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WA240Z

A Lime 240Z spruce up

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D3c0y, I agree that the air box could well be hindering performance I will know better in a few weeks when I get a chance to have the car on a dyno. The modified airbox to suit the mikuni's was something I have wanted to do for sometime, more do with the finished product I wanted to achieve rather than outright HP. The money I spent on having professionals build my original L24 would have netted greater HP if I had invested the money in an L28 based build, but an L28 wasn't what I was going for. When I compete in some club competition, sprints etc. I will likely remove the airbox and fit longer full radius ram tubes. But for street driving the airbox should be fine, and it completes a look I wanted to achieve.

 

Gav, the head is an E88 closed chamber, as you can see from the photo, But I have no idea what it originally came off I can only presume it was the EFI head. I am pretty sure it was 39cc chambers. The head is giving, with the eye browed pistons and slightly relieved block for the larger valves around 10.25:1 with 83.5mm bore and 73.7mm stroke. I did spend some time searching for it as all other E88 heads I had seen were open chamber. Before the engine was rebuilt it only had 69000 genuine miles on it and it was kept in good tune and serviced very regularly. But the torque with this new head, even before fitting the mikuni's is fantastic, I can only imagine just how good an L28 based build is if done properly.

 

Billy.

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Hi Billy,

 

I have the same head that I will be using on my wife's 260. It will be going on a L28 with 87mm bore, triple 45 dellorto's etc.

 

Just wondering if you did much with port size as from what I understand optimum port size is really about 34 to 36mm for a given 44mm intake valve and displacement to keep the air velocity up within the port.

 

I'll have to remove a bit out of the chambers to keep the compression down at 10:1 which will be good as I will be able to unshroud the valves.

 

Justin

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Hi Justin,

 

Sounds like a very nice build you are undertaking. Yes my head had a lot of work completed on the ports and bowls, sorry I don't have the port dimensions, the inlet ports are the same size as the gasket and the exhaust ports just under the size of the Stewart Wilkins exhaust header, this was to reduce reverberation (I think that's the word). The photo is a bit blury unfortunately but it shows some of the port work.

 

post-101127-0-68815700-1466205402_thumb.jpgpost-101127-0-14287100-1466205445_thumb.jpg

 

The head head work, compression and ignition timing was all specifically done for the original Nissan Motorsports inlet manifold and Mikunis as that was my build plan all along.

 

Gav, happy for the above photos to be included in the head section if they are useful for others. Unfortunately I don't have a photo of the ports before they were worked on.

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Top shelf Billy! This car just keeps getting better and that airbox looks like it came from the factory.

 

What's the plan with the Dyno, will you do some runs with it on and some with it removed for the comparison? It will be interesting to see, someone on the forum used a prince GTB airbox on their Z and that provided gains over open stacks IIRC. I think the GTB airbox is smaller than this?

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Hi Billy,

 

Thanks for the pictures, looks very good. What valves and springs are you using?

 

Yes they say the exhaust works better if there is a step from the head to the headers.

 

I'll be keen to know what it produces on a dyno Stewart's headers are fairly expensive aren't they? Do you know the size of the primaries?

 

Justin.

Edited by 600Z

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Hi Justin,

 

The Stewart Wilkins headers are well priced I think honestly for both the quality that you get and the knowledge that they have been designed, tested, modified and tested over the years to offer the best torque and performance. I also had mine ceramic coated. I am a away for work at the moment so will check the primary pipe sizes and lengths for you next weekend. Though I am sure someone else on here will be able to supply that info, or just give Stewart a call this week, he is very helpful.

 

One thing to be mindful of using his headers, they will only fit with certain intake manifolds. I know I needed to file my Nissan Motorsport inlet manifold's cross brace sections so it all mounted up nicely. When I ordered mine he told me that there would be clearance issues with some inlet manifolds, best give him a call to discuss your setup.

 

Billy.

Edited by WA240Z

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So another quick update, I purchased a Les Collins overhauled 260Z gearbox with 2.9 first gear and short throw shift conversion two weeks ago. I pulled the old 3.3 first out and installed the new one yesterday. I now understand why everyone loves that gear ratio set so much. 1st-2nd and 2nd-3rd ratio spreading is so much better, and the short throw shift is really nice to use as well.

 

After I had the gearbox in and tested I spent a bit of time this afternoon working on my mikunis to get better throttle response and A/F ratio readings. I leaned them out two steps down to 140 main fuels and also brought the airs down to 190 to level the A/F ratio out across the rev range a bit better. Its driving very nice, but its still quite flat between 3000 to 4000 rpm, it may be because of my short velocity tubes. So I think its time to get in on a dyno and tuned properly now. Will hopefully have another update in a couple of weeks.

