L24- Stroke Or Not To Stroke

[locklock]

Hi guys, need some advice and info on the engine. I will be overhauling the engine soon, might aswell upgrading it since its going to be all taken apart. Im losing sleep weather i should stroke it to 2.6, or stay 2.4.

Its a matching engine, i dont really want to risk boring it. My question is if i use L28 crank with light conrod and piston will it still be "pig" as people claim?

Or should i stay 2.4 with just new light conrods and light pistons? Read on a honda forum, on a k20- engine, 130grams less per rod equivalent to almost 5hp gain per cylinder, not sure how true is that tho.

 

I also have a 275 cam, fujisubo header, exhaust and triples 40phh to be installed. My target is around 225-250, is it achievable?

Dont really intend to swap L28 as there is alot of paperwork to be done for engine swap in my country.

[Patch]

If you want to drive it and have a smile on your face, keep it L24, If you want a family car and eat a burger and shake while driving thd 28 crank will give you the same boring motor as the 260 was.

If you go L28 or L26 you will have to spend a lot of money to put a smile on you face.

[C.A.R.]

Just do what CBRJeff has done:
L24 block with a stroker crank = 3.1ltrs   

Edited September 21, 2016 by Lurch ™

[theremm]

I was thinking about this same question just today as well. I also want to retain my original L24 block, however I agree that it defeats the purpose of retaining a matching numbers engine if you are overboring the block. May as well do away with it all together in my opinion then.

 

It seems using the L26/L28 crank to just create an L26 isn't a worthwhile option then... but how would the L24 block perform with an LD28 crank or an 89mm RB crank, keeping stock bore, and with head work/intake/exhaust etc to suit?

[CBR Jeff]

Hi locklock this can be a vexing question. I'm my case I decided to go with stroking the matching numbers L24. Its ended up at 3066 cc due to the use of the RB crank. There were a few things that influenced my decision. Firstly I want to use my car to take trips around the state and country. The attributes of a standard L24 performance are not sympathetic with this type of use. The short stroke free reving engine develops most of its get up and go at higher revs. With a standard diff ratio this equates to a car that is suited to touring at speeds above the speed limit. The two options to change to this are either use a lower diff ratio or modify the engine to get better performance lower in the rev range. Both options have positives and negatives.

After going through all the options I decided that stroking the engine and modifying the head would be a better option for me as the car would be a nice driver on the highway but still provide a degree of performance and retain authenticity.

As for getting your desired HP, you should be able the archive the numbers you are looking for. My motor reached over 300 HP from 3066 cc. You can do the maths it's just a ratio. It's the torque that you need to chase to make the car more drivable.

The performance will come mostly from head work and porting, and that's the part that costs the $.

 

Jeff

[gav240z]

Jeff did your block get over-bored? Or just stroked to 3.0ltr? I know that some blocks may not take much of an overbore so your matching numbers engine may not always be suitable for bigger displacement.

[44014]

Why not just put it on the shelf and put a L28 in it? That way you just dont care what happens to it.

Its win win

[locklock]

Thanks for the reply,

Cbrjeff your engine is hardcore! I saw your post on the build. I wish i has the guts to go that route. Im using 3.9 lsd subaru diff btw. The fear i have is, if anything goes wrong with boring and porting i will have a hard time sourcing a new head/block. I wish LCR has a branch here.

L engine is very scarce in Malaysia.

How would the engine respone like if i just change the L24 light conrod, 83mm light pistons 275 cam? Rev? Hp? Or should i stroke to L26 with L28 crank and light rod+pistons? The price for 130mm and 133mm rods are the same anyway.

[CBR Jeff]

Jeff did your block get over-bored? Or just stroked to 3.0ltr? I know that some blocks may not take much of an overbore so your matching numbers engine may not always be suitable for bigger displacement.

No it's not over-bored. Bore went from (from memory) 83 to 85mm. It still has enough for another bore if required down the track and there was no modifications to the block so you could put an L series crank back in if you wanted. I did look at an LD crank, when I costed it all up the total cost was not much different (about $500) but there was no guarantee with the LD as to what you were getting when you purchased it!!

 

Jeff.

[gav240z]

Justin, you could get your engine built over here and shipped back to you in Malaysia. Les Collins has been building engines for clients around the world.

 

They are helping me build my engine and I'm not doing anything fancy with mine.

