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2004 CM7 Accord - K24A4 - 5 Speed Manual
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Discussion Starter · #1 ·
Hey Guys

So, I'm in a position where I need a "fresh" block, and I'm also doing a mild rebuild (new rings/bearings/seals/etc.). this gives me an opportunity to get a k24a2 bottom end if I so choose, since they're not that uncommon at wrecker yards where I live. I've looked into some of the other posts on this matter, but I'm still a bit unsure as to if 10.5:1 pistons would be pushing it on my sort of turbo build. the main reason I want to go this route is for gas mileage and torque

Here's the rundown of my setup:
  • I'll be reusing the RAA valvetrain and head (I have perfectly good reasons for this)
  • 6800 RPM redline
  • MSR GT2871r rep turbo
  • It will be run on pump gas at <10 PSI day to day
  • Max boost it will potentially run is 15 PSI


My overall goal for the car is to have a strong powerband with lots of low end torque. Keep in mind, This is a daily driver that spends most of its time either cruising on the highway, or in low speed traffic. I have no plans to track the car

How safe will 10.5:1 be under these conditions? my main concern would be LSPE, but I'm not sure how much of an issue that it on our motors
 

· Super Moderator
Lotus Elise K20A2
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1,698 Posts
LSPE is mainly an issue with direct injection turbocharged vehicles. Oil vapours and deposits ignite unintentionally before the fuel is injected and ignited.
Port injection engines like the Honda K20a2 or the common k24 don't usually have this problem. They will plainly knock or if knocking for too long preignite. They can reliably be tuned so this won't happen.

Both CRs are suitable for 15PSI on good fuel and good tuning.
 

· Arouse the DAMPFHAMMER!
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10,384 Posts
6800 RPM redline...MSR GT2871r rep turbo...It will be run on pump gas at <10 PSI day to day
The map of that turbo is already on the chock side when running 10 psi [email protected] rpm. At 4000 rpm you hit the 76 % iso line and area (10 psi of boost) and at 2000 rpm and 10 psi of boost the compressor will touch the surge line. Not bad for a DD with some sleeper potential.

How safe will 10.5:1 be under these conditions? my main concern would be LSPE, but I'm not sure how much of an issue that it on our motors
As long as you keep the MAT (manifold air temperature) down properly it is no problem with the right engine oil. I've tuned an engine on 95 psi boost [email protected] rpm without LSPI. Oil properties, fuel droplet spread, size and mixture as well as mixture temperature are your key criterias. 10 psi at 1500 rpm on a K24A2 are quite challenging, but at 2000 rpm it is manageable. Your working area is fuel distribiution, LSPI surpressing oil, and MAT...of course enrichment, but with rational usage. The 1 point lower CR helps indeed, but the MAT control is the more efficient way regarding performance, mpg and response. Also a very important point, the A/R of the turbine...the less transient delay, the lower the inconsistent fueling time. Tuning of course is a key. If you tuner has know background knowledge and experience with LSPI, skip it, go to the next. I had a two year long deep dive at an OEM in that topic, during the combustion process development of a new engine series, that topic is basically very simple, but if you don't understand the background the simple solution is lowering boost, but there are always smarter solutions possible.
 

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2004 CM7 Accord - K24A4 - 5 Speed Manual
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209 Posts
Discussion Starter · #4 ·
The map of that turbo is already on the chock side when running 10 psi [email protected] rpm. At 4000 rpm you hit the 76 % iso line and area (10 psi of boost) and at 2000 rpm and 10 psi of boost the compressor will touch the surge line. Not bad for a DD with some sleeper potential.
I really hope so 😅

As long as you keep the MAT (manifold air temperature) down properly it is no problem with the right engine oil. I've tuned an engine on 95 psi boost [email protected] rpm without LSPI. Oil properties, fuel droplet spread, size and mixture as well as mixture temperature are your key criterias. 10 psi at 1500 rpm on a K24A2 are quite challenging, but at 2000 rpm it is manageable.
well, the intercooler I have is massive, so IAT shouldn't really be a problem. I'm looking at ways to reduce manifold temps though. I'm still using the RBB manifold (for the torque), but I'm not sure switching to a k20 manifold and using a seperate coolant passage would make a difference in temps
 

· Arouse the DAMPFHAMMER!
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I'm still using the RBB manifold (for the torque), but I'm not sure switching to a k20 manifold and using a seperate coolant passage would make a difference in temps
Cut it off (cooler neck) the IM and use an aftermarket adapter if you like. Some of them even supply a HowToDoIt-description (e.g. K-Tuned). For the IM thermal isolation if would help ;). I would not go to a K20 IM on a daily driver, the low end torque in part and full load sucks.
 

· Arouse the DAMPFHAMMER!
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figured this was the case, long live the RBB!
Yeah 😎.

What turbo manifold are you have in focus? This is a sensitiv topic regarding response on the low end. A K24Z3 or Z7 head would support a shorter turbo connection for a better low end response.
 

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2004 CM7 Accord - K24A4 - 5 Speed Manual
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Discussion Starter · #8 ·
Yeah 😎.

What turbo manifold are you have in focus? This is a sensitiv topic regarding response on the low end. A K24Z3 or Z7 head would support a shorter turbo connection for a better low end response.
its actually an HKS piece from their RSX-S kit from waaaayy back in the day. cast iron, log style, bottom mount. its actually a decently designed manifold with extra length given to ports 1 & 4.
 

· Arouse the DAMPFHAMMER!
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its actually an HKS piece from their RSX-S kit from waaaayy back in the day. cast iron, log style, bottom mount. its actually a decently designed manifold with extra length given to ports 1 & 4.
Sounds good, short ways to the turbine increases the transient pressure to rotate earlier instead of filling further runner volume. Do you have a picture of it?
 

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A manifold like that may work well in the Elise as there is limited room for the turbo below due to the axle half shaft. I would like to see a pic as well. The other option is the custom SS route which is not inexpensive.
 
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