How to estimate HP ???

hobieboy · 11-23-2005, 01:05 PM

I'm in the process of converting to EFI for my 930.

Part of the exercise is to select injectors. And that requires knowledge of expected horsepower.

So, I wonder how do you folks typically estimate horsepower for rebuilds & modifications? For my car, it seems that a similar build can have 100 hp difference

Example: CIS, K27, GHL, Cams. Some have 375rwhp. Some claims 475rwhp.

Any input would be appreciated.

911Velocity · 911Velocity's Garage

Depends on the method of measurement (sae,din and bar) bar is always the highest as it derives from and is directly related to how many drinks you had at the bar.

Best regards,

WydRyd · 11-23-2005, 02:58 PM

HIGHLY unlikely you will obtain 475RWHP with CIS injection. I've heard of people reaching 400-450 (max) engine HP with CIS, but nothing more than that.

If you want those sorts of numbers, you definately need to go EFI, 1.0+ bar of boost, aftermarket ECU and a bigger more efficient turbo and intercooler.

The factory 930 intercooler is well known for it's poor efficiency (~14% efficiency), so you would need a substantially bigger intercooler to get to those numbers safely.

mppickett · 03:33 PM

I just went through this problem - here's how I approached it. I have a 915 transmission and didn't want to change out right now. I figured that 450 hp was a reasonable top limit for me (even though the engine should be able to do much more). I found out what TT injectors usually put out (38 lbs) and then looked at the RC Engineering Injector Worksheet. Using a BSFC of .6, a max duty cycle of .85 and a fuel rail pressure of 72, the calculator told me I wanted 42 lb/hr injectors. A matched, flow tested set are on the way. I considered the 55 lb Siemans but decided I'd play it safe on the idle and drivability side since I don't really need that much head room at this point. I'll use a wide band 02 meter to keep the A/F ratios safe and set the max boost accordingly (or conservatively if it puts out more power than I think - unlikely, but possible

).

Mike

hobieboy · 11-23-2005, 04:05 PM

Thanks for the input guys (& girls?)...

I came across the same injector sizing tool from RC as well but I'm wondering how would one estimate the eventual HP to begin with?

The only factors I am convinced so far... a) dynos differ greatly, b) same build/drastically different HP had been claimed

I'll likely end up with a build that reads - 3.3 P&C with slight bump in compression, K27HF with GHL, 3.2 intake with matched heads, twin plug. I'm leaning on using 475 fwhp (@ 1bar) as my assumption - too high? too low?

donporfi · 11-23-2005, 04:19 PM

Do you care how much hp your engine makes? As long it is faster after the mods.
I think most of the hp figures given by particulars are just for bragging. If you car outaccelerates other or is faster, then you have more hp and torque that the other car. You can say it has 400hp and who will say it does not.

hobieboy · 11-23-2005, 04:25 PM

Absolutely... I don't really care hence I haven't dyno-ed my car yet.
But, I do need a reasonable target to size the injectors

55lb seems reasonable, but as Mike said, he's looking at 42lb. And if this build will make 500hp maybe I should consider 65lb?

TimT · 11-23-2005, 04:33 PM

As a baseline I built a 3.3 with a 3.2 manifold. K29 hybrid turbo, twin plugs, a bit of headwork, EVO2/ 935 hybrid cams , and saw 560 corrected RWHP on the dyno. Id have to check the build sheet but I think 55lb injectors were used @ 3bar fuel pressure.

This engine is close to the engine your building.

WydRyd · 05:05 PM

TimT, at what boost level though?

Many of us Protomotive guys are running 951/944 turbo injectors for our Stage3 systems, which output approx 550FWHP. The injectors are "over-driven" with a custom Protomotive fuel pressure regulator. This results in VERY high fuel rail pressures to flow upwards of 600-700HP capability at a very high duty cycle

It's a proven system that works fine, however, most tuners don't like to run their injectors at such high duty cycles.

BTW, I think 475FWHP is achievable at around 1.0bar.

RarlyL8 · RarlyL8's Garage

You do not list enough information to make an estimate on the power level of your engine.
At minimum you need to list the following:
Compression Ratio
Turbo Type
Intercooler Type/Size
Displacement
Boost Level (Bar)
Exhaust System
Cams
Any Headwork or Internal Mods

For Example - a typical CIS, 3.3L, K27-7200, Larger Intercooler, 7:1 C/R, SC Cams, 1.0 Bar, B&B exhaust is good for a solid 400HP

From what I have read you can pick up 50 HP by changing the CIS in the above system to a well tuned EFI.

hobieboy · 11-24-2005, 08:01 AM

Hi RaryL8, as I quoted earlier, my build is: "3.3 P&C with slight bump in compression, K27HF with GHL, 3.2 intake with matched heads, twin plug." The missing info that you said: C/R is a measured 6.5:1 (yes - factory said they are suppoesd to be 7:1 but we all heard about Mahle compression) so it should be 7:1 with the bump. Intercooler-full bay. And I'm going EFI (Megasquirt).

So it sounds like my 475fwhp is reasonable.