hey all
I was wondering what the RPM limitations are on a 2g and 1g 4g63 turbo. Is the 7000 rpm redline on the 2g acurate or is it really 7500 or something? I know that with t-25 the boost falls off a like 6000, is this the case with a 13g also(havnt got my gauge instaled yet)? What holds the rmp limit back, is it anything in particular? or is it prety much all the internals and head stuff together? Once you upgrade all your egine internals how do you know what your redline is?
Thanks

o and i know the tranny dosnt like high rmp shifting and all that.

As far as the stock engine, many people spin to 8,000 without any issues on stock valvesprings and internals.

As always, the more often you do it, the sooner you're engine's gonna break something.

The stock crank can handle high RPMs, as many, including John Shepherd, have found out. What I'd be worried about, personally, is the valvetrain floating. If you float a valve long enough, a piston is going to smack it.

At 7000 on stock internals and a bigger turbo(16g and up maybe 14b as well) is about as far as Id recommend. Valve float can occur at 6k and up depending on the conditon of your springs. You have to remeber rpms can make power but you also have to remeber that cams, valves and head/ manifold runners are the things that deetermine what youll make at those speeds. On stock internals go to 7k max unless you do internal work i.e cams pistons and such to handel the abuse.
Andrew

Originally posted by DSMeclipse4G63
At 7000 on stock internals and a bigger turbo(16g and up maybe 14b as well) is about as far as Id recommend. Valve float can occur at 6k and up depending on the conditon of your springs. You have to remeber rpms can make power but you also have to remeber that cams, valves and head/ manifold runners are the things that deetermine what youll make at those speeds. On stock internals go to 7k max unless you do internal work i.e cams pistons and such to handel the abuse.
Andrew

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okay cool, thanks, ill stick to 7k till my car can take it, cause i dont wanna float a valve. Lemme see if i got this straight, the reason it would float on a stock spring is cause the sping inst hard enough to pull the valve back in time when its going that fast??? is that right??? or am i missing stuff.

Yep, that's the basic explanation of it.

The more technical explanation is that the cam will bump the valve hard enough to overcome the spring's pressure so that the spring (and the follower) actually "jump" off of the cam for a split second. Since the moving valve and its assembly has mass, it has inertia, which the spring has to overcome to push it back onto the cam. Once the spring's force overcomes that inertia and it moves the opposite direction, it slams back onto the camshaft.

ooo okay now i see why its called "float" a valve. Cool, thanks for the help.

could you just buy upgraded springs?

Yes, you can. Crower makes good upgraded valve springs to keep your valves from floating, and they also offer titanium retainers that reduce the weight (and therefore inertia) of the valvetrain so you're a little less likely to float a valve (they save 7.5 grams per keeper).

Personally, I'd just go with the springs and use the stock keepers, but some people have a lot more money to drop than me and would want to go all-out.

Once you think about spinning your motor this high on a regular basis, though, you're going to be wanting some beefier rods, especially if you're making over 350WHP, EVEN MORE SO if you have a 2G. Even 8000RPM means that your rod is moving up and down over 133 times per second.

7500-8000 rpm is safe on a stock head, as long as everything is in good shape.

my tranny seems to do fine shifting at 7k, i use syncromesh, i figure that helps some. How high of a rpm before i put anything in my stock tranny at alot more risk then shifting at 7k? shifting at 8k would be just about as bad as 7k right? its not gonna like be a disaster after the first time of a 8k shift, is it? 7k isnt like the limit on the tranny is it? i do know that faster shifting will hurt it more im just curious if theres like a line i dont wanna cross with my shifting.

Unless my car is retarded the rev limiter kicks in at about 7200 or 7500RPMs never really paid attention. You'd need modifications to go beyond that point.

Mitsubishi put it at 7.2K to be at a safe point I'm sure it could go a little higher on stock internals but I wouldn't push it, thats why its there after all.

2G trannys are awesome, I'd worry about the engine before I'd worry about the transmission. Yes, there is a difference between a 7K and 8K, thats an entire 1,000 more revolutions per minute.

i got rid of the rev limiter a while back, it was pretty easy, theres a tech article on it on this site. only took about 20 min and its a free mod. Ive never crossed 7k though, i guess im gonna go find out if my boost will hold past 7k and then try it out in a race soon, if i come back and im bitchin about how i messed my car up then dont feel bad for me cause ive sorta been warned, .


edit-im still fuzzy as to if my tranny will take a 8k or 7.5k shift though, i know its gonna be bad, but will it even do it? will it do it more then once, ?

