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L26 refresh - thought I'd share the results


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  • 1 month later...

Hi Guys

An update on the L26 engine refresh project

Well the Triple 44 Mikunis are now finally fitted and tuned and the results were pretty much as expected but a little short of the 130 rw giggawatts hoped for.

After installing the Mikunis and dynoing the car with just straight ram tubes we made around 123 rwkw at 6000 rpm but had a flat spot at around 4-5000. The next step was to install the Prince GTB cold air box and 280z (US spec) front filter housing and a retune.......bingo ....flat spot gone, 15 % gain in mid range torque and hp and no loss of top end hp. The power delivery is very linear with instant throttle response, pulls fifth gear at 60 kph and pulls away with stumbling....feels just like fuel injection......final figures were around 125 rwkw (165 rw hp) at 6000 (possible a little more at 6500 bit sustained hot dyno runs are not ideal) with great on road drivability. This is due to the 34mm chokes and 70/30 cam. Les Collins (ex Datrally) suggests that 140+ rwkw is achievable if I go to 37mm chokes and a 72/73 cam but this will be at the sacrifice of low down torque and will move the power futher up the rev range......think I'll stick with this setup to keep the car well mannered. Highway cruise needs just the slightest throttle pressure, lambda and CO readings are bang on the money right through the rev range so no horrible fumes and no difference in hwy fuel economy over the old 240 carbs  .........all round a very pleasent drive with plenty of welly when required ;D

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The dyno I use does not have a computer printout function however the torque figures were calculated to be around 255 nm at 4200 (up from the "optimistic" stock figure 206 nm).

Again not in the league of turbo morors but still quite respectable for an L26


I'm also going to experiment with a Cyclone vortex generator placed in the induction pipe between the front airfilter housing and the cold air box, I have heard mixed reports on these adding power and bettering fuel ecconomy so I thought I'd try it for myself on the dyno and see if it improves air flow and HP 

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  • 2 months later...



Whilst my engine is out (for the engine bay refresh) we will be running it up on the engine dyno tonight to experiment with exhaust headers, the aim is to compare the HM headers with those supplied by Stewart Wilkins Motor Sport and experiment with shortening the secondaries.

The Datrally engine dyno (now Power Play) is very accurate and provides measurements in BHP (actual fly wheel HP) so it will be intersting to compare the Brake HP to the rear wheel hp figures from the chassis dyno........and see what sort of losses there are thru the drive train (rumour has it around 25-30%).







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Th engine run up last night for the first time with initial results being very disappointing, upon further investigation the cam that is supposed to be a 70/30 grind in more like a 67/68 which is little different from the standard 240Z A grind.


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The cam came from Camtech in Sydney, I have emailed them with the results and await there reply........ ???  I don't hope for much of a response . I sourced the cam from Camtech as they were the only ones with a billet at the time.

The cam has now gone to Wades to be re-cut to a 72 grind which means I can retain the stock valve springs and only have to go to fat lash pads .....so an easy swap out


The Stock A grind 240z cam made around 170 bhp and the Camtech "70" not much more  :-\ but it did hold power to 6000 rpm  the A grind fell off after 4500 rmp, so according to the L series gurus in the know, a 72 should be good for around 220+ BHP at 6500 rpm.


(My dyno guys ran up an L28 a few years back fitted with a very mild 68 deg cam and it only turned around 110 rwkw, then fitted a Wades 72 grind and it then shot up to 142 rwkw !!!)


Not sure if anyone else has done back to back chassis dyno to engine dyno comparisons but 124 rwkw (163 hp) made at the wheels against around 180 BHP.....thats only around 10% lost thru the drive train. :o


Unfortunately I have no time (or the $$$) to experiment with various cams beyond a 72 as the valves springs will need to be replaced and I will run out of piston clearance....a 72 will be the limit unless I then pull the head and flycut the pistons and install heavy springs..... I need to engine back in next week so I can get it ready in time for the Nationals in QLD

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I think the expected power figures for the 72 degree cam maybe optimistic.


I'm getting 150 rwhp with an injected L28 with 76 degree cam running Haltech F9 with turbo throttle body, 62mm diameter,  and log plus regraphed 280ZX electronic dizzy.


Using the accepted 25% loss through the drivetrain that gives me 200hp at the flywheel.


But as we all know the only true measure of power is the track ;)


I do know that my car will put out 300hp with the right dyno operator........


As 260 said the only real way to check is multiple runs on the same dyno at the same conditions to get the relative changes in power.

