F54 L28 bottom end rev limit?

[EricB]

So I'm slowly building up a nice cylinder head with some good bits from Japan (Kameari Titanium retainers & 8000rpm safe valve springs) but when wondering about picking out a cam I got to thinking about the bottom end's rev limit.

Mine is an 81 F54 which I had cleaned up (hot tank, hone, check for straightness, etc) a year ago and to which I fitted new bearings and rings. Having only the seen addition of a deeper and baffled sump & a higher flowing oil pump it is basically stock.

I know the L28 revs less than the L24 but does anyone have a specific number I should keep in mind?

For example if the bottom end can only handle say a max of 6500rpm it doesn't make much sense to pick out a cam that only comes on between 6000 and 8000 rpm. Know what I mean?

So with that said? Anyone know what's safe on an F54 bottom end?

-e

[beandip]

Send a PM to Phred this is his area . He builds Z engines

[e_racer1999]

i would guess that the bottom end could rev to at least 8... are you planning on doing any work on the bottom end? (i.e. balancing, different pistons, etc.)

[thehelix112]

Jason,

Can you tell us what you are basing that estimate on? Not trying to have a go, just want more information. I've heard stories of harmonics popping the ends of cranks (both ends) at 7500+ but thats not really pertinent to this conversation as I don't KNOW anything.

Keen to learn.

Dave

[Phred]

A safe rev limit is like safe sex, there's still plenty of risk involved. Its also a very open ended question. I'll try to explain the variables that effect and change rev limits. First, the part everyone is aware of, displacement/stroke. An L-24 has less mass and stroke than an L-28, so its physically easier to throw a smaller pist/rod/stroke back and forth. So generally it can handle higher revs before it flies apart. You can quickly see why lightweight components are important for high revs. Less weight means less stress on everything that goes around or up and down. Balance, the higher the revs the more important balance is. If you have a balanced crank, and an unbalanced rod/pist. assembly, it can literally rip the crank out of the main caps at high revs. (see pics for proof). Note: to help prevent this, main caps are reradiused, and shotpeened. Then attatched with an ARP stud kit. Balance moocho important. Ok, so its perfectly balanced. Everything needs oil to continue going around. All a deep sump does is ensure a larger supply to draw from. Volume, for continually suppling fresh lube to the bearings. Pressure, ( rule of thumb here) ten pounds for every thousand revs used when hot. Z cranks have another limiter. The supply of oil to the rod bearings. The Z crank delivers oil to the rod bearings through the main bearings. But its not an equal system. the center main feeds two rods, while the rear main dosen't feed any. It works ok to 7000rpm, but if you want extended high rpm, the crank must be cross drilled, and heat treated ( another subject). Yes, I know drag racers can turn 8000+ on a stock crank. But an entire season lasts about as long as one SCCA practice session. I know the difference, I have built L-cranks that can last a full season in a GT-2 9000rpm engine. Point being, high revs? how long? how often? and how long do you expect your engine to last? I could go on, but I think you're getting the idea. Other considerations, everything else in the engine that will allow it to turn higher revs effectively. In the mid eighty's I had a customer with two L-28 GT-2 engines. One had steel valves, retainers, and a cam which gave max power at 8200/8500rpm, depending on cam timing. The lowest rpm it would run at was about 4000rpm. It wouldn't rev any higher because there was too much weight in the valve train, and it would float the valves. So the other engine had Titainium valves and retainers, and a cam that was designed for higher revs. This one would rev reliably past 9000rpm with less valve spring pressure, and of coarse it made more HP, alittle over 300. But it also didn't want to run under 4500rpm. While on this subject, I have to say that Titainium retainers are a waste of money unless the engine will see very high revs. There's much more to consider than high revs. Budget, intended use, expected life, and the ability to transform all those high revs into usefull energy. Remember to look at the engine as a whole puzzle, not just one component.

Phred

[e_racer1999]

Jason,

Can you tell us what you are basing that estimate on? Not trying to have a go, just want more information. I've heard stories of harmonics popping the ends of cranks (both ends) at 7500+ but thats not really pertinent to this conversation as I don't KNOW anything.

Keen to learn.

Dave

depending on the tune of the engine......

there's really nothing i can say that phred hasn't already covered..... besides, he said more than i could've anyway!

[EricB]

Thank you Phred

-e

[260DET]

Crank harmonic balancer?

Seen plenty of problems with the stock item literally falling apart, a lot of this may well be due to the age of the component concerned. But the ultimate solution seems to be to use a different type, Stewart Wilkins in Sydney for one supplies a special, based I believe on a BMW item.

I'd assume that something similar would be available in the US.

[thehelix112]

ATI make a twin-dampener for the L28 too:

http://www.atiperformanceproducts.com/products/dampers/charts/damnissan.htm

And Chris Wood (of Speed Technologies Melbourne) makes a very similar unit, also based on a BMW I6 dampener.

Phred, nice post, people like you are the reason internet forums work as well as they go. Much obliged. I'm going to get laughed at, and I'm sorry for hi-jacking the thread, but while we're on the topic of high revs, say I was interested in getting my L28 to spin to 9000-9500 safely, you are saying this would obviously require titanium retainers, valve springs approximately how stiff? This magical (expensive) engine would be running custom forged billet crank, rods and pistons, dry-sumped obviously. What are the limits of standard nissan main-caps with ARP studs in terms of torque, assuming a precision balanced setup? Have you ever experimented with girdles?

I fully expect to be laughed off as an internet-dreamer, so feel free to ignore that in its entireity.

