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Other than stocking up on transmissions and installing a transmission oil cooler, the other progress items are super bearings in the torque tube and a new boost pipe Y.
The new boost pipe Y is kind of interesting. Recall that we blew completely out of the range of the underlying stock Bosch MAF sensor. It flatlines at some air flow level, where the flatline point is dependent on temperature, etc. This means that no very high power 928 is tunable with the stock MAF sensor, modified or not. JDS’s super MAF compresses the voltage to get around a LH limitation and is a good solution for medium power cars, but there’s not much that anyone can do to the underlying sensor going out of range. One option would have been manufacturing a larger housing, but the stock housing is large enough from air flow perspective and changing that MAF housing size while retaining the stock intake manifold would have been a project.
Because of these considerations, John decided to go dual HPX-E MAFs which then are processed into a single MAF voltage. This in turn allowed him to rework the piping to flow better. The extra inches freed up by the removed stock MAF housing allow for a gentle Y pipe that is made look like an air box from the top::
This is on the lowest boost setting that the system can produce, just shaking the car down. The tach reads maybe 500 too much over 6000 rpm, so it's more of a decoration. Any ideas how to calibrate the tachometer to given an accurate reading?
I like the 15 extra mph of wheel spin at the top of 2nd gear. That’s going to be a hairy ride when you turn the boost up.
With a slow ramp rate on a dyno, the torque curve is almost exactly flat 3500-6000 rpm. The reason why it spins wheels in low gears and high rpms is the turbos catching up.
Very clean install. Best of luck with it. A suggestion: those worm-gear hose clamps will not be up to the task of holding much boost pressure. Suggest you convert those to T-bolt clamps. Again, looks great so far - keep going!
Very clean install. Best of luck with it. A suggestion: those worm-gear hose clamps will not be up to the task of holding much boost pressure. Suggest you convert those to T-bolt clamps. Again, looks great so far - keep going!
Which clamps specifically do you mean?
Given the pipe diameter and the pipe lip shape, the current boost pipe clamps in the most recent photos (around the new MAFs) would hold up much more than what they'll see.
With the stock MAF housing in place, those larger clamps that connected the stock MAF housing to the boost box were a problem. That problem went away with the box-pipe-y rigidly bolted to the engine with those brackets. The forces are much smaller now on the clamp and you string up the whole engine from the ceiling from the box-pipe-y.
The situation in which there's some clamping uncertainty is when you have a large aluminum alloy pipe with clamped to a hose with a steel clamp. The thermal expansion differences there can cause the steel clamp to cut into the hose over the heat cycles. The best solution that I know of is the "Breeze" constant-torque clamp. There's one such spot in the system currently.
Here's an example of what a too sharp edge on a large aluminum pipe does to a rubber boot when clamped in place with a standard steel clamp:
Any of the following will help. First, create a supporting structure that holds the two ends together. Stock MAF boot clamps have those steel strips doing something like that, and John's boost box is now rigidly bolted to the engine. Second, radius the lip on the pipe such that there's no sharp edge that can cut into the boot. Third, match the thermal expansion of the pipe and the clamp. Fourth, use "Breeze" constant torque clamps, such as these here: https://www.normagroup.com/norma.nsf/res/Breeze%20Constant-Torque%C2%AE.pdf/$file/Breeze%20Constant-Torque%C2%AE.pdf. Fifth, change the material of the boot.
07-21-2019, 10:57 AM
That’s going to be a hairy ride when you turn the boost up.