Originally posted by clownface
edit-im still fuzzy as to if my tranny will take a 8k or 7.5k shift though, i know its gonna be bad, but will it even do it? will it do it more then once, ?

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It isn't as much about your transmission as it is doing damage to the valvetrain.. If you float a valve, and a collision occurs, you are going to be down for a rebuild on the head.

I know plenty here in CO that are shifting at 8-8.5K RPM on the stock head.....stock heads with 100+K on the odometers.

I also know that more than a few of these guys have TRE built trannys too

Do DSMs have issues with lifter pump-up?

And _why_ would you want to spin it that fast anyway?

why do I ask.

Originally posted by Defiant
Do DSMs have issues with lifter pump-up?

And _why_ would you want to spin it that fast anyway?

why do I ask.

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For racing i guess. I never pass 3k in any gear on the road and the only time i go to 3.5k is on the interstate and only in 5th, so this would be a racing only thing, and i dont really race to much. I know about the possible consequences now so im not gonna be doing it much and if i do break something then its my fault and stuff and i wont come crying about it and all that. I mean as long as my boost dosnt fall off higher RPM=better time slips dosnt it?

If you set the car up properly, higher engine speeds will generate more power. Power is what wins races.

I am sure some have you have seen that I am pursuing a ti full buildup . I have found the valves cheap . I mean really cheap , to cheap to even say what Iam paying. So this will mean more money for the titanium spring manufacturing .

The bottom line is that I want to be able to rev to 14,000 safely . 60 mph in first gear is what I am after, and a little extra.
It will come down to how much air the 2.0 is going to need .

What are the cfm requirements going to be at 14,000 ? What about fuel requiremnets ? Will the aem ems be able to mantain spark at 14,000 ? Oil supply will be a factor ?

Has anyone approached these rpms ? And if so what was there setup?

I really dont want a whole lot of Horse power . Whatever I get is good , but I need to start planning around cfm .

Will I have to ditch the stock slack adjuster and go with a manuel ?

I have alot of questions I have to answer and alot of learning in the next year . Please any wiseman or knowledgable tuners contribute.

how are you going to shift at 14k rpm?

you sound concerned with the top end of the motor the most, when what you should be worried about is your bottom end as it is under the most stress, especially at those rpm levels. rod bolts ahoy!

also at those rpm levels you will be asking far more of the head than you can ever hope to get, i don't care if its a BJ stage 12. peak power is also going to be wellll before 14k. and unless you get a turbo that is rediculously oversized, like 100 lb/min, its not going to make much boost up there either

are you wanting to build this motor just to say "i rev really high." just seems like a waste of time and money

Wasting money is somthing that I do best
Really shifting at 14grand is not going to happen very easy if at all . Double syncros and straight cut gears and double clutching should do it though .
I am building this motor , for the the sake of building this motor. I have the bottom end covered ,billet crank and ti con rods, forged pistons ,ti wrist pins .

Peice by peice this is coming together . I am in the process of starting another business and funds have not been to bad so I have around 2 grand a month to spend on my car . Why not build somthing rediculous unique?

I still need to find m cfm requirements along with a turbo that will provide good boost .

I am working on several ideas to alleviate turbo lag.

It seems that it would be a lot easier to get longer gears for your transmission. The engine wasn't designed to rev to 14k, and it would take one hell of a turbo to reason revving that high.

How long are the rods? How long is the stroke? Have you considered the piston speeds that will be occuring at these rpms. With an 88mm stroke you get 8084 feet per sec pistons speed. With a 100mm stroke its 9186 feet per second. That is just scary.

You're going to need a plenum on the intake the size of a 55 gallon drum and to get the car to perform at 14k it is going to idle about 3k due to all breathing modifications you are going to have to do to get it be efficient at those rpms.

With piston speeds like that, its not going to live very long if at all. You want to rev to 14K, build something with a rediculously short stroke.

jeff

you want cfm rates? just use one of the 8 million online calculators such as thi

i guess you'll have to guess on your volumetric efficiency, or do some research

I am pronouncing this guy the king of worthless threads.


I dont even know where to begin with this other than you have no clue what your talking about. If you have to ask these questions on a Internet forum your not even close to ready to tackle a goal like this. THE fastest imports in the country dont rev that high and we are talking about 100,000+ dollar a year funded teams. If it was feasible or even necessary to rev that high to hit better times they would be doing it.