Hey guys I just did a dyno run on my stock 08 ISF with 93 octane and was wondering what the average drivetrain loss percentage is? My top HP after SAE correction was 337 so I lost about 19%. I've heard that the loss percentage is anywhere from 17-20%. Can anyone here confirm this?

 

Yes. I can confirm that 337 is a 19% drop from 416; and that 19% is between 17% and 20%

 

I can’t remember what stock Dyno numbers I’ve seen, but I want to say around 350 is the higher end. Your car is also aged. What’s the mileage? Engines tend to lose a little steam after they rack up miles.

 

If you believe every engine leaving the factory makes the rated power, I've got a bridge to sell you in Brooklyn. There is significant variability in power output between cars. They're machined and built to tolerances, and they make sure the tolerances stack to ensure there are minimal warranty claims. The only way you get confirmation of the power you expected is to test and see what you actually got. For example - when I was building race engines, I built my own Yamaha FJ1100 and measured the combustion chamber volume, piston dish volume, deck height, and stroke. They got the stroke right in all four cylinders. That was the only measurement they got right. The deck was 2 mm too tall (measured 3 mm, should have been 1 mm), the combustion chambers were 2 cc over spec, and the factory spec for compression ratio was 9.5:1, but it measured out to 9.2:1. OK enough for the vast majority of users, but I wanted this thing to make some power. The cam timing was also problematic with this configuration - either the exhaust opened a little early or it opened a little late because the stacked tolerances and fixed nature of the sprockets only gave so much. So, I bored the block 3mm to fit FJ1200 pistons, milled the head to the edge of the intake valve seats, milled the deck 2 mm, slotted the cam sprockets and built an 11.25:1 compression ratio engine the way the factory couldn't. After replacing the OE carbs with Keihin CRs (stacks with no filters at all), adding a Supertrapp exhaust with 32 plates and spending about 40 hours reworking the ports, manifolds, and valves, it would do roll on wheelies at 90 mph and added 12 mph top speed.

To be fair, the factory configuration would pull redline in top gear to 144 mph, but I liked it a lot better when it pulled 156 mph. I did a lot of other stuff to this bike, like reworked the ignition with hotter coils (needed for higher compression) and recurved the advance by reducing full advance from 34 degrees to 28 degrees (more efficient combustion chambers need LESS full advance or they will detonate themselves to death, AMHIK). This doesn't sound like much now, but it was a big deal in 1988 when I was doing it, and running 11.04 at 126 mph at Sac Raceway with 220 lb me on it was vindication it was working.

This was my own personal project. We did a lot of other projects in the shop where I built engines and did some fabrication. One of the really cool ones was modifying a 400cc Yamaha engine by fitting a 600cc cylinder block with a spacer so we could run 2.2 rod ratio rods in it. It screamed on the dyno! Anyway - the factory will give you what they can, but they are completely biased toward reliability and surviving warranty, not making best power.

 

I completely forgot to look at the replies on here, but I thank you for being the only person giving me a real response. I had about 93000 miles on it. I have already added Joe Z, PPE headers, and a tune to it so I'm happy with my car right now regardless of the HP. I was just curious what the ISF gets when stock, because a lot of people told me that my HP was pretty low. It is what it is.

 

didn't mean to double post

 

The 1st thing that should have been asked was, what Dyno type? Some read lower than others?

 

It was a dyno jet

 

I've seen anywhere from 335-380whp reported on stock ISF's over the years, with most in the 350-360 range. Wouldn't put too much faith in any dyno other than to measure same day pre/post modification runs.
With headers exhaust and tune on dynojet it should be around 400-420whp. The bigger question is maintenance upkeep (spark plugs compression/fresh fluids/filters/checking KCLV and fuel type etc) and real world testing via rolls, 60-130 drag runs, quarter mile etc.
Have you had a chance to redyno it after the mods?