Running in rpm, raising rev limit later?

**spetz** · 16-03-2007 01:48 AM

So, as everyone has heard this "run it in like you'll drive it"

My question is this though
Say I build an engine, which will rev to 9,000rpm (example figures only)
But at the time I don't have the money to do cams, intake and exhaust
And therefore this engine will not make much power after 6000rpm
So it's tuned with a rev limit at 6500rpm

What happens if I run it in, and drive it hard to the 6500 limit, and once I get more money and do cams, exhaust, intake and raise the rev limit to 9000rpm

How will the engine wear react to that?
Is this ok or a bad idea?

**aaronng** · 16-03-2007 03:14 AM

Originally Posted by spetz

So, as everyone has heard this "run it in like you'll drive it"

My question is this though
Say I build an engine, which will rev to 9,000rpm (example figures only)
But at the time I don't have the money to do cams, intake and exhaust
And therefore this engine will not make much power after 6000rpm
So it's tuned with a rev limit at 6500rpm

What happens if I run it in, and drive it hard to the 6500 limit, and once I get more money and do cams, exhaust, intake and raise the rev limit to 9000rpm

How will the engine wear react to that?
Is this ok or a bad idea?

The problem is not the rev limit. But the stretching of the rods as you drive the car at redline. If you drive the car normally at low RPM, you wear a ridge after a long distance of about 50,000km or more (guessing here). If you use 6500rpm, your current rods will stretch and avoid that ridge forming. Of course, the more the rods stretch, the quicker they will come to the end of their service life (and eventually snap).

How many kms will you drive your car before working on it for 9000rpm? If you will plan to rev it that high, you'd probably replace your rods and pistons to support that too, so you can bore away that ridge when you have the block out.

**silver_screen** · 16-03-2007 06:08 AM

ok champ. i build engines... dont baby the motor, dont listen to those "dont go past 3500rpm"

Drive it semi hard, put load on the motor and thats not to say to throw it in 4th gear n just step on the gas goin up a hill

If ur gonna go to 9k, then i suggest u drive it to around 7-8k

dont let it idle for long, dont use shit fuel and make sure u use running in oil for atleast 1000km and after that use high quality oils

Just drive it like u normally would, but dont thrash the shit outta it.

Change cams whenever u like, the motor wont mind it

**string** · 16-03-2007 12:01 PM

Originally Posted by silver_screen

ok champ. i build engines... dont baby the motor, dont listen to those "dont go past 3500rpm"

Drive it semi hard, put load on the motor and thats not to say to throw it in 4th gear n just step on the gas goin up a hill

If ur gonna go to 9k, then i suggest u drive it to around 7-8k

dont let it idle for long, dont use shit fuel and make sure u use running in oil for atleast 1000km and after that use high quality oils

Just drive it like u normally would, but dont thrash the shit outta it.

Change cams whenever u like, the motor wont mind it

He is asking the negative effects of only initially using only ~80% of a motors rpm range, not specifically run-in methods (since he obviously has an idea of the one you had in mind, with the mention of high rpm). Where did you get the 7k-8k figure from? Reasoned calculation or random guess?

Go and find a decent mechanical engineer because you won't get a very good answer on these forums.

What motor are we talking about here? If it's a non-vtec, give up. Revving non-vtecs to 9000 is going to make your life a nightmare. If it's a vtec, then the stock cams will still make power to 8000 regardless; so I fail to see the problem

**silver_screen** · 16-03-2007 05:02 PM

reasoned calculation champ.. and non vtec a nightmare??? how so?

Any engine can be made to rev so long as it has the components that will allow it to do so

**string** · 16-03-2007 05:56 PM

I'm all ears for the reasoning you used to calculate this figure...

Single cam profiles are only good for a given rpm range. A head design and cam profile for 9000rpm power, will NOT be very fun in the lower half of that. Nothing to do with reliability, although, VTEC heads are cheap enough to warrant the conversion for the far more reliable valve-train and far better port and combustion chamber design for starters.

**aaronng** · 16-03-2007 11:11 PM

Keep it on topic as per the threadstarter's question or I'll close the thread.

**spetz** · 17-03-2007 12:25 AM

Well realistically with an engine that revs to 9Krpm I would start easy for a 100km or so and then gradually ease it to 7-8K rpm. By gradually I mean maybe go up 500-1000rpm every 50km of driving
With no WOT of course

Anyway, to give more info. The motor is a MIVEC. I want to up the displacement from 2 to 2.5L but I'd like to assemble the motor and then start on other mods for more power
Meaning, run it at 2.5L with the stock 2L cams, intake and extractors. The MIVEC makes peak power close to 8000rpm so with 2.5L I'd assume the peak power output rpm would drop considerably. Meaning also I couldn't rev it out too hard to run it in.
It'll be built with forgies and once all is done to it I would like to make peak power in a similar rpm range as the stock 2L (just so I have less issues with gearbox etc)

So, would it be ok to build it like this, or should I do everything at once?
cams, extractors and ITB is like close to $8K on the engine

**silver_screen** · 18-03-2007 06:39 PM

WOT is fine, revving a fresh motor is also fine and i recommend u do. just dont over do it.

Baby the motor will kill it. so dont do it

Ur combination will work fine, sure the engine wont get the air it needs uptop, it will make more than enough down low

**DynoDave** · 18-03-2007 06:56 PM

Originally Posted by silver_screen

ok champ. i build engines... dont baby the motor, dont listen to those "dont go past 3500rpm"

Drive it semi hard, put load on the motor and thats not to say to throw it in 4th gear n just step on the gas goin up a hill

If ur gonna go to 9k, then i suggest u drive it to around 7-8k

dont let it idle for long, dont use shit fuel and make sure u use running in oil for atleast 1000km and after that use high quality oils

Just drive it like u normally would, but dont thrash the shit outta it.

Change cams whenever u like, the motor wont mind it

Why would you use running in oil when the first 10 mins of an engines life is the most important ?
Regards Dyno Dave

**ProECU** · 19-03-2007 05:09 PM

Originally Posted by silver_screen

ok champ. i build engines... dont baby the motor, dont listen to those "dont go past 3500rpm"

Drive it semi hard, put load on the motor and thats not to say to throw it in 4th gear n just step on the gas goin up a hill

If ur gonna go to 9k, then i suggest u drive it to around 7-8k

dont let it idle for long, dont use shit fuel and make sure u use running in oil for atleast 1000km and after that use high quality oils

Just drive it like u normally would, but dont thrash the shit outta it.

Change cams whenever u like, the motor wont mind it

Where do you work exactly? So I know NEVER to take my car there...

**silver_screen** · 19-03-2007 07:27 PM

Runnin in oil doesnt have any friction modifiers. Its ability to lubricate will not change just because its colder, or hotter. It will (unless its cheap running in oil) more or less stay the same. Only downfall that i can guess ( n this is from the old guys that ive learnt from) is that it doesnt last as long.

As for not taking ur engine here.. good

We're busy enough!!!

first 10 mins??? now i take it, that ud let the engine idle for those 10mins now wouldnt u