raleighBahn

I'm in the early stages of planning some upgrades, and the goal will be to match the weight-to-power (or power-to-weight) of the Cayman S family, from 987.1 to present. I think it's an achievable goal without major modifications, and is interesting as the Cayman now occupies the paddocks where the 951 population really found a home.

Forgive any errors in the table below (my own notes), but it is remarkable how close in weight these cars are to the 88S/89 951. What is even more ironic is the displacement and weight between the 951 and the 718 Cayman S - (2479 cc vs 2497cc, 2998lbs vs 2988lbs).



First things first - I'd like to baseline my car (A-tune, 3bar, LBE, K26/88, 3" Fabspeed) where it stands today. I've not dyno'd a car before, so open to advice on which dyno to use (dynojet, mustang, etc) and any other advice for getting a good reading. I have a new Tial 38 on the shelf and an EBC already wired in my car, so that would be a second dyno session. Given that I still have AFM and the K26/8, the end result (over time) could produce a good set of dynos for relative comparison if I add a MAF, turbo, etc.

V2Rocket

i like the new 718 as a "target" as well.

2.5L DOHC...
102x76mm borexstroke
9.5:1 compression
350hp @ 1.1bar

seems like a somewhat easy "match" for a 944 to make. it's going to be my "target" whenever i get around to building my engine.
i mean think about it...take a 944S engine, drop the CR a bit, hit it with 1 bar boost...350 should be "easy."


http://press.porsche.com/newyorkauto...ifications.pdf

raleighBahn

Thanks and I agree. I'm going to be doing some upgrades anyway, might as well have some fun with it. I don't want to set a goal that is overly ambitious, and to borrow a term from turbo-speak, out of the efficiency range of the stock 951 itself.

V2Rocket

your real question should be..."will that VGT turbo fit a 951"

raleighBahn

Ha! No thanks. This is going to be bolt-on city, 93 octane gas. We'll see how far the DP wastegate, MAF, injectors, and possibly turbo take it. From there, the car has to lose weight. However I will make no modifcations to the Driver Weight as that is unreasonable

Interested to hear dyno type recommendations, as well as what I should assume the 951 driveline loss is.

odonnell

If you lighten the car to 2600 lbs, and can get to 325hp (not hard), you're at 8:1 weight/power

Or, 340hp and you only have to shave down a little under 100 lbs to match the 718. By removing the spare tire, maybe some interior lightening, a FG rear bumper, and some other small things you should be a good way there.

raleighBahn

From what I have seen anecdotally, the Caymans have about 10% driveline loss between their published horsepower and their measured rear wheel horsepower. Meaning, for the 718's 350HP, a 10% driveline loss (35) puts it in the neighborhood of 315 rwhp - something that should be achievable here.

V2Rocket

FWIW, I once parted out a 951 race engine with these specs before i got it...

steel-sleeved block, 101.6mm bore + stock stroke (2.55L)
8:1 compression
stock 951 head (very light casting cleanup in the ports, something you could do with a sanding drum in a few minutes)
"supposedly" had some kind of cam, maybe milledge? but nothing extreme

with a Vitesse "stage 3R" turbo/tune etc bolted on it made 360+whp at 16.5 psi



so with a good turbo, tune, and maybe a cam...you should be most of the way there...

raleighBahn

Yes indeed. And the Cayman numbers in the table are FWHP, so in reality I need to hit 315 RWHP as I assume they lose 35 HP at the wheels. I combed through stock Cayman S dynos and most agree 10% driveline loss for their cars. I haven't yet seen a stock 718 dyno, so that is TBD. 10% seemed to be the case for the previous generations.

V2Rocket

for 944 cars the commonly thrown-out number is 15% loss.
in my dyno testing on my NA that seemed to pan out too so i'd say its safe to use as your "rough estimate"

raleighBahn

To keep this interesting, I'll try and get some Caymans to whatever dyno I use. I have a PCA friend with a 2011 Cayman S 6sp. Maybe can find a 718 as well.

rlm328

As far as dynos go you just need to know how they are measuring HP. Whether it measures a load or inertia, and then adjust your numbers accordingly. Inertia will give you the RWHP, I believe on the load dynos you need to add the load back in to get your RWHP. The transaxle is more efficient than a transmission / differential set up, so I divide the RWHP by .87 to get BHP.

raleighBahn

Wastegate removed... Tial 38 set to go in. For whatever reason, I thought removal would be difficult. Very easy - let some PB blaster set over night, used socket extensions, and finally a soft mallet to unseat it from the exhaust. Tial is opposite of the stock wastegate, so will re-orient correctly.

raleighBahn

Ok - have nice new crush ring, Fejjj adapters, Stage 8 locking fasteners, except for two which I needed to drill for safety wire. Thanks to URG8RB8 whose post gave me the idea for the excellent Stage 8 product.

raleighBahn

Alright, the cycling valve is now bypassed everything is buttoned up on top. Last year I installed an AEM TruBoost and have the solenoid hooked in at the cruise control servo, so the plumbing was mostly done. Last step is to mount the wastegate and then we'll see what we get. My Tial 38 has a .5 bar (7.25 psi) spring, and the goal is to use the EBC in dual port mode to hold 14-15 psi.