Performing Honda K24a3/AST5 6spd Conversion

Thanks for the input, Rodger.

I also used the K-Tuned upper housing (the one on the back side of the head) to connect to the t/stat/water housing - I was also concerned about the very small passage, however it does seem to be an non-issue.

The other thing the tuner suggested (if I really wanted to do it) was hooking up the ECT control ground for the rad fans - to use the engine temp to govern onset vs. rad temps. At this point, running an extra wire (neatly) in the loom from the bay back through the cabin and on to the front of the car would be more work than I care to do. Maybe I'll run supplemental harness inside the water tunnel ..... He did also say though, he tracks his K24/K20 motor & can see 220-240 temps, while far from ideal, he was not concerned about the motor suffering/ performance loss simply because the operating temps climbed that high.

On the exhaust, I tried looking for your post regarding the muffler - I recall you found a quieter muffler - how is that performing? Have you driven the car hard to put the VTEC to the test? Did you Dyno your setup, I don't recall. EDIT. - found the post - had to go through several pages of your post history - can't select "threads by xxx" in the User CP.
I am very happy with the new Solo Stealth muffler. It is their quietest performance muffler, but I would not say that it is quiet by any means. It has a nice deep resonance at idle and cruising but no drone and makes for enjoyable driving. It's almost a kind of V-8 deep resonance. Step on the gas and it definitely opens up but not to the level of the SSW and no where near the Magnaflow. When you are driving at a steady speed and back off the gas slightly, the exhaust has a wonderful "burble" to it. When decelerating with your foot off the gas, there is a bit of drone sound then, but that is a short lived situation. I still want to do a driving video but just haven't gotten to it yet.

Yes, I have definitely stepped on it to get the VTEC to engage. My VTEC doesn't kick in until 5600-5800 RPM. The tuner said that any lower and he would actually have a drop in power for a bit until the revs built up. When it does kick in, it just howls and you can feel the push in your back. :D It seems like I can hear it right behind my head, so it seems like most of the VTEC sound is coming out of the air filter as that is where it is located. It will run right up to 8500 and pulls strong all the way. Only problem is finding a place to do that as you are hitting 100 MPH pretty fast. I have thought about taking it back for another dyno session with the new muffler, but it seems to run great with plenty of power so I don't see it being worth another $400.
 
Back & forth with this issue. The system AFR's not registering actual AFR's are baffling. The AEM wideband controller shows what certainly seem to be accurate AFR's under load.

The fact that the value isn't changing in the system is likely the cause of my 3K rpm woes also - I reckon

I made a test pipe & ran that, to eliminate just the cat. No change (AFR's still don't jive)

Yesterday, I removed the test pipe & ran the car around with open exhaust - besides being ear splitting the AFR's still didn't register in accordance with the WBO2. So, no way backpressure is the cause of my issue. I've ordered another new (Denso) O2 sensor. Should be here Mon. I put the cat back in the meantime, as I'm not a big fan of the loud flame-pops on hard shifts.

K-Tuner can take the WBO2 input for comparison/overlay, so I'm going to have to wire that. Very annoying to be adding more to the harnesses at this point.

PXL_20210614_212745787.jpg



screenshot-www.ktuner.com-2021.06.16-12_20_38.png
 
After some input from the Honda guys, I did some research on K20a.org regarding RSP intakes (purportedly better torque producers than the RBB I have (albeit modded) - eventually found this thread where they tested The RSP on a K24 comparison Dyno w/ RBB

Basically, no point as I would be making less torque than I do now :D

theirs
RSP_vs_RBB_125001.jpg


mine

index.php



OK - so on with the exhaust / O2 setup - I moved the two O2 sensors further downstream - I welded new bungs in the pipe at the flex coupler and in the cat inlet.

As it was

PXL_20210616_174444203.jpg


welded new bungs...

