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#1
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Small block Magnum RPM?
I think the normal max rpm for the average stock LA motor is around 5000. That has been what I have seen most often. What I want to know is, what is the normal max rpm for the average magnum small block? It seems that I heard somewhere that it was several hundred rpm lower. And if this is so? Why?
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#2
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weak valve springs and heavy hydraulic roller lifters is probably why...
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#3
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So ,,,,,,,,,,,,,,,,,,,,,,
Are you saying that the magnum small blocks turn less rpm in stock form? If so this is something that needs to taken into account when building a magnum.
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#4
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i have no first hand info...but the lifters are somewhat heavier then a hydraulic lifter...
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#5
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I have a 360 magnum 4x4 truck and yes it don't like to rev and makes peak torque around 28-3000rpm or so.
So stock magnum max rpm 4500rpm. They have next to no camshaft in them and the spring pressures are a testament to that. The lifters, being roller, weigh a lil more. Oiling is the same in relation to potential max rpm capability. Yes this should be accounted for when building one being that the factory tends to match cam,comp,heads,exhaust to work together which is why the swirl port was designed for low air speed mixing of the fuel, not really aimed at big flow@max rpm /max race effort, hence the fact that there are no finned bulged wall swirl port crap in w series, eddelbrock, or even indy/brodix heads. See when air is moving as fast as it does when buzzing high rpm's down/around the track all that finned swirl crap just gets in the way and ends up being removed with a grinder by the poor soul who was stuck having to use them in a high/max output app in the first place and when he hits water trying to really get the flow he needs, well thats probably why mag head proponents who race have no hair left.lol As for max rpm in an stock LA small block, thats 1st determined by the amount of cam/comp, 318=48-5000, 340=6-6200rpm, 360=48-5000rpm. In both LA/mag if the cam/comp is there about 8000rpm then you need to modify the oiling system. |
#6
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The above is my opinion and based on my experience so hopefully no one will take it as a personal attack on there combo and go on a crusade.
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#7
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3.9 magnum in my truck which is same stroke and bore as 318, basically a 318 with two less cylinders and redline on it is about 5100rpm...
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#8
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Passing You, dead on. It gets ground out at first opportunity. As to a magnum revving, needs several things.
Heavier springs (preferably beehives for better harmonics) Ganged and upgraded rockers to prevent stud pullout Lighter lifters and lighter PR's More cam. These things can make a Magnum rev like anything else, but stock bottom end may be good for about 6, and not much more. The pistons are a little on the brittle side. |
#9
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Quote:
LOL, OK,......... joking.......... Your 100% correct, other than the 318 MAG is the total opposite of the 360......... (They ruined both when they went to magnum, IMO) To add, the 318 in my plow truck simply has a R/T 360 cam in it, and it runs great up to 5600, where the rev limiter is set on the MP computer. Of course, I haven't done that in 100,000 miles or so....... Once i gave up trying to make a 3:55 gear, 318 power 5680 pound 4x truck move faster than your average 4 cylinder car.................. |
#10
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Thats what my 95 318 ram revs limits at too, but it seems to run good to that point.
My valiant has bone stock magnum heads on it, my shift light is set at 6 grand, and it pulls real hard to that. 580 lift with the 1.6's. its a 273. |
#11
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MAx rpm on a Magnum engine before racce like mods?
6600 - 6800. Oil feeding is the issue.\ Stock for, LOL who the hell cares..................BWa ha ha ha ha |
#12
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Magnum 318 sure, but the 360 will stretch or break stock rods at 6500+. I have not dealt with too many 318's. I just got my third one in the dump truck. Drove it today for the first time. :-) PCRMike
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#13
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So because of the heavy lifters..........
They are hampered in revving up like an LA? And to match that the factory created the magnum heads that are designed to perform at lower rpm? Part of reducing emissions by reducing rpm and fuel consumed? But if the reduced flow is designed, shouldn't the 360 heads increase the flow and the rpm in street driving with the stock engine?
Are the magnum lifters and rockers capable of turning 6500-7000 rpm with a proper bottom end? |
#14
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Good question.
Not proof by any means, hughesengines shows hydraulic rollers going past 6600rpm. Even mention 8500rpm. These numbers seem high but ..... http://www.hughesengines.com/TechArt...rollercams.php Their larger regrinds use 135 pound seat pressure, inverse ramp design with lots of lift. Just click on the HER2836ALN and read. Says 8500 !?!? Maybe give them a call ? |
#15
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Over 6000 or so I doubt they are talking stock lifters.
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#16
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Quote:
Heard of them, but never have been able to lay my hands on one. 340's? Shit, they blow like Big Blocks......... |
#17
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I haven't seen any factory 318's lose their guts, but have a 318 in my yard, that some knuckle head built, it ate a rod and trashed the lower half of a cyl.
