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Old 04-29-2004, 02:06   #1 (permalink)
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Safe Rev Limit of 351 Crank and Rods?

Given the current finishing techniques and bearing and rod bolt availabilties, what would a safe rev limit be for 351 cranks and rods, after what treatments? Would the limits vary with intended use, say forced induction versus high compression natural aspiration?
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Old 04-29-2004, 19:39   #2 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Forced induction set-ups do not need to rev as much to produce their power.

5000 for a stocker clevo
9000+ for a mega dollar pro-stocker
6000-7000 for most well built street motors
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Old 04-29-2004, 19:57   #3 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

My NA 10.5:1 comp 351 running 351 crank and rods has seen 8500rpm and it's done plenty of work since.

Although I'd personally say 7000-7500rpm. A cleveland has quite large connecting rod bolt etc. So it is quite strong. How the engine is preped also makes a big difference. The main difference being longevity of the engines life.

I agree with StrokeXD with the force induction comment. Forced induction motors don't need to rev.

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Old 04-29-2004, 20:03   #4 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

7000-7500 on standard parts is rubbish.
STROKEXD is right on the money.

Not only the crank and rods, but anything above 5500-6000 and your valve train won't last.

Also brenx your 8500 rpm must have been an over rev. 8500 pahh
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Old 04-29-2004, 20:20   #5 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Quote:
Originally Posted by TICK4D
7000-7500 on standard parts is rubbish.
STROKEXD is right on the money.

Not only the crank and rods, but anything above 5500-6000 and your valve train won't last.

Also brenx your 8500 rpm must have been an over rev. 8500 pahh
Sorry oh mighty god. Who mentioned valve train?? You should re-read the post as poster also asked about what prepared parts would do. He only asked about crank and rods. Prep them and the rpm is able to be done. I did

It was on a dyno at the time. It did three 8500rpm runs.

Theres plenty of 7500->8500rpm clevo's around running nothing fancy rod wise. It's all in the balancing and prep.

[edit] Yes, I am surprised it didn't go bang. I am also very happy that I now know I have a strong bottomend that is capable of rev's.

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Old 04-29-2004, 20:28   #6 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Clint : Shot peen the rods/run ARP rod bolts etc/run light weight quality pistons/balance and clean up the rotating assembly and your well on your way.

My bottomend un-assembled was $2872 three years ago.

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Old 04-29-2004, 20:45   #7 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Quote:
Originally Posted by Clint
Given the current finishing techniques and bearing and rod bolt availabilties, what would a safe rev limit be for 351 cranks and rods, after what treatments? Would the limits vary with intended use, say forced induction versus high compression natural aspiration?
Factory 351C rods with ARP (or similar) rod bolts after magnufluxing, shot-peening and resizing, will live well to about 7500 RPM depending on total power output and the weight of the pistons and pins used with them (lighter is generally better).

Factory 351C crank underground 10/10 and re-nitrided will live well to about 7500-8000 depending on total power output and the total bob weight hung on it. I wouldn't recommend going over about 6800-7000 RPM using an externally balanced stocker/worked crank/rods setup, but I know guys who regularly do...and a few that shift at 7800 with them. Also, total power output should be about 450 HP or less with a stock/worked bottom end, but as everyone knows, Pro Stockers ran destroked (offset underground on the rod journals) factory cast iron Cleveland cranks upwards of 9000 RPM back in the day.

You can easily run a stock crank/rods setup to 7000 RPM safely with everything else matching, especially valvetrain like a nice solid lifter cam and double coil springs matched to the cam. However, at those RPM, you need to start looking at other places where the added weight will be "bothersome" like the intake valves (on 4V heads) and the pistons/pins, even pushrods will need to be chrome-moly to shave the weight while adding strength.

