Dyno Pull yesterday (OBX Headers)

[Shrek]

Originally Posted by Marc Haibeck

Road racers should be aware that water pump cavitation occurs at 6100 rpm. Engine speed over 6100 rpm for more than a few seconds can overheat the engine.

Reducing the pump speed can raise the cavitation speed. A ZR-1 Products under drive water pump pulley will raise the cavitation speed to 6400 rpm. If an under drive water pump pulley is used with an ATI under drive crankshaft pulley the cavitation speed will increase to 7500 rpm. Use of the two pulleys may cause the engine to run hotter at idle with the AC on.

Thanks Marc! Shouldn't be a problem getting her to short shift for her first couple of track days. She's pretty good at using a shift light vs. having to read the tach. I'll start working on getting a set of pullies installed real soon.

[lbszr]

Originally Posted by Shrek

Headed to VIR next weekend for her first event!

Done so far!
Vansteel coilover package
Banski spherical/heim camber rods
Banski spherical/heim toe rods
Banski spherical/heim trailing arm rods
SPC spherical/heim front upper A-arms
Exotic Muscle adjustable sway bar end links
Del-A-Lum lower A-arm bushings
Poly sway bar bushings (w/front relocation block)
DRM camber rod brackets
DRM trailing arm brackets
Carbotech pads
DRM brake bias spring
Nitto NT-01
Hurst short throw shifter
C beam plates
Elite Engineering oil catch can
Block plenum/TB coolant flow
Removed secondary vac, actuators & blades
OBX headers
Removed secodary vac system
Haibeck reprogram for secondaries & headers
DRM Chassis bar
Kirkey seats
Crow harnesses
MOMO steering wheel and adapter (2 ohm resistor for airbag light)

What group do you run with at VIR? That track is on my list to try sometime. Looks like some great mods!

[Tyler Townsley]

I might as well interject a thought. While cavation could be a problem and is a known issue with the LT-5 I would contend that the bypass system is the root of the problem and much easier to solve.Mark is correct that the engine heat generated by rpms over 6100 rises faster than one in a racing environment can contend with, however this is due more to the fact the water ceases to flow through the radiator when the rpms pass 5800 or so rpms. In fact over 5800rpm the water is routed directly back into the block via the bypass which helps explain the dramitic increase in temp.

I do not have the skills to reengineer the bypass but I have tested in normal driving and at least one owner tested in racing the following.

1. Install a radiator that can flow at least 100 gpm.
2. Cut the thermo spring so that it is always open.
3. Block the bypass flow path with a plug.

I ran this configuration for over 50k miles with no overheating, in fact I had to block the radiator with cardboard in winter to have enough heat for the heater. This configuration was what Fastlane used in his car (it was he who told me this trick) and was tested by at least one roadracer with satisfactory results.

Tyler

[Shrek]

I'm all ears! I'll explore all options!!

[rhipsher]

Originally Posted by Shrek

After 2 months of thrashing on the track conversion, I finally got the car to my buddies shop for a track alighnment. While there, we strapped it down for a quick dyno pull to make sure all of the changes worked properly (OBX headers/Plenum coolant elim/Secondary vac elim)
Only had time for one quick pull, but I'm pleased with the numbers! 339.8 HP/342.2 TQ. That's compared to 309 HP/310 TQ in 2003 through the stock manifolds with Flowmaster cat back. The Flowmasters sound even better throught the headers!!!

***EDIT***OOPS.....I just went through all of my files on the car, and the first numbers were through the stock exhaust (NOT THE FLOWMASTER CAT BACK)***

Headed to VIR next weekend for her first event!

Done so far!
Vansteel coilover package
Banski spherical/heim camber rods
Banski spherical/heim toe rods
Banski spherical/heim trailing arm rods
SPC spherical/heim front upper A-arms
Exotic Muscle adjustable sway bar end links
Del-A-Lum lower A-arm bushings
Poly sway bar bushings (w/front relocation block)
DRM camber rod brackets
DRM trailing arm brackets
Carbotech pads
DRM brake bias spring
Nitto NT-01
Hurst short throw shifter
C beam plates
Elite Engineering oil catch can
Block plenum/TB coolant flow
Removed secondary vac, actuators & blades
OBX headers
Removed secodary vac system
Haibeck reprogram for secondaries & headers
DRM Chassis bar
Kirkey seats
Crow harnesses
MOMO steering wheel and adapter (2 ohm resistor for airbag light)

Although Im glad to see the increase in hp do to headers and by no means want to burst any bubbles but 309rwhp tells me there's a problem somewhere. At the very least a healthy stock LT5 should put down 325rwhp. Mine put down 340rwhp 335 ft with stock manifolds and just an old Borla. Mine once dynoed at 309 only because my drivers side cat decided to expload and exit the exuast and Corey took his foot off the gas. Corey said it was actually pretty awesome. A big flame shot out the muffler and honeycomb substrait hit the wall. Lol!

