TCCoA Forums banner

1 - 20 of 36 Posts

·
Registered
Joined
·
987 Posts
Discussion Starter #1
Not a new topic, but what is the current thinking on the power (and/or RPM) limits for a Teksid aluminum block, and for a cast crankshaft? My 2V set-up includes these two components along with a big bore (3.700") kit and forged rods and pistons. I'm planning to upgrade cylinder heads and positive-displacement supercharger to make more power. The current assembly has done fine at 470 crank HP, but I want to move up to about 650. Rev limiter is set at 6500 RPM, and that will not change. This is primarily a street car, but it does go to the drag strip occasionally. Am I asking for trouble?
 

·
Super Moderator
Joined
·
7,526 Posts
The block will be fine, but the cast crank is going to be the weak link, if anything. Personally, I would dial the rev limit back to 6000 if keeping that crank, and make sure the tune is spot on, since with forged rods and pistons, detonation, especially at high rpms, can snap the crank, and a broken crank will likely take out everything else with it.
 

·
Registered
Joined
·
987 Posts
Discussion Starter #3
Thanks for the feedback. The tune is set up to shift at 6000-6100 RPM and I typically leave it in Drive at the strip. But, when shifted manually it sometimes goes hgher and I have occasionally banged off the rev limiter. Don't see why it couldn't be lower than 6500, although I am interested to see where the power peak ends up with the new combination.
 

·
Super Moderator
Joined
·
7,526 Posts
Yeah, you would have to see where peak power is on the setup. If peak power isn't happening till 6300-6500rpms, then you will be leaving power and speed on the table to drop the rpms. If it is happening down at 6000-6200, then the safety margin would likely be worth the loss on the top end. Plus you also have to factor in where peak torque occurs, since you definitely don't want to your rpms to be much below your peak torque rpm after the shift. That would cost you more time at the track than not getting those few extra hp at the top end.
 

·
Super Moderator
Joined
·
17,043 Posts
nickmckinney said:
Well if you are using rods and pistons that weigh less or the same as the stock stuff, the cast crank is good to above 600RHWP and no higher than 6800RPM boosted, and basically unlimited NA from what I have seen. In the NA use you want the lightest rotating assembly possible and the cast crank is better there for sure. One issue with switching is not having to get a different flywheel if yours is already a 6 bolt.
...
 

·
Registered
Joined
·
440 Posts
I've talked with a pretty good engine builder out at (RPM Engine in Northern California) and a forged Cobra crank is a must for those power numbers.
 

·
Registered
Joined
·
987 Posts
Discussion Starter #7 (Edited)
Presumably my pistons weigh more than the stock ones, since they are the bigger bore diameter.

I'm not against changing to a forged crank on a philosophical basis. It is just more time and money added to an already lengthy and expensive rebuild.

If I do decide to get a forged crankshaft, which supplier have people had the best luck with?
 

·
Registered
Joined
·
440 Posts
Presumably my pistons weigh more than the stock ones, since they are the bigger bore diameter.

I'm not against changing to a forged crank on a philosophical basis. It is just more time and money added to an already lengthy and expensive rebuild.

If I do decide to get a forged crankshaft, which supplier have people had the best luck with?
I'd get a stock Cobra crank that hasn't been marked up because it's "professionally balanced" by swiss cheesing the crank counterweights and all that crap and have it balanced perfectly by a good machine shop in front of your own eyes.
 

·
Super Moderator
Joined
·
9,304 Posts
I killed a teskid once...






Although not in the way you might think. :gapteeth:

</troll> Carry on...
 

