Corvette Z06 Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Just wanted to drop a line and say thanks for all the excellent content on this site. I sold my PTE/TTE Miata a few years back and have been saving up for a C5Z for track use and finally found a good (but aesthetically rough) example that I don't feel too bad butchering up for use in NASA ST3 eventually. It's a 2003 Z with 111k miles and was sold to me as-is with no history. I took a bit of a gamble on it but the test drive showed it was actually well kept up and just needed some work for reliability improvements for street use. This is my first Chevy car (well first domestic car too) so I have been learning as I go and taking what I can find from this and other websites.

Since most of the modifications or work on this car were unknown besides the obvious bolt ons, I have torn down as much of the car to identify everything and modify as needed. I pulled and IDd the cam (COMP Cams XFI XE-R Camshafts 54-444-11), replaced the timing gear, went with an M295 oil pump to accommodate my 25 row oil cooler, installed an ATI damper, new accessories including a Turn 1 PS pump so I don't run into heat issues, Ron Davis radiator and DRM external oil cooler, poly mounts, flushed all fluids, stainless steel caliper pistons so to avoid a BBK for now, etc etc. It is running very lean at WOT which tells me the previous owner(s) didn't get this car properly tuned (and I found out the ECU is locked by a tuner so I had to get a flashed PCM) so it will be getting dyno tuned in a few days.

I am still in the process of finishing the base setup, with a Marrad ST3 driver seat, 315 Rival Ss on 18x10.5 Speedlines (square), probably the Van Steel JRI shocks and fr/r adjustable sways on stock Z06 springs for now. Once I get used to the car, I will do a full cage and dive further into suspension and aero tuning and if heat wrap around the exhaust doesn't keep the trans/diff temps down up here in CO, then definitely a trans/diff cooler. I learned from the Miata that heat management is the most important part of building a proper track car. Can't wait to see what this does!
 

Attachments

·
Z06 Tech Advisor
Joined
·
1,816 Posts
That CAM is radical, added to the elevation your at where there is less density and air with the LSA it has
expect issues at startup, idle and low end RPMs as in total vacuum will be low and MAP will be higher then PCM expects for each engine load.
Look at the specs below

The stock fuel injectors are only (unless they changed them) 28 lb/hr (stock) and will be too small for your location, high heat and racing and will never
get rich enough

Your really best in doing all this is check if that is stock clutch and also how old as it will not last long in racing trim

This engine makeup really requires a solid tune and that cannot be done on a static dyno drum, load bearing type better but really needs a full tune from startup, idle, decel, power enrichment and WOT which requires street driving and a good OBD-II scanner that records and then with that data swing the tune for that and then when your sure (cold and hot engine) all engine conditions are dialed in you then could if you want is check tune via a chassis dyno
If you do not get the proper fuel injectors and tune is not right expect engine internal issues

Assure valve springs and pushrods are correct for this build and race conditions and consider using water/Methanol injection to cool down charge to cylinders

Engine will lose maybe 15 plus MAP KPA (elevation) overall and at idle maybe 15 KPA loss at idle.
 

Attachments

·
Registered
Joined
·
4 Posts
Discussion Starter #4
Mike,

I appreciate the feedback! I actually got the inspection plate off the trans a week ago and found it has a fairly new LS7 clutch in it so it should last this year hopefully. I am in the process of finding larger injectors actually, this car definitely runs lean (not tuned correctly to begin with). My dyno session is on Tuesday so hopefully I can get it figured out by then and since they know this will be for road racing, will be tuning it to run on the rich end of the spectrum for NA motors. I will talk to them about load based tuning (on the street) once the base maps are figured out, since as of now, it's not driveable at WOT in it's current condition.

I have no idea what the previous owners were thinking when they put this cam in since they left the heads stock and didn't seem to get it running right. I may consider a smaller cam depending on how things go this year. It does have proper pushrods, dual valve springs, Ti retainers, etc that came with the cam package that is advertised online, so at least there is a plus with that. I just did the brass trunnions since they left the OEM rocker bearings in.
 

·
Z06 Tech Advisor
Joined
·
1,816 Posts
If you tune before putting in larger fuel injectors you'd be wasting your money
Contact fuelinjectorconnection
Can either buy higher flowing from them but best is to send them your stock injectors and they can clean, flow match and resize them to
the flow you want them to be up to 55 lb/hr
That way the specs on how GM had them designed will work well with GM calibration except changing what the injectors then are flowing

Tuning for WOT first is backwards, as how fuel and timing is going into power enrichment is commanded by PCM needs to be tuned first so that going into WOT
is commanded correctly.
At the least car has to be street driven with a recording OBD-II scanner and see how lean it is to know what size injectors should be used.
 

·
Moderator
Joined
·
21,337 Posts
I had basically the same cam in my 02 Z06 with AFR 205 heads and long tubes, no cats. I was running Delphi 36 lb injectors and logged duty cycle at max RPM was around 85%, so well within the safe range. And yes, they were scaled to the PCM using EFILive.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #7
Right on Mike, I actually found a set of flow matched 42# injectors (EV1, 42# at 3 bar) that should be well into the overkill range but I already talked to my tuner and should be able to work with them perfectly. They said they start with idle and part throttle tuning and only do WOT tuning towards the end of the day. I know it's not ideal but at least gets me to a point where the car is very driveable once they finish it up tomorrow and can improve from there. They have actually done a VERY similar setup (similar cam but he had head work done) the shop owner's C5Z who runs in NASA TT so I have some faith in their abilities. I do have the ability to data log so once they get the baseline ready, I can log and talk to them about any further adjustments. A good conservative tune that will favor the rich end of the spectrum will make me very happy.

If you tune before putting in larger fuel injectors you'd be wasting your money
Contact fuelinjectorconnection
Can either buy higher flowing from them but best is to send them your stock injectors and they can clean, flow match and resize them to
the flow you want them to be up to 55 lb/hr
That way the specs on how GM had them designed will work well with GM calibration except changing what the injectors then are flowing

Tuning for WOT first is backwards, as how fuel and timing is going into power enrichment is commanded by PCM needs to be tuned first so that going into WOT
is commanded correctly.
At the least car has to be street driven with a recording OBD-II scanner and see how lean it is to know what size injectors should be used.
 

·
Z06 Tech Advisor
Joined
·
1,816 Posts
Keep in mind those 42 lb/hr injectors at 3 bar (43 PSI) become 49 lb/hr at Corvettes 4 bar (58 PSI) rail pressure
That is about double of stock 28 lb.
At high elevation where there is less air those injectors will look even bigger

Also those injectors will require in tune all the values for the injector offset voltage values

If too rich will cause engine to be sluggish below WOT and PE.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #9
Yup, I did the calcs and they should be just a bit above 49#s assuming 58 psi fuel pressure. The shop is going to check my fuel pressure and do the scaling accordingly. It is not ideal but it's the best I could come up with in the time I had since I couldn't reschedule the dyno session within the next 2 months since they are so busy. Will update once I get the car back tonight or tomorrow!
 
1 - 10 of 10 Posts
Top