Flat top pistons

[jay28]

Ok thanks for that,

Ill send them an e-mail and see if they have them in 86mm, closest I can find so far is 86.1mm, but that means getting the block bored out.........

Jay

[mark belrose]

Ok thanks for that,

Ill send them an e-mail and see if they have them in 86mm, closest I can find so far is 86.1mm, but that means getting the block bored out.........

Jay

FYI your machine shop would most likely perform a quick hone on the cylinders to accept your slighly larger pistons. A lot cheaper and faster than boring the block.

Mark

[Arne]

so which head do you recomend using? E88 or p90a with the solid lifters?

If the combustion chamber of the UK P90a is the same shape as the US P90/90a, it is a superior head than the E88. Bigger valves, much better combustion chamber shape, supposed to have better flowing ports, too. The compression with a P90a and flat-top pistons will still be less than you'd get with the E88 (probably around 8.5:1, I should think), but on the whole I'd think that the rest of the improvements of the P90a would still make it the preferable choice.

[enzo250GTO]

Hi, I agree with Mark Belrose. Buy the 86.1mm pistons and get the machine shop to hone the cylinders to suit the pistons. The .1mm is only about 4 thou and will probably be taken up by normal wear in the bore anyway. Good luck and happy motoring. Regards David.

[Zs-ondabrain]

I got mine about 10 years ago from Victoria British (now called Black Dragon), Here is the link http://www.blackdragonauto.com/icatalog/z/t.asp?page=54

I think I paid $240 USD for the set of six with rings and pins back when I got mine. That was considerably cheaper than anywhere else I could find at the time.

I can barely make it out but it says.....

"One complete set includes all pistons, rings and pins necessary to complete one engine. Replace your old pistons today to avoid engine damage in the future."

But that's it. same results as Jeff got.

Sorry.

[Zs-ondabrain]

I just found that exact page in my BD book. Here ya go Let me know if I got it right.

[beandip]

I am running a F-54 na engine , flat top pistons with a P-79 head milled .030''. This gives me 9.5 to 1 compression. Someone here should be able to tell you how much to mill a P-90 head to arrive at a suitable ratio. At .030 removed you do not have to shim the cam towers. My flat topped motor with the unmilled head was at about 8.5 .

[jay28]

Ok thanks for all the help guys,

Only prob is Ive already ordered a stage 4 cam for the E88 head......will that cam work with the p90a?

Cheers,

Jay

[Zs-ondabrain]

Sorry for "jacking" the forum but I have a similar question for anyone who knows.

I want to rebuild my 2.4 and I'm thinking a 30 over bore should suffice. I have a rebuilt N42 head that has also been resurfaced for clearance (least amount possible). I'll be using my 470/280 stage 2 cam and the triple 40DCOE's and ceramic coated header and Mallory Unilite w/ MSD 6A and promaster coil, So my questions are these.........

Is it cheaper to go with a 20, 30, 40 or 50 over bore?

Flat tops are probably the better style for a standard rebuild (not looking for serious power or CR) so should I go with Forged or Cast pistons? Milled?

Are they comparitble with my existing rods or should I buy new? Also, which-ever is better, should I ballance them beyond stock specs.

I'll obviously ballance the crank and likely have everything polished. Is "Knife edging" the crank even possible or needed?

I will ballance and lighten the flywheel. but I don't want it so light that it effects daily drivability. 10lbs is too light, standard is 24lbs? do you think 16lbs is a good round number?

I hear alot about NOT going with the Centerforce 1 or 2, what is the best clutch pack to go with for the build I have in mind.

ANy info is greatly appreciated, I'm not looking for all out HP, the car will still be a daily driver, Fuel milage is still a consideration, and I'd like it to last as long as the original did. A Conservative build is what I have in mind, extra HP is obviously in the works but Hi numbers aren't necessary.

All this will be on a "Daves" Budget. (under $1000) Are used piston and new rings even an option?

Sorry again for jacking the forum but I really need some basic answers.

Thanks in advance,

Dave.

[jmortensen]

It's easy to find pistons in 1mm overbore, which is .040". I think you'll have to eyebrow (notch) the block for valve head clearance if you run the N42 on the L24 block. If you're mixing and matching anyway and aren't worried about staying original, why not find an L28 and use the N42 on that? Should be worth about a 15% jump in power due to displacement alone.

Knife edging the crank is overkill for your usage. It's expensive and is really about removing rotating weight, which based on your flywheel comment you aren't too concerned about. Cast pistons would do fine if you aren't really upping the compression or revs a lot.

The L series has enough low end torque that the 10 lb flywheel is really pretty easy to deal with. Stop and go is no problem at all. The one thing I'll say about it is that it's tougher to keep a totally steady pace on the freeway, the car instead always seems to be accelerating or decelerating. You will get used to it and learn some finesse with the right foot, but it does take a little time. 16 lbs would be a big improvement over stock as well and you can have your stock flywheel turned down to that weight for about 1/3 to 1/4 the cost of a lightweight replacement.

My clutch recommendation is ACT with a stock clutch disk or their CF clutch disk. A puck clutch is unnecessary for your likely power levels and will make the car uncomfortable to drive daily due to chatter and harsh engagement.

If the bore of your engine isn't badly worn (and they usually aren't) you will most likely be able to just hone the block, swap rings and bearings, and reuse the old pistons. No problems with that and it really keeps the cost down.

[Diseazd]

Very well said Jon! Guy

[wishihadaz]

Hi all,

I was wondering is it possible to get standard size 86mm flat top pistons to increase my CR.

This is my first rebuild so if anyone has anyother sugestions please feel free to advise me,

Thanks,

Jay.

Standard pistons do not increase CR by themselves.

It depends on the head/piston combo you use.

The reference from the Brian Little website is a good rule of thumb as you can make subtle adjustments with head gasket thickness and mild milling of the P90.

Let the machine shop take the responsibility for getting the bore/piston right.

You couldn't find a piston source in the UK?

ITM is another supplier of stock/cast pistons as well as other internal parts.

http://www.itmengine.com/index.html

I did not use them because I got a deal on some forged pistons instead.

Perhaps someone else may be able to vouch for them?

Good luck!