[Corbusa]

Ok as far as heat - would it not help if the water pump was ported in some way ( to create more flow)? what about using waterwetter ? Are there any part numbers for a higher flow radiator?
I too used to cut the spring (center) out of my thermostats and just use it as a restrictor to help slow the water down a little... it always helped..

[RHanselman]

Originally Posted by rhipsher

Although Im glad to see the increase in hp do to headers and by no means want to burst any bubbles but 309rwhp tells me there's a problem somewhere. At the very least a healthy stock LT5 should put down 325rwhp. Mine put down 340rwhp 335 ft with stock manifolds and just an old Borla. Mine once dynoed at 309 only because my drivers side cat decided to expload and exit the exuast and Corey took his foot off the gas. Corey said it was actually pretty awesome. A big flame shot out the muffler and honeycomb substrait hit the wall. Lol!

Yep, my 91 was about average, stock with B&B's and some light plenum porting by Aaron in the old days. It did 346 and 337.

This is from Marc's website:

Upgrade: '90-'92

Original equipment engine power 375

Low back pressure exhaust system +10

Performance engine calibration (chip) +10

Subtotal 395
Long Tube Headers +25
Subtotal 420
420x.85=357

So not too far off...

Cheers,
RH

[Paul Workman]

Shrek,

Asside from a (low?) 309 hp baseline, 30 hp gain seems about right compared to the results others have had for the same mods, as well as what Marc H's web site data suggests. That's a good thing, but it tends to support (in my mind anyway) that the baseline number may be even more indicative of something else that "ain't quaht raht" here.

For example, here is a bone stock 90 (except for a Borla cat-back exhaust) that pulled 339 rwhp - pretty close to what yours makes after headers, etc. THIS is what makes me wonder if there is a gremlin that needs to be rooted out in the base case, as your car responded very much in line with what others experience for the same mods.

Note: On the dyno runs (below) the A/F ratio was getting too lean - turned out the secondary fuel pump was not working - so the operator was cutting it off at around 6k rpm. And, note it was stock except for a Borla cat-back. (The resonator tubes diameter were something like 1-3/4": no resonance, but also "a bit" restrictive too.)

Shrek, I hope you don't think I'm being a "Debby Downer" or throwing cold water on your improvements. It is because the improvement value is typical that it brings attention to the fact the baseline and end results are not what is also typical, and there may be a reason - maybe even a simple fix - for it.

For example, Dom discovered the secondary throttle plates in his TB weren't opening fully when the accellerator was floored. A simple adjustment and voila! Same thing happened on my wife's C3.

I'm just sayin, 20+ hp is 20+ hp. And, hell...guys spend $300-$400 to pick up 5 hp from porting the TB! So, I'll shut up about it now, but I just thought it might be worth a look. Could be dyno error too, for that matter.

Good luck!

P.

PS: I just noticed something... The new torque number is higher than my baseline number, but the hp is not. Is the torque/power curve dropping off suddenly above 6000 rpm or was the run cut off prematurely? Any chance we could see the dyno sheets - before and after??? That might be the answer to this question. If it is, then we'll know.

[Shrek]

Not a problem Paul. There could have easily been a problem with the motor way back then. My guess would be injectors! I was always a little bummed about the 309, because the other two 91's that day pulled high teens and low 20's. But the car always ran smooth and felt like good power for a weekend cruiser for the wife. That was until the injectors caused it to start bucking and missing last year. I put in a set of FIC injectors and could tell right away that we had more power than before but never got it to the dyno to confirm my butt dyno. My guess is we could probably get more power now with a custom tune. It was definitely running a tad rich on this tune from Marc, but since she probably wouldn't notice the difference, I'm going to play it safe and let her have at it like it is.

I'll get a copy of each dyno posted up.

***EDIT*** Here are the sheets!

2003



2012

[Shrek]

Originally Posted by lbszr

What group do you run with at VIR? That track is on my list to try sometime. Looks like some great mods!

She's going to run with the NASA group first, then we'll branch out to some other clubs. Even though she has many, many laps on track with the NCCC, we're going to start her off in group one until she learns to play nice with other cars on the track.