NA KA24 compression & octane questions.

Spectraeon · Aug 31, 2011

I am currently planning out a na KA24DE.
S13 DOHC block
S13 SOHC pistons (for 11.6:1 compression) :heyhey
'95 S14 head (supposedly flows better and 95 is still OBD1)
hot cam swap - 248/240 intake/exhaust cam lift (stock cams, switched and rotated for valve clearance)

Exhaust will be handled by a 4-1 with 2.5 inch straight pipe. Power will be applied to the pavement via a clutch lsd with 4.63:1 r&p gears from the front diff of an '03 Xterra.
twin fans, an extra large oil pan, with an oil cooler and long oil lines, a radiator sourced from a car with a larger, hotter engine and an extra large coolant tank are somewhere in the future to help keep things cool.

I may be converting to E85 or ethanol in the future and I may also be converting to Mikuni 44 side draft carbs.

What kind of octane do I need to be running to prevent detonation with 11.6:1 compression on a KA? Im just going to throw all of this in there and roll with it, it might take me a few months to get a retune.
Also, is it safe to run that kind of engine on the street? I know it will be a pain in the ass, due to shitty idle, high cost of gas etc, but will that compression put my engine in danger if I am running high enough octane fuel?

I can buy 93 octane at the pump, so if you say pump gas, that is what Im getting.

I've been lurking here, freshalloy and nicoclub the past month looking for advice on N/A setups and it seems like everyone disagrees on what is good octane for a high compression KA with a stock tune and cams.

Also, if I go with carbs, do I still need my ecu? Some people are saying I still need it just to make my fuel pump run (?) and some people are saying I do not need it whatsoever.

thanks

(to those of you looking forward to seeing a build thread soon, sorry, I'm in Afghanistan right now, this is plans for when I come home in 6 months.)

Spectraeon · Aug 31, 2011

probably gonna throw on a thicker head gasket until I get my tune in order to bring the cr back down a little, $50.00 for a gasket is worth reducing the risk of detonation.

Scoot · Aug 31, 2011

1. That's too high for pump gas but as you said there's many opinions. I just don't see you running any decent amount of timing to make anymore power than something with a lower ratio in the 10's.

2. Your stock ecu won't let that motor live very long without a tune.

3. If your going carbs then you don't need the ecu and can just trigger the fuel pump off any ignition trigger to a relay.

Scoot · Aug 31, 2011

1. That's too high for pump gas but as you said there's many opinions. I just don't see you running any decent amount of timing to make anymore power than something with a lower ratio in the 10's.

2. Your stock ecu won't let that motor live very long without a tune.

3. If your going carbs then you don't need the ecu and can just trigger the fuel pump off any ignition trigger to a relay.

Spectraeon · Sep 1, 2011

So, would you suggest the late pignose pistons with a 1.2 mm head gasket? This should give me just under 11:1, maybe 10.9:1 or so, Im not quite sure how big of an impact the gasket will have on it.

What octane, in your opinion would be safe with the 11.6:1 and what would be safe with 10.9 or 11:1? I think you can use octane booster up to increase it up to 97 or 98 octane but beyond that you need race gas.
I may also increase my injector size in order to make it run rich.

I'm going to start researching stuff about triggering my fuel pump off of the ignition trigger, but I have no idea what search term would be good for that.
Would it be cheaper converting to carbs than getting a retune? I can put off my diff til later in order to convert to carbs if I need to, the carbs aren't expensive but I have no idea how much work and extra parts are required. I couldn't find a price estimate for converting a KA to carb'd if you do all the work.

fakingdeath · Sep 1, 2011

All you need is an ingnition hot to the fuel pump relay (which should be how it is factory) You will need an adjustable FPR to crank the pressure down to about 7-10psi. You will also need a way to control the ignition system if your removing the computer.

I usually wont run anything over 10.5:1 comp. on pump fuel. There is a lot to take into consideration though. Certain cam profiles and such. Aluminum heads are said to be safe to run high CRs with pump fuel but its just speculation. You could also retard the timing to get rid of knock, but like scoot said youll be sacrificing performance.

I personally dont trust octane boosters.

If your going for max power, id look into some way of tuning the computer or going stand alone. Larger injectors arent going to change much, and if your going carbs, you will be eliminating the injectors.

Scoot · Sep 1, 2011

Fuel pumps controlled through the ECU from the factory but it has its own relay so all he needs to do is take a Ignition trigger and put that where the fuel pump relay trigger from the ECU was.

Octane boosters don't do shit and its been proven time and time again.
As for the ignition you'd need to put a trigger wheel on the crank. I believe MegaSquirt makes/made them for KA's specially for the carb guys.

Spectraeon · Sep 1, 2011

Thanks for the advice guys, I appreciate it.

Bow · Sep 6, 2011

You can combat detonation with more fuel.

I have a buddy that ran a High Compression 9KA24E Pistons) KA24DE in a '95 240SX on 93 Octane just fine.

you can also tune the stock ECU just as well as a stand-alone by adding a daughterboard.

E85 will cover the high compression as well, but you will need larger injectors (my stock compression KA24DE runs SR injectors, 370cc, on a tuned ECU, but the ECU isn't tuned for the larger injectors, it didn't need it, and the ECU doesn't know they are bigger injectors).

KAman19 · Sep 15, 2011

octane boosters wont work on fuel injected engines as well as carb'd cars the ecu can make minor changes to suit the different octane... it would just burn cleaner instead of producing more power. carbs only put out a certain amount of fuel per amount of air, so if you run higher octane your still getting the same amount. same air, same amount of fuel but high grade of fuel so in short more numbers.

