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Old 04-22-2015, 01:18 PM
cdlong cdlong is offline
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Default KA24DE Street Prepared engine build

I'm getting ready to start building up parts for an new engine build for my DSP autocross car. I'm getting ready to purchase a used engine to work on and then swap in with a bunch of upgrades, so I guess you could call this a long term build thread plus some questions.

For those not familiar with Street Prepared, the engine rules are essentially - the long block must remain stock; can be rebuilt but only using factory specs, repair methods, etc. There's some advantages to exploit such as decking the head/block. Specific allowances inside the engine are cam gears, 1.12mm overbore, forged pistons (stock configuration) and port matching up to 1" inside the head.

Outside the block/head is essentially free. Any intake/exhaust manifold, TB, ignition, ECU tuning, raised redline, injectors, fuel, etc. No adding a turbo/supercharger.

In DSP, the main competitors are the RX-8 and BMW 3 series (primarily E46). From a power standpoint, the E46 is the main contender so I'll use that as the target. Using Jason Rhodes' thrust calculator chart, I'm not in as bad of shape as you might expect. Due to the weight and gearing advantages of the 240, I'd have to make only about 207 whp to match the e46's 237 whp. That's not really feasible given the build restrictions, but the weight, size, and CG should be advantageous everywhere else where I'm not at full throttle. I put together a chart showing a roughly stock KA dyno, a KA that would match the thrust of the e46, and a guess at what I might really expect out of an engine build.


So those are the restrictions and the goals. Now for how to get there. Here are my thoughts on the build.
S13 KA24DE - you can't change cams, but you can update/backdate the engine as a whole part. The s13 and s14 KAs are essentially equal but the s13 has better cams.
JWT cam gears - no idea on where to start on degreeing these, starting point suggestions are welcome.
1.0mm Overbore w/stock configuration/weight forged pistons. These will likely be custom. Where should I start shopping?
Deck head and block to max out available compression - is there any danger of valve/piston interference here?
E85 and bigger injectors - might need 480cc's if this actually makes good power. Otherwise, 370cc SR injectors will work.
New intake, plenum, z32 TB, z32 MAF, bigger filter and intake tube.
Full exhaust - currently have a hotshot header, highflow cat, and 2.5" catback with a muffler but I can go to burns header, no cat, and shorty exhaust.
Pulleys and LW flywheel - ASP pulley and Fidanza flywheel already installed and will be transferred to the new engine. I could go to a tiny FW, but I'd rather not for a number of reasons.
Nistune ECU - 7000rpm redline, dyno tuning, cam and ignition timing, etc.

So about my power goals, 180 lb-ft and 170 whp. Is that reasonable? Conservative? Pipe dream? Any holes or issues I'm overlooking?

Last edited by cdlong; 04-22-2015 at 01:24 PM..
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Old 04-22-2015, 06:22 PM
orion orion is offline
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I think the cams are really going to hold you back. They won't be making power at 7k...but I think you can hit your goal (HP, yes...maybe not 180rwtq).

Here's a chart from my car, from *way* back in the day (March 2002)...stock S14 motor, S13 cams, Injen intake, GReddy 2.25" exhaust, JWT ECU (mail order tune), and I believe it had an ASP underdrive pulley installed.



157rwhp at just under 6k.

Factoring in the lightweight flywheel (and can you do a 1-piece AL driveshaft?), E85, more timing, better tuning, a tiny bit of compression, etc...I think 170rwhp is realistic.

My $0.02 - Hope that helps...

- Brian
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Old 04-22-2015, 06:41 PM
Def Def is offline
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Doing a nice valve job and all the stuff you list, I could see 170 rwhp, maybe a hair more if you really tweak stuff. But stockish CR is going to limit gains on an NA engine. Plus factory cams which are really mild. Could you get them reground to the limit of factory tolerances? Not sure how much power is in that, but it might help some when you're so flow limited.

I would definitely spend a lot of time on the intake and exhaust manifolds.

I have a set of S15 480 cc injectors I would part with for the build for a reasonable price. I don't think 370s will do it with E85 and stock FP. They'll be on the ragged edge if you make anywhere close to your goal.

I'd just get cast overbore pistons, no sense in a custom forged piston if it has to be stock weight IMO.
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Old 04-23-2015, 12:40 AM
cdlong cdlong is offline
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Quote:
Originally Posted by orion View Post
I think the cams are really going to hold you back. They won't be making power at 7k...but I think you can hit your goal (HP, yes...maybe not 180rwtq).