Dave

[Phred]

Dave,

You can't do what you don't dream of first. Your questions are valid, but you must understand that high rpm is NOT the goal, but the results of trying to build the most HP out of a regulated size of engine. Thats why F-1 engines rev so high. They are regulated to a certain displacement, and the only way to make more HP is to up the revs. While the opposite is now found in some drag racing classes. With no (or very high) displacement limits, they are using large displacement engines with relatively low rev limits. So the old saying "there's no replacement for displacement" has merit. First, make it as big as you can, then work on the details. In the attempt to build the most HP out of a L-6 engine, we first maximize the displacement. For SCCA roadracing, that is an L-28 bored +.040. Then we deal with the details such as the questions you ask. Knowing it would take 9000+ rpm to achieve Max HP, titainium valves, and retainers are mandatory. Consider, a Ti 1.425 in. exh. valve, weighs about 48 grams. A steel 1.383 in. exh. valve weighs about 75 grams. Thats a 35% weight savings! And its the most important kind of weight. The type that has to get pushed open against the valve spring pressure, stop, and get pulled back down with the valve spring. At 9000rpm, a valve/spring assembly ossilates 75 times per second!!! With that kind of weight savings, a Ti valve engine can use a lighter spring and rev higher than a steel valve engine with heavier springs. Lighter pressure springs also have other HP increasing properties. They create less heat, and produce less internal friction. This is known as mechanical efficiency, where developed HP gets to go out the back of the crank, rather than lost turning over an engine with stiffer valve springs. So, one of the tricks is to use the lowest spring pressure you can without valve float. The range for a full Ti valve L-28 engine (depending on max rpm) is from 100/120 lbs. on the seat, and 265/300 lbs. open. I have built steel main caps, but its a real job. I found that by re-radiusing the area whrere the bolt head spot face cuts into the main cap, then shotpeening, they would hold up to high revs without cracking. The ARP studs are best for clamping the main caps on. Their specs are 60lbs. with ARP moly lube. I never built a girdle simply because of the work involved. But I have installed, and used them on other types of engines.

Dream on, I do. It doesn't cost anything.

Phred

[thehelix112]

Phred,

I do understand that revs aren't the goal, horsepower is, not even that, torque is the goal. However in order to get the torque I want with a usable power-band I fear the engine will be required to spin to 9000. If i can get what I require from less than so be it. Good advice re valve spring pressure, all these little things that I haven't even considered yet. On a related note, how does one determine if they are getting valve float? Or is it extremely obvious once the engine is running?

Light-weight valve-train sounds like a must. On Ti though, I have heard/read that Ti has limited life cycles unlike steel? Ie, it will fail after a given number of cycles?

WRT displacement, I understand that the concept behind `there is no replacement for displacement' I believe, however, I have to weigh up the benefits of reducing cylinder wall thickness (reduced block rigidity and strength), increasing the likelihood of piston-jamming, and undoubtedly a host of other things I haven't considered when the HP increase could be made up with another few hundred RPM and/or few PSI of boost. That being said, interesting that you only mentioned 0.040 overbore? Taking bore to 87mm I believe. What are your views on the guys running 0.120 overbore on L31 engines etc? I'm not seriously considering it, more fishing for your comments on block strength?

Also while I'm dreaming and picking your brains, on SCCA engines (which I'm assuming you have worked on judging by your comments) did you have any issues with blowing head gaskets between #5 and #6? If so, what was the solution? A fellow here in Melbourne (RPMZ) has had his head drilled and uses an external water manifold to ensure correct coolant supply (I think?).

Also, what was the HP achieved from the SCCA turbo L28s? Around the 600hp mark as noted in various books?

Kindest Regards,

Dave

[Phred]

Dave,

Ti valves do require special care. But they do not reach a cycle life, and die. They degrade because of the less-than-perfect conditions their subjected to. A steel valve can survive those same conditions simply because the steel alloy is more durable. A pure Ti valve needs a slightly wider seat width than steel, or it will wear abnormally. They also need a nice, straight, honed valve guide bore, or stem wear will result. And, the tips will fail quicker than steel when subjected to valve float. In the past, a hardend lash cap had to be used on the end of the stem, but now most companys offering Ti vaves have a hardend tip manufactured into the stem. There are a couple of high tech companys now offering special treatments that will extend the life of Ti valves. One buzz word used to describe these finishes, is "Diamond Like Coating" or DLC, Very trick stuff. Do a web search for "Casidium". or "Black Diamond" high performance coatings. As far as trying to find the limit where valve float occures, that has been described as being the same as cleaning your gun without unloading. Formula V, Formula Ford, and Sports 2000, are what I call non-leathal engines. They have single springs, and can RPM exceed the springs capability to follow the cam. It can be seen and heard on the dyno. An experienced "ear" can detect it on the track. There are usually no devestating effects, because they use stock cams which have very mild ramps leading onto and off the lobe. When radical lobe profiles are used its much harder for the spring to control the valve. Thats why you need stiffer springs. That's also why some cam manufactures have gone to a asymmetrical lobe profile. The on-ramp is nearly flat, and hammers the valve open. Then, the off-ramp is gradual to allow the valve/spring to follow the lobe closed, and not "float" down. If this float is allowed to continue, such as in a massive over-rev, The valve will bounce on the seat, just when the cam wants to open it again. The spring ossilates, gets confused, and all mayhem can result. I have seen (post mortum) Valve locks spit out, Broken springs, spring seats, valve locks sucked through the retainer, rocker arms broken, or dislodged, and of coarse the final insult, valve hits piston. When engine building reaches this level, its very easy for the "do it yourself builder", to get into very expensive trouble. I think I've use up my space and energy on just one of your questions. I'll try to answer the others tomorrow.

Phred