Safe RPM range

[CarlK60]

Hey Guys, got a quick question. What would be a safe rpm on a completely stock 348 truck motor for extended periods of time on the interstate? I usually drive around 3000 rpms on the interstate, but it kinda scares me. I am going to the NIA meet in spearfish next week and its an 8 hour drive. Should I really worry about it or just drive? Also what is a safe rpm to shift at? I dont like to wind it out over 4000....too much. My last 2 motors (small blocks) didnt like excessive RPMs too much, so Im trying to baby this one a little bit.

Thanks guys for any input. I would appreciate it.

CK

 

[29Coupe348]

im usually at 3000, without any ill effects, i've been driving like this for like 3 years now.

 

[models916]

Safe to shift?

If your VALVEtrain is stock, 5500 is about it. Valves and springs being the limiting factor. Crank and rods are forged steel and will take quite a bit more. ONE PIECE VALVES and new springs and hardware will crank it up a lot.

 

[RPO587]

Carl,
Your safe rpm range is a bit higher than 4000. Peak hp will be reached at probably around 4400, with peak torque at more like 2300. Three-thousand for continuous operation isn't ideal, but shouldn't be harmful either. Ideally, if you had the gearing to run at 1900-2200, you would prolong engine life and probably see a significant mileage increase. I'd definitely watch the engine temp closely when running at such high rpm for extended periods.
Interesting comment on the small blocks. The SBC is an "rpm" engine which usually produces power at higher rpms than many others. Cam profile and spark advance/total timing, etc.. not withstanding.
I'm sure that other more knowledgeable "heads" here will reply with their $.02 worth.
RPO

 

[tripowerguy]

This advice is over 40 years old. Don Nicholson told me that 3000 and above rpm will do in the valves if it is run at that rpm over long periods of time. I ran 4:56's then so I spent most of my freeway driving in the right lane at 50 mph. Of course today we have unleaded fuel which is hard on valves also, so I would drop it down to 2600 to 2800 and let the rice rockets go by. Or you could put an overdrive trans in and have the best of both worlds. Roy

 

[RPO587]

Tripowerguy,

I wasn't trying to give Carl any bad advice. What exactly do you me when you say that today's unleaded fuel is hard on valves? There is a long-standing myth that lead was added in gasoline to be some sort of valve lubricant. The lead was simply used as an inexpensive way to boost octane levels in gasoline. If you are referring to the need for hardened valve seats then perhaps this makes sense.

Not trying to start something, just curious.

Maybe you can educate me too.
Thanks!
RPO

 

[Fathead Racing]

Lead.

Yes, lead was added to boost octane level ,but it also helped to protect the valves under extreme load it was found.

 

[Bungy]

At the very least I would run some lead substitute in the gas and also try to keep the RPMs as low as possible. It will just take you a little longer to get there. I found out the hard way what happens to non-hardened valve seats when run at high rpms for a long time. The exhaust valve was sunk into the head about an eighth of an inch.

 

[tripowerguy]

Tetra Ethyl Lead was added to raise octane but as compression ratios became higher cylinder temps became higher and the lead coated the valves and seats so it seaved a two fold purpose. It raised octane rating and protected the valves. When unleaded gas first came out Chrysler tried to run all it's cars without changing any valve seats. They had a massive recall and replaced thousands of heads in thier line of cars. I run hardened seats in my 58 so I won't have that problem but some of the people with W engines are afraid of hitting water so they run stock valves and seats. I don't fault them at all but back to the basic question. High rpms and high pulling loads raise head and exhaust temps and are hard on vavles. Why do truck engines have valve rotators? I think that if you can run the engine at lower RPM's you have better longevity. Just an old mans opinion. Roy

 

[CHEV601234]

I seem to recall the late '60s when Detroit was producing musclecars of the golden era that had compression ratios of 11.0:1 and higher. I also recall Amoco producing an unleaded high test gas. (Remember "white gas"?). I do not seem to recall hearing of any warnings to stay away from that gas back then due to valve recession problems.
I'm no chemist, but it would make sense Amoco had something in the gas to lubricate valve seats. Bad news travels fast............and I didn't hear any. Aren't there valve lubricating compounds in today's fuels?

 

[gearhead409]

Roy

high cyl. temperature, lean fuel mixtures, and long periods of high engine load will sink a valve. i have seen this many times on 70s and 80s cars and trucks. on our type cars with big cams and rich fuel mixtures and short periods of high rpm shifting i've not seen this. i have hotrod engines that i built come in for tune ups every couple of years that are over 10 years old and the valve adjustments are not off more than .001 or .002. that tells me the seats are holding up without hard seats. i just can't prove not using hard seats in a hotrod engine is a problem.