Scoot · Sep 15, 2011

Octane boosters don't work.... It's been proven too many times for anyone with time to search to say it does.

StatusQuo209 · Sep 15, 2011

I reccomend e85. The most cost effective way to do it is get some 94-96 q45 370cc injectors and put that on. should be enough for whatever you want to do if you are not going with a carb setup..

Spectraeon · Sep 15, 2011

Thanks again guys, sorry for not responding for a while. If anyone is curious, I decided to grab the carb set up off of an old Datsun Z24 engine (Datty 720) to simplify things. I'm going to run me some 93 octane and run it rich with high compression.

an ebay Pacesetter header with a 2.5 inch Cherry Bomb muffler from Jegs will be my exhaust, and I will be fabbing up an intake and plenum that sucks in air from that useless vent under the passenger headlight.

That's all I know for sure right now.
If anyone has any tips for converting to carb or any threads/forums you could point me to that would be great, as this is my first time doing anything with carbs.

Thanks for the help.

EDIT:
About E85 on a carb vehicle... I've been reading up on this and everyone is using a kit that changes out their carb and a few other things. It makes sense to me, though that I could run E85 in a carb setup just by changing my jets to be ~30% larger. Would I also need to get a carb that flows 30% more? Right now I'm looking at getting a carb that flows about 250 cfm for peak power in the 5000s, would I need one that flows 330-340 cfm? Or is it just fuel that I need 30% more of, and I use the same amount of air so it runs rich?

Spectraeon · Sep 15, 2011

About octane boosters- I really was not sure if they work or not. I know most people say they don't, but also there are a lot of DIY threads that reccomend throwing octane booster in your tank after installing a turbo or anything else that increases risk of detonation.
The general consensus seems to be that they are snake oil... I will take your advice and stay away from them.

Scoot · Sep 16, 2011

If you are gonna spend money on something that UPS your ocatne look into DIY Race Gas. Now that works. But its also $$$. But if you have E85 then well you shouldn't be looking at anything but that. Atleast I wouldn't.

Bow · Sep 16, 2011

Spectraeon said:
an ebay Pacesetter header with a 2.5 inch Cherry Bomb muffler from Jegs will be my exhaust,[\quote]

Bad Idea if you like torque.

The KA24DE does not like a 4-1 header (which the Pacesetter is). You will do better to get a 4-2-1 (Tri -Y style) like the Ebay copies of the no longer made HotShot header.

EDIT:
About E85 on a carb vehicle... I've been reading up on this and everyone is using a kit that changes out their carb and a few other things. It makes sense to me, though that I could run E85 in a carb setup just by changing my jets to be ~30% larger. Would I also need to get a carb that flows 30% more? Right now I'm looking at getting a carb that flows about 250 cfm for peak power in the 5000s, would I need one that flows 330-340 cfm? Or is it just fuel that I need 30% more of, and I use the same amount of air so it runs rich?

Click to expand...

You need to have E85 compatable seals/gaskets/hoses, as well as larger Jets.

Spectraeon · Sep 16, 2011

I chose the Pacesetter header with its 4-1 design to flatten out my torque curve and move it higher. I do like torque, its very nice, but in race conditions I will (optimally) never drop below 4,000 rpm so I don't want to sacrifice anything about 4,000 in order to get power below that, even if I would be sacrificing 2 torque in the upper range to gain 5 in the lower range. The cars a toy, not a DD lol.

If that sounds stupid, please let me know. I'm sure most of you guys know more about engine design than I do, I just don't think I explained well enough what I want out of this engine. I don't see the point in building for what I won't use for more than a few seconds per race.

Another question to shoot past you guys: since I am running high compression and a wrapped header my exhaust will be much hotter than stock, and therefore flowing faster. Since I am planning to operate in the high range of my engine, my exhaust will be flowing even faster.

When hearing about my plans for my engine a friend suggested that I go with 2.75 in or 3 in pipes instead of 2.5. I thought this was overkill, until he explained that what I was aiming for would be flowing a lot more and hotter exhaust than stock. What do you guys think? is 2.5 in sufficient for an engine that runs mainly in its high rpm range with extra hot exhaust? or do I need to increase it by a quarter or half inch?

Thanks for the advice on E85, I will order new seals/hoses/gaskets before I build.

@Scoot: I'm fairly certain I will be going with E85. I think E85 is supposed to have the detonation resistance of around 105 octane. The fact that I can walk down to my gas station and purchase race gas for cheap is a big plus in its favor.

EDIT:Nevermind about the exhaust size, I read Scoot's (240 kid? did you get a name change or something? I remember you helping me out back when I first got a 240 and didn't know shit. Wow I miss a lot when I'm gone for a bit.) wonderful little compilation of every useful thread about a KA24 ever and there happened to be a link on exhaust which I read and it solved my problem.

Yes, it seems 3 in exhaust removes low end tq and provides high end hp but it isn't really worth it on a stock KA. On mine it will probably be worth it as it will move my powerband more towards what I am looking for. Also, that thread (http://www.240sxforums.com/forums/nissan-240sx-f-q/86298-basic-guide-n.html) contained some very enjoyable reads.

NA KA24 compression & octane questions.

Spectraeon

Spectraeon

Scoot

Scoot

Spectraeon

fakingdeath

Scoot

Spectraeon

Bow

KAman19

Scoot

StatusQuo209

Spectraeon

Spectraeon

Scoot

Bow

Spectraeon

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