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Hollywooding 07-15-2003 09:25 AM

Raising the Redline
 
Hello once again to the forum of car gods and goddesses

When a person does a search on roller cam* in the index the list is a mile long but i read them and still came out blurry. So here goes.

When a person wants to raise the redline of a motor, what is the most important step to beef up Rocker arms? valve springs? valve pushrods? Lifters? Piston Pushrods?

I understand the following: Roller lifters allow a steeper cam lobe profile allowing quicker open / close times, also 'cause their roller no break in period, less friction, allows higher RPM, Correct?

Roller rockers follow the same prinicipal correct (needle bearing type roller tip) roller = less friction between the top of the rocker arm and valve. However the 1.5 ratio means that the movement of the lifter pushrod will be translated to vertical valve movement at 1.5x the distance, the same for a 1.6 ratio correct?

stiffer valve springs create the need for more pressure to be applied by the valvetrain and prevent valve float at high rpm.

So provided all this what will allow for a higher RPM and how do all you guru's know what to set your motor at? I know cam's come with the card that says their rpm rating, but isn't that based at a stock valve train. Basically how far does one have to go to reach 5500, 6000, 6500 redline, before he spends more than the neighbor did on his new garage.

Thanks to everyone in advance.

Hollywooding :cool:

johnsongrass1 07-15-2003 09:58 AM

Roller lifters are heavier and won't rev as high as no-roller's before the spring can no longer control the lifter.(float)

Yes, the ratio you describe is correct. Roller rockers also allow more movement on the vertical plane and better alignment of the valve seat face with the valve head creating a better seal to trap combustion pressure. A non- roller has a tendency to push the valve stem out of position increasing wear on the giudes at higher than stock lift's.

Stiffer springs can control the oscillations of the entire valve trian by reacting faster to cam. They won't lose controll as soon.

RPM ranges are just intendes to give us an idea of what to expect based on 350 engine's. More cubes will make a small cam act different then if that same cam were to be used in a small cube engine.

Hollywooding 07-15-2003 10:20 AM

So from what you said..

Given a street motor that will be used at the track, such as the 4.3l v6 in my tracker,

running a roller cam is good for wear and tear, great for lobe profile, but needs a stiffer valve spring to maintain high RPM.
Using a Roller Rocker is usually a good bet for durability and rpm.

So overall if i use a roller cam, the card will tell me the rocker arm ratios, duration and spring tension to reach maximum rpm of that cam before valve float or Redline.

I guess I should phone the cam manufacturer for details.
Thanks for the help johnsongrass1 'preciate it.

Hollywooding :cool:

engineczar 07-15-2003 10:34 AM

Engine RPM will continue to climb so long as a few conditions are met. 1. Most obvious is that the engine does not suffer from catastrophic failure. This encompasses anything from broken connecting rods to a broken rocker arm to ......... whatever. 2. Valve float. This is pretty much going to dictate to itself where the engine RPM stops climbing. Once you lose control over the valves all heck can break loose. 3. Airflow through the motor. This encompasses the carburator, intake manifold, heads, camshaft profile, and exhaust. A really poor flowing set of heads will starve the engine of airflow and prevent the engine from turning over a certain RPM as will a short duration, low lift cam.

All this being said, you have to look at the combination of all three. A really good lightweight bottom end, high flowing intake track and a roller cam with high spring pressures will spin all kinds of RPM. Pull off those heads and stick a pair of stock 441's on there and it probably won't spin past 7200 even with adequate spring pressure.
or put that awesome top end together with stock rods with stock rod bolts and don't expect 9000RPM's. Expect to be pulling pieces of cylinder wall out of you teeth.

There's always more to it and I'm sure that others will add their 2 cents.

4 Jaw Chuck 07-15-2003 10:36 AM

Redline is determined by power production, if an engine produces 400Hp at 6200 rpm then the redline should be set at the rpm at which a single gear shift places the engine back onto it's torque peak. For example if the above engine made 400Hp at 6200 and peak torque occured at 4000 rpm then the redline should be placed between the two peaks at a point that is above the peak torque but below the peak HP. In the above example we could say anywhere between 4000-6200 rpm would be a good redline mark. Remember torque is what accelerates the vehicle...not horsepower.

The question then becomes "should I turn it to 6000 rpm or 4700 before I shift"? This question is answered by the actual loss in rpm between shifts. Lets say your 1-2 shift causes a 1200 rpm loss in rpm so ideally you would want the shift to occur anywhere between 5200 and 6200 rpm to accomodate the rpm drop so the engine never falls below it's torque peak. Each gear will have a certain rpm loss so it is entirely likely you will have a different shift point for each gear. The actual chosen shift point is determined by experimentation or calculation of the torque area under the power curve which results in the most power available for accelerating the car, weight of the car and rear axle gear ratio directly affects where the shift point is placed. Suffice to say heavier cars with stiffer gear ratios need more rpm between shifts and shifts should occur closer to redline to obtain the best times. On lighter cars it may be found there is little effect shifting closer to redline.

The question then becomes should I build my 400 Hp@6200 rpm engine to handle 6500 rpm or 7000? In general 1000 rpm is a good cushion to build into the motor so your peak power at 6200 rpm should handle a peak rpm of 7000 in case you miss a shift and also to build some durability into the engine. Valvetrain dynamics close to valve float is a dangerous combination of harmonics and spring surge so the engine ideally should never approach those conditions. Building your valvetrain to handle 8000 rpm but never turning it higher than 7000 is a good way to make an engine bullet proof, in this case more is usually better.

