Penguinracer

I know this question is a bit like "How long is a piece of string?" but assuming a 2.5 litre is built with a big-valve N/A head, appropriate cam, decent headers, intake, throttlebody, standalone, fuel system, decent turbo etc - what is the realistic hp limit of a 2.5 litre assuming the standard rpm redline is maintained & boost is set at level which ensures reasonable reliability (say up to 23 psi max).

The reason I ask is because armed with a realistic expectation of the maximum power attainable from a 2.5 with a standard rev range & sensible boost - turbo size can be better matched.

Tim

Chris White

I feel that I am qualified to answer this question….

The piece of string is 36” long +/- 1 mile.

I am sure you know that the question is not really answerable with the parameters you have included – if you narrow it down a bit more then people can give you a better idea based on past experience. Street use/ Dyno queen run? Track use or race engine. And you have to define ‘reasonable reliability’. As HP goes up so does wear. Is a yearly rebuild OK? A past famous 944 race engine effort was good for a weekend of racing before it had to be rebuilt.

Willard Bridgham 3

Twice as long as it is from the middle to one end........

Penguinracer

Okay, Chris let me come clean. I've plonked down my hard earned on GTX3071R which is rated to a max of 560 bhp & I'm wanting to know if I'll ever out-grow it with my 2.5 litre as I maximise it's breathing & efficiency while respecting the stock redline & running a boost level which will allow it to run at DE days & on the road for a number of years between rebuilds. This is not a DD. This is really a post-purchase disonance situation where I was deciding between the GTX3071R & the GTX3076R (rated to 640 bhp)- the good advice from most was to go with the 71R.

I get the advice that driving a smaller 'charger harder & right across both sides of the map will give more power & torque than under-employing a larger unit.

I'm assuming the 560 bhp is at the flywheel, which would conservatively be about 450 rwhp (assuming approx 20% transmission losses).

elargentino

That turbo is a perfect turbo fo a 951.

It taked advantage of the real forte of the 951 engine/gearing, TORQUE, not HP.

Josh B

First of all generic turbo HP ratings are pie in the sky - most likely just some number the manufacturer calculated as physically possible given the CFM the turbo could flow. Certainly not a number that a 23 year or older porsche 944 could attain.

Unless you are incredibly mechanically gifted or have a money tree out back that never wilts there is only a certain amount in the pursuit of HP that makes sense to spend on these cars. It is possible to fly to the moon but certainly not something I'll be doing soon.

IMHO the "hp ceiling" for 97.5% or more of 2.5L 944s is going to be between 300 and 350 at the ground on pump gas. That is between 15 and 17lbs of boost. Using race fuel or E-85 you can go beyond that but for comparison using common gasoline 300 to 350 is about as good as it gets. That is close to double what these cars left the factory with so not too shabby.

As has already been said though - who cares what peak HP is - for driveability it is a lot more important to focus on how quick the turbo spools up and how flat the Tq curve is.

ChrisJ951

I agree with Josh. My first 951 with a vitesse stage 2 kit, exhaust, mild head work put 342 to the tires on pump gas at I believe 17 psi. That was the max I would push a 2.5 liter on pump fuel. On race fuel or E85 maybe 2 more psi. To run 23 psi on that block IMO is not safe.

JohnKoaWood

https://rennlist.com/forums/944-turb...ph-inside.html

I can say, I have driven this car, after everything was done, but before it went to this dyno sesion. It is downright fun, but also VERY demanding to drive.. much more on a basic setup and you are looking at BIG $$ for very little return.. not to mention the driveability and useability on the street is almost negligable for much mroe power or torque delivered!

Were he putting down more power or torque, he would need to do some additional modifications to not just the driveline, but the suspension / tires / handing to be able to drive the car!

And yes, I did put it sideways entering the highway at 70 mph (rolled into full boost in 4th gear)... should have seen the look on the Hyundai drivers face when I did it, then recovered, then merged into traffic!

As far as the GT3071R, it is a great turbo, sized very well to compliment these cars, and with supporting mods you will find yourself turning down the boost not uping it! What significant other mods are you considering, as I will ultimately be using the same turbo, and compared to the price of the turbo, many of the other mods can be rather pricey (you mentioned pause because of the $$ spent on the turbo, in reality this is just the tip of the iceberg!)

thingo

I'd say 450-500 crank horses(bhp) with that turbo and those mods, good fuel will give you more safety.You need a proper oil cooler for track work.

Penguinracer

John, I'm proposing to go with Motec standalone, N/A flowed head, higher lift cam, uprated fuel system, aftermarket intake & some headers.
The chassis will be uprated - Leda coilovers, Elephant Racing sphericals, Tarett bars, Big Blacks, Yoky A048Rs, KEP clutch, Spec F/W, Guard 50/80 etc.

I've been drip-feeding ithe parts collection for quite some time now.

JohnKoaWood

Might I suggest you consider a 16V S head / piston set as opposed to these.. the 16V head will make MUCH better use of the intake / headers (the available AM intakes will shift your "curve" to the right as they are short runner, large plenum setups, GREAT for top end.. not so much for street drive-ability IMHO, on an 8V anyway.. but both are required for a 16V setup).. although runner length has little affect ON boost, it kills the off boost behavior which is already anemic on these cars!

add in a slightly lightened crank, and perhaps a set of AM rods and you end up with a heavy breathing, fast revving, monster that at reasonable boost level will put down very respectable numbers in spite of remaining at the lowly 2.5L displacement..

Stand alone.. take your pick..

Clutch.. have you looked at southbend? VERY nice for the price...

This is all just alternatives... if you already have $$ invested in the direction you are headed stick to it.. sounds like it could be fun, and I am sure it will be a handful once completed!

schip43

+1 for South Bend if my Kep Spec crap has failed after 2 years and under 10,000 miles that's the direction I'm going. Stuff is chattery anyway. ( car won't go in gear, I'm still bitter...just saying!)

schip43

I don't see him saying anything about a lighter lower end? Stock pistons and rods for this project?

pole position

I strongly recommend meth injection, I prefer the Aquamist HFS3 due to the failsafe, you can up the boost and you can run a very aggressive ignition advance either 50/50 or 100 meth which will put you in the sweet spot on your turbo choice.

Reimu

I don't get why we don't see more meth/water injection around here. Is it because you have to refill it? You can make it where the stuff kicks in once you reach a certain psi, and you don't see full boost for a long duration when you think about it. Running more boost/timing with no downsides, even keeps your internals clean.

Also our wiper fluid tanks are pretty huge if you have the headlight nozzles..