[locklock]

gavin, shipping fees would be a killer.. Maybe i should invite Les Collins over to malaysia for few days like how RWB nankai does his cars lol...

[Patch]

What you are asking is all a personal choice on what you want to do with the car, Race it, Sunday sprite around the hills or everyday drive car with trips away, and how you drive, and if you can drive.

 

I personally have always liked both sides of the fence and have different setups for how I want to drive that day, Years ago I raced trikes, I had a TT500  87mm x 84mm,, stroke for everyday riding and tours though the country and track racing, I also had a wild CR250 for racing only 70mmx 64.4mm in a race against the TT500 I could lap it in a 6 lap race on the CR250, but I would use 4 times the fuel and heaps more fun, but you have to know how to ride in the power band.

 

Today I have a ZXR750  71mm x 47.3mm and a Harley 1340cc with a 88.8mm x 107mm, The Harley is a good bike for group riding and tours away, The ZXR750 is a race bike that I ride alone for a kick zip around the hills to put a big smile on your face and only suitable for small rides and you have to know how to drive it to keep it in the power band.

 

I also have a 306 Peugeot convertible that has 2.0L 86mm x 82.7mm again a great car to whip around the hills take the dog for a drive to put a smile on your face, The wife hates this car as it is close ratio and she can't drive it to get the maximum out of it to keep it in it's power band, she will be taking the hill in 4th instead of 2nd and wonder why she stalled so she  prefers the Renault Scenic 2.0L 82mm x 93mm great family car around town and trips away and can go up the hill in 4th, Lazy drive.

 

I bought my 240Z back in 1986 and a 260z 2+2 in 1992, I put the motor out of my 240z into the 2+2 and I was amazed at how different the car was, a lot more fun to drive.

 

With putting in a high lift cam I bought a MK3 Zephyr 2.5L 82.5mm x 79.5mm off my Brother in-law about 1980 with a full race cam, it was fun to drive on a race track but a absolutely nightmare to drive around town, I ended up replacing it back to a sports style.

 

Just for a bit of info The RB26 has 86mm x 73.7mm which is the same as a L28 with a 240 crank in it.

 

It is all what do you want.

Edited September 22, 2016 by Patch

[sydney mike]

Why not just put it on the shelf and put a L28 in it? That way you just dont care what happens to it.

Its win win

 

This....what Doug said.

[CBR Jeff]

 

Just for a bit of info The RB26 has 86mm x 73.7mm which is the same as a L28 with a 240 crank in it.

 

Sorry Patch but the RB cranks being used are offset ground so you end up with 89mm stroke.

Jeff

[PZG302]

For me, just rebuild the L24 keeping the standard crank.

 

Parts for you will be readily available, compared to getting a RB crank sorted, and assembly should be able to be done by the guys you have access to.

 

The benefit of the L28 would be not worth the effort with what you have to go through to keep it all legal, plus a well built L24 should spin quicker than a L28 with the same dollars spent, so would be more fun.

[jock]

If all is equal with regard to bore diameter, CR ect, then the  piston and rod weight  HP gains are BS. It may spin up quicker but power is not made that way. The engine is a heat pump, the more VE the engine is and the higher the pressure can be had inside the cylinder (i.e. highest CR for given fuel used and state of tune) is how more power is had, if only it was that easy! Leave it be and just freshen the engine to OEM specs.

[d3c0y]

Just for a bit of info The RB26 has 86mm x 73.7mm which is the same as a L28 with a 240 crank in it.

 

RB26s have crap rod to stroke ratio for what it's worth too, less than ideal for N/A. What's it's relevance in this conversation?

Edited September 22, 2016 by d3c0y

[gav240z]

Like Billy Squier says "Give me the stroke".

 

 

If you have an L28 crank, rods and pistons. I don't see why not. I doubt you'll notice a massive difference in the response from the engine.

 

A lot of the difference in my opinion comes down to cam specs, flyhweel (rotating assembly) and ignition timing / advance.

 

Personally I'm going to follow along this path.

http://www.viczcar.com/forum/topic/1738-l26-refresh-thought-id-share-the-results/

[locklock]

Ive decided not to stroke and keep its originally short stroke L24 and make a high revving L24 thats generates more hp on high rpm.

Need some advice, im targeting 8.5k rpm red line and power peak and drop around 7.5k/8k to be safe?

