I know one of them personally.

 

I did not name names.

 

sounds like a personal problem

 

There are a few of us locally that have forced induction on our S197s and have blown everything from motors to rearends, clutches, transmissions, oil pumps, trutracs etc etc. The cars are raced at a local NHRA dragstrip and are subjected to repeated heavy stress. We are all tuned on a mustangdyno and the difference in numbers from the dynojet that we were tuned on previously, can be 20%.

Our car is fairly advanced in terms of power and supporting mods (for dragracing) and we have the distinction of blowing a fully built motor, trying 28lbs of boost (normally run at 22lbs boost). We were running 100% methanol to keep the IATs down and discovered (after the fact) that the stock intake manifold is not designed for the mixture of gas and fluid. Some cylinders were running rich while others lean, while the overall A/F showed very safe.

We have rebuilt motor stronger than before, added a custom intake manifold, changed from a 4r70w to a 2 speed powerglide and lost 200+ lbs. We expect car at the same 22lbs boost to run way faster than our previous best and we also expect sooner or later, more things to blow up.

 

It's all good! I'm just happy to report that the factory cast POS rods and pistons are no longer in my new motor.

 

I've always known that dynojets read higher than mustangdynos (5-10%), but 20% differences? Wow. I guess I don't feel so bad about my 07 GT Automatic only putting down 364 rwhp on a mustangdyno. I've been thinking of putting it on a dynojet just to see how differently it reads rwhp for my car. Ultimately, dynos are just tuning tools, but I'm still curious.

I think the weak link in my car will probably end up being the transmission. When it goes boom, then a TCI or Level 10 5R55S goes in its place.

 

That's just our experience. It was surprising. I've also heard of numbers in the 7-11% range. We did the math on two different S197s with different sized turbos and different boost levels. On the base mustangdyno runs (no tuning, no change in power levels) both S197s showed a 20% drop in rwhp numbers, from the previous numbers off the dynojet. At the end it's just a number that I really don't care much about. Only numbers I look at are ET and trap speed.

 

Isn't the cause of failure usually revving the engine too high? Literally "pulling" the rods apart on the downward stroke.

So in theory you could get away with a higher HP or boost level as long as you keep the RPM's below 6000 or so...

 

I've been running a twinscrew for almost 2 years at 481 rwhp/440 rwtq(dynojet). I've tracked it once, and had a few spirited sprints on back roads. No problems so far.

I'm not going to offer any opinions on what's safe and not safe, because there are so many variables.

 

I survived 467whp on my stock block with ZERO issues before getting greddy and building an engine.

I am very skeptical of your tuners "observations".

 

Mine let go at around 4700 rpm's.

 

Correction. I know of 3 on this site.



Wasn't yours decelerating when it let go Bill?

 

Gary, it cut loose during acceleration.. maybe 80% throttle?

It went uber-lean and went kaboom.

 

This

 

+1.

You're going to have discrepancies with dynosheet numbers from one type of dyno to another, from one operator to another, from one transmission to another (since the figures come off the rear wheels).

Who runs race fuel...most folk don't. Fuel from a drum is much more reliable and consistent than pump. Then conditions on the dyno are not the same as those at the dragstrip. You're not launching, banging gears, doing burnouts on the dyno.

You dyno today....then go to the track maybe a week or month(s) from now. Tune is the same. Weather is different, things have changed on the car. You rock and roll at the track, things shake loose, car parameters change. How many folk datalog at the track, make fine adjustments on the tune or just shut it down if warranted, based upon the log? Very few.

Go to some other mustang forums where more folk are running boost or nitrous, and shooting for 11s or 10s or 9s...and see all the stuff that blows.

 

Amen. I'm amazed that my GT's paltry 364 rwhp ran a 12.14 @ 113 last trip to the 1/4 mile. I've seen plenty of guys who supposedly have 400+ rwhp run high 12's @ less than 110.