A good set of lightweight forged pistons with coated skirts in a flat top design with a set of reworked factory rods with ARP bolts and tapered wrist pins, a factory crank turned 10/10 under and (straighted as needed!) re-heat treated with a cam like this:

Isky Cam

...with a FunnelWeb 4V, modestly ported 4V CC heads with screw-in studs and guideplates and an 850 DP will make 470 HP at 6500 RPM and 410 TQ at 5500. It will spin well to 7000-7500 but power will begin dropping off very quickly after 7000-7300 RPM. It will run fine externally balanced with a SFI dampener and flexplate/flywheel. Use oil restrictors to keep the oil in the mains and run a crank scraper to keep oil down. If I was planning to build this engine for the street, I would probably keep the MSD set at 6800 as a maximum RPM for it. I would probably buy a set of chrome-moly I-beam rods for it with full floating wrist pins for a regular "track" car that was also driven on the street.

Nothing but "mostly stock" parts are needed with attention paid using a good set of Manley (or similar) one-piece taper-neck stainless steel valves, 7* single groove keepers and I'd probably spend a few extra bucks on titanium retainers, since they don't cost that much more. I'd definitely use 3/8" guideplates and pushrods with the recommended valve springs matched to this cam. I'd run a set of Crane "Gold" extruded aluminum roller rocker arms and a Jomar stud girdle. I would use ARP studs and main cap supports in the bottom end and ARP head studs on the top end.

I would probably recommend using a set of the AFD 4V aluminum heads (due out soon) if the wallet was open wide enough for them. Matched up, you'd have an easy 500 HP on a very budget minded Cleveland that would sing smooth like the wind and howl past the competition like a banshee.

This is the perfect combination for a lightweight, early Mustang with a 9" rear end and a Mustang II front end conversion kit (to give plenty of room for the extractors!). I'd use a 5-speed Richmond transmission with a 3.50 rear gear and a 10.5W slick or DOT slick like the ET Street. An 8-point chrome-moly cage and you'd have a slick little car that would run very low 10s--all engine that you could drive to and from the track.

I'd keep a very close eye on my clearances and every dimension during assembly and try to start out with a 4-bolt main block if I planned on using the AFD heads as it would be very near 550 HP by the time everything was done. I would also use a Mellings "regular volume" oil pump and a Milodon chrome-moly oil pump drive shaft with a Milodon street/strip pan like the 30927 part.



I would also weld up a pan-protector cross-member as added insurance in keeping the deep-sump pan safe on the street.

A set of Hooker 6211-1HKR extractors might fit, but I'd probably build my own from a Stahl kit.


....sorry...what was the question again!

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Old 04-29-2004, 20:45   #8 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Quote:
Originally Posted by brenx
You should re-read the post as poster also asked about what prepared parts would do. He only asked about crank and rods. Prep them and the rpm is able to be done. I did

It was on a dyno at the time. It did three 8500rpm runs.

Theres plenty of 7500->8500rpm clevo's around running nothing fancy rod wise. It's all in the balancing and prep.

[edit] Yes, I am surprised it didn't go bang. I am also very happy that I now know I have a strong bottomend that is capable of rev's.

Brenden
Maybe you should re-read the thread.... Safe Rev limit.
Ask anyone who builds Ford engines regulary Mick Webb, Ford muscle Parts, Shanes race engines, Herrods.....anyone.
7000-7500 is not safe.....
Why go to 8500 rpm on the dyno, surely you are not trying to say yours makes power all the way to 8500 rpm.
The load on a dyno is hardly anything like the load when driving on the road.

Why don't you or who ever built your magic engine to start building Pro-Stock engines, you can teach these boys a thing or two by the sounds of it....LMAO
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Old 04-29-2004, 21:00   #9 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Quote:
Originally Posted by TICK4D
7000-7500 is not safe.....
I think that it is safe to say that running any engine that makes as much power as a well designed/built Cleveland is unsafe on the street at anything approaching 7000 RPM in any gear! However, the engine won't mind as long as you build it properly EVEN with stock (reworked) rods and crank. Of course, everything else has to match.

As I said, I'd probably run a limiter at 6800 RPM for it with stock rods. I would probably do a set of chrome-moly I-beams with full floaters on anything where I was really planning on spending a lot of time "ripping" it at those RPM.


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Old 04-29-2004, 21:03   #10 (permalink)
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Re: Safe Rev Limit of 351 Crank and Rods?

Agreed
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