Street/trackday engine build

[Darkstar]

Hello,

I'm a Z newbie from Europe, and I've been doing a lot of research recently. I found this site some time ago, and searched through the archives - talk about lots of info in one place. This forum is great!

Back to the topic: my dad (we're both classic sportscar nuts) found a nice euro '73 240Z in Switzerland for an acceptable price. The body seems to be straight with no major rust spots. The car still has the original L24 engine, and quite probably it's never been rebuilt before. The plan is to rebuild it to the best possible condition and modify it so that it will be possible to drive it daily and race on weekends. There should be no problems finding parts for the drivetrain, braking and suspension. My main concern is the engine, and I just wanted to share my thoughts with you guys.

As far as I know, most of the higly modified NA Z's run stroked L series motors, like those that have LD28 Maxima cranks. However, I'd like my engine to rev quite high (over 7500RPM would be perfect), and make most power from 4000RPM upwards. This means that a stroked motor is not an option, as more stroke creates more force on the cylinder walls, and this means the lack of possibility to rev it to the levels I'd like it to.

There's also another possibility - increasing the cylinder bore will result in more power in high RPM range, just where I would like those ponies to be. Increasing the bore in a stock L24 block can be a bit risky, as it may involve installing new sleeves, thus reducing the block stiffness. How about the N42 or F54 blocks from the L28? The bore is slightly bigger than in the L24, and the later F54 block should be as strong - if not stronger - than the factory one. If combined with the factory 240Z crank and rods, some nice high-compression pistons and the factory E88 head (is it possible to get an early E31?) it should have about 2,6 liters of displacement, which should make a slight difference from the stock lump. I was also thinking of getting a nice camshaft (something like 270deg. duration for both intake and exhaust), delicate head work, Weber or Mikuni carburetion, and a ZX Borg Warner T5 'box. Didn't Spike Anderson make such motors? As far as I recall, the british Big Sam had that combo, but soon after the installation the block split in half when revved to 8300RPM...

So these are my personal thoughts. I'd be glad if somebody gave me a piece of advice, as I'm in some kind of confusion what to do with it. I'm not going to leave it stock, that's for sure!

Regards,

Tony.

[SteveK]

Hi Darkstar

You choice of engine needs to be considered in line with the type of driving you are most likely to be doing

Fast road, track, drag etc and engine configs may/will differ for all of these

Don’t forget that the 2.4, 2.6 and 2.8 are all pretty much the same animal, are all closely related to each other, essentially with different bores and STROKE combinations and some as yet un quantified changes to block design (the absolute benefits of which are yet to be agreed upon).

There are varied opinions regarding block strength verses the different blocks but I would say that which ever option you choose, over bores (3.1, 3.2 etc) are not without risk due to instability/porous blocks etc.

What’s wrong with the 2.8.... it can be made to rev to reasonable levels reliably, with a little care and attention, and make good power in the right hands, enough to embarrass the occasional BMW and Porche driver :classic:

The N42 and P90 heads are crackers and can yield good results with the right valves and chamber set up.

Regarding Big Sam’s engine configuration (its a relatively well know car here in the UK) ... this has changed several times over the years (as has big Sam) the current engine config (last I heard) was attributable to one of the best L series engine builders around (now lives in New Zealand) --- Tim Riley. Big Sam utilises a steel billet crank, Cosworth pistons etc and don’t forget (no disrespect), there are cars of equal/greater stature around today, although people sometimes forget where the Z came from.

The owner of Big Sam is a member of this forum and occasionally chips in (not often enough Nick)

IMHO I wouldn’t necessarily agree with a 270-degree cam, I have seen bigger duration cams (300) work well, with not much more than stock lift.

Don’t forget other factors in your quest for speed

Brakes, the stock brakes on a Zed (not Zee) are prone to fading under enthusiastic driving.

And as you mentioned Big Sam , one of its greatest tricks was the handling advantage it had over its rivals

So suspension/handling will need work, as they were not particularly good from the factory let alone after 30 years.

[jmortensen]

I agree with what SteveK has to say, particularly regarding the camshaft. 270 is not enough duration for 8000 rpm. I don't think 270 is enough lift for 7000 rpm really. You'll get there sure, but you're wasting time waiting to hit 7000 rpm with a cam that small. 300 degree cam is a much better idea for turning rpms above 7000.

8000 rpm is going to sacrifice the longevity of the engine, as the L6 crank has some vibration issues at 7500 (which Big Sam probably avoided by using a custom fully counterweighted crank). Search for "stroker" and "destroked" and you'll find threads about both options. I'd pay particular attention to Dan Baldwin, who argues pretty convincingly that the rpm limit of the stroker when measured in piston speed feet per second is something like 150 rpm less than the 2.8.

The best argument against the stroker is cost. The increase in power should be proportional to the increase in displacement, so if you go from a 2.8 to a 3.1 you're looking at gaining 10%. That's nothing to sneeze at, but when you figure the ultimate streetable potential of a 2.8 vs a 3.1, then you might have a more difficult time justifying the several thousand US dollars in return for 25 or 30 hp.

[Darkstar]

You choice of engine needs to be considered in line with the type of driving you are most likely to be doing

Fast road driving with a tad of trackday fun and occasional local rally usage. Definetely not drag racing ;-)

The N42 and P90 heads are crackers and can yield good results with the right valves and chamber set up.

Ok, but what about the late 240Z E88? As far as I know, they have smaller combustion chambers, which results in higher CR. It should not be a problem to get higher CR, as I'm planning to mill the head and block just a bit to make them flat.

The Big Sam's current engine specs sound impressive - it seems that this is what I should be aiming for! :-) Back to the realistic world - I came up with the L28 block/L24 crank idea because I'd like to use at least some factory parts. Of course, saving money in an area like this is pointless, I've seen too many cars broken because of that.

