How many rpms....

["Turbo-T"]

...are stock heads good up to?

And what about the stock intake?

Thanks!

 

[BetMinesFaster]

How many RPM is a hard question, valve springs are a major factor, they get weak and the valves float big time, the stock intake will go into the nines, stock heads with work will too, look at Grumpy.....I try not to put mine over 6K and I have had plenty or people tell me over 5500 is too high.....So....They are good enough to go fast anyways:biggrin:

 

["Turbo-T"]

The reason I ask is because I was thinking there's a certain rpm where the engine can't flow adequate air thru the heads and/or intake.

For example look thru the Summit catalog at the intakes. They're usually advertised to work from XXXX rpm to XXXX rpm.

 

[Nasty]

They are for designed naturally aspirated engines, not turbo cars. The more air you have moving through the engine, the more fuel you can add which equates into more power. Non-turbo cars need large lift/higher rpms to move more air through the engine at 1 aptmosphere, specially designed intakes and heads will acheive this with more efficency than stock stuff. On the other hand, a turbo car uses more manifold pressure to get the air into the motor via the turbo. This can be done without lots of rpms or huge cams. Both get the air into the cylinder, just different approaches. Stock ported heads with larger valves are good enough for most, if you need more then Champion and TA aluminum heads are available (they flow more & can are more efficent at higher lifts and rpms), intakes are available too.

 

["Turbo-T"]

Thanx Nasty for the clarification.

As you can probably tell I'm used to working with non turbo engines, specifically V8's. Yes you are right in order to try to get more air/fuel crammed into the engine often a large cam is employed and also an aftermarket intake/carb and in some cases aftermarket heads.

But with stock heads and intake for a turbo 3.8 I was thinking there came a certain point to where the turbo would not be able to push anymore air in than the intake and heads would allow for.

Also I want to say I saw somewhere a stock LC2 3.8 was all done and out of breath by 4400 rpms, was this solely attributed to the cam? Or were there other restrictions?

 

[BetMinesFaster]

If it ran outta steam that early I would have to think it was related to worn valve springs!

 

[notacarlo]

I refreshed the heads about a year ago with new rocker shafts,rockers, valves, guides, springs, retainers.

I have not really tested how far I can go, but she still pulls hard at 5600. I think there's a little more in her.

This was a low 12 at moderate boost. I really need to get the 60' action down to utilize more of that upper end.

 

[Nasty]

Stock untouched heads and intake can easily take you into the 11's with a larger than stock turbo, supporting fuel, tune & traction. I think I recall reading some getting into the 10's with a BIG turbo, lots of boost and fuel.

Ported units will flow more, resulting in the need for less boost pressures to make the power. Lots of advantages to this.

As far as RPM's are concerned, I would guess they start to loose their efficency around 5k rpm non-ported. I ported head & oversized valves probally will get you to about 6k. This, of course is a crude generalization. Being turbo cams are usually not designed for high rpms, this is all you need.

 

["Turbo-T"]

Yeah I have noticed my engine lays down at 4700....it has a GN110T cam advanced 4 degrees. Postons says this cam is good up to 6200.

But if I leave the car in OD she pulls hard and goes fast for a long ways. Just can't wind her up past 4700 or she lays down. That's in 2 and 3 gear.

Feels like hitting a wall, but I can't tell yet if it's running rich then or valve float. I've got the alky running then and pushing 22-23 PSI.

 

[Alky V6]

That's a hard question to answer since most turbocharged 3.8L owners stick with very small cams. It's a well known fact that intake duration has a very large affect on the operating rpm band of the engine, turbocharged or not. As in a n/a application, the short comings of the breathing ability of a head can be somewhat overcome with the right camshaft design if high rpm operation is desired. Most people desiring to operate their turbocharged engine at high rpm are very serious about generating HP and will not stick with the stock head, but will move to an aftermarket head that will give them more bang for the buck.

My project is probably the closest thing to someone trying to get the most rpm out of a head that is the closest thing to a stock head. It could have gone even higher with more cam and money spent on the valvetrain at the expense of midrange. My present rpm limit is 7,800. The camshaft design is the major factor in keeping to this limit.

 

[cool 84]

With a 212-212 flat tappet and mildly ported stock heads, I've accidentally bumped the limiter at 6,200rpm a few times and it was still pulling hard. I think it's safe to say that with mildly worked stock heads and intake, you can run more rpms than the stock bottom will take. I've thought about going to a bigger 218-218 cam with my 4.1 but I don't see the point if it pulls hard to the limiter already.

 

[imjoesnuffy]

With a 212-212 flat tappet and mildly ported stock heads, I've accidentally bumped the limiter at 6,200rpm a few times and it was still pulling hard. I think it's safe to say that with mildly worked stock heads and intake, you can run more rpms than the stock bottom will take. I've thought about going to a bigger 218-218 cam with my 4.1 but I don't see the point if it pulls hard to the limiter already.

Did the same thing once at the track, bouncing repeatedly off the rev limiter at 6600 at 25 psi for about a second I had it in second without realizing it. I got lucky and didnt break anything either.

 

[V6UnderPressure]

Back to the original posters question, what rpm limit would be good to have on a stock block untouched from intake to pan. (stock valve springs too)? Is 5k rpm safe or can it go higher. Lets just say figuratively speaking the stock valves can take up to 5600 rpms. Then I would set mine to shift at 5500. Just trying to be safe here. So lets heat it.:biggrin:

 

[Alky V6]

If the engines laying down at 4700 rpm, it's not the heads. Weak springs could do that.

 

[TURBOPOWERED68]

At how many miles should the springs be replaced?
And with which ones?

 

[Alky V6]

At how many miles should the springs be replaced?
And with which ones?

Someone who has bothered to monitor their spring pressures on a mild build would have to answer that for us.

The spring to use as a replacement should be what the cam maker recommends.

With my setup, I check the valve adjustments (mechanical rollers) and springs every 3rd outing. I should do it more often, but the adjustments have stabilized pretty well. I look for broken springs, abnormal wear and check the seat pressures (incar) with a special tool. It's been recommended to me that if I see a drop in seat pressure of more than 10 psi, it's time to change the springs. The springs drop pressure pretty quick and I've let it go longer than I should. I'm waiting for my new set of springs to come in, as a matter of fact.

I have a friend with a Reher Morrison engine, and he's been instructed to change his valve springs every twenty something runs. Egads!

 

[Hot Air]

For a tired stock motor, keep it under 5,000 rpm. Fresh valve springs, fresh timing chain and no detonation, go wild and wind it to 5,500 rpm...maybe!
Conrad C.

ps...how lucky do you feel?

 

[TURBOPOWERED68]

Someone who has bothered to monitor their spring pressures on a mild build would have to answer that for us.

The spring to use as a replacement should be what the cam maker recommends.

With my setup, I check the valve adjustments (mechanical rollers) and springs every 3rd outing. I should do it more often, but the adjustments have stabilized pretty well. I look for broken springs, abnormal wear and check the seat pressures (incar) with a special tool. It's been recommended to me that if I see a drop in seat pressure of more than 10 psi, it's time to change the springs. The springs drop pressure pretty quick and I've let it go longer than I should. I'm waiting for my new set of springs to come in, as a matter of fact.

I have a friend with a Reher Morrison engine, and he's been instructed to change his valve springs every twenty something runs. Egads!

WOW.
Hard core racing is definatly not for me. i am way too lazy.

 

[TURBOPOWERED68]

Let me rephrase the question.

On your Stock engine with a stock cam with stock lifters and stock valve springs,
At about how many miles did you replace the valve springs?