This is a complex issue and everyone will have their own opinion of how to do it, since engines will handle all kinds of abuse you may find people shifting their peak power at 6200 rpm engines at 7000 rpm with no ill effects whatsoever, of course how close you want to cut things is up to you. Durability takes a serious hit if the engine is revved too close too valve float territory. Frequency of abuse directly influences how you should build it. Most engines die from valvetrain failure resulting from valve float/surge at high rpm.

Another factor to consider is durability of your rotating assembly, just because you can cam and spring it to take 8000 rpm does not mean your stock Chevy 350 rods can handle it, off hand I would say a stock 350 rod will take 7000 rpm for extended periods of time assuming good balance and no weak links. A ford 302 would have similar limitations but a 351C Ford might be capable of 7500 rpm. By comparison my 400 Ford will never see the high side of 5500 rpm because of it's weaker rods, the build of the engine kept this limitation in mind.

Does this help?

Hollywooding 07-15-2003 11:26 AM

So far it sounds like most refer to a redline as where the ideal shift point is, not where the point of boom really is. Which of course is smart as 4 jaw mentioned. Since a 4.3 (to my knowledge) is a 350 w/ front 2 cyl missing. I'm gonna assume same bore and stroke. therefore same rods.

when I look at this setup comp cams hydraulic roller, (say 280 duration, 1.5 arm ratio, non roller arm, standard spring) non balance shaft, non computer, .030 overbore, balanced crank rods (heard of a way to do it at home verrrry carrefully), intake port match, polish, 3 stage valve grind(30 40 45) (yeah yeah overboard i know but hey ya only live once) headers (1 5/8), edelbrock 2111 intake (or vortec compatible depending on head), 500 cfm 4bbl, possibly the vortec heads (I still dunno about that one, are they really better?). The card would say 6500 valve float, but a maximium 5000 (still unsure why 2 values there but....).

The next step to ensure safer upper rpm ranges would be springs and rocker arms keeping the same ratio. Knowing this if i did the springs and arms would 6000 or 6500 blow the motor? According to what people have said I'm gonna say no. But I also understand that It may not be the quickest to shift at that rpm as 4 jaw pointed out, however It should be safe to that hit that range by accident or overzealous running at the track once or twice a month.

I know it's kinda broad and I hope I'm gonna get a whole bunch o' answers but ever since I came to this forum I have learned that I know a lot less than I thought, so I'm asking the hard questions, putting some fears at ease about the next motor build up.

Hollywooding :cool:

2wld4u 07-15-2003 11:32 AM

Remember torque is what accelerates the vehicle...not horsepower.


hmmm...I thought (could be wrong) that if a motor made peek horsepower @ 6200 you should shift it past the peek hp...500 or so rpm...Torque is what moves the car, horsepower determines how fast the work is accomplished...cause if what your saying was true diesel powered vehicles would be the fastest cars on the planet...lol

2wld4u 07-15-2003 12:04 PM

well, so everyone can understand what Im saying, here is an example....It doesnt matter how powerful a runners legs are, if he cant move them quickly he wont be fast>>>>

Hollywooding 07-15-2003 12:38 PM

zzzzzoooooooooommmmmmmmmmm

:snicker:

Hollywooding :cool:

However 2wld4u, How fast you use that tourqe is dependant on the gearing!!!! If diesel mack's put 2.73's or taller in they would haul ***** too (not atrociously, but for most serious street apps, tourque was always where it's at. that's what i was taught) after all 500 lb/ft of rotational force is still torque, apply it to taller gears and you use that power to make it turn faster.
doesn't matter how fast the runner can run if the legs cant' take the weight of the runner, what good is speed.!!
touche

Hollywooding :cool:

johnsongrass1 07-15-2003 02:21 PM

How fast can a runner run if his legs are faster then...

How fast can a runner run if he's carrying a 2:73 gearset...

How fast can a runner run if he's pushing a diesel...:confused:


LOL

Hollywooding 07-15-2003 02:29 PM

Point taken

:spank: :rolleyes:

Hollywooding :cool:

4 Jaw Chuck 07-15-2003 02:38 PM

Quote:

cause if what your saying was true diesel powered vehicles would be the fastest cars on the planet...lol
They would be if you could shift an infinite ratio transmission fast enough with no slip...and pumped enough boost into it. Try running 60 psi of boost at 21:1 compression with gasoline, only diesel is capable. Just because race rules favor gasoline dragsters does'nt mean a diesel couldn't run with the big boys, take away nitromethane and diesel would rule.

gt2betubbed 07-15-2003 02:51 PM

2wild, I thought the same thing as you. BUT! In reading 4 jaw's post, I realized that there just a lot more to it than going 500 past the peak HP. From what I read, I figure the best way to find out is to go from a dyno print out and take it to a track and test.

2wld4u 07-15-2003 06:42 PM

:sweat: Im learning more and more every day, It just goes to show just how complicated the performance world is..........And without this great forum I suppose Id still be left in the dark....lol

Mikey123 07-15-2003 08:33 PM

well to start off with the 4.3L chevy has different rods than any of the other tradishional small block chevys, even including the 3.8s the 305 knock off, they are the same bore and stroke, even the rod length and wrist pin is the same, however the rod journals are not, they are larger in diameter than the rest therefore they will not interchange with the rest, Secondally the diesel usually makes more tork primairly because of its size and because of stuffers ( blowers-turbos)however they suffer from rpm range which limits gear selection favorable to having any power at high speeds without having 20+ gears or highway gears which limit take off , and they are set up that way for a couple of reasons, most heavy trucks need power now not when they can rev up to it , lower rpms mean better mialage,and in order to stand up to high tork loads on the bottom ends they have to be built quite large espically the berings, large and wide diameter berings will keep oil suspention better than small narrow diameter berings will, however the big stuff creates way more friction at higher rpms thus causing bering melt downs sooner in the rpm range. see ya mikey


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