PRV engine: what breaks at what speed question

[stevedmc]

I've noticed the car breaking whether at zero or 100 mph. Stuff breaks when it wants to break, irrespective of speed unless your car is carbureted. Motorcraft 2100 carburetors don't break.

[EarlHickey]

Typically at higher and higher RPM's the valve train can't keep up. The valves start floating (staying open). To compensate you go to higher spring pressures but that wears the valve train faster. Next to go typically are the pistons and rings.To compensate you go to looser pistons and rings. If everything is dynamically balanced and you damp out the harmonics the bottom end is usually the last to go. You do need to upgrade the hardware and probably increase the oiling. You really don't want to go too high, the curves for the HP and torque start dropping off anyway.
David Teitelbaum

I love using KB's fitted with a skirt clearance of 0.0005".... half a thou.... not a typo.

Have you ever run them?

Forged units at 5 thou are some rackety cold slapping ring rocking heavy bastards.

Heck, I just wonder how much HP the stock bottom end can handle without grenading.

I've noticed the car breaking whether at zero or 100 mph. Stuff breaks when it wants to break, irrespective of speed unless your car is carbureted. Motorcraft 2100 carburetors don't break.

I can't imagine carbureting and not using webers, dellortos, or even zeniths.

Don't you think 2 3's would be sexy? Maybe with a 6' tall NHRA top fuel air snorkel grabbing some cold clean air and shoving it into the chambers?

Something like that would have to have some zoomie headers maybe with tractor exhaust flapper valves to keep the rain out.

[David T]

Now you are talking HP and not RPM. As you increase HP you are also increasing combustion chamber pressure. The pistons won't take a lot of that before you break the lands between the rings on the stock cast pistons. That's why on the turbo-charged cars the boost pressure HAS to be limited to 5 psi unless you go to forged pistons and reduce the compression ratio and spark advance. Trouble with that is by then you are reaching the limit of what the transmission can handle and you start breaking input shafts.
David Teitelbaum

[Kenny_Z]

Motorcraft 2100 carburetors don't break.

Going to poke Steve with a stick on this one. The Motorcraft 2100 on my Mustang was the source of all my headaches on that 289. It was a piece of junk. I dumped it in favor of a 4 barrel Holley.

I don't know if Casey hangs around on the forums but I've seen his D and heard her revved in the high RPM range. He put forged pistons and hotter cams in when he rebuilt it. It was August when we spoke about that motor so I can't remember everything he said. That motor was a work of art and the Delorean around it was even better.

[stevedmc]

Don't you think 2 3's would be sexy?

No.

[Delorean Industries]

I love using KB's fitted with a skirt clearance of 0.0005".... half a thou.... not a typo.

Have you ever run them?

Forged units at 5 thou are some rackety cold slapping ring rocking heavy bastards.

Heck, I just wonder how much HP the stock bottom end can handle without grenading.

Alot. Tried some crazy things here. Valve train is the weak link when it comes to rev's.

[stevedmc]

Going to poke Steve with a stick on this one. The Motorcraft 2100 on my Mustang was the source of all my headaches on that 289. It was a piece of junk. I dumped it in favor of a 4 barrel Holley.

Nonsense! It is impossible for a Motorcraft 2100 to break because it is a solid piece of metal. One of the power pump or booster valve thingie may have needed to be replaced, the choke wasn't set correct, had the wrong size jets, or the idle mixture screws weren't set correctly, but the carburetor itself wasn't broke.

You simply had an ID ten T error.

[EarlHickey]

No.

Some people do not enjoy tuning, or know how to tune multiple carbs.

2 3's are easier than doing 8 1's on a temperamental Italian thoroughbred and webers are pretty much fuel injection with human brains.

I can think of many mere two barrel carbs that are much more highly refined and tunable metering devices, but, at least the 5100 isn't a Holley.

Now you are talking HP and not RPM. As you increase HP you are also increasing combustion chamber pressure. The pistons won't take a lot of that before you break the lands between the rings on the stock cast pistons. That's why on the turbo-charged cars the boost pressure HAS to be limited to 5 psi unless you go to forged pistons and reduce the compression ratio and spark advance. Trouble with that is by then you are reaching the limit of what the transmission can handle and you start breaking input shafts.
David Teitelbaum

Well, trying to discuss RPM specific weaknesses seemed to be a fruitless discussion.


Tell me, why is the cam timing different from one cylinder bank to the other and are the ports actually sized different from side to side?

[Kenny_Z]

Nonsense! It is impossible for a Motorcraft 2100 to break because it is a solid piece of metal. One of the power pump or booster valve thingie may have needed to be replaced, the choke wasn't set correct, had the wrong size jets, or the idle mixture screws weren't set correctly, but the carburetor itself wasn't broke.

You simply had an ID ten T error.

You said Motorcraft 2100 carburetor not Motorcraft 2100 housing. By that logic I can insist that the KJet never breaks. The carb itself was junk, I couldn't tune the issues out of it. It probably had a mechanical problem that could have been repaired but for a little bit more I replaced the entire thing with something better and modern (for a carb anyway).

[Rich W]

I am not sure you are going to get the answers for "boost until failure" questions for the PRV V6 on this forum.

In fact, I am not sure if you have answers for "forced fed" versions of Pontiacs, Ducatis, Scotts, Nortons, etc.

For more details in taking the PRV V6 to the limit and beyond, both stock and boosted, you may want to check
the "older" Volvo forums, especially for work done by John Lane in the Pacific Northwest (Seattle, WA area).

John runs a Rally Car version of a Volvo 262 SPE with probably the most powerful PRV V6 in the US.

In the past, the car was running 515 ft/lbs at the rear wheels on the dyno while running 11 psi boost.
The car is currently running 18 psi boost and it is known to implode K&N cone filters on a regular basis.

If you want to go WAY OUT THERE, check the back issues of Race Engine Technology (not sure the issue).
There is an article about how to get in excess of 900 BHP out of both a 2.8L and a 3.0L PRV V6 engine.

Later,
Rich W.

Do you know any specific rpm of which specific components break?

Like I can tell you that a big pontiac v-8 loves breaking connecting rods and trashing those huge main bearings at speeds over 6000 rpm.

I can tell you that a pre-pantah Ducati will make very expensive grumbling noises when the needles skate at speeds over 9000 rpm.

Scott two stokes destroy your bank account with metal horror at 5200 rpm.

Norton Atlas and Commandos tend to break cylinders at 7200 rpm and change.

I could go on and on, but, I'll explain instead that I'm only trying to learn what breaks beyond the 6500 rpm redline as it's short stroke will certainly have the piston safe all the way to 9500 rpm without forged or eutectic pistons.



Have there been any repeated failures of any components with force fed engines?

What failed, how much boost and at what engine speeds?

Now beyond all that, I'd love to have one of these singing it's song at 9500 rpm hooked up to a stick car, but, I have far more productive things to do.
I'm not a "starry eyed" kid or boy racer type at all.

Crazy enough to consider building one and taking it to the salt flats? Maybe and skilled enough to do it if I make my mind up that's the plan.

I did run across some highly tuned Renault Alpines claiming reliability at 8000 rpm. I've not found any F1 versions running 2-4 atmospheres.

I have yet to learn if they run the same crankshaft, rods (I doubt that) or even oil pump as the B28 stuffed in the back of the DMC.

I don't know if any oil galleys or passage were enlarged or modified... etc.