Redline on 6.5td?

[C.K. Piquup]

Is the redline 3,500 or 4,000 RPM?With HP rated 190@3,400 RPM it wouldn`t be hard to over-rev trying to get this HP w/3,500 redline.I always figured 4,000 was redline & 3,500 was warning/safety-zone(orangeline).I use 3,500RPM as redline.

[gmcheek]

The 6.2's were governed to at around 4,000 RPM's. The 6.5's are governed around 3,400. The max engine speed is determined by the injector pump, so if you are running a 6.2 injector pump than the engine will be governed at the 6.2 max speed. I hope this helps.

[Diesel Dan]

The GM 6.2 manual I had listed 3600 as max governed speed. I also had a 1993 K3500 6.5TD/4L80e, held it in 1st and it only went to 3600 as well.

[CaseyR]

I have heard that the engine will last a lot longer if it is seldom or never subjected to maximum,or near maximum, revs.

[gwaidman]

WOW! I know my tach (factory GM) readlines at 3500, but it seems to fall off past 2700. I have never dreamed of pushing it that far, although I am certain it would do it. What are the thoughts out there? Currently I have a stock truck, with exception of air intake mods and K&N filter.

[britannic]

The last inj. pump in my truck was governed to 4100rpm, with 4.56 gears and a TH400, it wasn't unusual to be pushing those revs in the fast lane on the freeway.

The new pump is set to 3800rpm and my 700R4 ensures that only overtaking sees 3500rpm for brief periods.

[C.K. Piquup]

Thanks,Brit.I`m running a Peninsular300hpMFI6.5TD and am not concerned w/governed speed or 6.2 ratings(although they should be the same).This motor wants to keep climbing.With these motors rated at redline,I just wonder if GM is telling Joe Public it`s pointless to rev any higher,so why get any closer to limits,or has it truly reached it`s threshold of stress.If GM tells us we have 190hp@3400RPM,we`re going to do that,and that seems odd that they`d have us bring an engine that close to self-destruct to make power(and high liability for GM).This motor is coming to life at 2,500RPM and wanting more.I`m at 750miles and have only just revved past 2,200 up to 3,500RPM,and let me tell you,she wants more.It seems moreso w/a Powerstroke,Cummins,or(yes)even a Duramax in sight.Blessed be the"underdog".

[rapidoxidationman]

The Diesel Engine As I Know It...
With a higher compression ratio (20:1 to a gasser's 7:1) comes a much longer piston rod, limiting the reasonable rpm's a diesel can achieve as opposed to a gasser's ability to reach 5, 6, 7000 and beyond on the tach. All this talk about how it comes on strong after 3000 and how the hp rating is all the way at 3400 rpm makes me wonder if y'all remember why you bought a diesel: TORQUE!!! That torque is achieved at only 1900 rpm, and it beats the hell out of gasoline in and around that range. If you are driving your poor diesel habitually at anywhere above 2700 then don't be surprised at the web cracks around your main bearing. Don't complain when your water pump starts to leak, and virtually every pulley-driven accessory to the engine is screaming for mercy. The forces those piston rods generate are huge in the normal range of rpm. At higher than designed, they must be scary. Want high rpm's? Drive a gasser. You'll get higher hp too, but I'll be the one passing you with a camper behind me going up the pass...
Regards, and I hope I do not offend.
Rapid

[Diesel Dan]

Stock 6.2s ran in the 3-3200rpm range all day long when they were built. Do the math if you have a TH400 and 4.10 gears. That and 4.56s were about all that was available in the older 1 tons. I ran my 6.2 at 65-70 quite often before I installed the gearvendors. I'm amazed at the CUCV military pickups that run 65mph with 4.56s! For hours down the highway.

[britannic]

The real limiting factor for diesels is the amount of time available to inject enough diesel to make power. A gasser (unless it is one of the very newest DI engines) draws in a fuel/air mixture which is only limited by injector flow rate and pressure, since the compressed charge is touched off by a spark.

FYI: the stroke on the 6.5L is 3.96" as compared to 3.75" for the 400ci and up to 4.375" for the 454ci.

[ 01-10-2004, 05:47 PM: Message edited by: britannic ]

[C.K. Piquup]

Rapid,I`ll try not to sound offended when I say"I wasn`t asking for opinions,but facts."I just want to know if the redline is 3,500 or 4,000 rpm.If I designed and built an engine for thousands of people,the hp would not be rated at 100rpm before redline.If anything,I would think GM would build in a buffer-zone to keep the general public from destroying their engines/reputation.I`ve always said I feel those"mysterious"web cracks may be caused by over-revving(driving them like a gasser).Most owners are new to diesels.I`ve been running GM diesels since`88(1984K3500srw).My`95`s original motor had no cracks and I plan to rebuild it to install in my`72GMC(presently running a 383stroker).It`s fast,but I love the torque,longativity,and economy of a diesel.Do they really make gas engines with 7:1 ratios?

[britannic]

Those cracks are caused by less nickel in the block (GM was trying to save money) and high loads. If the engine isn't too stressed, then higher rpms aren't a factor. Obviously, if the block is one of the GM cost cutters, then going easier is the best policy.

High revs are more likely to wear out the accessories more quickly, but the engine will lap it up. The valve gear can certainly handle it and although the compression is higher than a gasser, 3400rpm isn't a big deal.

