RyanPerrella

James,

I think the auto's are dogs compared with the manuals. There does seem to be a pretty big difference in RW numbers between auto 928's and manual ones. The rogerbox does seem to eat quite a few extra ponys.

Tom. M

We are most used to seeing dynojet numbers..so referencing Jim's numbers to those really doesn't apply. Seems that dynojet's aren't being used lately for whatever reason...so spreading numbers around and comparing just can't be done. However, in the long run, Jim going back to the same dyno after his mods...will yield good comparisons for him.

These GTS curves look really nice, and very typical shape as I've seen on the dynojets curves from the few GTS's Ive seen run.. Look forward to seeing more data..
What mods are you planning Jim?

Jim Morton

Tom:

There are various stages in the works.

First up is the install the same cams as installed in Dennis Kao's engine and tune things in.

Second is to complete a 6.1 liter engine. The 6.1 engine will be intially tuned on an engine dyno, then dropped into the car. The 6.1 is still 6+ months away.

Possibly third is to build a 5.2-5.3 engine to experiment around maximizing power / liter numbers for the 982 4V heads, normally aspirated. I've been collecting cores to work on this new idea, but all this stuff is $$$ out of pocket, so if I get to finishing stage 2, I'm sure I'll be very happy.

BC

Engine Dyno? Sounds fun. Is that alot of $$ to do?

mark kibort

Looks like most S4 , or flappy equiped 928 engine dynos.

Here is the holbert dyno runs . dotted line would be with the flappy working.
second curve is with it working. dips at the 3700rpm range where it opens.

mk

jorj7

Looks good Jim, I can't wait to see how it improves as you build up this one. Also look forward to
seeing how my car does on those rollers.

mark kibort

As you say, there is a range of HP that you will see with any engine design.

Ive personally tested 3 911s )84s, all with 210rwhp, when the factory rating was only 220.

Most of all of the S4s are in the 270ish range. The holbert car was basically GT. without a cat, it ran 290rwhp, and 335rwhp as a max with a bunch of stuff missing, vents in the airbox, coding plug corrected, headers, 3.5"pipe, and new tune up stuff.

A dynojet is abolutely accurate. you either moves the drums at an acceleration rate over a speed range, or you dont. you cant fool it. rolling friction is not a huge variant either. I think i measured the total coast down HP as being 20hp at 150mph down to 10hp when it got below 80mph on the roller test. This doesnt take into account gear ratio efficiency losses. strap down forces could be a factor, but the last time i was at the dyno, i went a little looser than the prior run and it didnt make any diff. So, unless the drums have been lightened, the rolling dyno is absolute. Rpm sensing, and HP calculation are calculator functions. Its like questioning a digital stop watch.

Now, the SAE correlations can be tweaked, so thats why I always get an actual dyno run with my SAE plots.

mk

RyanPerrella

Jim,

Ive been curious, how do you get to 6.1L?

Are you using a 95mm crank and some slightly larger piston?

or are you keeping the 85.9mm GTS crank and boring the block out?

or some other combination?

Bill Ball

Nice, Jim! Let me know when the work starts!

mark kibort

I think the devek strokers were the 6L engines. they only used the devek stroker crank for the displacement change. that way, the bores didnt have to be touched. I cant remember, but didnt they use the stock S4 piston, but the skirts trimmed off and a custom rod which you would have to use anyway?

The slight bore increase to 103 (968 pistons or equiv) from 100 gave the extra 400cc to make the 6.4 liter we see around here.

Now, using the 968 piston on a GTS would be interesting. now you get just an overbore. Still a little work to find custom rods to make them fit, or some custom pistons that have the same pin placement as the GTS. Has anyone done this?

mk

RyanPerrella

Yeah i am looking at some combinations to bump the GTS displacement a bit. I would like to keep one component stock (just to reduce the cost) by component i mean that if its stroked i need a new crank, most likely rods too and pistons. If its bored i need new pistons , possibly new rods and work to the block of course.

I would love to find some combination where i could change only 2 components but i cant see how i could accomplish that. Boring anything you need block work and pistons, stroking you need new crank and new rods or crank and new pistons.

I think GTS pistons need attention anyway, i think early GTS rods need attention. Im looking for an outside the box solution to bumping displacement on a budget. Otherwise i would just drill some oil relief holes in the pistons, possibly deepen the valve cutouts for higher lift cam and replace the rods with the later 2R rods and live with 5.4L. Which if i follow the Bay area guys tuning practices think can make 400plus RWHP with some intake, exhaust and cam modifications and a ton of dyno time.

Bill Ball

No intake changes so far and with Jim's processs of using the Sharktuner, not a lot of dyno time was needed.

RyanPerrella

even better to hear about not a lot of dyno time! Dyno's are expensive!

so a reasonable person would think that with 5.4L and not just 5.0 that even better results could be attained then then 387.

I would plan on doing intake work, to the manifold itself and to the filtering system and produce something like the blackbird setup, or preferably buy one if they ever become available. Add some headers, full exhaust and buy myself a shark tuner and a wideband o2 and just drive a ton and work out the bugs.

i think 400 is attainable if similar things are done, i would just have 400cc extra so possibly another 30 HP but probably another 40 plus ft/lbs of torque

I would love to see what Jim does after this simple baseline with cams, exhaust and all the simple bolt on stuff. Im curious to see what kind of maximum you get get out of a stock GTS long block with some go fast goodies.

GregBBRD

Yes, that's it! Keep thinking that Porsche left a hundred horsepower, on the table, from only regrinding the cams a bit and increasing the ignition timing.

mark kibort

Thats what i thought you were talking about. My first pass at a bigger displacement S4 was to use a used GTS crank and do the bore for the 968pistons. I thought it was going to be cheaper, even with a deal on a GTS crank, but ended up finding out that the new rods, piston mods, were going to take some work. the differene in the stroker crank vs gts crank, was not that much of a deal. why shave $1000 off a $7000 DIY project, to loose 400ccs.

Now, if you already have a GTS, it becomes a little more compeling because you already have the crank. rods and pistons will have to be done. You might be able to re-use the GTS rods (which ive heard are good and bad) and just buy pistons, while boring out the block to 103mm. Now, you need 968pistons, so you dont have to worry about the coating and fuss with ring packages which becomes another science with a nicasil block. Just have it bored and alusil treated as many of us have done. If this is the way, then you need to find a custom rod that works. You are still in it for rods, pistons and block boring. (saving the crank purchase) I have a feeling that the lower stroke and the wide bore could buy some good performance up top. we got near 40hp for this kind of bore change with scots 97mm going to 100m with no other changes. I bet most of the stroker gains that we see are due to the bore increase. the 6liter, stroker only, make near 300rwhp (up from 268rwhp) with no other engine mods (and torque in the 370 range). Yet the 6.5 liter can make near 370rwhp with few mods, and torque in the 400 range.

Tweak a GTS with the hopped up GT cams, and some dyno tune, you would probably have a pretty hot set up.

mk