PXL_20210618_194151300.jpg


wasn't sure whether to put the System WBO2 in the pipe, or in the cat....

test fit
PXL_20210618_200804735.jpg


test fit - harness not secured away from pipe
PXL_20210618_200816171.jpg



PXL_20210618_200829616.jpg


ended up with the AEM Controller O2 in the pipe, and the system O2 in the Cat - easier to route that way. I can always swap them if others feel there would be an advantage

PXL_20210618_210603486.jpg


clearance for system O2

PXL_20210618_210607616.jpg

Driving, the engine feels more responsive. The System O2 values now change (13's instead of 14's) )under high RPM/VTEC range - still not the same values as the controller though. I have to run wiring to hook up the controller to the ECU - then I can view/ record both

afr2.png


afr3.png


afr4.png


Also here the cam advance didn't match requested - not sure what's up there - EDIT - just transition state - cam doesn't respond so quickly

camCMD.png


So, it does feel like I am moving forward at least, since before the AFR would not drop below 14.3 in the same range... I have a new O2 sensor coming Monday - I'll swap this one out to see if there is a different result with a new one.
 
Last edited:
Sorry I not intend to post the same image three times. But to summarize I think that the Honda water pump at idle does not like the long coolant lines and bends that it takes to run through the Fiat system. I also have an under-driven pulley and assumed that was part of my problem.
Davies -Craig 12v EWP80

index.php



Bringing this back - did you take any pics/measurements of the pump assembly prior to install? I'm also assuming you have it set as a puller since it's on the outlet side of the rad?
There seems to be no question that the stock Honda w/pump doesn't like the system length - on mine, the rad outlet is cooler to the touch (after driving) until the car sits & engine temps go over approx 205f, then the temp finally goes up at the rad outlet & low temp fan comes on, shortly followed by the high temp fan. This seems to be 'normal' for the K24, and the tuner said not to worry about it - I'm just not sure I can live with looking at the gauge sitting at 210 (past center 190 marker) - I just have too much PTSD from years of overheating issues :D.

I am going to wire the Honda ECU fan control & drop the onset temp, and see if that changes anything - however it does seem like any fan control adjustments are all reactive - bumping the coolant flow at low rpm seems like a more proactive arrangement.
 
Davies -Craig 12v EWP80

index.php



Bringing this back - did you take any pics/measurements of the pump assembly prior to install? I'm also assuming you have it set as a puller since it's on the outlet side of the rad?
There seems to be no question that the stock Honda w/pump doesn't like the system length - on mine, the rad outlet is cooler to the touch (after driving) until the car sits & engine temps go over approx 205f, then the temp finally goes up at the rad outlet & low temp fan comes on, shortly followed by the high temp fan. This seems to be 'normal' for the K24, and the tuner said not to worry about it - I'm just not sure I can live with looking at the gauge sitting at 210 (past center 190 marker) - I just have too much PTSD from years of overheating issues :D.

I am going to wire the Honda ECU fan control & drop the onset temp, and see if that changes anything - however it does seem like any fan control adjustments are all reactive - bumping the coolant flow at low rpm seems like a more proactive arrangement.
I have been thinking about en electric pump for my X (whether it is needed or not). Having the pump in the engine bay puts the pump in the loop of the engine to thermostat to pump to engine, as well as the heater loop which is engine head to heater core to back of pump to engine. When the thermostat is open it is engine to thermostat to radiator to pump to engine and the heater loop continues to function as it is within the thermostatic loop and the inlet and outlet of the pump.

Depending on how the thermostat works the front mounted pump would be pushing against the closed side of the thermostat giving effectively no flow through the engine and for the heater system the flow would be more of a siphon when the thermostat did open.

The X and the 124 thermostats work in a similar fashion, shunting coolant from the engine over the thermostat to the pump and then back to the engine.

The plumbing for the 124 has a T at the front of the head with a large outlet to the radiator and a small opening leading back to the thermostat. The thermostat has an inlet to the ‘return‘ from the head (the small opening in the T) with flow back to the water pump. This ensures flow through the engine and then actuation of the thermostat when the flow heats up. Prior to the thermostat opening there is effecively no flow through the radiator as the pump is pushing against the back of the thermostat which is ‘closed’. Once opened all or the majority of flow is through the radiator directly to the thermostat and then the pump, on the 124 this adds one hose to the mix which is pretty simple (beyond the two hoses the heater loop adds.

With an electric pump on the X standard system one would need to collect the heater return into a new pipe for the remote pump and then introduce the primary flow into the engine at the back of a standard pump housing with the impeller removed inside and allow the pump pulley to act as an idler if needed to retain appropriate belt geometry (likely not in which case it could be direct run of a larger diameter transition into the side face of the block.