·
Super Moderator
Joined
·
7,526 Posts
Yup, that's mostly what I'm going on! I personally have only seen 2 broken cast cranks in 4.6 applications. One was broken due to over-revving (7500rpms on a 4V, and while the teksid block was cracked, it did at least keep all the parts contained within) and the other was I bought a PI motor off craigslist for $100 that had a broken crank, pulled the heads off it, and scrapped the rest, so I have no idea what broke it. I have seen the cast crank take lots of boost, but when they do fail, it usually seems to be RPMS that does them in, so personally, if I were building a motor with plans of over 6500 rpms, I would get a forged crank. It isn't that you will necessarily break the cast one, hell when my MarkVIII was still NA I used to rev the complete stock bottom end to 7K all the time, but if that broke, I was out $300 for a used MarkVIII mtor, but if his breaks, it is going to take a lot of expensive parts with it. Considering he already has forged rods and pistons, and a big bore setup, he is into the bottom end for probably at least $5K, every last bit of which would be junk if the crank fails. To upgrade to a forged crank when he was first building it probably would have cost another $1000. To do so now will probably cost another $13-1500. Spending $1500 to ensure that you don't destroy $5K worth of parts plus having to pull everything back apart again doesn't sound like a bad idea to me. Alternatively, if it isn't in the budget to upgrade the crank, it isn't the end of the world, but I would keep everything conservative, and set the rev limit at 6000. Maybe that will be leaving a little hp on the table, but it will still be a bad-ass motor and a ton of fun.
 

·
Super Moderator
Joined
·
7,526 Posts

·
Registered
Joined
·
92 Posts
I was curious as well since my bottom end is basically stock Lincoln 4v but it is said the crank is same but drilled to 6 bolt. I think its cast by looking but the rods are floaters and the pistons are hypereutectic according to Lincoln. I ran 6 lbs boost for a while and now I'm going NA with a 150 progressive shot.
 

·
Super Moderator
Joined
·
10,651 Posts
I was unable to find a cast crank for less than $1000.

You can find butchered cobra stuff cheaper, but why, lol.

For the rpms you are Planning to run, I'd want to go forged; I'm not, but I'm building a street car.
It may end up at 500hp before I die, but I doubt I'll break the crank. :)

The Eagle cranks are slightly cheaper than the rest, but I've read that's chinese steel. :)

I hope you find something good; I'll probably buy one too. :)



MadMikey, when you were here, I wanted to do my bad Joe Piscopo impression; But I didn't really want to get beat up, lol.

That's one of my favorite movies; Alan Hale (The Skipper) is the radio dispatcher, one of his last things.

"The car is covered with duckies and bunnies... that's it, if you want me I'll be at the bar..."

:grin2:
 

·
Registered
Joined
·
987 Posts
Discussion Starter #15
OK, lots of good input. And yes, I probably should have gone forged crank from the beginning, but now is the time for the upgrade if I'm ever going to do it. And yes, there is a substantial investment in the rest of the motor. So, rather than live with doubts and/or limitations, I'm going to go forged.

I lucked into a local deal for an unused, stock stroke Eagle 4340 Forged Steel crankshaft at a very attractive price. The guy has changed direction on his engine plan and no longer needs this crank. I'm going to see it and presumably bring it home tomorrow. Understand that the Eagle cast cranks have a very bad reputation. Opinions seemed to be mixed about their forged cranks. Anybody on here had one actually fail?
 

·
Registered
Joined
·
440 Posts
Cranks whether cast or forged are very strong, the thing that really kills them is improper balancing and harmonics at high RPMs. A stock cast crank that's been balanced perfectly might survive 600hp, but a forged one will most definitely survive. It's about reducing the chances really.

I think if you're rotating assembly is very well balanced and weighted down to the retaining clip on the pistons, then you're probably good lol.
 

·
50 years of Mercury Cougar 1967/2017
Joined
·
1,265 Posts
I have an eagle crank and rods (forged) in my cougar since 2009.

Still running 6500 rpm shifts.
 

·
Registered
Joined
·
987 Posts
Discussion Starter #18
I talked to the guy who built my engine 10 years ago, and got his thoughts on crankshaft choice. Given what I'm trying to do with the new combination, he recommended forged, with Cobra OE (made by Kellogg) as the best bet. I'm negotiating with a seller on eBay for one at present.
 

·
Registered
Joined
·
987 Posts
Discussion Starter #19
OK, the forged Cobra crankshaft is on its way. Next question: what is the Ford part number of the correct 164-tooth, 8-bolt flexplate? Is it F249?
 
1 - 20 of 36 Posts
Top