Alum rods

[Thad]

Playing with the half of a 460 Mercruiser 470 four banger. Collecting pieces. So far have Edelbrock alum head.

What your thoughts/ opinions on alum rods for street, limiting RPMs to 6-6500 max for very limited time. Located a set of NIB Super rods. Cheap, cheap!

What was the magical rod length to stroke ratio?

 

[StrangeRanger]

Aluminum rods don't last very long and when they come apart they make really interesting paperweights. Unfortunately, they will also turn your boat engine into a boat anchor. They are strictly a race-only item that gets replaced every 10-12 hours or so.

The "magic" ratio is L:S ≥ 1.75:1. Anything under 1.75 is considered less than optimum, anything over is better but gains are minimal

 

[Stubby]

I know some guys who have ran them on the street. I have had dirt trackers run them for a season or two with no problems.

The key is to get the lightest piston possible. Not an easy task with sirup buckets for pistons. However the rods for a BBF are beefier than most.

The next task is to keep the oil temp below 200, Also not an easy task with a street engine. It might be a little easier with that aluminum block.

The trouble with your application is it would be a lot of trouble to check your rods. When using them in race engines you freshen it often enough to be able to keep track of their condition. When you start to fatigue aluminum it will show up while measuring them.

You can check a the rods when new and record everything. Especialy the big end bore and length. When you freshen the engine you check the rods and compare the measurements. After awhile you will notice the big end of the rod will get smaller or distorted. Distorted is bad but smaller is not as bad. At a half a thousandth smaller you can remove the dowels (sometimes very difficult) and hone them back to the proper size, reinstall the dowels and put them back in. When they get to a half a thousandth again you toss them, make realy cool stearing colum and muffler mounts, or sell them on Ebay. The biggest problem I have seen with aluminum rods is after a trans failure or terribly bad tire shake or on dirt tracks that are rough tracks(most of them). These conditions add to the cycling loads.

They are a ptia but a possibility. I think the bigger gain would be to lighten the crank extensively and maybe run BBC rods with light pistons. You would have to consider the slightly shorter deck height, but you could stroke this thing to half of a 514 There are lots of aftermarket BBC steel rods out there. I am sure you could pick up a partial set real reasonably. Now that I think about it, the early 514 kits were built with big block six rods. The problem would be a partial set of stroker pistons.

HELP I am dreaming and I can't get up

Now for the voice of reason.
You have a lightweight engine. 8)
You are building a lightweight car. 8)
If you keep unsprung weight to a minimum there won't be a need to get out of hand during the engine build. 8)
If you look at HP per LB this thing in stock form will be fun to drive
If this thing won't keep a headgasket on it, how much of your investment can you recoup?.
If blow the engine, will your wife ever trust you again? You did say roadster didn't you? These can be real fun to blow an engine in.

 

[Thad]

Yah, I actually think the same way, but the rods are beautiful and then there the bragging rights so ------ sorta hoping someone could convince me to give in to temptation.

 

[Stubby]

I have always thought about it.

I have seen cast aluminum rods in many air cooled engines. I have never checked the average oil temp on one.

The aluminum pistons see alot of heat. The wrist pin boss on the piston sees about half as much load as the small end of the rod.

The aluminum block will dissipate alot of heat.

Aluminum rods are beafier than steel rods.

I think it would work. I know it would work if you had some rods like the alcohol and fuel guys run. Those wouldn't save much weight.

 

[ASMART]

Are these 470s easy to bolt up into cars?

 

[Thad]

Some one did a rod failure study believe it was Crower. The data show most failures were in the area just before the small end.
the veolicty X mass of the piston exceeded the tensile strength of the rod as it reversed piston direction. This stretching of the rod is why records are kept of rod length by full boggie racers to change before failure.

470 in car, not a drop in but not overly difficult. And the car is planned to be designed around it. Ford six 250 flex plate fits, both engines and flexplate are zero balanced. Will have to fab a bellhousing much like a explosion proof aftermarket unit. Simple: front plate with engine bolt pattern, 14" dia x +/-7" can section and back plate with C-4 trans bolt pattern welded together.
Biggest problem is find a harmonic dampner that will work in place of the wierd one Mercury used. Not performance rated either.

 

[ASMART]

Would you have any links to info on using these motors in cars? How does the height compare to a 250. I am wondering about hood clearance. It sounds like a unique opportunity. Imagine replacing an iron 200 or 250 with a 228ci aluminum 4 cyl that make 165 horse stock! It would be lighter or at least the same weight, make more power , move the center of gravity rearward for better weight distribution, all of this and you haven't laid a hand on it yet. Of course, the trickwould be mounting it in the car and attaching to atranny. A t-5 would probably work great. Add a header and larger carb or injection and you coul deasily be in the neighbor hood of 200 HP. Hmmm.

 

[Thad]

Do you remember pics of the little green roadster some one posted some months back, that has the 470.
Info is spotty but it out there, others have used. Kaase use as a development mule to test some of his BBF monster motor heads. Necessary to mod only one head at a time to test developments. Did have a web site about the motor but lost. Ended up as 600 hp dragster.

 

[MustangSix]

I think that in your application aluminum rods would be ok.

1. It's not going to turn extremely high rpm. I wuld think that 6000-6500 might be the upper limit.

2. It's not a daily driver. there won't be a lot of lugging it thru traffic, lots of stop and go, etc.

3. You won't be expecting a 100,000 miles without a tear down. One of the issues with aluminum rods is that they can work harden over time and become brittle. That's not an issue here.

I think you just need to watch deck height carefully so that you don't have any contact due to rod stretch or elongation.

 

[ASMART]

Thad, I actually grew up around where you are. Pre high chool was in the CHina and Sour Lake area west of Beaumont and High School was in Lake Charles. Now I am in the Dallas Area.

If you dig up any websites let me know. Everytime I search I get flooded by so many marine sites I can't find anything on using in a car.

Later