 

Billy.

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Awesome I'm going to get my 260z close ratio box rebuilt for my 72 240z. I also want to install a 4.1 R180 LSD, thinking of slapping the Triple Mikuni 44's on it also. I can't wait to see what difference it makes.

 

I'm envious because I really want to get to the point where I have the early 240z up and running and can spend my weekends tinkering with carbs ;). Honestly I do, I have loads of fun doing stuff like that.

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Finally was able to get a day off work and get the car onto a dyno and tuned properly. The car is very smooth with great torque and power, I'm very happy with the end result. The surprising thing was my cut and shut air box, with the air box on it made an extra 4hp, so happy with that also. Time to start really enjoying the car with the new setup and stop working on it.

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4HP in comparison to what?

Yeah, what was the other setup?

A graph comparison if you had one would be very interesting.

I do like your air box. :)

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Hi Guys,

 

The extra 4 RWHP was with the air box with 25mm ram tubes, air filter and cold air piping fitted compared to just the backing plate with the ram tubes. The A/F ratio was ever so slightly leaner with the air box fitted so the extra HP may have come from that. 

The two different scenarios below. 

post-101127-0-21678100-1469335889_thumb.jpg post-101127-0-56165400-1469338408_thumb.jpg

 

Final result was 155 RWHP @ 6,500rpm and 185 Nm @ 4,950rpm. The torque curve was pretty well flat from 4,200 - 6,200rpm. On the road it has a nice steady idle @ 1,000rpm with a bit of torque down low for pottering around on the street, but it really comes alive at about the 3,500rpm mark and pulls smoothly all the way to the 6,500rpm ceiling I am setting for the engine. Also I have to be honest the car feels much quicker than the dyno results show, comparing to my 225kw- 440Nm daily driver, the 240z feels every bit as quick once up over 4,000 rpm. I guess at the end of the day the dyno is a great tool for tuning but the real proof in the pudding is on the track. Will see how my little engine goes against some of my mates with their Z's at upcoming sprints.

 

The engine specs are:

Original L24 with 0.5mm overbore to 83.5mm, standard stroke.

Original con rods.

Cast flatop pistons.

E88 closed chamber head, 39cc with port, bowl and chamber work.

44mm inlet and 35mm exhaust valves.

10.2:1 compression

 

Billy

 

 

 

 

 

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Immaculate...

Hmmm Im running open ram tubes at present, wouldnt have thought youd pick up a simple 4 hp by enclosing it, good result.

I think I need to get a box for mine now

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Would the better hp result from a slightly lower intake temp with the box on? Cooler air would be denser and account for the leaner afr.

 

What were the final AFR's?

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I think it is the cooler intake that has given the bump in HP, if I had thought about it at the time I should have taken the cold air piping off and given it another run with just the air box, would have been a good comparison. The high speed A/F ratio ended up being 12.4:1. Unfortunately I didn't get torque figures to compare during the runs, only the end result. Its the first time I have had a car on a dyno so I didn't know what to expect I just let the guy do his thing without getting in the way. 

 

The good news is though the air box isn't causing a big deficit.

 

Just took the car for the second drive of the day, it is so enjoyable to drive, and that is the whole reason I have it.

 

Billy

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I'm genuinely impressed, I guess the L24 with 40s just doesn't need that much air. I wonder what the tipping point is?

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I'm genuinely impressed, I guess the L24 with 40s just doesn't need that much air. I wonder what the tipping point is?

With jst under 400cc pots, and valve overlaps/duration, they dont really suck in that much air, and a 40mm hole has way more capability.

Its s quite pissible to run the same 40mm holes, with larger diam choke, into a 500cc pot with no drama, at 7000+ rpm.

 

Heck, i ran all six pots at 490 odd CC's through one only single 53mm diameter hole, and quite capably managed 214hp at the wheels.

( but, as you know, ts a bit f effort to get the complete induction setup to all work correctly!)

 

Yep, a cold air box, with a nice big volume of air around all the trumpets, s a good move!

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Cheers guys. 

 

I was conscience of making sure I left as much volume after the rear carb as I could.

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What gap do you have from the end of the trumpet to the air box surface?

I made one some 25 years ago out of scrape alloy and I found there is a sweet spot for trumpet length and air gap to the box surface for best performance . I also left the box open at the end with a filter for air flow. Keeps the air cooler I think

It's are bit of a dark art getting it right. Air temp and air flow, but it does make a difference..     

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