IMHO I wouldn’t necessarily agree with a 270-degree cam, I have seen bigger duration cams (300) work well, with not much more than stock lift.

I agree with what SteveK has to say, particularly regarding the camshaft. 270 is not enough duration for 8000 rpm. I don't think 270 is enough lift for 7000 rpm really. You'll get there sure, but you're wasting time waiting to hit 7000 rpm with a cam that small. 300 degree cam is a much better idea for turning rpms above 7000.

In this case, what cam should I be looking for? Something 290-ish or 300-ish with not much over the stock lift? Except for the camshaft itself, what should I buy for the head - harder springs, maybe valves?

8000 rpm is going to sacrifice the longevity of the engine, as the L6 crank has some vibration issues at 7500 (which Big Sam probably avoided by using a custom fully counterweighted crank). Search for "stroker" and "destroked" and you'll find threads about both options. I'd pay particular attention to Dan Baldwin, who argues pretty convincingly that the rpm limit of the stroker when measured in piston speed feet per second is something like 150 rpm less than the 2.8.

I'll have to limit it to the 7500RPM then. It's not going to be a full race car, so it shouldn't be a big disadvantage... ;-)

Brakes, the stock brakes on a Zed (not Zee) are prone to fading under enthusiastic driving.

And as you mentioned Big Sam , one of its greatest tricks was the handling advantage it had over its rivals

So suspension/handling will need work, as they were not particularly good from the factory let alone after 30 years.

Thanks for mentioning, I'm going to ask about the specifics in the Suspension and Chassis section. The brakes alone shouldn't be a problem - I've seen some ready kits available for the 240Z.

Thanks for the info guys! To tell you the truth, I wasn't expecting anybody to write this much so quickly. It's a shame that there aren't many forums like these...

Regards,

Tony.

[jmortensen]

Search here, search www.hybridz.org, search www.zcar.com. You'll find so much info on strokers and destrokers and camshafts and heads that it will make your head spin. Once you've read for a couple days you'll be able to ask better questions. There are lots of resources and information is readily available online. You'll be amazed at all the crap you find. If we just hit you with a whole load of info I think it might be hard to digest. Might want to order the book "How to Modify Your Nissan/Datsun OHC Engine" by Frank Honsowetz.

[260DET]

One thing to keep in mind with a high revving L is the front crank pulley/dampener. The stock one is not good enough. Stewart Wilkins Racing in AU for one makes a replacement, based I believe on a BMW unit.

[SteveK]

260DET spot on mate

6 months ago I had my crappy euro damper disintegrate and fall off (split along the keyway) luckily I was only doing 5mph but earlier (5 mins before I was doing 135) …. It was a brand new one.

The Euro damper was a cast item designed by Nissan to be mass produced and serve a purpose, the moment you begin to tune a car beyond manufacturers limits then a component level rethink is required.

Several companies do good quality dampers

ATI (my preferred) is an elastomer damper used on race applications world wide but not cheap !!!!

We did comparative dyno runs which showed some of the shortfalls of the euro damper verses ATI-- the results were very revealing, gaining as much as 4 HP in one area and an overall gain right the way along both the torque and power curve to 7000

"How can a crank damper improve power" because it is tuned to dampen out the parasitic harmonic vibrations, letting the engine run smoother and more efficiently, plus with a quality damper you get the most important factor --a degree of security in knowing you have the best, those vibrations can destry a high reving engine in a heartbeat.

Don’t forget to plan for a good exhaust system; all of your hard work can be fruitless if you bolt on any old tubular manifold and system. The Nismo chromed steel, inch and 5/8th 6 into 2 unit is good but needs a well thought out collector to work to its optimum, look to converge the pipes somewhere at the back of the gearbox (600mm or so), any less may loose you power/torque. Once again this is based on dyno time and experience, we saw over 20HP gained by the use of a well-designed collector.

Carburetion ---huge subject. Some folks run SU’s and make great power .. Guy on here (Norm I think) runs 12 second quarters using SU’s. Most people get a set of triples and slap them on without thinking, air speed, chokes, ram pipes and air boxes – once again we saw huge differences between open ram pipes and cold air induction – like you wouldn’t believe.

With a performance cam you will need good quality springs and valve retainers etc, you don’t want valve bounce if you intend to rev the engine. I can also recommend stainless valves with 3 angle seats.

Head gasket type and thickness is important, there are various ones around varying in thickness from 1mm to 1.4 mm --- this of course changes your compression ratio (can be a good or a bad thing) I use a 1mm metal Gasket from HKS, as the engine is designed around a specific CR and squish area, this needs to be planned for.

Chamber volume and consistency of chamber volume is critical, choice of piston, ring, bore finish, bearings etc all need to be thought of, it’s a long list and a forum is not the ideal place to build a definitive “must do” list.

As jmortensen said you could do al lot worse than buy "How to Modify Your Nissan/Datsun OHC Engine" by Frank Honsowetz.

[Darkstar]

Looks like I'm going to need to do lots more research. There are some exhaust system specialists over here, so designing and making a well-working system shouldn't be that much of a problem. As I thought before, one of the most improtant issues when revving high are going to be vibrations, so I'll have to balance the whole bottom end (crank pulley/crank/rods/pistons/flywheel) and buy some lighter parts for the head. Is the HKS head gasket still in production? There's a possibility to make a custom one in Poland. I suppose that the CR shouldn't be much higher than 10:1, as the fuel quality isn't really good. Before doing anything, I'll try to get my hands on the book you mentioned. Is it available new or will I have to search through the US eBay?

Regards,

Tony.

P.S. - Steve, thanks for the PM!