So we all know that if you don't like being able to see through your motor, you should keep your torque below 400. For those of us with a bigger/laggier turbo, you can usually tune it so that the torque will not peak, but instead, carry a nice flat line out the redline. While you don't get the nasty torque fall off common on stock frame turbos, your powerband is limited by the fact that these turbos will not spool up for quite some time.

In my case, I know the 5858 is capable of holding 350wtq through the stock rev limit (7600). I've seen people run much higher torque levels (peak at 450, dropping down to high 300's to low 400's at 7500RPM. If I wanted to raise the rev limiter, to say, 8500, I'd need stage 2 cams (e.g. Kelford 214B, GSC S2, etc) and springs/retainers.


My question.. is it safe for a stock motor to rev out to 8500 provided the necessary valvetrain work is completed? I haven't been able to find much about the relationship between RPM and piston/rod durability.

 

Bump, subscribed.
Very curious to see if anyone has legit info on this. I've been debating cams/springs/retainers since I upgraded my turbo and lost the low end stomach-punching surge of power I had with the tuned stock turbo. Cobb tells me cams will get that back for me, but I like knowing it would be really hard to window my block on my current setup.

 

I know that the stock valvetrain with factory camshafts can rev up to 8k, its not efficient but its still within tolerance. I assume that with proper headwork/cams/springs and retainers with a good tune youll be fine. Rods are the weak point in the bottom end but as long as torque levels are kept smooth then it should be manageable.

 

So as long as torque isn't too crazy, the rods will hold up to a higher RPM?

 

Thinking you need to look at a lot of other factors other then the highest RMP you can reach. Yep, if you build a good valve train--then that will take the increased rpm without floating. However, there is a red line on your stock motor for a reason-- I would suggest using it if you are uncertain about the rest of the motor--or in you case its stock. If you read some of the post on the torque factors you will see some of the folks have motors over 450 tq and have run it for a long while with no issues, some have shelled there blocks on 350tq. So its a good rule of thumb but not gospel. Your cam choice is also rpm limited as is your turbos efficiency range, I would suggest you determine those and limit yourself to the lowest functional rpm range. In the event you find yourself meeting or exceeding the predetermined 8500 rpm you mentioned--then thinking once again you could do it but you need to start saving money for a rebuild soon. I leave the math to you but there are formulas for maximum piston speeds that will help you better understand some of the issues behind high rpm and keeping a motor together... If it aint built, dont think you can exceed the set stock rpm range without consequence. Can you do it? Sure. my .02-- good luck.

 

I ran a stock block and stock valve train out to 8500 for about 9 months.
i was running 10-40 brad penn oil

When i tore the motor down to build, what I learned is this...
The main bearings held up just fine, little to no scuffing.
The rod bearings seemed to also hold up just fine - light scuffing.
I had 2 bent rods, about 10* deflection
The rod bolts seemed to hold up fine.

the valve train was good, no damage to pistons, but I was running milder mivec at the top end, just in case of valve float.

I do know that at 9000 rpm and high mivec, on a stock valve train- the exhaust valves hit first. Personal experience.



Therefore my conclusion is that a stock bottom end with upgraded valve train can handle 8500 with the correct oil and a safe tune. Keep in mind that if you hit heavy counts of knock running at that speed, the rods can pretty much disintegrate, and its usually #2 or #3

 

Oh hey look, it's mr limpy

 

Hey what's up. Just a tag im interested