Extreme Engine Tech, Building the Ultimate K24 Part 2 The Bottom End!

By Mike Kojima

In the last edition of our series, building the ultimate streetable late model K24, we had focused on the engines top end switching to an earlier model K20Z3 head with Vtec on both the intake and exhaust sides of the engine and a removable exhaust manifold - all big steps in getting more performance.

We have been questioned on our power goals. Sure we know the K motor is capable of producing a lot of power, but peak power isn't our goal.  Practical useable power is.  We are not going for max power or king of the street power. We want to be able to reliably make our power on 91 octane gas, not 93 or E85.  We also want to have a nice wide, very driveable powerband where the car will be on the pipe from 3000 to 8000 rpm. This is fun and practical power and we will be tuning and sizing our BorgWarner EFR turbo with this in mind.

Now we will be turning our attention to the engine bottom end, fortifying it for turbo power!  Like the head, our goal will be to use off the shelf parts that are readily available and in stock at Motovicity. This engine is not some super esoteric custom build, but one anyone could easily duplicate relatively inexpensively and quickly without long back or special orders. 

We started with a brand new late model K24Z7 block, the engine found in the current Honda Civic Si.  We don't normally recommend building an engine bit by bit like this as it can get quite expensive. By ordering piecemeal the cost of all the little parts will kill you.  If you don't want your brand new car to be down, it would be good to find a core engine from a wrecking yard to start off with.  This is much cheaper and less aggravating than figuring out every little part that goes in/on an engine.

The K series block is a high pressure die cast aluminum part which gives good strength and light weight. The casting techniques used enable features such as a lot of ribbing for stiffness, but thin sections for lower weight.

The die casting gives a very clean block interior that does not need a lot of prep work like a sand cast block does.  Normally the interior of the block is deburred and polished to prevent entrapped sand from breaking loose and doing damage to the engines internals.

We selected JE's asymmetrical FSR pistons in standard bore for the bottom end.  The FSR is a strut type piston meaning that it has a reduced slipper skirt profile.  In the past slipper skirts meant light weight and low friction, but lots of noise and sometimes rapid wear.  Not so with FSR pistons.  JE has the piston design and barrel profile down and we have found FSR pistons to run quietly when we have used them, great for street engines.
Page 1 of 11 Next Page
Bookmark and Share
Wednesday, June 03, 2015 8:09 AM
Does cutting the balance shafts affect life of the oil pump like it does with the 4g63? With that engine if you cut the shaft right after the gear it doesn't have the support of the rear bearing and it wears extremely fast in the front bearing in the oil pump.
Wednesday, June 03, 2015 8:23 AM
Excellent point ab0z...not much explanation given on that modification and not sure how that would be quantified without some FEA on that particular part(s) under varying engine loads/speeds. Guess they will just hope for the best or have some real world feedback from others who have run this without failure. Otherwise, excellent article and let it be known the Acura RDX world is watching as folks are fast approaching the limits of the stock hardware (turbo/injectors/IC, etc.). Some are already beginning to get into the head and block upgrades:


Mike Kojima
Mike Kojimalink
Wednesday, June 03, 2015 8:46 AM
All the 4g63 race engines on cars I have worked with had no balance shafts with no oil pump issues. Removing balance shafts on Hondas is normal. Balance shafts cause a lot of problems with extended high rpm use as mentioned in the story.
Wednesday, June 03, 2015 8:51 AM
Excellent article, but I saw no mention of bearing clearances or ring gap placement in there.
Wednesday, June 03, 2015 8:59 AM
Understood Mike about the 4G63 mod on race engines, however this build was not set out to be a race-spec, boutique built engine rather an achievable, budget-oriented street driver as said many times over in your articles. As such, would be cautious about guiding others to make this modification and potentially affecting the longevity of engine, especially the gears driving the oil pump.

Either way, no disrepect intended, just wanted to raise the flag and should make folks aware or the risk/benefit trade-off. As said before, very excited to watch this build and the implications it has for the few RDX enthusiasts with the K23A1 motor.

