Blairm
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| posted on 30/8/09 at 04:28 AM |
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Xflow with Alfa pistons
Hi Cross flow experts,
About to rebuild my crossflow and have a Nissan L18 crank and L16 rods to go in it (common option to get steel parts down under). The rods are 133mm
long (basically same as BDA items so I have a better rod ratio and a lighter piston hopefully) so I need pistons with lower compression height.
Around 37mm with 40 cc dish roughly. I don't won't to spend huge sums on forged or custom units and have read Alfa pistons are used a lot
but cannot come up with any more information.
Can any one help with what is normally used. I am aiming for 83.5 or maybe 84mm max.
I have found Toyota Supra 7MGTE pistons will work. 33mm compression height and 18cc dish so not Flat piston and flat head, but somewhere in the
middle so should have some squish and will hopefully not need to much advance.
Any ideas much appreciated
Regards Blair
[Edited on 30/8/09 by Blairm]
[Edited on 30/8/09 by Blairm]
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Ivan
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| posted on 30/8/09 at 07:49 AM |
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In SA I know that they sometimes use Peugeot pistons in Xflows - but don't know which or under what circumstances.
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Blairm
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| posted on 30/8/09 at 08:29 AM |
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Thanks Ivan, I think guys in SA are a bit like us in New Zealand and probably Australia for that matter. Echange rates often prevent directly buying
he "correct" bits and looking for more cost effective alternatives.
Will try and see what I can find. The hunt continues :-)
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thunderace
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| posted on 30/8/09 at 09:01 AM |
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what block are you useing?
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Blairm
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| posted on 30/8/09 at 09:04 AM |
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Hi
Using a 1600 711M block (have a couple to choose from). Hence only wanting to go 83.5, maybe 84 mm to make sure we don't get to thin.
Blair
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MikeRJ
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| posted on 30/8/09 at 10:39 AM |
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Not heard of this conversion before. If you don't use pistons with the correct crossflow shaped dish you are going to lose the squish band
which surely can't be a good idea on an engine that already has a pretty poor combustion chamber shape? Or is it possible to find pistons that
retain this?
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Blairm
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| posted on 30/8/09 at 07:41 PM |
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Mike, I agree.
Have heard the Alfa piston is heavy which may suggest it is a full dish similar to the Crossflow. I have seen in some of the ford forums like
Turbosport a lot of talk about building flat on flat engines with no dish. Lotus Twin Cam pistons are used a lot (very hard to get here and very
expensive). 3 or 4 more degrees advance is required to account for reduced squish, but is a race engine at high RPM's it is considered not as
big an issue. Also Nissan CA18ET flat top pistons have been used apparently.
The Toyota piston does no go all the way up the bore (about 2.8 mm short after decking for around 12:1 compression ratio) but does have a dish similar
to the Xflow, so not proper squish but combined with the inlet port turbulence the flat on flat guys talk about may be OK.
The compromise is around taking prices listed in the UK for of the shelf options and essentially multiplying the price by over 3 to get them here in
our dollars 
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MikeRJ
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| posted on 30/8/09 at 08:11 PM |
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Thinking outside the box, I wonder if it would be possible to incorporate a ring of cast iron that would protrude into the bore slightly to create a
squish band with flat pistons? Perhaps it could be a top hat shape that hangs in a recess machined at the top of the bore and is clamped by the head
and gasket.
I'm interested in the Nissan crank and rod conversion, does this require considerable machining of the block?
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Blairm
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| posted on 31/8/09 at 06:23 AM |
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Hi Mike,
The guy who has done mine seems to be the "expert" down here and is quoted all over the web. He has some really usefull stuff on the
web.
Start by looking at this:
http://www.geocities.com/marty7_nz/datsuncrank-index.html
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thepest
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| posted on 31/8/09 at 09:03 AM |
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I use the fiat 2L flat-top pistons... yes I know it defies logic but have been using them for years and close to 2400 miles with no problems 10.5:1
compression ratio.
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Blairm
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| posted on 31/8/09 at 09:17 AM |
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Great to hear from someone who has actually run flat on flat.
Do you know what model piston they are from?
What rod length are you running?
Do you know the compression height?
Have you decked the block?
Regards Blair
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Blairm
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| posted on 31/8/09 at 09:24 AM |
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Mike
Your out of the box idea is interesting. I have heard of a similar modification used by one of NZ'd top engine builder which is to create a
sqish zone by bonding a plate which the correct profile cut in it between the block and the head. In this way you don't have to chamber the
head and shroud the inlet port and use lighter flat top pistons.
Oh to have the skills and a full machine shop in the garage!
Cheers Blair
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