Here's a chart from my car, from *way* back in the day (March 2002)...stock S14 motor, S13 cams, Injen intake, GReddy 2.25" exhaust, JWT ECU (mail order tune), and I believe it had an ASP underdrrive pulley installed.

157rwhp at just under 6k.

Factoring in the lightweight flywheel (and can you do a 1-piece AL driveshaft?), E85, more timing, better tuning, a tiny bit of compression, etc...I think 170rwhp is realistic.

My $0.02 - Hope that helps...

- Brian
Thanks. I'll compare that plot to what I have in there now, it's more acurate starting point I think. Given that plot, I think (hope) 170 may be conservative. If only a little. No one piece driveshaft. And the s13 cams are the best I can do (and stay in the class). If can't make any power up top no matter what, maybe I should focus on low end grunt.
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Old 04-23-2015, 12:57 AM
cdlong cdlong is offline
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Quote:
Originally Posted by Def View Post
Doing a nice valve job and all the stuff you list, I could see 170 rwhp, maybe a hair more if you really tweak stuff. But stockish CR is going to limit gains on an NA engine. Plus factory cams which are really mild. Could you get them reground to the limit of factory tolerances? Not sure how much power is in that, but it might help some when you're so flow limited.

I would definitely spend a lot of time on the intake and exhaust manifolds.

I have a set of S15 480 cc injectors I would part with for the build for a reasonable price. I don't think 370s will do it with E85 and stock FP. They'll be on the ragged edge if you make anywhere close to your goal.

I'd just get cast overbore pistons, no sense in a custom forged piston if it has to be stock weight IMO.
The only valve or cam work has to come right out of the FSM. The valve work was going to be part of the rebuild and I'll leave that to the machine shop, but if I should push to one end of the spec or the other, I'm curious what that would be and why. I'm not sure any cam regrinding is legal, but I can look into it.

The exhaust will likely stay the way it is for a while, Matt and I had a brief discussion in the s14 NA KA build thread about it. The intake manifold I was planning on removing the lower plenum and section of runners and making a new plenum out of RMR extrusions and giving it a big taper. With a z32 TB and MAF, hopefully flow won't be a problem.

I'm interested in the injectors, PM me more info.

If you can find 1mm overbore s13 pistons, that would be great. But I figured I would have to go custom and forged would add some cushion for tuning errors.

Thanks for the thoughts guys, keep it coming.
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Old 04-23-2015, 01:06 AM
cdlong cdlong is offline
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Just reviewed the FSM and it says for any issues with the cams, to replace them. I can't imagine justifying any regrinding.
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  #7  
Old 04-23-2015, 07:11 AM
djsilver djsilver is offline
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I dyno'd 168rwhp on my S13 in DSP trim. 1mm ACL cast pistons, JWT ECU, JWT exhaust gear retarded 5 degrees, S14 stock intake, generic CAI w/K&N filter, S14 MAF, Apexi Neo3, Hotshot header, Random cat, generic 2.5" exhaust, 93 Octane gas. A custom intake will give you more top end but pay attention to your torque curve. E85, bigger injectors, and more timing will probably get you there. I tested 2.5" vs. 3" exhausts back to back with zero difference.
I never did any port matching. Fancy multi-angle valve jobs, zero-gap piston rings are not allowed. 240's only came with 1 final drive ratio, so tuning ratios is limited to playing with tire diameters.


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  #8  
Old 04-23-2015, 08:52 AM
cdlong cdlong is offline
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That's good to hear. Do you still have the dyno plot? I wasn't going to do anything fancy, just a fresh engine and a bunch of upgrades that I could likely do individually but will be easier all at once. Does ACL have those pistons as a regularly stocked part or custom? The only thing I could find in their catalogue was stock bore.

Luckily the stock gearing works pretty well with a 275/35/17 and 7000 rpm redline. 66 mph at redline in 2nd.
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Old 04-23-2015, 01:34 PM
Matt93SE Matt93SE is offline
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I know of a guy several years ago (about 10) in an S13 that put down 170whp in STS trim. it was a fairly decent budget, but I would think you can easily get 170whp in SP trim if you can do it in STS...

that's all I can provide tho.
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  #10  
Old 04-23-2015, 03:58 PM
cdlong cdlong is offline
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Jason Rhodes? He's one of few well published fully prepared STS builds. I didn't think about that until now, but his build thread isn't up on nicoclub anymore. Good info anyway. Though the only major difference between ST and SP is the intake manifold/TB and flywheel.
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