What other mods should i do to achive the goal? Currently the parts i have is rods, pistons, racing valve springs , 275 cam, triple 40 solex, extractors and 3.9 lsd diff.

 

The forged rods and pistons im saving up to 250grams per cylinder.

Is it achievable?

[d3c0y]

To answer your question, yes it is achievable. What about cylinder head, what about the bottom end? You seem to only have half of the picture.

 

You need to buy a copy of this book and read it. All your questions will be answered and then some:

 

 

These motors are now closing in on 50 years old. It's been done before.

Edited October 26, 2016 by d3c0y

[C.A.R.]

Is it achievable?

 

Yes, but not with that combination.

As with most people embarking on a performance L series engine build, I'm afraid you've missed the bigger picture...

 

3.9 lsd diff.

2 thing you haven't considered:

 

Gearbox:

Have you ever driven a high revving, low torque, 'peaky' engine?

Even a standard 260Z CR unit won't be close enough to suit the nature of an engine with the powerband you're wanting.

It'd fall off the cam between gear changes & make it rather unpleasant to drive on nice twisting roads, let alone around town in traffic.

 

Depending on the year of your 240, I suggest either a S13/14 or R32 gearbox with a Kameari Ultra-Close ratio gear-set fitted (2.4 1st) 

 

Diff

Same issue - with a 3.9 you'll bog down when taking off & compromise the engine's ability to accelerate through to the next gear.

I'd suggest a 4.4 or a 4.6 ratio. 

 

I STRONGLY suggest you look at the above issues first.

 

Engine: 

I'm not sure you fully understand what you are asking & wanting to achieve...

Anyway, without knowing what parts you've specifically bought already, here's what I suggest:

 

Crank: a std L24 crank won't be happy LONG TERM if you want to regularly rev it to 8500rpm.

As they are only 1/2 counter-weighted. Even with careful prepping, you'll eventually either crack No.6 big end journal or snap off the nose of the crank (or both).

I'd suggest investing in a fully counter-weighted, hollow journal billet EN26 crankshaft. Less reciprocating mass & more strength to cope with the higher RPM.

 

Con Rods:

Rod/Stroke ratio is already OK, but I suggest you look at getting a slightly longer rod - something around 136mm C to C.

Make sure the rod is as small as possible - to help with reciprocating mass, acceleration rates & bearing wear.

I suggest a custom Carrillo with their tiny 3/16" rod bolts.

 

Pistons:

You'll want more static CR along with at least a 1mm over bore.

I suggest a custom forged lightweight 'lumpy top' piston (CP, Weisco, SPS), with a very narrow ring pack & thin rings to cut down on internal friction,

which will help the engine acceleration.

 

Cylinder head:

Probably an E88 casting, heavily ported by someone who knows what they are doing!

You'll need some good quality chrome stem valves & brass guides.

Springs you'll have to spend serious $ on to eliminate valve bounce at the RPM you're targeting. I'd look at Cosworth's.

What's a 275 camshaft?

I'd be looking at a Works style 76deg cam but ground with more lift - definitely over .550 thou.

To run to that RPM range with a cam that big, you'll want to run a VERY high zinc oil & regularly inspect the cam lobs for wear.

 

40mm carbs are too small & wont flow enough air to reach your target RPM.

You'll need 45's at a minimum.

 

Exhaust: You'll also need a properly designed set of extractors & a 3inch system.

 

Good luck,

L.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[CBR Jeff]

Good post Lurch. Lots of data. All of the points about drivability are exactly why I went the stroke option. After talking to Les it became very apparent that if I wanted a car to drive at the speed limit using std diff ratios and gear box I needed the engine to work within the rev range that would result from that usage. Unfortunately you cannot cruise along at 200 kmph in Australia!!

Justin why don't you leave the engine as is and start with changing the diff ratio? You might get close to what you want, without huge expense then re think your engine after that.

Jeff

[locklock]

Justin why don't you leave the engine as is and start with changing the diff ratio? You might get close to what you want, without huge expense then re think your engine after that.

Jeff

Too late..

I have bought the subaru diff and kameari axle stubs. My country has limited supply of r180/r200 differentials.

[Cozza]

What ratio and type of subi diff you get?

[d3c0y]

Just get a 4.44 from Japan. STi Type-7 RA