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Pro's and Con's with increasing engine displacment through boring/sleeving

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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Currently Im working on a honda K24 project, and I'm disiding on how I will build this engine. However at the moment i'm unsure as to the Pro's and Con's involved with sleeving the engine to a larger bore (90mm). I understand that it will increase the displacement thus a bigger bang as long as i can get the air-flow up, but I'm unsure if their are any other pro's / con's.

This will be a circuit/time attack build not drag.

Thanks

Turbo or non turbo? What fuel are you running?

N/A and will be running E85

The main disadvantages are part load fuel efficiency and knock. Since you are running E85, for a racing application, I wouldnt worry about either.

Yeah I will be going with E85 as it's burns cooler, thus helping with engine temp.

Im chasing 400hp, so I'm looking at my options regarding stroke and cylinder size pro's and con's.

the rods at standard are 152 with 0 TDC clearance. Which does not leave to much opinions with increasing the length of the rod to get a better rod to Stroke ratio. Currently they use a 99 stoke which will give a 1.53 ratio, but if I stoke it the ratio will drop below 1.5 so not ideal.

i would like 2.5-2.6 displacement so if I leave the stock as 99 and sleeve the engine to 90mm this will make 2.5 how ever I may be sacrificing torque.

And if I stroke the engine which makes more scene to me I will pick up more torque but drop the rpm height and the k engines like to rev, which will put stress on the internals.

would love to get a taller block height lol make it a bit easier to figure out

With a high revving engine like that the manifold designs and valve timing are very important to keep the powerband in high rpm. Your application doesn't call for steetable torque curves. It needs to breathe really well at high rpm, which means big cams, short intake runners.

Think about the s2000. F22 engine.

Hi Raymond

I have looked at the F22 engine, however this build is focused around the 1990 CRX, so it want work in my favour.

As for the intake I have Hypertune hooking me up with a full custom plenum, these guys are the leaders in their field and have teams and workshop all over the world using their expertise.

Its going to be a fun project with great challenges.

thanks for your input too, much appreciated.

Boring and sleeving a block can provide the advantage of additional capacity but there are some downsides. You really need to work with a machinist who is competent with sleeving as if the installation process isn't correct then the sleeves can cause more problems than they solve. For example it's common to have sleeves suffer from dropping in service which results in the head gasket leaking. As you increase the bore diameter you also can run into problems with the area between adjacent cylinders becoming narrower which affects head sealing - This part is very dependent on the base block and some give a large potential for a bigger bore while others really offer no scope here.

The other issues you need to consider are in line with the combustion chamber design. Often a reasonable increase in bore diameter will result in a significant step between the cylinder and the combustion chamber which can be detrimental to combustion propagation. Often this will require some reworking of the cylinder head in order to correct this. On the plus side a larger bore diameter can help unshroud the valves at low lift and improve low lift airflow.

Thanks for the input Andre.

I remember you talking about the sleeves potential for dropping if not done right, so I have spoken to Wilfred from JHH performance in QLD and he will be doing the work on the block. We are still discussing the cylinder head as I maybe using 4pistons 163 cnc head from the states which will give me a 385cfm flow rate also they will cnc the combustion chamber true as well.