Pistons/compression ratio

[vikebo]

The piston ring clearance of the upper compression rings are approx. the double of the specifications in Wilkins' book. Also, the cylinders has got some ridges, so I guess I have to get the block rebored and some new pistons.

Looking in Burtons catalogue, it seems like they have got two solutions.

1. Asso/Cast pistons at ~?100 each + a ring kit at ?115. Total: ?515.
Compression Ratio is stated as 9.5:1.

2. Accralite Forged pistons at ~?120 each with rings & pin. Total: ?480.
Compression Ratio is stated as 11.9:1.

The forged pistons are more tempting due to lower price (and they look very nice on the picture...).

Wilkins gives the compression ratio as 9:1. I guess the shape of the pistons is different for the forged pistons (Bowl Apex cc is given as +6.00).

My question is what will the increased compression do to the engine? I understand it can give a power increase, but will I need an octane booster, or can I adjust the ignition to avoid knock?

Any other reasons to choose Asso cast pistons instead of Accralite forged, or maybe other options?

My pistons are marked +0.030.

Eivind

[types26/36]

2. Accralite Forged pistons at ~?120 each with rings & pin. Total: ?480.
Compression Ratio is stated as 11.9:1.
My question is what will the increased compression do to the engine? I understand it can give a power increase, but will I need an octane booster, or can I adjust the ignition to avoid knock?
My pistons are marked +0.030.
Eivind

A c.r. of 11.9 seems rather high for a road engine, dont know what fuel you get there but I'm sure you would need an octain booster, if your engine is as we suspect a 1600 block/crank + a new bore of 40thou is going to give you approx 1640cc. This in its self increases the compression and in my opinion will make it to high for a road car. Increasing the compression can and does give better performance but the the combustion temp's are increased and more stresses are brought on the engine components.
Brian

[vikebo]

OK, about the same as I suspected.

Seems like they can supply other specs for the Accralite pistons. Guess they will be more expensive, but maybe I will ask them.

Thanks!

Eivind

[denicholls2]

You're being quoted ridiculous amounts for either piston set.

We did a buy on Europa Renault pistons a couple of years back from Wiseco and I paid about $400 for forged pistons, pins, and rings. They're works of art. They'll copy any piston you give them, so you can get the CR you're looking for (Europa Renaults run 10.5:1 on unleaded premium.)

I cannot believe that Twink replacements are either harder to find or more expensive, yet your prices are at least double.

Shop before you buy.

[M100]

I think the pistons I used on my last twincam rebuild (0.040) back in 87 or so and made by Hepolite were less than 100 quid a set. The Lotus ones were much cheaper at about 15 quid a piece but were only available in standard and +0.015". Go forward nearly 20 years and we find Lotus currently have standard size Twincam pistons on offer at 25 quid or so a piece but sleeving the block will cost 400 quid and a set of rings 80 so it's not such a great deal it first appears.

If we can bring the price of some alternative pistons preferably designed for road usage down to 200-250 quid a set I'd buy a couple of sets but only from a manufacturer with previous good experience of the engine/specific piston design. Reverse engineering parts sometimes achieves what the original designer intended, other times it can go horribly wrong.

$400 dollars US @ 1.85$/? translates to 215 quid

Add on 17.5% VAT and we are up to 250 quid. There could be duty to add as well (unknown) Add on shipping (cheap from the US but again subject to VAT) and they could easily end up costing 300 quid, so not such a huge saving. But they might never be cheaper than they are now as the raw materials cost of Aluminium is going skywards.

To top it all off and going back to the original poster I bet Norway has some even more prohibitive tax on imported engine bits, anything even vaguely resembling fun is taxed.

[Dag-Henning]

- there is no tax on women yet, and we just got rid of the luxury tax on chocolate......... Things are improving.....

Dag

[vikebo]

I am currently looking around a bit to see what I can find. I'm waiting for a catalogue from QED based on a suggestion from Dag.

Tax for most things (even if they are far from fun) is 25% if I remember correctly.

Another factor is shipping rates and customs processing fees (or whatever it is called). This usually makes it more economical to order all the parts from the same supplier.

Eivind

[M100]

Dag, as a chocoholic It's almost tempting to emigrate! I think it is taxed at 17.5% here although I might be wrong - if it is classed as food then it is tax free.

QED are more or less the same price. I was down there a couple of weeks ago. Neglecting a couple of gasket sets a box just 250mm square filled to a depth of 80mm was 700 quid!

The prices below are not including VAT (unlike those in Burtons catalogue)

[vikebo]

Thank you for the information regarding QED's prices. Considering the cost of all the parts I will need, and the high petrol prices, maybe I should consider a rubber band motor instead?

http://www.lindsaybks.com/lab/rbcar/index.html

Unfortunately, I don't work at the Postal Service...

Eivind

[steveww]

What you need is a TARDIS if you can borrow it from Dr. Who

Go back to the 70s and buy your parts from VeganTune, I quite fancy one of their rally engines

[M100]

Got a date for that ad Steve?

Go back to the 70s and buy your parts from VeganTune

With the emphasis on BUY. They were the incompetent bastards that buggered up my cylinder head after me believing that a "Club Lotus approved head specialist" knew what they were doing. How wrong could I be. Huge grooves in the head face (but only at one end), seats cut way too deep (40 thou shims needed), cam follower sleeves replaced and honed too big, a cam stud thread stripped and bodge repaired so the cam cap was out of line and a lost oil filler cap "because we insist you bring the head complete and then we can make a complete assesment of the parts needed"

Complete Tw*ts

[vikebo]

Just to mention it, the pistons I currently have are marked with an ?. From this site

http://www.davebean.com/images/stockistpage.gif

it seems like it is Clevite Engine Parts.

From theire web site it seems like they make piston rings, but they do not mention pistons.

Eivind

[steveww]

Alas no date for the VeganTune advert. It is in the history folder that cam with my Elan along with an old Christopher Neil catalogue. There is also a receipt for an engine rebuild that cost ?1400, I wish those prices were still available

[vikebo]

Fun to see some old prices. I think it is best to forget what things cost, if I accept the price when I buy the stuff. With my memory, that is not a problem...

Eivind

[thor]

When buying from Norway it's simply best to buy from a small company that will be prepared to put ONE invoice in the box, and send ANOTHER one to your address, with a ALTERNATIVE amount. I've done this with parts from the UK for years, must have saved me a couple of grand in total..




So, Vikebo, no car ready for V?rm?nstringen on sunday then (the biggest Norwegian sportscar show). Dag Henning, du kommer vel?