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Thread: l28 pistons 120thou(3mm) over??

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    Default l28 pistons 120thou(3mm) over??

    Ive done a bit of a search and a few have touched on this but id like more ideas.
    I understand that with a LD28 cranl/l24 rods, there are pistons the can be made to fit- with fly cutting etc.
    But im more interested in keeping the std l28 crank and rods and just using 120thou flattop oversize pistons- without having to get them made up custom(too much $$$).
    Anyone know of any other piston combo that would work.?
    thanks
    71 240z -stock as a rock

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    Registered User NZeder's Avatar
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    See http://www.escort-us.com/piston/nissan_c.html#3
    I am thinking the same for one of my spare engine (installing a stock L28 to get the car back on the road + to sort out my MegaSquirt setup) then build up a good 3.0l using L28 rods and crank with 89mm pistons like the ones they have listed (or maybe even a good 2.9) spending more time and $$ on the head
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    Thats a good web site..
    Nice looking gear but a bit too pricey.
    $660 is in US dollars right? So prob about $800-900 AUst dollars with freight- Im not sure if they come with rings.
    Are the big valve recesses needed--Dont most people use flattops-even with high lift cams?

    L28 40thou+(87mm) flattops sell for approx $260 approx here in Australia +$150 for rings , but of course im really keen on 89mm ones.

    I'll keep that website if i plan on boosting my budget
    Last edited by datfreak; 01-13-2006 at 01:36 AM.
    71 240z -stock as a rock

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    zguitar71 zguitar71's Avatar
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    The pistons from the pickup trucks (I can not remember the part number) with a 135mm rod and l28 crank is the combo I would like to have. The pin height of the piston and the 135mm rod combo would put the piston flush with the top of the block. I think the L20 motors have the longer rods but I am not sure, the L24 rods are 133mm, I might have to get custome made rods too. In the end the result would be a high revving motor (assuming it is built right). A high revver is more appealing than a lower revving stroker, no real reson, I just like to wind up a motor. The hole thing would cost as much as a stroker too.
    Did I hit that cone?
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    You also must remember that all the power or most of the power from a L series head, comes more from head work then from upping the displacement.

    Though you will get a bit more power it is negligible in comparison as to what you could get from proper porting and work on the head with a good cam selection.

    It is also not always necessary to go to the largest bore either.

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    zguitar71 zguitar71's Avatar
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    Quote Originally Posted by boostedz
    You also must remember that all the power or most of the power from a L series head, comes more from head work then from upping the displacement.

    Though you will get a bit more power it is negligible in comparison as to what you could get from proper porting and work on the head with a good cam selection.

    It is also not always necessary to go to the largest bore either.

    An over square motor has more potential to rev high without comming apart so with the right head work, intake and exaust and cam the motor could rev to 8K+ thus moving quite a bit of air in and out of the motor making a lot of power. The bump to 3.0L does not hurt either. I do not know the reality of making a street motor like this, it is more of a dream than anything else. I agree that changing the displacement without making the head flow properly can be a waste of time and money.
    Did I hit that cone?
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    Christopher Gray

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    The reason for posting that was simple, if you ever go to see or look at some of the specs of the Bonneville salt flat cars, you will see that most of theyre work was spent on top end building.

    I also agree whole heartedly that a over square motor does have great potential to rev and run well.

    The reason for sayign it isnt really necessary to up the bore so much is to just look at Norman Simpers 240Z. Its only a 2.9 stroker and is a 12 second quarter mile car.

    There was no need for him to up the cylinder bore to 3.0 or 3.1 litres of displacement.

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    another classic car guy EricB's Avatar
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    for those of you that have or will shortly be overboring those extra mm's to 89mm... where are you getting a headgasket from with matching larger bores in it? Curious...

    -e

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    Quote Originally Posted by EricB
    for those of you that have or will shortly be overboring those extra mm's to 89mm... where are you getting a headgasket from with matching larger bores in it? Curious...

    -e
    HKS makes a gasket with a 90mm (I think) bore.
    Did I hit that cone?
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    Would a 3mm overbore help with the head work?..
    ie -its more room for bigger valves without notching the block-
    and more room for chamber reshaping, valve deshrouding etc
    plus the bigger overbore will increase the C.R. (with the bigger displacement) with flattops anyway

    THere is some place here in aust that made copper head gaskets to any size overbore for approx $100aust. I cant find their web page now but ill dig it up somewhere.

    but if these pistons are going to be hard to get/make, its prob easier and cheaprer to use 40thou flattops.
    71 240z -stock as a rock

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    Registered User ZSaint's Avatar
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    I have a 2995cc engine in my '71. It has the LD28 crank, 240Z rods and Z22S pistons. The machinist had to maching the top of the piston because it sat above the block. I have a P90A head and have a compression ratio of 9.0:1. I am presently running ZTherapy SU's with a stock turbo camshaft. I just received a .480 lift/268` duration hydraulic camshaft for it. I will see how it performs with the new cam. I have plans for getting a bit more flow into the head. It now has a LOT of torque and spins very well to 6500. The short block was built by Hatch Engine Service. They also ported the P90A head/intake manifold and did a trick valve grind. I am very pleased with the performance of this engine.
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    Z Saint, the vintage racer! I've traveled a long way and some of the roads weren't paved.

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    Hi ZSaint, nice looking motor. Can you tell me if the crank scraper is held down by the main cap bolts? Looks to be, I'd like to put one of these on my Z but don't want to drill and tap ANY area for the scraper hold downs.

    Thanks in advance,

    Chris A.
    1973 240Z HLS30-156693

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    Quote Originally Posted by datfreak
    Would a 3mm overbore help with the head work?..
    ie -its more room for bigger valves without notching the block-
    and more room for chamber reshaping, valve deshrouding etc
    plus the bigger overbore will increase the C.R. (with the bigger displacement) with flattops anyway

    All that should be able to be done on an L28 block with out the over bore.
    Did I hit that cone?
    1/71 series II 240z, 920 gold (AKA baby poo yellow, but I love it anyway)
    Christopher Gray

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    Registered User ZSaint's Avatar
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    Yes! The crank scraper is only held on by the main bolts. I ordered this scraper for the LD28 crank but it had to be fitted to the "throws". I also use the aluminum pan with a nice set of oil gates.
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    Z Saint, the vintage racer! I've traveled a long way and some of the roads weren't paved.

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