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In that thread, you will find we sought to confirm that putting a stock 5.0L intake on a 6.5L stroker motor was holding it back, and that HP could be gained from an intake upgrade.
A stock intake, and extrude-honed intake, and an all-new intake were all dyno tested on the same 6.5L motor having made no other changes.
The difference between the stock intake and our 654 Intake was 154 HP.
Here are a few pics of that intake and the dyno chart that compared it and the stock manifold.
The hand-made intake manifold found us more than 150 HP on the same motor over the stock 5.0 manifold - so it certainly proved out the theory that the big 6.5L motors were being choked off by the 5.0L intake.
On average, we build about four of these 6.5 motors per year for customers, so its obvious we would benefit from having an intake manifold for them.
There were two things about the manifold that we made for Catorce's engine that we wanted to change:
His manifold will not fit under the hood of a 928. It tucks under at the rear, but sticks out of the hood at the front. Catorce was fine with that - even likes it - but for me to sell more of these, I know other customers will favor a stealth approach that keeps everything out of sight under the hood.
Price and Lead-time: Catorce's intake was a hand-made one-of build. Translate to very expensive. It also had a long, long lead time. In order to make this a popular option for my customers, I need to bring costs and the lead-time to get one down.
To that end, we have begun our next model. Pics below are of our new intake manifold flanges cut from 6061 T6 billet. To these, the runners will be added, the plenum, and the throttle body plates as before. Only this time, the whole package will fit under the hood of a 928 as mentioned before. I plan to make about 6 at a time, which will bring the costs down significantly.
Now that I have workable flanges in hand, I will start the mock-up I need to make patterns for the plenum sides and floor so I can have some of these bits production-made to lower their costs.
What can a stock engine do with these manifold? Isn't the 5.0 l also choked off by the intake?
No one knows what a 5.0 motor will do with this manifold. I will be trying it on my 5.0L 928 GT to find out. We did discover 6 HP with our before-and-after intake manifold spacers tests, but that doesn't speak for the rest of the intake or the throttle body.
I believe there will be some gains because the Porsche engineers were tuning for the touring car market; bottom end torque, smooth throttle response, cruising in the mid-range.
In contrast, we will designing for more mid and top end performance, so I expect we should be able to uncover some upper-end HP if only because of the re-mapping of the power band that we will be doing.
If we find and alleviate any restrictions along the way, that will just be gravy.
Because I will be using the same throttle body diameter and intake runner length, diameter and taper, I expect the dyno chart will look very much like the one I posted at the top of this thread.
The difference will be in the plenum, where I will reshape it to fit under the hood. The difference in plenum volume will be slight, so I do not expect it to have a large impact on the outcome.
Those are pretty beefy. If I ever ran a set of mine again, I would probably bulk them up a bit more too to help with potential warping when welding. Just as a friendly suggestion from my development, check that front passenger runner location. You may have a clearance problem with the water bridge (although it can be ground slightly on the back side for clearance). I am assuming you also used the 22.5deg entry angle, which does help, but it still gets darn close right there. Its just worth thinking about at this stage.
I also found that locating the mounting points for the fuel rails on the lower flanges made the overall fit much better. I did find some tolerance issues trying to re-use the factory fuel rails with the machined lowers. I speculate that the oversized lower o-ring on factory injectors were used to help seal with the inexact tolerances of the brazed fuel rails and high-magnesium content intake casting.
All good points Hans, and well in hand. This is the fourth intake manifold I have developed for the 928, and I am keenly aware of the interference issues with the block off plates and the water bridge.
The thickness of the flange base is a carry-over from when we used this CAD file to make intake runners in GF Nylon for my race car. We went thick to add rigidity, the nylon needed some help there.
04-16-2018, 01:47 PM
The next Intake Manifold for our 6.5 stroker motors