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well the engine dyno does not lie (as chassis dyno's can) and was recently recalibrated (whithin 1hp at 180hp so within 0.5%)


They had some L28s on from Stewart Wilkins MS on the duno recently that made around 290bhp on a 76 deg cam and when a 72 was installed they still made around 275 bhp but lower down the rev range.


Well stay tuned as I hope to get the 72 deg cam in this evening and have another run.....(but I may have to go from 34 to 37mm chokes to get over 200 bhp)

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Also depends on the motor, my motor won't compete with one of Stewart's, but mine costs a lot less to build than one of Stewart's :)


Also it may have a lot of top end power but what is the torque like??? Knowing Stewart's work they will be torquey, but for some builders all they chase is a number that can give a not very user friendly engine, an example being a rotary, they may make a scary power figure, but at scary revs, generally have no torque in comparison and need to be driven a lot differently than say a big six or eight with a bucket load of torque, but may not have an enormous amount of power.


Well prepared motors with the best of everything will always outperform a pretty standard spec motor no matter what cam is in it.

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yep I agree........I was not after huge HP but a nice tractable engine that is street friendly and my L26 was not built for outright performance but it is encouraging to see what can be obtained froma little "science" .

Stewart engines always pull like train but we have proved his exhausts to be not so good as they create a huge hole between 4000 and 4500rpm (we tested one up against the shortened HM headers and the HM's killed them on power everywhere)

......anyway after replacing the 70 deg cam and installing a Wades 72 deg we hit 193 bhp at 6000 rpm and maintained this to 7000.........The low end figures were very linear from 2500 to 5000 with climb to 6000 and continued flat to 7000.

We then cut around 350 mm of the secondary pipes of the old HM headers and bingo.....we hit 201 bhp at 6000 and carried this to 7000 with power and torque up right through the rev range, we then swapped the 34 chokes to 37mm will little change so I think 201 bhp is the limit with this setup and I'll revert to 34 chokes to improve low down response. Torque figures were good right across the range and very flat (progressive) from 3000 to 6000, we calculated around 78 hp per litre which is a little down from 85 expected (220 bhp) with this setup but I think the inlet manifold is the issue.

The Cannon manifold has a balance tube connecting all the inlets together (good for brake booster) which may be harming power and torque by creating a resonance between the individual manifolds ....so I may plug the balance tube and retest later 

Anyway the donk is going back in the car this weekend so we can then compare a chassis dyno figure to the engine dyno and calculate the actual drivetrain loss.


I always thought 25% to be approximate loss between chassis and engine dynos.....but our tests have proven this not to be the case (in this instance anyway) as they are more like half that .





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I like what your doing here, always wondered what the actual loss is through the drive-train. I was also interested with the results of 34 to 37mm chokes as was basing my last motor build off a 72 cam and thought the 40 dells would be sufficient. Look forward to the next dyno results.

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I'll be a happy chappy if the drivetrain losses are up at 50%, 150rwhp for my old motor will give me 300hp, woohoo I can quote the same numbers as the other big boys ;D ;D


It will be interesting to see what the drivetrain losses are and what effects different components and condition may have, also different tyre, wheel and gearing combos can have.


I know tyre sizes can affect the final figures as can whether the gearbox is an auto or not as the torque convertor can act as a torque multiplier fo rthe dyno.

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Glen according to the "Dyno Guru" 34mm chokes should be good to flow 200 bhp and still provide good low down response (high intake velocity at low rpm) ....hence I reverted back to the 34's as the 37's made no difference in peak HP.

I should have the car back on the chassis dyno later this week to make a direct comparison between BHP and rear wheel HP....so the yard stick is 163 rw hp = 180 bhp...(initial results on chassis and engine dyno) .....so with 201bhp we should get around 180 rw hp or approx 135 rw kw .

Nothing else in the driveline has changed so apart from atmospheric conditions (air pressure and temp) it will be as close a comparison as possible.

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  • 12 years later...
  • 5 months later...
  • Administrators
On 8/6/2021 at 8:17 PM, Oliphips said:

Ps are the 240z twin carbs better than 260z?

Yes and no..

240z Hitachi (Round Tops) are easier to obtain part for and more simplistic, but they always seem to have a compromise between selecting the right needle (fuel jetting) for idle and top end (the right mixture at higher rpms, tends to create a fat/rich idle).

The 260z Hitachi (Flat Tops) were designed with emissions requirements in mind, but also had the benefit of a separate idle circuit, so you could adjust idle mixtures separately to engine speed mixtures. The problem with these is obtaining parts and dealing with all the comments of "boat anchors" from those who have parroted this information for years.

Refer to Gordon Dobbie's comments here:

and XNKE


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