924Board.org

[Racing]

Hmmm....
So,the engine is back in the car.
Just started her up,and have put a couple of miles on her so far.
So far so good,and the major difference is the throttle response.
In fact to a level that one wouldn´t think it´s the same engine.
At this moment run fixed timing @25 degreees,and as she´s just started up with measily amounts of boost-just to get a feel for her.
Haven´t even connected the add on injectors yet.
had to turn the TB body upside down as the throttle linkage hit the hood on trial assy.
Now comes the fun part!! To make the little yellow POS roar!! Need to tweak it..

None the less.
Was is worth it?
Without a doubt!!!!
Now i feel confident that the TB isn´t the hindering culprit anymore.

..and without further delay;

..and

[Racing]

Had to return my anodized adjustable cam sprocket btw.
Seemed it had a hardening fault as it got chewed up by the belt.
As i install the new one i´ll most likely make up some new tubing from the cooler to the TB out of aluminium too.

[924RACR]

You rock! Very cool! Can't wait to make my own...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Joes924Racer]

Thats nice ..so what are the extra injectors and what about the plumbing
to the fuel dizzy..Hey racer will one of those help a na 924 like mine.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Racing]

Joe.
Simply put the OEM fuel dist will deliver fuel ´til the 240hp region-and that´s it.
When you pass those levels the culprit of getting more fuel in-for instance when you run a bigger compressor and IC aso as i do-is easiest solved by some sort of so called "piggy back" computer.
In this case i run an ad on controller about as old as the car.
One called Microdynamics PIC 5.
Thing is that it´s more or less just a rev dependant on/off kind of deal.
On the other hand that isn´t as bad as it sounds as it comes into play first when i reach approx 0,8 bars of boost-and in that scenario the fuel input needed from there on out is fairly linear-which makes the PIC work fairly ok.
I bought mine used for the equiv of 50 bux and the injectors-which for the record are VERY large-were something i had laying around the shop since an earlier project on a vette.

Building a one off intake for an NA would be questionable at best IMO.
The point is that the OEM head lacks in so many several ways that the head needs to be adressed first.
After that tho..sky´s the limit.

As you can gather making sheetmetal intakes isn´t as hard as most people think.
The software needed to do the basic calculations are even freeware on the net i believe.
Can´t remember the URL from the top of my head,but if you feel the need mail me at hrt692@hotmail.com and i´ll be happy to send you a copy.



RACR.
I take a deep bow!
Thanx for the comment.

[Racing]

On the subject.
What i´m gonna do the next couple of days is to tune the SOB.
To do this i´ve got a wide band O2 installed as well as a boost gauge for the intake and exhaust both.
Then i run a pyrometer(thermometer) to see what´s going on-and in situ adjust accordingly.
Have already noticed the need for different settings then before.

[Joes924Racer]

Ok thats pretty nice. I hope your around when I get a turbo
thats all I got to say.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[J1NX3D]

that looks pretty mean!!

so please tell me- im pretty green to this kind of mod. how and why does doing this work? what does it improve over stock? have you been driving it abit more and if so does it leave u any more impressions than better throttle response?
Cheers!!
_________________
'86 944

[Tigger937]

WOW..............a homebrew GT-R. Don't forget the chute!!!

[Racing]

J1
The deal with the 931 is as with any turbo car really.
To minimize pressure drops in the system as best as you can.
One PD point seems to be the stock 79 throttle body-at least the general consensus seems to be that-which i by now how found to be very true.
What i can tell you from a practical standpoint after driving the SOB for the last couple of days is that the 70mm TB most def makes the engine behave like nothing before.
Throttle response and tip in is GREATLY improved.It simply picks up faster and better.

As far as total power diff.No idea yet.Still tuning.
Installed the exhaust temp pyro today.Shows approx 700 deg at full throttle and boost so far with a wideband AF of 12,6.
Gonna narrow that down considerably over the next couple of weeks i believe.
Shows i´m safe so far,on the other hand we´re still limiting boost as of yet until she´s had a chance to "break in".
1 bar is it at the moment.
Runs stronger on that amount than before tho.No doubt there.

Next mod up is to enlarge the outlet of the CIS housing.
..another area of sure fire pressure drop.
OEM the outlet is a mere 52mm.
Gonna make that 3"...
Likewise i´m still waiting for my new adjustable cam sprocket.
Old one had a hardening flaw and was chewed up way to fast by the belt.

[-nick]

I'm curious what sort of template you used to decide on the plenum volume and runner length?

PS- since the TB is upside down, does that mean you accelerate when you lift and slow down when you mash the pedal

Lookin' good though!

-nick

[Racing]

Nick.
What i did was to measure intake volume and average taper as well as diameter.
Then i put those numbers into some software that calculated the whole deal for peak at 7 grand based on Helmholtz third wave.
That netted me runner lenght-total.
After that i did the same for plenum volume-which amounted to about the same thing.
Anyways.
Runners are 40mm diameter and the plenum based on a 120mm pipe.

Actual machining was done through use of the intake gaskets and the gasket for the throttle body.

[Alex Roy]

I just may have to make one of these myself. Looks really straight forward. What were your dimensions for the runners and plenum materials?

[Racing]

Throttle body= Alfa 3 liter
Runners=40mm*1,5mm
Plenum=120mm*2,5mm
Endplates=4mm

[Alex Roy]

what are the cut lengths of the pieces used? I had gathered that they were 40mm diameter runners and 120mm plenum from your previous posts.

Thanks for the info