high comp ka

[biggin07]

i want to raise my compression to 11.1:1 by using a set of used pistons out of a auto kae but i was woundering if i need to up grade the fuel pump or the injectors or wat would i need to upgrade. and if i raise the comp that high would i still be able to pump gas or would i have to us some more octane. also has any one done this swap before and how much did they end up spending. thanks biggin

[biggin07]

anyone

[Ajax]

Bumping Compression up to 11:1- its probably best to up the octane to premium- at least 91 to keep yourself safe from detonation. you shouldn't need to replace the fuel pump or injectors, unless they are old and not at 100%. It might be a good idea to do it for peace of mind though.

[biggin07]

well also i was talking to one of my friends about doing a high comp motor and he said it would blow head gasket left and right. but i dont think it would blow head left and right would it.

[Ajax]

If you've got a decent headgasket, it shouldn't be a problem. There are a few HC KAs floating around on this forum as well as plenty of junkyard KATs that don't seem to have problems with headgaskets. Continue to search around on the forum, you'll find this topic has been hit on many times.

[3dKa24]

well also i was talking to one of my friends about doing a high comp motor and he said it would blow head gasket left and right. but i dont think it would blow head left and right would it.

Only if you raise comp by using a thinner head gasket.

As for knowing if you should upgrade fuel pump or run bigger injectors is by dynoing and checking your A/F ratio.

[cdlong]

you can also calculate how much power the stock injectors can support. i'm not sure how to do it, but google could probably help you out. how ever you do it, it's like 240hp at the crank or something for the stock 270cc, you won't get close to that with just HC pistons.

a fuel computer or ECU tune would be a good idea too.

i've been thinking about doing this too, i've got another question since we're on the topic. is it a good idea to use stock used pistons? they could be had for cheap but do pistons wear out? i assume new rings would be used but is that enough?
Modified by cdlong at 4:54 AM 7/5/2006

[SX APPEAL]

I'm in the process of putting togather an HC motor right now and this is what i've found. I took the block down to the machine shop just to have it checked out and honed for new piston rings. Keep in mind this engine had 217K on it and has been revved quite frequently. They told me that the cylinder bores were slightly out of round and the block needed to be bored. Therefore I had to get aftermarket oversized pistons too. Total bill for all this was about $100 for the machine work, and about $150 for the pistons. You can try it with used pistons and new rings if you want, but from what I've been told its not a good idea to do it without atleast machining the block, otherwise the rings might not seal completely to the cylinder walls, which would cause a loss in compression, and that kinda defeats the point of building an HC motor doesnt it?

[3dKa24]

[QUOTE=cdlong]you can also calculate how much power the stock injectors can support. i'm not sure how to do it, but google could probably help you out. how ever you do it, it's like 240hp at the crank or something for the stock 270cc, you won't get close to that with just HC pistons. [/QUOTE=cdlong]

Yeah thats about right these should be good to about 230-240CHP

[QUOTE=cdlong]

i've been thinking about doing this too, i've got another question since we're on the topic. is it a good idea to use stock used pistons? they could be had for cheap but do pistons wear out? i assume new rings would be used but is that enough? [/QUOTE=cdlong]Just make sure they dont have cracks and find out why that person is parting with them. YOu would definately have to buy new rings though.

[biggin07]

also i heard the 91 and some other year head was the best because of the cams but i was woundering if they really make a diff and does any one on if the 92 do the same thing

[DjPantsSpecR]

its pretty much accepted that 91-93 KA's are the asme, same heads, same cams, same motors.

94s are a little different, but you dont have an automatic convertible, so you wont have to worry

[Bigvinnie]

you can also calculate how much power the stock injectors can support. i'm not sure how to do it, but google could probably help you out. how ever you do it, it's like 240hp at the crank or something for the stock 270cc, you won't get close to that with just HC pistons.

a fuel computer or ECU tune would be a good idea too.

i've been thinking about doing this too, i've got another question since we're on the topic. is it a good idea to use stock used pistons? they could be had for cheap but do pistons wear out? i assume new rings would be used but is that enough?

Modified by cdlong at 4:54 AM 7/5/2006

It would be best to modify injection flow to atleast 300CC injectors.KA's already run lean a little after 4000RPM with bolt on's, 9.5:1CR and the stock ecu.If the ecu is left stock it would be best to upgrade, since the higher compression compresses more air it will make a leaner ratio than normal, I would defeniteley upgrade injectors. Stock pump will still be fine to use.Used stock pistons are fine as long as you have all new assembly to go with it, and you know that there is no damage (that means rings and pins need to be new). May not be the greatest idea but it works.

[Bigvinnie]

also i heard the 91 and some other year head was the best because of the cams but i was woundering if they really make a diff and does any one on if the 92 do the same thing

91-94 heads are slightly different than 95-98 heads the differences are not noticable. It just changed the flame front same CR ratio's.91-93 cams are the same, don't know about 94's, and 95-98 had the weakest cams ever.

