headers and Boost, What is the relationship?

[JeremyH]

Octane doesn't matter. The trend has been that random rod failure starts occuring roughly around 450HP. Some guys run a lot more with no problems. Some guys less and popped the motor. Tune is key preventer no matter how modded and how slight the mods. Maximum repeated efforts seem to accentuate the problem which, not to shocking.

Octane does matter, higher octane runs cooler and will absorb more heat before compression ignitin/detonation. Its def a key factor in pushing the limits of the stock block with boost, its safer and more forgiving.

Its a combination of power level (pressure and heat) and rpm, with a nod towards rpm for the main factor for rods. Running 10lbs of boost at 3k rpms is less load than 10lbs of boost at 6k rpms as far as the rods are concerned. In other words even with a spot on tune excessive rpm can kill the factory rods. Especialy on a belt driven power adder since power goes up with rpm.

 

[Greg Hazlett]

^^ this man speaketh truff.

 

[Fastbreak]

Octane does matter, higher octane runs cooler and will absorb more heat before compression ignitin/detonation. Its def a key factor in pushing the limits of the stock block with boost, its safer and more forgiving.

Its a combination of power level (pressure and heat) and rpm, with a nod towards rpm for the main factor for rods. Running 10lbs of boost at 3k rpms is less load than 10lbs of boost at 6k rpms as far as the rods are concerned. In other words even with a spot on tune excessive rpm can kill the factory rods. Especialy on a belt driven power adder since power goes up with rpm.

Thanks for the insight Jeremy.

 

[weather man]

Octane does matter, higher octane runs cooler and will absorb more heat before compression ignitin/detonation. Its def a key factor in pushing the limits of the stock block with boost, its safer and more forgiving.

If you are at 450HP on a 87 octane safe tune and your rod lets go. The octane didn't matter. The limiting factor is not the octane, it is the rod. My octane response was in that context.

You are right that the higher the octane, the more HP you can safely generate. Hard to imagine anyone pushing 400+ not running the highest octane available to them. Of course, it can be perfectly safe and still push the stock rod beyond its design limit.

 

[JeremyH]

I wouldnt call 450rwhp on 87 a "safe" tune in the first place and yes it would be a contributing factor no matter how you look at it or reword it.

Less heat mean less cylinder pressure which means less force on the pistons and rods as rpm goes up.

The same car with the exact same tune and timing will run safer with 93 vice 87.

I digress lol, why risk it? Your asking for trouble when pushing it regardless. Your more likely to pop a motor pushing 87 octane to the limits sooner than the same setup on 93.

 

[Greg Hazlett]

I don't know of anyone who would run anything close to 450 hp on 87 octane.

 

[weather man]

I don't know of anyone who would run anything close to 450 hp on 87 octane.

Greg the 87 was just used to illustrate the point. The point being that in the 4.6 3v the rod approaches its design limit at around 450HP no matter what fuel you are using, assuming a good tune.

 

[Greg Hazlett]

Understand; granted the rods tend to get all the attention but another thing to consider is the stock valve train is not designed for high rpms either....or the stock oil pump....

 

[JeremyH]

Greg the 87 was just used to illustrate the point. The point being that in the 4.6 3v the rod approaches its design limit at around 450HP no matter what fuel you are using, assuming a good tune.

There is just no truth to this point is my point lol
Where did you come up with this magical number for the rods?
The power the car makes is one of many factors on the limit of the factory rods on a boosted car, the type of fuel used is also one of them.

The only hard limit I would put on the stock rods with boost is an rpm limit not power. And again Im not going to throw out a number sense every setup/stlye power adder etc. is different.

Understand; granted the rods tend to get all the attention but another thing to consider is the stock valve train is not designed for high rpms either....or the stock oil pump....

Stock valvetrain is actually pretty stout its been pushed repeatively to 6500-6800 rpms and recently read some where that ford rated it to 6500. And with just a spring upgrade you can rev to 7k all day long.

Now would I rev this high on stock block with boost, defiently not.

Stock oil pump gears and rpm dont play well together at all when running bigger power but I dont think I've seen one fail on a stock block. All the failures usually occur when going bigger than that on built engines.

 

[weather man]

Holy cow...how many people post up saying they were fine around 400-450HP, then bumped to 500-550 and popped a rod. Granted, bad tunes and over speed probably accounted for some of them, but the stock rod just couldn't hack it. Ford only designed it to handle 300.

 

[Fastbreak]

Well this turned into an interesting read.

 

[HOLLYWD69]

Very Good information in this thread!

 

[JanShelbyGT500]

So it is safe to say that the rods are the weak link of this motor. Lets say we upgraded the rods and pistons. Valvetrain. What is the limit of the stock block? What would be next the tranny? Axles? The list goes on and on. So remember that the HP bug, is going to led you to a shopping list of upgrades.

