smayo144
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| posted on 22/12/06 at 09:56 AM |
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Crossflow revs
Thinking of doing the 1300 piston mod in my 1600 crossflow. Its an all new engine rebuild so all parts will new / good condition and balanced.
Anyone know what they will rev to. I will have a shift light & rev limiter fitted for safety.
I currently rev the 1600 pistons to a 7000 max, but only in short bursts. Without problem so far.
Any advice appreciated
Si
PS No I can't afford to go forged 
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MikeR
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| posted on 22/12/06 at 11:50 AM |
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don't know the exact answer but the cast 1300 pistons don't like lots of revs repeatidly. They are quite (in modern terms) top heavy, wear
the bores and risk the gaps between the rings breaking.
Its a good mod - just not for sustained high revs like on a track.
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smayo144
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| posted on 22/12/06 at 11:54 AM |
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Do you reckon they would cope with sprints and hillclimbs as they tend not to require maximum revs for sustained periods i.e long straights and lots
of laps !
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MikeR
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| posted on 22/12/06 at 01:48 PM |
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no idea - i just know of the failure points & the fact that a lot of crossflows have had them & get rebuilt after (by modern engines) low
mileage - 5 - 10 - 20k miles.
They are (where) standard i think in the caterham 135hp engines.
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Memphis Twin
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| posted on 22/12/06 at 03:09 PM |
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The 1300 piston is fairly weak, but you'll be fine to 7000+ in short bursts. Make sure you've got good rod bolts fitted; K-Max or ARP.
Your 1600 X-Flow will make maximum power well below 7000 unless you've installed a monster cam, brilliant head and big carbs, and with a high
lift, long duration cam you're going to need deeper valve pockets in your pistons.
Chris.
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viatron
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| posted on 22/12/06 at 05:32 PM |
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We ran a fully balanced and lightened 1760 xflow last season in the tiger series and ran it with a limit of 6800, max power was tailing off at about
6600 to 6700 so not much use running up past 7k unless you have the cam to make the most of it.
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smayo144
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| posted on 27/12/06 at 04:23 PM |
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quote:
Originally posted by Memphis Twin
The 1300 piston is fairly weak, but you'll be fine to 7000+ in short bursts. Make sure you've got good rod bolts fitted; K-Max or ARP.
Your 1600 X-Flow will make maximum power well below 7000 unless you've installed a monster cam, brilliant head and big carbs, and with a high
lift, long duration cam you're going to need deeper valve pockets in your pistons.
Chris.
It had 140bhp on the dyno with a Piper 285 cam, big valve head, 2x40's on +0.90" 1600 pistons.
Following breaking a follower and wiping the top of a cam lobe off out, I have changed to a Piper 701 cam (Edited to add its a Piper 391, not 701
!)and am just trying to decide whether to put 1300 pistons in before having it on the rolling road. Not expecting loads more power just a bit more and
more torque.
PS The current 1600 pistons have now got cut outs.
Any advise welcome as to whether the 1300's will be better than the 1600 pistons with this spec or just a danger waiting to go bang ??
Some have also suggested Lotus Twin Cam flat top pistons with a bowl machined in, as an alternative ?
Simon
[Edited on 28/12/06 by smayo144]
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Marcus
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| posted on 27/12/06 at 04:34 PM |
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I hope they're ok, 1300 pistons are part of my rebuild over winter. I'll be sticking to 6500 revs though with a kent 244 cam, bike tbs and
megasquirt. Hoping for 130bhp - any chance do you think?
Marcus
Because kits are for girls!!
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MikeRJ
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| posted on 27/12/06 at 05:12 PM |
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quote:
Originally posted by Marcus
I hope they're ok, 1300 pistons are part of my rebuild over winter. I'll be sticking to 6500 revs though with a kent 244 cam, bike tbs and
megasquirt. Hoping for 130bhp - any chance do you think?
Power is made or lost in the head! If the head is good enough then that's a reasonable target.
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smayo144
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| posted on 28/12/06 at 09:36 AM |
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Anyone have any experience of the Twin Cam piston in xflow route i.e having a bowl machined into the top.
Also has the 1300 piston got a lower max rev limit than the 1600 pistons. The advice I have recieved from engine builders re 1600 pistons is that they
will go to 7k, but everyone seems to say the 1300's max 6500 (even Burton).