[DjPantsSpecR]

tloof had an insane post about the variations of 94 cams. its a serious read, and its very interesting.

I would also opt for 300s for sure, but usually the 370s will be easier to find. Either way, you should also pick up an SAFC, and either some dyno time or a wideband (for the price of dyno time, i would buy the wideband)

seriously, i hear vinnie saying it all the time, but basic bolt-ons make you start running lean very early. I even start running lean after 3k.

Everyone (w/bolt-ons) should have at least an SAFC, but HC definately requires some more squirt. WIth higher compression your going to want more fuel to keep temps down. 11.2:1 isnt ridiculous so you dont have to go outta control trying to prevent knock. You can get away with just an SAFC, but im not sure what the duty cycles on the injectors is gonna be. Thats why i would go bigger.

[biggin07]

thanks u guys

[Bigvinnie]

Everyone (w/bolt-ons) should have at least an SAFC, but HC definately requires some more squirt. WIth higher compression your going to want more fuel to keep temps down. 11.2:1 isnt ridiculous so you dont have to go outta control trying to prevent knock. You can get away with just an SAFC, but im not sure what the duty cycles on the injectors is gonna be. Thats why i would go bigger.

RC injectors actually fine tune the stock 270cc injectors to what ever displacement is to the CR, + matched to the duty cycle. They can actually bore the injector flow rate for a perfect match to your engine, not necesarilly 300cc, but what ever the needed flow would be. This means that an SAFC wouldn't need to be used on a stock ecu tune if the injectors are fine tuned for that CR ratio, and displacement...http://www.rceng.com/technical.htm#WORKSHEET

Too make a 230BHP KA24de I came up with 282cc injection @ 26.8 LBs/HR, this was at 48% of it's duty cycle.


Modified by Bigvinnie at 10:49 AM 7/16/2006

[DjPantsSpecR]

Good link vinnie. RC engineering can definately get that done. Im more of a do-it-yourself kinda guy, so i would get the SAFC. I wonder which one is cheaper, an ebay used safc (100 shipped) or RC reworking the 270s

either way the difference is going to be: RC doing the work means its going to be done right. SAFC can only correct for so many points, while injectors would actually do the right thing constantly.

Good idea. i wonder what it costs too, i know its outta my league so ill be getting SAFC, but if you dont plan on doing any more modifications getting injectors built would be a good idea

[Ajax]

Not that its definitive, price-wise, but I was charged $135 for RC to give my injectors the once over. Of course, who knows if that's actually true- I got charged $39 for iridium plugs that I never received, etc, etc.

[DjPantsSpecR]

this sounds like a viable solution. what if i were to send in malfunctioning injectors, would they handle that?

[Bigvinnie]

Yes they overhaul injectors from what I understand. Alot of KA injectors were known to be leaky.

[essfourteen]

hey guys, first time posting here...

but what my question is, is what CR does sohc pistons set you at in a de motor. i was planning on doing this in thew near future

[Ajax]

try a search. this has been discussed before.IIRC its 11.1:1 or 11.6:1 depending on what year SOHC pistons.

[essfourteen]

yeah, sry about that, i happened to find the answer right after i posted. i didnt know that one raises it higher than the other. which ones raise it more? '90 or '89?

[3dKa24]

I beleive it is 89' that give you the highest compression.

[SX APPEAL]

I have a question now. The pistons I used were out of a 90-92 stanza with the KA-E, so which compression ratio would that give me?

[Bigvinnie]

90-92 stanza's yeilded the same CR as the 240sx KA24e's from 1990. In a DOHC that would make it 11.1:1.I would recomend that no one mentions the 1989 pre pistons that yeild 11.6.1 the raised dish will destroy the valve train. Only use the 1990's that yeilded the 11.1:1

[SX APPEAL]

Awesome, thats what I figured but never had found out for sure. That makes me wonder, are the 89 pistons domed on top or something? Cause the 90's have a .030" dish to them, which is practically flat toped whereas the stock DE pistons have .230" I think, something like that. So what would the 89 pistons have to have to bump the CR up that much higher? Just food for thought

[DjPantsSpecR]

yeah they have a slight dome. And you can use them, but they have to be flycut, and in the end im not sure its worth it

[Bigvinnie]

yeah they have a slight dome. And you can use them, but they have to be flycut, and in the end im not sure its worth it

It's not worth it when you get the engine to run leaner than usual. When ever fly cuts are put into a casted piston that wasn't designed with flycuts in the cast it weakens the cast under load and heat, it can cause stress fractures eventually, or hot spots.I'm still looking for the EXACT CR when the NAPSZ pistons are installed into the KA24de. I've been told 10.3:1, and the dish is sucken in a tad more than the 1990 ka24e pistons, making it a good candidate for high lift cams. But I am having a hard time getting my hands on an actual piston for measurements.