I mention all this as it is important to consider the flow around the three effective circuits: warm up; heater and at temperature running. This is quite different on the Honda but it will have similarities of function and require judicious rerouting and consideration. I know Odie and a gentleman from England were having a fair amount of problems with just a standard pump.

I know there is a plate for deleting the standard Honda pump from Ktuned (I am sure there others). The ones I have seen for the K24 delete the thermostat but the 124 thermostat could allow a more standard flow which I believe other members of the K Swap Club have used.
 
Last edited:
Davies -Craig 12v EWP80

index.php



Bringing this back - did you take any pics/measurements of the pump assembly prior to install? I'm also assuming you have it set as a puller since it's on the outlet side of the rad?
There seems to be no question that the stock Honda w/pump doesn't like the system length - on mine, the rad outlet is cooler to the touch (after driving) until the car sits & engine temps go over approx 205f, then the temp finally goes up at the rad outlet & low temp fan comes on, shortly followed by the high temp fan. This seems to be 'normal' for the K24, and the tuner said not to worry about it - I'm just not sure I can live with looking at the gauge sitting at 210 (past center 190 marker) - I just have too much PTSD from years of overheating issues :D.

I am going to wire the Honda ECU fan control & drop the onset temp, and see if that changes anything - however it does seem like any fan control adjustments are all reactive - bumping the coolant flow at low rpm seems like a more proactive arrangement.
Hi Hussein, Anyone correct me if I'm remembering this wrong, but I thought the original water pumps on the 128 motor (x1/9) and also the 124 motor (scorpion) were different than their mid-engine counterparts due to this reason. I remember on my original X1/9 needing a replacement water pump at some point, and when I went to order one from International or Bayless (this was in the early 90's) I was told that I could not use the 128 pump they had in stock because the impeller blades were different. The X1/9 pump needing to push the coolant the extra long distance vs. the short tubes on the regular FWD 128 cars, so the pumps wee not the same. I've been wondering if this will be an issue on my K24 swap as well.

It seems an electric pump would be a good alternative, but reading recommendations on K20a.org, it seems the electrics were not recommended for street use due to high service or replacement intervals, which is fine for a track car. Even the K-Tuned electric pump kit is listed for "race only." Anyone else concur on this or have better news about using one for street? It seems that a no-thermostat system with a variable speed pump would be perfect and could even be set to run after the engine is shut off like the Abarth 500 or many turbocharged Audi's.
 
Hi Hussein, Anyone correct me if I'm remembering this wrong, but I thought the original water pumps on the 128 motor (x1/9) and also the 124 motor (scorpion) were different than their mid-engine counterparts due to this reason. I remember on my original X1/9 needing a replacement water pump at some point, and when I went to order one from International or Bayless (this was in the early 90's) I was told that I could not use the 128 pump they had in stock because the impeller blades were different. The X1/9 pump needing to push the coolant the extra long distance vs. the short tubes on the regular FWD 128 cars, so the pumps wee not the same. I've been wondering if this will be an issue on my K24 swap as well.

It seems an electric pump would be a good alternative, but reading recommendations on K20a.org, it seems the electrics were not recommended for street use due to high service or replacement intervals, which is fine for a track car. Even the K-Tuned electric pump kit is listed for "race only." Anyone else concur on this or have better news about using one for street? It seems that a no-thermostat system with a variable speed pump would be perfect and could even be set to run after the engine is shut off like the Abarth 500 or many turbocharged Audi's.
The Davies Craig units have had good longevity. Their design is much the same as what you see on Bosch and other supplementary cooling pumps.

Davies Craig also offers a controller which doesn’t run full bore all the time so the flow when cold can be less. Having the pump on the “cold” side of the flow is likely an important consideration ie after the thermostat and before the engine with the most tempered coolant.
 