My engine, doesn't stop pulling until it hits the rev limiter and before I installed the 700R4, I covered many freeway miles at those revs, with no problems. The engine has seen many miles (at least 180K now), but there wasn't any real wear in the mains or piston skirts when I dropped the caps during a rear seal install (The 6.2L has the 2 piece seal design, so the pan has to come off to R&R it).

[gmcheek]

Come on guys! all diesels have a max governed speed and thats it! The 6.2'S and 6.5's were originally manufactured with different govered speeds! That's a fact! The 6.2's is much higher. I know because I've owned both. I have also had a 6.2 with a 6.5 mechanical pump {thus 6.5 governor speeds} and it wouldn't even upshift when my foot was on the floor. The governor would limit RPM before the transmision was set to upshift, being set up for the 6.2 max RPM.

[Diesel Dan]

Originally posted by gmcheek:
The 6.2's is much higher.

My '88 1 ton crewcab, ex-military, with 6.2/th400 was governed to 3600rpm. 77MPH was max with a 30.5" tire. Also our '93 CC with 6.5TD/4L80e would only go 3600rpm. After I get a few miles on this '93 ext cab(had 6.5) I may run it up to the gov and see where it's set.

Now it is possible that the military CUCV pickups were governed higher. Don't know for sure.
But I will state again, my GM diesel manual does state a 3600 rpm max governed RPM for the LD & HD 6.2L diesel.

[C.K. Piquup]

I`ve owned both 6.2 & 6.5,too(still do).One,now,with the higher nickle & beefier main webs manufactured,now,by the new General Engine Products division.The CUCVs also have always had higher nickle(GEP now produces the HummV`s engines,and will be at least `til 2007).I think you are missing the point,there.We`re not talking about what the governer will let it do,but,what it can do(with or without mods)and still not harm the engine.I may be wrong,but I`ve always taken redline to mean,"safe rev limit".Not top of power curve or"all she`ll do."Am I right?Performance engines need rev-limiters to keep from over-revving,not that they won`t do more,just to keep from self(or driver)destruction.Got one on my Harley set at 6700rpm,which is just past it`s max output,so it really doesnt need to go there anyway.It could be set up to 7000rpm,dyno says 6500`ll do it(100hp).

[mhagie]

C.K. Piquup, I believe you have answered your own question.
GM set a rev limit in my opinion for the reasons you stated on last post,That being the upper rpm limit that they believed was best for long term durability, it is my belief that as Britannic mentioned you can if so desired run at that limit for extended periods of time without comprimising the integrety of the engine.
Few however would want to do as such but all circimstances are different.
Californians are famous for running huge gears in vehicles so they can do the off-road scene hence they pioneered the hybred overdrive units so they could drop the rpm down to a reasonable limit while commuting between home and the dunes and still approach freeway speeds.
As mentioned in a earlier post the 3/4T 6.2 trucks in the early 80's used the TH400 with 4.10 gears and there are some still around screaming down the highway engines still intact.
I believe the limiting factor in a 6.5 is heat not rpm,keep it cool it will last and last....Merle

[C.K. Piquup]

I hear you,Merle.I really just wundered if GM is redlining these at 3500 or 4000rpm.Are the markings on the tach at 3500 intended as a warning that you are approaching redline,or that you really should stay off 3500 as well.In other words,does GM feel operation in the 3500-3900 range ok?I don`t need to run at that range w/OD equipped truck.That would be dang fast on the hi-way.My truck is a manual 5spd w/a 300hp motor & 4.10s.When"gittin`it"through the gears is what I`m concerned with.It wouldn`t be hard to run over these numbers if only for a few strokes.I have no intention of doing this,yet I`ve been known to get a little excited when feeling"the power".

[mhagie]

C.K. Pikuup, Now I understand your quandry a little better I can say to you I believe the red marks are there for a warning If you will Of course the part that makes the diference is the governor, they are likely fairly close to each other.
I'm surprised Tough Guy hasen't stepped in here he has a 300Hp that he tows with constantly and has probably seen action at the high end of the rpm scale.
I do know the truck has well in excess of 100k since being reborn as a 300hp engine and has had no ill effects with the hp boost.
I seriously doubt that the unit has been babied that much as they built it to use more so than to
look at. altho its not a bad looker.
Good luck with yours,I wish mine was a 300.....Merle

[Bobbie Martin]

If you bought the engine from Peninsular, they should be able to provide you with the max RPM. They may balance the engine or make other modifications for sustained high RPM. I see they list the max HP on their engines at 3600 RPM, so its at least that high. I would make sure you have a new balancer (if it didn't come with one) if you plan on hitting the redline regularly.

[Diesel Dan]

Originally posted by C.K. Piquup:
We`re not talking about what the governer will let it do,but,what it can do(with or without mods)and still not harm the engine.I may be wrong,but I`ve always taken redline to mean,"safe rev limit".Not top of power curve or"all she`ll do."Am I right?

Depends on the manufacturer.
I had a '90 Dodge/Cummins. It had a rotary pump similar to the GM ones. The engine was governed to 2500rpm. Same longblock with a P7100 inline pump is governed around 3500rpm. From what I understand from the TDR site is the stock pump couldn't adequately fuel above those rpms. Mechanically the engine can handle it.

As loud as the 6.2/6.5s get at 3600 I don't have any desire to run them higher.