Dennis K

Six months and 5000 miles after the first start of the motor, it’s time for an update. From the first time this motor went WOT, we knew it was strong. We weren’t sure exactly how strong, but if you can get Bill Ball to cry “uncle” during an acceleration run, chances are good you have a beast on your hands. Now we’ve been able quantify just how strong this thing is.

Recapping the specs, this is a stock displacement engine with stock 5.0L ’91 GT pistons, connecting rods and crankshaft. The rotating assembly was re-balanced. The ’88 S4 heads have the stock S4 intake and exhaust valves, no porting or polishing. The heads have been shaved 0.020”. The intake manifold is stock and does not even have spacers. The airbox is stock. A post with all the specs for this motor and a few pics of build is here.

Since the main goal for this engine was reliability during track use, there has been a lot of work that has gone into the oiling system. The crank has been drilled, an I-J crank scraper kit has been installed and the oil pan has been spaced 3/8” down. If you want to learn more about the drilled crank, I wrote a post about it last year here.

Essentially, the cams and the headers are the two major performance mods. The intake and exhaust cams are from ’85-’86 S3 32V engine and have been modified by Elgin Cams. The driver’s side exhaust cam has been modified to fit the S4 heads by extending the bearing area at the front cam cap. All the cams have been reground by Elgin w/ a smaller base circle for greater duration and lift. The base circle difference is slight enough that no modifications were needed for the lifters and no lash caps were needed for the valves. We took great care to make sure these cams were timed accurately, as you can see here.

This type of approach was typical throughout the build. Jim Morton had the Cam Doctor files with the exact dimensions for these cam lobes. He was able to precisely determine the dynamic compression ratio and even model the airflow for the engine. I have dozens of Excel workheets where we measured & calculated things like bearing clearances, fuel injector sizing, cam timing, piston speeds, etc. We never took any piece of data for granted, whether it came from a sensor, from the internet or from a vendor. We tried to confirm everything as much as possible so we could make informed decisions as we went along.

Since the engine was built, we have been using Jim’s Sharktuner to bring the engine into tune. We’ve been learning together how to use this powerful tool (which has generated yet another raft of Excel worksheets). We started out doing full throttle runs on the freeway, trying to gather data and make appropriate adjustments to the various fuel maps. We found out quickly that the throttle position sensor was bad and then later that the old re-installed MAF was faulty.

As of late we have been using the Mustang Dyno at Holleran’s Performance in Pinole, CA to do our tuning. Over the course of 40+ dyno runs over three days, we’ve been able to log data via the Sharktuner and a Techedge wideband O2 box. We’ve spent a lot of time sorting through all the data to come up with revisions to the fuel & ignition maps. Once we had the air:fuel ratios controlled throughout the rev range, we have tested various AFR's, flappy actuation rpms and ignition timing mods.

So here are the results from our latest dyno session (these numbers are at the rear wheels):


Here's a comparison of the engine in its untuned state (first dyno run, first day) to where it is now:


Here's one of the Excel charts I spoke of, showing the AFR & ignition advance:


And here is a video I made from our second dyno day. (We’ve gained a little hp & tq since then.)


To say I’m overjoyed with this result is an understatement. I can honestly say I’ve enjoyed every minute of this build. (aside maybe from paint stripping the intake manifold & cam covers, that kind of sucked) Seeing these numbers has made everything absolutely worth it. I’ve had two months to digest the data and I still can’t believe it. Even with this level of performance, there is no compromise in driveability. All of these runs were made on plain CA 91 octane gas. The car idles completely normally at the stock 928GT idle speed of 775 rpm. It even passed a CA smog check a few months ago with a slightly different exhaust:


In closing I have to thank my friends Jim Morton & Bill Ball once again. The genesis of this project was the seizing of two motors in two track days. I was seriously considering moving on to racing Spec Miatas but Jim & Bill reeled me back from the abyss and offered me their help to build this motor. They’ve been good to their word and have gone far beyond any reasonable expectation of help. Jim has spent an incredible amount of time to engineer the result you see here. Bill has been available at every single opportunity to work on this motor. His only questions are “where and when?”