Hi Hussein, Anyone correct me if I'm remembering this wrong, but I thought the original water pumps on the 128 motor (x1/9) and also the 124 motor (scorpion) were different than their mid-engine counterparts due to this reason. I remember on my original X1/9 needing a replacement water pump at some point, and when I went to order one from International or Bayless (this was in the early 90's) I was told that I could not use the 128 pump they had in stock because the impeller blades were different. The X1/9 pump needing to push the coolant the extra long distance vs. the short tubes on the regular FWD 128 cars, so the pumps wee not the same. I've been wondering if this will be an issue on my K24 swap as well.

It seems an electric pump would be a good alternative, but reading recommendations on K20a.org, it seems the electrics were not recommended for street use due to high service or replacement intervals, which is fine for a track car. Even the K-Tuned electric pump kit is listed for "race only." Anyone else concur on this or have better news about using one for street? It seems that a no-thermostat system with a variable speed pump would be perfect and could even be set to run after the engine is shut off like the Abarth 500 or many turbocharged Audi's.

I would not consider removing the stock Honda pump & going solely electric - seems a recipe for disaster to me. The only issue with flow is low rpm idle, so wiring like homegrown so electric pump acts assist when over a predetermined coolant temp seems a safe way to make sure the electric pump is not stressed with continuous service.

This is the Honda flow - I followed the stock layout in terms of bypasses & T/stat operation - with the only deviation being the t/stat offset from the water housing, which required a 20degree cooler t/stat to keep the stock 185-190 fully open range

Based on Darwodious' comment - it does seem likely his pic has a reverse flow setup - so I would add the pump on the right side of mine (matches stock X1/9 configuration) to push the coolant back to the t/stat & into the water pump housing


PXL_20210621_150113216.jpg
 
I mention all this as it is important to consider the flow around the three effective circuits: warm up; heater and at temperature running. This is quite different on the Honda but it will have similarities of function and require judicious rerouting and consideration. I know Odie and a gentleman from England were having a fair amount of problems with just a standard pump.

The only deviation I would consider is where the electric pump is running w/ fully open t/stat, at idle, when the flow is reduced & allowing engine temp to rise (204-210degree range). In that regard, there should be no conflict with the stock flow - I definitely am not interested in replacing the stock water pump with an electric - (so far) I have no flow issues besides idle, and only then with ambient temps in the 80s-100 range.
 
My swap is not to the point where we can compare notes yet. Because there are relatively few X conversions running down the road, information is a little scarce. You might want to invest a little time searching the Lotus Elise forums. The K20/24 swaps have been wildly popular with tons of them completed. The Elise cooling system is very similar to an X and if anyone has run into cooling issues it would be this crowd. Might be worth a shot?
 
My swap is not to the point where we can compare notes yet. Because there are relatively few X conversions running down the road, information is a little scarce. You might want to invest a little time searching the Lotus Elise forums. The K20/24 swaps have been wildly popular with tons of them completed. The Elise cooling system is very similar to an X and if anyone has run into cooling issues it would be this crowd. Might be worth a shot?

Thank Jimmy - one of the guys who has been responding on K20a.org is specifically an Elise swapped owner who knows his stuff - so he has been helpful. English is not his first language, so nuance is tough when describing specific conditions.

I was hoping to have the WBO2 resolved before I drive to Ithaca, NY on Friday - however that's not gonna happen - the new Denso Sensor I ordered sets a 'heater circuit' CEL (should have known - it was listed as being able to operate upstream/downstream, and the price was so much less) so I'm gonna have to drive with the original O2 this weekend - that's fine overall, just would have been nice to take advantage of the long drive to do some field testing & cam adjustment - my wife has been helpful as diagnostic/ setup adjuster on the laptop in the past....
 
Last edited:
OK - so the sensor arrived - I got the new Denso 234-9066 WBO2 installed this morning, and did a pull on the 200 mile drive upstate NY. I definitely had a defective WBO2 (only 2K miles on first one) - It's easy to see in this log screenshot that the AFR in the WOT/ high load/cam range that the system AFR's are rich (too rich, IMO) - at least now that the AFR's in the system reflect actual AFR I can get the cam timing sorted out & probably lean out the tune (if needed)

NewWBO2log.png


I don't know what normal oil temp is on these things - mine stayed over 220ºF (!?) with sustained rpms around & over 4K - with factory K24 oil-to-water cooler

IMG_20210625_211608.jpg


IMG_20210625_211630.jpg
 
Last edited:
Back
Top