Now, how to convince the wife to let me start modding it......
Wednesday, June 03, 2015 9:52 AM
I have one of this blocks right now but i really want to use it but i want to run a RSX oil pump have you guys looked into that? If not i need to find a older block.

Mike Kojima
Mike Kojimalink
Wednesday, June 03, 2015 12:02 PM
I have lost many motors to balance shaft failure even in mild performance use and now know better. Spinning 2x crank speed is nasty and when they seize they take a lot with them. I am not kidding that they suck and this is based on experience. Enjoy better oiling, more power and have a little more vibration. Big deal.
Wednesday, June 03, 2015 12:36 PM
Mike thanks for your comments, I consider you an authority and great source of information. I'm certainly not trying to second guess your advice, just trying to learn more about this.
In the example of the 4g63 (I understand that these are different designs) there are various vendors selling "racing balance shafts" that retain the shaft but remove the weighted lobes. Example:
Is there sound reasoning behind this? Are the reported 4g63 oil pump failures anecdotal evidence and caused by factors other than chopping the balance shaft down to the "stub shaft"?
I have also been told by a chicago area shop specializing in mitsubishi tuning that using the short stub shaft method of balance shaft elimination results in premature oil pump failure. Is this just a myth that is being propagated by internet "experts"? (like me? :P )
Wednesday, June 03, 2015 12:57 PM
what chassis is this going into?
Wednesday, June 03, 2015 2:06 PM
The stubby shaft is an OEM part on the 4G. It comes from the 4G61. Them leading to early oil pump failure is complete BS.

Guys screw up their T-belt tension, making the belt too tight. This then kills the oil pump and then they blame it on the stub shaft. The reality though, the stub shaft DOESN'T change support on the drive gear at all. With or without the OEM balance shaft, the drive gear is still only supported by one journal bearing surface. Excess side load (t-belt tension) will kill the bearing surface with or without the OEM balance shafts.

I have seen TONS of 4G63s die from eating B-shaft belts or seized B-shaft bearings. It's the first thing I change when I get a car with a 4G in it and I've probably clocked 200k miles on various 4Gs without balance shaft without ever having an issue.
Wednesday, June 03, 2015 2:12 PM
Thanks for the info. What are they doing to create excessive tension on the belt?
Wednesday, June 03, 2015 2:22 PM
I agree with Mike 156 re the cause of the failures.

Excesive belt tension is created by clocking the tensioner pulley too much.
Wednesday, June 03, 2015 2:23 PM
The more you rotate the tensioner pulley the greater the tension of the belt.
Wednesday, June 03, 2015 2:24 PM
ah so the root cause is a failure to read the instructions. This has been very informative, thanks!
Nick B
Nick Blink
Wednesday, June 03, 2015 4:03 PM
@warmilk - Check out the last page, it's a giveaway engine we're working with Motovicity Distribution on. No specific chassis, it's up to the winning shop to install in whatever car they want.
Thursday, June 04, 2015 8:35 AM
I noticed regular heavy weight motor oil was used instead of assembly lube. Why is this Mike? You guys must have some reasoning why you choose to stay away from assembly lube?
Mike Kojima
Mike Kojimalink
Thursday, June 04, 2015 8:37 AM
Because oil works fine
Thursday, June 04, 2015 1:58 PM
Assembly lube is only really recommended if you're not sure how long the motor will sit after assembly. If it's going right in, motor oil is perfectly fine.
Tuesday, June 16, 2015 12:42 PM
I'm curious as to how you properly set the desired oil clearance on the main bearings when using King or other performance bearing sets. I found this to be a PITA with my build, as I could not get the same clearance accross the board with ACL due presumably to slight differences in the journals. I solved this by buying Honda bearings in each of the different colors to establish their respective clearances and then ordering the correct ones (Honda). How are you able to do this with ACL or King without a "line honing" process?
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Partners:

© 2018 MotoIQ.com