We’re out of fuel and air to make any more hp improvements . . . for now. The story isn’t over yet though. Currently, we’re prepping the car for a track day. In a few weeks I’ll be able to post some video of this motor being exercised at Thunderhill.

hacker-pschorr

Wow, that is a strong motor!! Nice work.

What type of exahust is on this motor? I didn't see any pics on the web site.

IcemanG17

Dennis
WOW.......very impressive......on a stock-ish motor.....new cams and a perfect tune.....

What is your AFR set too? It looks like around 13.0-12.5 up top? Far better than my lousy 11.2 on my track shark.....but easy to fix with a bit of tuning.....

Dennis K

Thanks Hacker. Exhaust consists of Devek L2 headers, long Y-pipe to single 3.5" w/ two Borla XR-1's in series.

Thanks Brian. AFR is ~13.0.

RyanPerrella

WOW

so i am seeing 387 HP at the wheels?

On a 5L block with modified cams and headers and full exhaust, a drilled crank, pan spacer and windage crank scraper.

WOW

Im sorry, I just dont understand how you got that much power out of those mods? If thats even remotely repeatable (the engine stats on another motor) then i think i just learned to live witht he 5.0L block and will forgoe any hugely expensive stroker engine ideas.

WOW

RyanPerrella

whats the crank drilling cost? and where is Taylor located, The shop that does the work on the crank?

Mako 928

Dennis
Congrats. on this very well thought out and planned build, and congrats. to your team ( Jim/bill).Did you use the stock fuel injectors?

Jim Morton

Adding in $0.02...

What makes this story quite cool to me beyond the tech stuff is the personal story.

Prior to assisting on this engine, I had bought my GTS only a few months earlier. I had built a few varied 928 engines in the past and only knew Dennis through a mutual friend. I would see Dennis at the ocasional group gathering assocaited with either Rennlist or local track guys. Also around this same time I had just met Bill with his offer to assist me with my GTS clutch replacement. What happened next was a phone call from Dennis' and my mutual friend with a request to assist Dennis get his engine seized car home from Thunderhill raceway. This was the spring of 2007...

Since that phone call, a lot has happened. Most important to me is the building of two great friendships with Dennis and Bill. I have gotten to know these two well beyond the turning of wrenches on our 928's. While building and tuning this engine, both of these guys became regular attendees at my family's Wednesday night dinners. What started out as a technical assist and curiosity became something very social. As Dennis' motor heads to the track, my family's Wednesday dinners will be less crowded and void of all the fun talk of this and that 928. I will miss the Wednesday night fun.

What lies ahead is fun of a different sort. I still have my own 6.1 liter engine to complete and need to consider what if any opportunities exist from the knowledge gained from working through all the details of Dennis' 4V engine. There's also the very cool tools I acquired along the way.

If anyone is curious in more detail than what has been posted, please PM me for more detail. There's lots of good stuff surrounding these 4V engines and tuning them.

To Dennis.... THANKS and ENJOY !!!

AO

Impressive! Way to milk that motor!

hacker-pschorr

Thanks for sharing.

Projects like this is what makes the 928 so much fun. Like Shane's project from April, the car takes a back seat to the get together portion of these builds.

Keep us posted on your car!!!
I'm working with Todd on a 16V track motor for my 79. The only detail we've set in stone is the use of a 928 engine......lots of work to do.

Bill Ball

Taylor Engine, Whittier, CA. IIRC, it was about $700.
http://www.taylorengine.com/

slate blue

That is way impressive, nice power curve too, better than stock which is saying something given it is producing much more power than standard! Very well done, you have raised the bar.

Greg

BC

Taylor is what I mentioned in my PM Ryan.

Jim bailey - 928 International

Looks like the crank scraper and lowered sump may have reduced the power loss from churning the oil. The modified 85-86 cams sure seems like the hot ticket !! Now IF we only could get KIBORT to LISTEN Great job .... Glad they saved you from the Spec Miata series that is too much like a rolling destruction derby

RyanPerrella

How much more lift comes out of the S3 cams with the reduced base circle over GT cams?

we are talking like 1mm additional lift here right?