is it possible to machine 7cc in the piston and say 4-5 by unshrouding the valves (and similar techniques) to enlarge the chambers?

zach, did you follow up on dishing your dad's pistons?

john maher posted a formula to calculate the max. dish:

I limit depth of dish to .060" (1.5mm) max
Max dish diameter: 20mm less than piston diam
Better squish with smaller diameter dish
Juggle diameter and depth to arrive at target cc using formula below

dish diameter (mm) squared x depth (thou") x .01996

meaning for an 88mm piston, 68mm wide dish, .050" deep.....

68 x 68 x .050 x .01996 = 4.6cc

following up on this, you're now at 40cc meaning you need at least 5 out of the head.

most importantly, could anyone tell what our limit for CR is with the VZ-14 cam?
.462” @ 1.1 274º advertised
.420”  242º @ .050"

or is there anyone who runs a VW shop that would exchange our unused new vz-14 for a bigger cam that would allow us to run a higher CR?

[Neil Davies]

Dieds, you could add a spacer under the barrel instead of a copper head gasket?

[Diederick/DVK]

neil, thanks for your thoughts!
to my understanding a barrel spacer would need to increase the deck height past 1.5mm, which is not good for the combustion, right?
and i've noticed 1 cc does more for the CR than a .01mm increase in deck.

but cheers!
i'm off to have a beer in the sun, here's to hoping more will post

[Zach Gomulka]

zach, did you follow up on dishing your dad's pistons?

Yes, they were dished according to Maher's reccomendations. I think it gave 7cc's which was perfect for that application.

[Diederick/DVK]

good news buddy, would you happen to have a picture somewhere?

[Zach Gomulka]

I do not. They are at my dads house though, motor is of course still unassembled so if I get up there I'll snap a picture of them.

[Diederick/DVK]

judging from the views, help threads again do not attract a great deal of visitors, which is too bad as we would still like to fire up this engine some time this summer.
i'm surprised no one suggested a hemi cut to the heads. i've only heard of it, and honestly i thought it was regarded as an ancient low CR berg mod. but in this case it might just suit our needs.
do let me know if i'm mistaken...

[Zach Gomulka]

I'm not a fan of the hemi cut. The fact that it runs better with loads more advance tells me that it is an inefficient burn (gotta light it off it sooner). It also increases the surface area of the combustion chamber, allowing more heat to soak into the head, rather than out the exhaust (but that's just my personal theory).

I think you need to double check your head CC's, they should only be that small if they were on a high compression race motor. What are the rest of your engine specs?

[Diederick/DVK]

all right, i need to bring this up again since we haven't worked this out and we're pretty much in dire straits here.

using this tool: http://www.wallaceracing.com/dynamic-cr.php
i managed to calculate the dynamic CR assuming we can get the CR down to 9.5:1 this is what i filled in:
4
3.4646
2.7165
5.325
9.5
46 (cam card)
target altitude, let's say 300ft (we're at sea level here)

and this is what i got:
Static compression ratio of 9.5:1.
Effective stroke is 2.39 inches.
Your dynamic compression ratio is 8.42:1 .


here's the cam card:


but, i don't know what the dynamic compression is supposed to be? we'll be using 95 octane fuel...
for reference i calculated my DCR for my 1915 and it came out 7.67:1, which tells me we're still a little high here.

perhaps a cam swap is an option, though not quite our last resort, we'd prefer to still use the vz-14 if possible.

[Zach Gomulka]

I think a cam swap is mandatory. If you want to stick with the VZ series, look at the VZ25. More duration and only slightly less lift than the VZ14, so in theory it should be easier on the lifter bores. It's along the lines of an Engle 110, but with more lift.

Are we sure the heads have only 36cc in them? Have the chambers been unshrouded around the valves? Do that and you will get more flow and more CC's.

You're using 5.325" rods? Stock is 5.394"...

[Diederick/DVK]

oops, that was a mistake then. just checked and the DCR didn't change.
i think my brother took a VW break for a few days after the bad news. i haven't seen a photo yet. i'm hoping we can gain 10cc by unshrouding valves and dishing the pistons.
or going with a w120...

thanks for chiming in again zach!

[Jim Ratto]

I would worry about, if your heads truly are down to 36cc, that you're going to have issues other than worrying about cam profile. If the heads have been flycut that far, you may (probably) find that the fins of cylinder and fins of head will collide. Then finding an 88mm copper head gasket may prove tough.

I'm not sure why you are worried about a cam with 242' @ .050 "not working" with a compression ratio of 9._:1. That duration, in the scope of production engines, is very aggressive. In fact, I believe some of the orginal 356 Porsche stock cams ran a duration @ .050 almost that exact #, (I think it was 244 to be honest). If you're worried about the duration being too short for your static CR, you can change the timing of the cam vs the crank. Meaning turn it back to 108 on intake and 108 on exh. If you "drop it in" it will probably be 104/112, which builds cyl pressure faster, good for power, but if you're on the "ragged edge" as far as compression/octane/timing, it can exacerbate the issues. Straight up or a hint of retard will help, and not castrate power like not giving the motor the ign advance it needs.

FYI: the 1967 911S intake valve closes @ 50ATDC, it's "static compression ratio" was 9.8:1 if I remember correctly. No we are not comparing apples to apples, but by the variables the dynamic calculator takes into account, we're pretty close. The 911 has an intake system years ahead, efficiency-wise over 2 Kadrons though. And more tolerance for heat.

I'm not saying another cam wouldn't be "better" for the engine you're building, but honestly, you're not far off from a good cam for that small cc and Kadrons. Make sure you are fastidious about setting up geometry, spring height, the way the the keepers contact valve and maintenance.

95 octane "everyday" fuel. We should be so fortunate here. 

[Jim Ratto]

all right, i need to bring this up again since we haven't worked this out and we're pretty much in dire straits here.

using this tool: http://www.wallaceracing.com/dynamic-cr.php
i managed to calculate the dynamic CR assuming we can get the CR down to 9.5:1 this is what i filled in:
4
3.4646
2.7165
5.325
9.5
46 (cam card)
target altitude, let's say 300ft (we're at sea level here)

and this is what i got:
Static compression ratio of 9.5:1.
Effective stroke is 2.39 inches.
Your dynamic compression ratio is 8.42:1 .


here's the cam card:


but, i don't know what the dynamic compression is supposed to be? we'll be using 95 octane fuel...
for reference i calculated my DCR for my 1915 and it came out 7.67:1, which tells me we're still a little high here.

perhaps a cam swap is an option, though not quite our last resort, we'd prefer to still use the vz-14 if possible.

I entered your engine specs BUT closed the valve 4 deg later and I got 7.99:1

[Diederick/DVK]

my 1915 specs?

[Jim Ratto]

my 1915 specs?

no your brother's

[Zach Gomulka]

Jim has some good points. I'd also check the valve to piston clearance.

Double check the head CC's already! I have a feeling something got screwed up there.