Thats why i am not passing the 450whp. It is just not worth the hassle of breaking a engine on a 470-500whp quest.

on a lighter note, why rev a mustang over 6200rpm? Its not a S2000 for god sake! The torque with a supercharger is almost at idle! LOL. Some people just plain old abused these engines and them called them weak.

 

[JeremyH]

I've never seen a stock block itself break so I wouldnt call it a weak link at all. But yes you are right lots of stuff starts needing upgraded.

Because these cars make power up there with the vct and proper mods. I rev'd to 6800 rpms for 3 years when I was n/a and now rev to 7k with the turbo and comp cams/valve springs/frpp manifold.

I would def keep her under 6200 on the stock block with boost, its not worth the risk, especialy on a rpm driven power adder.

 

[TheKurgan]

There is just no truth to this point is my point lol
Where did you come up with this magical number for the rods?
The power the car makes is one of many factors on the limit of the factory rods on a boosted car, the type of fuel used is also one of them.

The only hard limit I would put on the stock rods with boost is an rpm limit not power. And again Im not going to throw out a number sense every setup/stlye power adder etc. is different.



Stock valvetrain is actually pretty stout its been pushed repeatively to 6500-6800 rpms and recently read some where that ford rated it to 6500. And with just a spring upgrade you can rev to 7k all day long.

Now would I rev this high on stock block with boost, defiently not.

Stock oil pump gears and rpm dont play well together at all when running bigger power but I dont think I've seen one fail on a stock block. All the failures usually occur when going bigger than that on built engines.

Lot I don't agree with there. There have been many, many rods let go around the 450 mark and usually it's with a whipple or saleen and it happens in the low rpms, not upper.

Also talking about reving to 7k with just a spring upgrade is not something I would do either. Limiters at a minimum with stronger springs then I would be worried about the strength of the valves themselves at that rpm.

 

[Greg Hazlett]

So it is safe to say that the rods are the weak link of this motor. Lets say we upgraded the rods and pistons. Valvetrain. What is the limit of the stock block? What would be next the tranny? Axles? The list goes on and on. So remember that the HP bug, is going to led you to a shopping list of upgrades.

Thats why i am not passing the 450whp. It is just not worth the hassle of breaking a engine on a 470-500whp quest.

on a lighter note, why rev a mustang over 6200rpm? Its not a S2000 for god sake! The torque with a supercharger is almost at idle! LOL. Some people just plain old abused these engines and them called them weak.

Why rev the motor past 6200? Because on some of them it's still making power...???????

You can't make the blanket statement that the torque of the s/c is almost at idle as there are other superchargers that that statement does not apply to like all centri s/c's.

And again, your blanket statement of some people abused their engines and called them weak is wrong again; I have yet to see someone who added FI to their car and break something call the engine weak, they know or should know they are playing with fire when they FI the engine. I am sure there are 1-2 cases where people have blamed the stock block but 99% of the people who break understood the risk they took.

Not even going to go into your laundry list of questions but I have not heard of anyone "breaking" the stock block nor have I read of anyone breaking the rear end or axles on the S197.

 

[Greg Hazlett]

Lot I don't agree with there. There have been many, many rods let go around the 450 mark and usually it's with a whipple or saleen and it happens in the low rpms, not upper.

Also talking about reving to 7k with just a spring upgrade is not something I would do either. Limiters at a minimum with stronger springs then I would be worried about the strength of the valves themselves at that rpm.

While I am not in the business I have not heard of "many" rods letting go with the whipple/saleen/PD blowers but if they have I can understand why as that is a lot of shock/power that is applied all at once vice the gradual build of power that a turbo/centri brings.

 

[JeremyH]

Lot I don't agree with there. There have been many, many rods let go around the 450 mark and usually it's with a whipple or saleen and it happens in the low rpms, not upper.

Also talking about reving to 7k with just a spring upgrade is not something I would do either. Limiters at a minimum with stronger springs then I would be worried about the strength of the valves themselves at that rpm.

Like I said there are many factors, type of power adder is one of them I agree the twin screw is more shock and load on the system and crank as well. Doesnt mean 450hp is the magical rod let go number. And doesnt change the fact that excessive rpm is bad for stock rods with boost.

Been revivng my 3v to 6800-7k rpms for 5 years now as many other do, thanks.

 

[TheKurgan]

Been revivng my 3v to 6800-7k rpms for 5 years now as many other do, thanks.

With boost ? I dunno, those valve stems just looked weak and discolored when I had my motor tore apart. They've been working fine with 13psi for 8000 miles @ 6500 rpms, but cnc heads and stronger valves are in the future before I upgrade springs and raise the rpms/boost. I don't trust em.

 

[JeremyH]

Yup 12-16psi for 2 of those years, stock heads, comp valve springs and ss retainers. And i still use vct.