Spun no.6 or 7 rod on a 440 before I haven't ventilated any 340's so far, then again the difference between tossing rods and smooth sailing is who's building/machining it and what parts go into it. |
#18
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and if it had oil in it, that will kill a 318 in a hurry. That is the only way I have seen a 318 die. Shame too.
I almost killed a 318 a few years ago, another couple burnouts it would have been a goner, the spirolock came out, and the wristpin was gouging the cylinder wall, I pulled it out and put the diesel engine in it. Pulled the 318 apart to see what I had, and it was almost a goner. I couldnt believe it ihad a good pistons in it and spiro locs, I always thought it wa s apocrap motor that ran like a raped ape, but it had some work done to it. Since it gouged the cylinder wall, It is going to become a 340 whenever I get spare money. yeah right. It can sit in the corner and wait till then. |
#19
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My dad had a 318 that snapped the crank in half in the #2 main at an angle. The motor still ran, just made racket. Drove it another fifteen miles till we got to a payphone (before cells). It had 318K on it! LOL! My brother put a crank in it and all was good, I drove it for another 80K.
The stock magnum lifters and rockers are also limited by the stock 5/16 rocker studs. Light springs too. IF you gang the rockers with a 3/8 stud kit and run lighter lifters, stouter springs, and lighter pushrods, yeah you can turn it harder with a little more cam. It is not a glass bowl design, but it then succumbs to some of the Chevy weaknesses/flaws. The Magnum heads flow better in the exhaust (important for emissions, less overlap/re-burning) and the emissions part comes in with the high swirl design. It is a good performance design, in the chamber, chintzy in the casting between the valves and thin walled, and flawed in the rocker department. |
#20
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Ok... but the chevy flows good in the exhaust too but what was the LAST car manufacturer out of the big 3 mandated by the federal government to run smog pumps? CHRYSLER.
Who were the first? chevy. ha ha The deal with the chevy, besides the poor intake flow, is that the exhaust flowed too good and over scavenging pulling intake charge out the tail pipe. |
#21
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notice the mags run hotter then LA's.
combustion/exhaust gas temp has a lot to do with emissions crap. |
#22
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Yupper. Smooth/polish teh cc face and the effects of the heat have less impat on the head. :-) PCRMike
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#23
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broke the crank and it still ran? how did the cam turn?
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#24
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So if you want to turn a SB Magnum............
More than 4600 rpm to say 6000, you need to change the rockers for lighter units and a hotter cam. Then you have to change the head studs to the larger Chevy size and Chevy? rocker arms? Plus re-engineer the oil system for the added rpm?
Do the Magnum Crate motors take this approach? I'm having trouble accepting that Chrysler would not engineer into these engines the ability to simply increase these engines for performance. They get bigger numbers pretty easily but what if you want 450 hp? |
#25
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It was broke at an angle, and it was inside the #2 main, held straight by the bearing. When he took it out, we could not believe it. Dad kept the pieces for years, as he had built engines for about 40 years at that time, and never seen anything like it. I haven;t either. Granted it chewed up teh bearing real good, but never made it to the saddle! He might still have that around here somewhere. I will see if I can get a snapshot of it. :-) PCRMike
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#26
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Just talked to Dad, (he walked in as I hit send) and he still has the rear part. It broke in the #4 main though, not #2. He said it was "the one behind the thrust bearing". he was gonna make a lamp stand out of it, but hasn't. I was only 17, I didn't remember right on which main it was. He is gonna dig it out so I can snap a shot of it. Prolly tomorrow if it is not raining. :-)PCRMike
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#27
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had a 400M Ford that did the same thing........
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#28
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Quote:
Hey man leave the big blocks out of this... Now I will give you that the 318's were tough little buggers, but no need on pickin on the big blocks. I've yet to see one with a rod hanging out the side... bearings knocked out yeah, spun bearings yeah, but they will usually seize before throwing the rods.... Now I can show you about 50 both big and small chebby's dead with a rod or more hanging out of the pan. |
#29
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I have hauled off at least 5K pounds worth of ventilated Blowties. The ONLY blown up Mopar I ever saw was a tutu that was hevily used, and had a HG replacement and never replaced the bolts, and hydrolocked the #4. Never ventilated. :-) PCRMike
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#30
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Ever notice when you tear down a 318 that there is never any ring ridge in the cylinder walls.
every 340/360 i take apart takes a ridge reamer just to get the piston out! Makes me wander if the geometry of the 318 block is better than the 340/360 Ive been toying with stroking a 318 just to see what it would do. |
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