9 replies to this topic

[lapider]

So the question is pretty much my title. a have an 87 a+ 998. i want a bit more out of it. its already got  an RC40, stag 1 kit. cone K and N but it also has a 12G295 998 cooper cylinder head with unleaded valve seats and double springs.

 

the car is off the road at the moment and here is my dilemma.

 

when i did the headwork it turned out that the head had never been skimmed before. so i gave it a very sympathetic skim as it wasn't even distorted, just to ensure a clean and flat surface, done at a professional engine shop who had advised as such. i was reluctant to skim any further as i didn't want to go near the water jacket and I've heard of problems where they are skimmed enough to give a suitable compression ratio, the head then cracked when the car is driven hard and you've got a junk head.

 

so i want to do it properly and acquire a set of D-top pistons (original 998 cooper pistons), my dilemma is i know the a plus pistons are generally lighter, but will the d top cooper pistons fit without an issue. i would be looking at using the standard con rods.

 

further mods hopefully include a kent 266 cam and twin 1.25 su

 

so will the d tops fit the a+ with standard con rods

 

 

[ace01]

You will struggle to find original D tops.  A better bet is to use a high compression 998 piston. 

 

Something like this:-

 

http://www.minispare...rch/classic/998 pistons.aspx|Back to search

[lapider]

ahh okay, will these have more compression than the standard pistons, i can't remember if my current pistons are flat top or dished.

 

lets imagine for arguments sake that i can find a set of d tops. although your point is very valid and if the piston on the link provides the same compression then i will likely get those. 

Edited by lapider, 26 November 2014 - 02:41 PM.

[ACDodd]

You can make your own, by having the piston crown machined. This is not cheap, as the block will also need a sizable chunk removed too. I would rebuild the engine fit new flat tops and deck the block to leave the pistons 0.005" proud of the block at TDC. This will minimise the requirement for head machining. You only need 9.5:1 to get a stock cam to perform at its best anyhow.

AC

[lapider]

wow okay. i do like that idea. although it obviously involves allot more stripping work. 

 

1. How much meat can the block loose before its getting unreliably close to the water jacket or oil wells. is there plenty enough there?

 

2. This would cause an intrusion into the piston, what are the chances that the piston will collide with the valves or cylinder head chamber sides?

 

3. Is that using the pistons previously mentioned (high compression), or standard pistons currently fitted.

[ACDodd]

Loads of meat on block. Easy 1/8".

No chance of valves or piston hitting with +0.005" pop out.

Your engine probably already has the flat top Pistons fitted they came as standard on all high compression engines"

Ac

[carbon]

If you have the flat  top pistons fitted then you are likely to already be running close to 9:1 with a lightly skimmed 295 head

[Dusky]

I was in your boat 2 months ago.

I just skimmed the 295 by 40 thou after carefully measuring the water jackets etc.

[Dusky]

http://www.benl.ebay...=item4d2882305a

[Wright&Wright]

If you scroll down to Number 57 in this list, you'll find they sell d-top pistons for a 998. I nearly bought some when I went to build my engine, however, I managed to salvage the ones that came with the engine so I never bothered. I think when I rang them they cost around £90 each.

 

http://www.scparts.c...c-a-series.html

Edited by Wright&Wright, 28 November 2014 - 05:05 PM.