Purple92

You can do it - but my question would be "why".

Look - 4340 Steel is Stronger than Ti (Typical Ultimate Strength of 4340 is 200 KSI and higher where the strength of the Ti alloy used on the LS7 rods is in the 150 - 160 KSI range). Where Ti shines is strength per lb. Ti weighs about .16 pounds per cubic inch - steel is bout 0.28. Both Ti and 4340 steel have good to excellent fracture toughness (read - resistance to cracking).

However - Ti is a more than 4 times more expensive than 4340 steel, and is a real pain in the **s to machine (so that costs a lot more as well). There are issues with Ti - Ti surface contact, and while the Ti is strong - it tends to "flex" a bit more than steel - so some areas have to be beefed up a bit to keep the deflection under control. So - if you are willing to spend some money to save some weigh - rather than spend the money on TI rods - how about a lightweight (read drilled) 4340 crankshaft. How about a lightweight flywheel ??? How about a small diameter dual disc clutch ??? IMHO - it seems that there are more effective ways to spend the money .... Especially when in many cases the LS7 rods require custom pistons that will run even more $$$...

Again - nothing wrong with TI rods - they are really neat things - but I would probably go for the lightweight crank and flywheel before I'd even consider going with Ti rods for almost any hardcore application.

Hot Rod Roy

Purple, did you read post #5?

C409

..... What I like most about this Forum is the depth and wealth of information , creativity , and experience that is freely shared .....

C409

..... How about #9 ? .....

MatthewMiller

Again, though, the point of low-mass rods isn't to reduce rotational inertia. As you note, there would be much, much more cost-effective ways to accomplish that goal. The point is to minimize reciprocating mass, which allows higher revs for the same margin of safety (more power) or more safety at the same revs. It's the same reason low-mass pistons are desirable. In the valvetrain, it's the same reason lightweight valves are desirable. In terms of the short block, rods and pistons are the only places where reciprocating mass can be reduced, and neither is cheap.

C409

..... Titanium vs Aluminum bulk-wise ... This particular alum. rod weighs 505g ... the LS7 Ti rod weighs 457g .....

drcook

excellent picture ! that really illustrates how much more aluminum is needed to get to the same strength points. the same disparity is shown when you put lightweight, thin wall steel rocker arms up against aluminum ones.

it also shows how much more material is in the big end which is rotational weight going along for the ride with the crank

There was a reason that the SR 71 Blackbird plane was skinned and air framed out of titanium. While this next post is not car related, there is an interesting tidbit of information down in the text. As you read down through, it talks about if anything that was cad plated (cadmium) touched the titanium, it made it brittle. this becomes something for folks to stick in their heads.

https://www.lockheedmartin.com/us/10...blackbird.html

MatthewMiller

drcook

Add in lightness and strength. Also, everytime the plane flew, it re heat treated itself. And heat. The leading edges would have melted.

Titanium has the highest strength to weight ratio of the structural materials. Of course GM knows that, otherwise why would they use them.

I think it is a pretty astute move to utilize the LS7 rods.

1985 Corvette

That interesting. What's the catch with using one of those mini clutches? I just went the steel flywheel and ZF clutch route and it is hefty when it comes to weight.

cardo0

Yes Ti really isn't any stronger than steel which is greatly misunderstood. And at best it's only 15% lighter than steel. Now Al is half the weight of steel but has only 1/4 the strength.Each material has it's own characteristics for deformation. As far as I know top fuel still uses only Al rods where durability is not as great an issue as in a endurance racer.

Something else I recall from D. Vizard is the lighter rotating assembly rev's faster more than it increases max RPM. Max RPM is usually limited by the cam and valvetrain more than the rotating assembly weight.

Just something to consider when re-engineering your engine.

Tom400CFI

*Cost.

*Not "plug and play"

*Easily "stallable". In other words, with essentially no fw and a very small, light clutch, you actually have to use the throttle and clutch pedal like the variable devices that they are -not like on/off switches.

If you've ever ridden a 2 stroke dirt-bike, it would require similar skills, when starting out. Not hard....but too hard for some.

C409

..... I had some Lunati Billet Steel I-beam rods that weighed 628g in another engine .....

C409

..... Time to rebalance the rods before the new pistons arrive .....

drcook

Is that a commercial fixture ? I have a really really good scale that I use for weighing bullets. With the correct fixture it would work great for rods.

Purple92

Yes - I read post 5 and post 9 and all the posts in the thread. Let me see if I can put this another way. Look at the cost of the Ti Rods - about $1K - then we have the cost of the custom pistons - I don't know what that'll be but I think it's safe to say $500 more than an equivalent se of "off the shelf" HP pistons.

So let's look at some other numbers ... If you check out the Summit Racing site - you'll see a set of 6.0" Scat 4340 Forged H Beam rods with the ARP 2000 Rod bolts runs about $560. So - the Ti rods are about $400 more - plus the upcharge on the pistons.

OK - let's look at Crankshafts. The standard weight 4340 Forged steel Scat crank for a Gen 1 SBC weighs in at about 48 Lb and runs about $690. The lightweight 4340 Forged Steel Crank for the same Gen SBC is about 8 Lb lighter and runs about $950. So - for $300 more ($100 less than the lighter rods) you save about 8 lb of rotating weight.

If you look at the cost of a standard weight flywheel - it looks like a nice standard 168 tooth steel flywheel for a SBC weighs about 30 - 33 Lb and will run about $225. A lightweight flywheel will weigh in right around 15.5 Lb - 16 Lb and look like they run about $450 - $500.

So - for less than the cost delta between the Ti Rods and the custom pistons - you can upgrade to the lightweight crank and a lightweight flywheel, and save on the order of 22 Lb or rotating weight.

To me - if you're concerned about the weight of the reciprocating / rotating parts of the motor - the lightweight crank and the lightweight flywheel make a lot more sense than the lighter rods. Yes - if you're going to be revving the daylights out of the motor - the lighter weight rods do buy you some things - but not all that many street motors see the super high revs where the rod weight really matters. And remember - the valvetrain typically give you more problems with high revs than the reciprocating assy - so if you're going to spin the motor to the stratosphere - plan on spending lots more $$$ on valve springs, and either top of the line hydraulic roller lifters - or more likely solid roller lifters ...

Purple92

That is Also correct. Supposedly NASCAR Monster Energy motors are running 4340 rods and cranks - and bottom end failures are quite rare - even though they are regularly turning 9,000+RPM (supposedly 10,000 RPM on the dyno is not exactly unusual.) Top end failures are a fair bit more common. Valve spring pressures are supposedly approaching 900 Lb wide open.

cardo0

Yea I've seen video of the top fuel motors getting tested for the maximum amount of fuel that can enter the cylinder chamber w/o hydro locking. Its almost scary how much fuel they cram into a cylinder and still get it to burn. I read top fuel is at the unbelievable 11,000hp level nowdays.

bjankuski

.16/.28 = .57 so by mass TI is 43% lighter. It is 20% weaker by mass so if you figure 20% more volume of TI it comes out to 20% lighter for the same strength as steel.

C409

..... Pro Form Part # 66844 ... you need a scale that's accurate down to .01 grams and with light parts , 1000g total as a minimum .....