Closed Deck Blocks

When adding boost in the form of a turbo charger to an engine, there is a risk of cracking the cylinders.  The reason for this is that when an engine is turbo-charged and the engine power output is increased, this will considerably increase cylinder pressure.  Cylinder pressure is at its highest at around 18 to 20 degrees after top dead centre, this equates to the piston being around 10mm down the bore.  At this point the cylinder pressure has a "barrelling" effect on the cylinder as shown in the illustration below.

closed deck block

When the pressure becomes too much the cylinder cracks from the top downwards and a failure occurs as in the illustrations below: 


Even before cylinder failure occurs, the distortion in the cylinder results in a lack of ring seal and therefore a loss of compression.  In addition oil bypasses the rings into the combustion area, raising the possibility of detonation, and of course oil consumption.


One solution to prevent the cylinders failing is to reinforce them as shown below:

 closed deck block


The block and reinforcing brace are CNC machined to precise tolerances to achieve the desired fit.  This ensures that the cylinders are completely supported in the area affected by the increased cylinder pressure; thus eliminating the possibilty of cracking.


Available for:

- Honda B series (B16/B18/B20)  

- Honda K series (K20/K24)

- Honda FK8/2/FL5 (K20C)

- Honda D series

- Honda R18

- Honda NSX (C30)

- Nissan VQ 350Z

- Subaru EJ

- Ford 2.3L Ecoboost

- Mini Cooper N14

- Mini N18

- Mitsubishi 4B11


Customers comment: -

"BTW anyone who's wondering I have been running their {CPL Racing's} block for a year 

now and I'm currently at 500 whp with no issues and going back on the 22nd for more boost"     Lee Ferrell

"Have built and mapped a B18 with a CPL CSS and all done 7k miles at 30 psi

600 bhp and all good"   Gordon Derby

Prices: -

Closed decking with precision boring and honing - Honda K, B & D Series, Mini N14/N18 - £649 incl VAT (Subaru 4-cylinder £725 incl VAT)


Above prices are for 4 cylinder, for other applications please email us



Frequently Asked Questions: 

How much power can a CPL Racing closed deck block handle?

A CPL Racing closed deck block is rated to 500 bhp, although we have received feedback from one customer who has successfully run 600 bhp.  (NB please note this excludes B20)

My engine is rated in excess of 500-600 bhp, can I closed deck my block?

For applications over this level the engine should be sleeved.  CPL Racing offer this service in-house, please email us for further details and prices.

Is it essential to have the block bored and honed after the closed deck procedure has been carried out?

Our recommendation would always be to bore and hone 0.5mm oversize after the procedure has been carried out for the reasons listed below: -

1- If the donor block has covered relatively high mileage then it is likely that the bores are out of shape

2 - When the brace is installed in the top of the block, the sleeves "close in" slightly, it is possible to loosen the fit but this partly defeats the point of installing the brace.

3 - A precision bored and honed block that produces a good piston to bore seal is free horsepower, if the piston to bore seal is less than perfect then horsepower is adversely affected.

I would like to have CPL Racing close deck my block, how do I proceed?

Please email us for an order form, on the form you just need to complete your name and address and select the services you require and send the form to us with the block (and pistons where appropriate).  CPL Racing can arrange to collect the block for you if required, details are on the order form.

What warranty is offered?

CPL Racing offer a 1 year warranty against machining/manufacturing defects for  the original purchaser.  This does not include use over recommend bhp levels or misuse of any kind.

Why shop with us?

Value For Money

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