dave_424
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| posted on 21/5/14 at 08:20 PM |
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ZX9 turbo engine build/upgrade
Hi guys, well I've had my turbo ZX9 engine at 7psi for a year and now want to turn up the boost. The engine internals are completely stock,
running megasquirt injection and spark.
Quick question, if I can easily run 7psi at 11.5:1 compression, what CR should I drop it to to be able to run 15psi?
I'm changing out to some forged Wiseco pistons for strength and a cylinder base spacer to lower compression. Also changing the waisted head
bolts out with some standard 12.9 allen head bolts.
I got another set of cylinder bores and had them bored out for my 1mm over pistons.
I measured the volume of the valve cutouts in the piston, then took the head off and measured the volume of the combustion chamber which I can then
use to calculate the size of the base spacer I need to get the correct compression ratio.
Next I need to put the pistons and cylinders on and measure the deck height, then I will be able to figure out the right thickness for my cylinder
base spacer.
I will update this thread with my progress
Photos below...
And a teaser for something else I am building with a friend, hayabusa powered
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matt_gsxr
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| posted on 21/5/14 at 09:26 PM |
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Have you got an intercooler?
Do you mind paying the extra for the higher octane fuel?
I went through the same decisions as you. It is tricky because dropping the CR hurts you when off-boost.
I think I aimed for 9.5 (on advice from old-skool suzuki guys), but owing to the limited thickness choice with spacers ended up at 9.
I have been only running up to 10psi.
Not much of a datapoint. Sorry.
http://jpsc.org.uk/forum/
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dave_424
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| posted on 21/5/14 at 09:53 PM |
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I have a Landrover 90 intercooler, not exactly efficient but that's what I have at the moment, could definitely look at going to a bar and plate
one which would be much more efficient.
I only use super unleaded since it's been turbo'd
Actually that's a pretty good point and solidifies what I was thinking, I was looking to go with 9.5 which is 2 points lower than stock but as
you say you kind of have to go with what base spacer you can get. I have a 1.6mm spacer but think that it might be just a bit too big. Anywhere
between 9-10:1 and I should be good.
What kind of power have you made at 10psi and on what turbo?
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obr_technology
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| posted on 22/5/14 at 08:35 AM |
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Hi Dave,
You might find this useful:
http://forums.pelicanparts.com/uploads13/PorscheGeometricCRchartrev212050102651218890694.jpg
I used something similar when doing my charger conversion and it helped me to have an undertanding of physical compression ratio and then the
effective compression ratio caused by the boost pressure.
Obviously the availability of spacers will dictate where you end up, but thought this might be of use?
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matt_gsxr
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| posted on 22/5/14 at 08:53 AM |
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quote:
Originally posted by dave_424
What kind of power have you made at 10psi and on what turbo?
Power is adequate (to paraphrase RollsRoyce).
Not had it on a rolling road. I should do as my ignition map is a bit random at the moment but life gets in the way.
http://jpsc.org.uk/forum/
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dave_424
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| posted on 22/5/14 at 11:04 PM |
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Got my bored out cylinders on and installed one of the pistons to figure out how much of a base spacer I need to drop the compression ratio to
somewhere between 9-10:1
I got my dial indicator and set it to zero on the face of the cylinders and then move it over to the piston (When set at TDC) and measure the deck
height which turned out to be 0.023" or 0.5842mm
Adding my base spacer which measures at 1.17mm puts me at a compression ratio of 9.44:1 which is good enough for me.
Here are the original cast pistons, unknown mileage and gets a pretty good beating when in my buggy, been running 7psi boost for about 30-40L of super
unleaded, excellent condition and will be used again if I manage to melt these forged ones.
Stock cast pistons vs forged, tomorrow I will be gapping the rings to Wiseco street/modified turbo specs.
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