 

[Ronnie Russell]

I think Gearhead makes a good point that I havent seen discussed. High cyl. temps. lean fuel mix. AND long periods of high engine load causes valve problems. It is my opinion that our w head cars dont see those conditions often. A vast majority of w head cars are used going to a cruise night, car shows, and a trip to the drag strip every now and then. I would guess that the vast majority see less than 1,000 mis. per year. I know that there are exceptions, JimKwi thinks nothing of jumping in his 57 for a trip, and there will be others testify of their long distance driving, but I do think most are less than 1,000 mi. per year. How many cyl. heads were pulled 20 yrs ago because the common belief was they had to have hardened seats? Plenty, I bet. It is also my belief that the properly rebuilt w head engine will easily out live its owner. Do you use lead additive? Thats for each to decide, but I dont see the need in the average w head. Would like to hear from some high milage drivers comment about their findings. Gearhead services the engines he has built in the past and has not seen valve problems from unleaded gas. That has always been my opinion however I have not put a lot of street miles on one so I cant say one way or the other, just that I agree with his assessment. I would say that if I were driving a w head on a long trip (200 to 300) mis. constant highway speeds, I would throw a can of lead additive in for the trip. It may or may not be needed , but seems as though it couldnt hurt.

 

[Bungy]

We have to remember that is exactly what Carl is going to be doing. Driving for 8-9 hours at 3000 RPMs then back again. I would definately run some lead attative.
You can get the good stuff from Jack Podell (he also rebuilds early F.I. units). Sorry I can't find his contact info right now but I'm sure somebody here can come up with it.

 

[Bungy]

Here ya go. Down at the bottom click on Max Lead 2000
http://www.jackpodellfuelinjections.com/

 

[Ronnie Russell]

Bungy, I agree that if anyone could use lead additive, it would be Carl. 8 hr. drive is a long way for a w head. I wish him a safe, no problem trip. I dont think my attempt to promote discussion on this subject was all bad because this subject afftects us all. Has Carl made this trip before? Have others recently made long trips with w heads? Am I wrong about a vast majority on our w head cars being low milage per year? Just trying to get opinions from those with experience of putting lots of miles per year on their car. " To add lead or not to add lead, that is the question"

 

[JimKwiatkowski]

I have never run Lead Additives,but I will now just to be safe

Carl,I ran over 600 miles round trip to Norwalk in June.I run my 409/425 with M/T Crossram 2 Carter 600's at 2,700rpm's and the 09 ran great I have 3.50 rear end gears and I run middle grade fuel and i got 11mpg.In 90 deg heat the coolant temp never went over 200 deg

 

[Mr Goodwrench]

my 348 truck motor turns 3000 at about 55. pulled 46,000 lbs to indy last year (4-5 hrs) have been on several 2-3 hr trips since, no hard seats but I do use lead additive religiously.......so far so good time will tell, will be up by chicago in a couple weeks and back in indy in september.

 

[RPO587]

C'mon guys, think this one through. How will lead (one of the SOFTEST metals) protect the valves? It does nothing to harden valve seats. I have seen the claim made that lead "cushions" the impact of the valve striking the seat. O.K., maybe so. But it doesn't/cant harden the seats. Most additives, (unlike that linked by Bungy) don't even contain lead. Usually benzene or TBT are added, and only to increase octane ratings. If you choose an additive, at least be sure that it actually contains TEL. I still think this is an old myth that's dying a hard death. Most likely the cause of valve recession is the poor quality alloy used in the head castings themselves, and/or engines being operated at very high temp/high rpm and too lean a mixture. Re-read gearhead409's and Ronnie Russell's posts. They make sense to me.
Again, not trying to start anything, but I'm still not convinced.
-My education continues........
RPO

 

[Bam59]

hi ,,i to need to know if these w head motors can make a long trip.
was planning on driving 1100 miles one way to norwalk next year.
was lead the only thing that is differant from yesteryear or has the w head always had this sinking valve problem?
i'm running new 4 row desert cooler rad.
oil cooler
trans. cooler
new 18" 6 blade 33 deg. fan
6 qts. 20-50 amzoil syn. racing oil.
msd dist. and coil
elelbrook carb.
so far i can't get it over 180 degs. water temp. which is good i'm told.
now if you can keep the cyl. temp down and add the lead will this keep the valves from sinking???.

the trans is a th350. rear gears unknow at this time will count the turns later
but at 60-65 the motor just purrrrrrrrs have not got the tack. hooked up yet.
but does not sound like 3000 rpm's.

or do i invest in a trailer? (bad word for a biker)
or take the back roads to ohio

 

[Ronnie Russell]

Mr. Goodwrench, 46,000 lbs.???? Now I am impressed. What in the heck were you pulling? I dont think my house weighs that much. Wow, I like that Bam, I dont think w heads have a sinking valve problem. So far I think we have had one guy express that problem, no doubt he had a problem, but that doesnt mean it was a 'w head problem". And so far you cant get it up to 180 degrees? Man, I know a lot of people that would love that problem. You drive that old Elky 1100 miles and you will get standing ovation, especially from me. You too, Goodwrench, drag that 46,000 lbs and I will stand up for you too.