Majestik Møøse

I've been casually looking at FI for a while now and stumbled upon the Stock Motors w/F.I. thread a couple of days ago. There were a lot of respondents and data but it wasn't really organized into any usable format, so I put it all into an Excel spreadsheet. I found some surprising results (for me at least).

The overwhelming predictor for blown stock engines seems to be the ratio of HP/PSI. Between two cars making the same amount of power, the one with higher PSI is much more likely to blow. Based on our data, the magic number seems to be around 42HP per pound of boost. In other words, if your kit is pushing 10 psi, you'd better be making at least 420HP at the wheels. Of course, this is just a wag; there were a few other engines that were relatively boost-efficient that blew as well, though some were attributable to other issues. To get a better idea of the trend, take a look at the attached graph and not the different efficiency lines.

Another surprising result is that a stock engine's tendency to blow isn't really related to the number of boosted miles. If you're doing everything safely FI can be somewhat reliable.

Not so surprising? Superchargers are less likely to blow up a stock engine. Turbo engines blew at a 14% rate while SC engines blew only at a 5% rate.

Download the Excel sheet (zipped) and check it out. Let me know how I can improve it and help make it better by PMing me your own data to fill in the blanks.

rcdash

iTrader: (18)

Great job. The other (more plausible, imo) conclusion you could derive from the data is that there is no statistical correlation, especially given the small sample size. That's a lot of work to compile - kudos for that.

Threads

iTrader: (13)

Great to hear, especially since I just installed my Vortech.

Major props on taking the time to compile this data. Great job!

twitch579

iTrader: (3)

Im putting a TN kit on tomorrow on my car. My engine has over 60k miles of nitrous abuse with usually a bottle a weekend or sometimes two.

I will be running 8lbs on a Osiris tune, also getting a oil cooler installed along with a oil catch can.

I really have no long term hope for the motor being boosted, I actually think it will blow within the first week. The engine has been mis-shifted about a dozen times from 3rd to second and probably revved to 10k rpm, sometimes this would happen while using N20.\

Ive been reading all these post and looking at other peoples results and have no hope for my engine, I will keep my results posted.

Excellent job on the graph.

2004Black350z

iTrader: (37)

u either have HUGE ***** and a damn good tuner or an idiot

rcdash

iTrader: (18)

^ he just has realistic expectations. Build (or plan to build) a spare block while boosting your stock motor - not a bad way to go about it...

boostedmaxima

In the s/c vs turbo comparison do you use the same number of each type to get the percentage, or did you take an overall number of messed up engines and got the percentage of s/c vs t/c from there?

Majestik Møøse

The current sample size is 132, 87 of which have PSI & HP data, so the N-number is 87. I ran regression in Excel and got a significance of 78%, correlated maybe but not well enough to draw a firm conclusion. Interestingly, however, if I threw out shaun_walsh's result, the significance jumps to over 97% correlation. I'm sure he's an outlier because his engine finally broke after 100k miles, but I'll leave him in anyway. What we need is more data, so everybody PM me with their numbers!

Well I guess we'll get some extra data one way or another!

Overall numbers, which have been revised already. 2 out of 36 superchaged engines blew for a rate of 5.6% and 13 of 95 turbo engines blew for a rate of 13.7%.

One final note about this, everybody remember that this survey data is non-scientific because it is self-reported. Many of the HP numbers are inflated/uncorrected. Blown engines are also likely to be under-reported due to the ego- and wallet-crushing stigma involved. This is all meant to be used a small tool (STS) in your FI decision making.

twitch579

iTrader: (3)

Im not really excited about putting FI on my stock motor. Actually it doesnt really excite me at all. Im going to continue my same driving habits untill it does come apart though. Then ill be excited to build and make real power.

So what is different about supercharged boost compared to turbo? Im talking why would a SP motor not blow? Isnt air just air?

2004Black350z

iTrader: (37)

its TQ thats the diff

binder

iTrader: (8)

you know why more turbos blow engines than superchargers? torque. HP doesn't kill engines, torque does.

turbo builds boost lower in the rpm range so the torque is a lot higher at a lower rpm which stresses the motor.

6MTG354ME

iTrader: (5)

Fantastic! I'm an Excel guru. Love the ability to sort & filter to find information in seconds instead of reading tons of posts.

maXmood

iTrader: (16)

thanks for taking the effort to put it altogether..

can we have another version as .xls (which can be readable in both 2007 and earlier versions).

on what bases you're getting HP/PSI?

i'm gonna post my setup here as well for you to update the sheet.

Vortech 2.87"
PSI 8.4
HP 304
TQ 290
Auto
2006
less than 1500 miles
Tuned with Haltech
4/16" spacer, Berk HFC, Boral TD exhaust, DW 600cc injectors, Walbro 255, AAM RFS stage 0, 1 step colder plugs (NGK)

wizard

Fantastic post! Hope we can keep this graph and spreadsheet going!

My car is making 33whp per pound of boost. 425whp / 360lb @ 13 psi. Does this mean that my set up is risky? Based on the 42whp per pound optimum?

The problem is there's no way to alter the boost level on a supercharged VQ35 car without changing the pulley? Currently have 3:13.

I've only run the car about a 100 miles since boosted.

ADMAN

iTrader: (9)

Nice info

djamps

iTrader: (1)

Turbo cars are more difficult to tune properly, tendency for boost spikes, and heats oil more quickly (oil cooled turbos). I think all of these factors play a much bigger part than the 'excessive tq down low' argument. Our engines were designed for high tq at low rpms...just look at the factory tq curve .

wizard

If that were the case, then why would turbo's be blowing more engines then superchargers?

djamps

iTrader: (1)

Maybe I should repeat myself.

^^ This is why they blow more motors in my opinion.

Majestik Møøse

I think BOTH arguments make sense. According to the data we have so far, peak torque is completely uncorrelated to blowing an engine. The blown engines are spread out evenly across the peak torque board. That doesn't account for where the torque is on the power curve, though, and for how much longer it's produced.

Let me get this right, do supercharger torque curves generally match the stock torque curve, just shifted up on the graph? And do Turbos actually change the shape of the curve to make it fatter down low? Somebody with more SA on this please chime in.

Also, I'd agree that turbos are much more likely to produce out-of-control boost spikes. How much boost can a typical street turbo produce before it's shed off? A metric s***load, I'm sure. The only thing limiting the PSI is a boost controller, and that is reactive in nature. A supercharger only spins as fast as it spins and only makes a particular amount of boost. Seems a lot safer to me...

Nexx

iTrader: (41)

maybe you should get a compression test to see if its even worth trying?