Most engine builders I have talked to about 1300 pistons usually turn there nose up and say "forged"
[Edited on 28/12/06 by smayo144]
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Memphis Twin
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| posted on 28/12/06 at 05:33 PM |
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Forged pistons are obvously the answer if money is no object. They're about £150 each(!) but are bulletproof.
The Lotus Twin Cam piston is very strong and very light, but will not take a combustion chamber because the piston crown is far too thin. They
actually have a lower compression height than the X-Flow by 5.75mm which, with the gasket makes about a 7mm combustion chamber in the cylinder bore.
It's been done hundreds of times before and DOES work. The crossflow inlet port creates swirl in the bore and concentrates the burn toward the
centre, so you should need no more advance than a normal hot X-Flow. The all-steel 1700 X-Flow in my Hillclimb Mallock had forged flat-top pistons
running down the bore about 4mm at TDC, together with a very small chamber machined into the head, but it was effectively a flat-head/flat top piston
motor. It made a genuine 180bhp (dynoed) at 8000rpm! (175bhp at 7500).
The 1300 X-Flow piston has a large gap just below the rings which weakens it, hence the need to keep to a sensible rev limit.
You pays yor money and makes your choice....
How good is your cylinder head? Has it been properly ported?
Cheers Chris.
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gazza285
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| posted on 28/12/06 at 06:20 PM |
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The 1300 pistons have a smaller bowl in the top, giving both a higher comp ratio, and a heavier piston. It is this extra piston weight that gives the
1300 a lower rev limit.
I'm using flat top pistons with a 1300 steel crank in a 1600 block, no chambers and the pistons are about 5mm down the bores. Gives a ratio of
11.2:1, not had it dyno'd yet since the last rebuild as the car has changed from a Mk1 Escort to a Westfieldish, which you might be surprised to
find out, is in bits.
DO NOT PUT ON KNOB OR BOLLOCKS!
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MikeRJ
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| posted on 28/12/06 at 07:22 PM |
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quote:
Originally posted by gazza285
I'm using flat top pistons with a 1300 steel crank in a 1600 block, no chambers and the pistons are about 5mm down the bores. Gives a ratio of
11.2:1, not had it dyno'd yet since the last rebuild as the car has changed from a Mk1 Escort to a Westfieldish, which you might be surprised to
find out, is in bits.
Does the lighter weight of the pistons offset the dire combustion chamber shape you get?
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gazza285
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| posted on 28/12/06 at 08:15 PM |
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As opposed to the dire, square edged chamber you get from using forged pistons, or opposed to the dire combustion chambers of the standard pistons?
Did you read Memphis Twin's post? Many similar engines have been built and have run effectively.
DO NOT PUT ON KNOB OR BOLLOCKS!
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MikeRJ
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| posted on 28/12/06 at 08:32 PM |
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quote:
Originally posted by gazza285
As opposed to the dire, square edged chamber you get from using forged pistons, or opposed to the dire combustion chambers of the standard
pistons?
The standard one isn't great I agree, mainly because it moves! But it has to be significantly better than a wide cylindrical shaped combustion
chamber, simply because the majority of the charge will be reasonably close to the spark plug at ignition, rather than hanging around next to the
(reltaively) cool bore walls, i.e. shorter flame path.
Not saying this can't make good power, but it will doubt be at the expense of economy and emissions (obvioulsy not an issue on a track car).
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Memphis Twin
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| posted on 28/12/06 at 11:45 PM |
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If you can put it on an ignition management system (DTA Megajolt etc) the flat-head/flat-top piston setup will work even better...if you know a good
rolling road man. You'll have optimum advance at all engine speeds.
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Memphis Twin
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| posted on 28/12/06 at 11:53 PM |
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quote:
Originally posted by gazza285
I'm using flat top pistons with a 1300 steel crank in a 1600 block,
Is that the crank I gave you Gazza? If so, which bearings did you use?
Chris (ex Darley Dale)
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gazza285
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| posted on 29/12/06 at 04:13 AM |
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Chris, how are you?
I used CVH rods in the end, they're just short of 2mm smaller big ends, have a narrow enough bearing, and needed just over .6mm taking off the
width. My engine man was worried about the crank running off when I had it re-nitrided, but it all came back running true. Cost me a lot less than a
new crank anyway , cheers mate.
DO NOT PUT ON KNOB OR BOLLOCKS!
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