I just recently decided to order a Cosworth Plenum. The purpose behind my buying the plenum was NOT for any type of performance gain.**** I want to make that abundantly clear. *** I already run a Crawford Upper Plenum which has enhanced the airflow capabilities for my set-up and has been working well over the years. But, on the outside chance that there was a gain in hp, I wouldn't be upset either.
Here is my starting point. Crawford Plenum that I had polished (just a little weathered with vented hood):



However, with the more recent upgrades (bigger Injectors) space has become somewhat of a rarity and something has got to give. I am using 1200cc injectors which are not the biggest ones available, but they are significantly taller than stock sized injectors. This upgrade forced me to utilize the Cosworth Plenum spacer (made by Injected Performance - NOT Cosworth) seen below to clear the now taller injectors:



This inherently pushed my already taller plenum up even further to the point where the CF hood actually rests on it when closed. The CF hood is actually stressed and difficult to close as a result.

I installed the Cosworth plenum after consulting with my tuner (Larry @ SP) and I was advised that the ProEFI would be able to compensate for airflow changes upwards of around 15% in either direction (give or take). No problem, so I went ahead and purchased the Cosworth and installed it. See below.





After installing it, I attempted to start the car and discovered that it was running extremely rich!!! The AFR at idle went directly from 14.0 to 10 - 10.5 and stayed there. The car obviously doesn't like running that rich unnecessarily and still works, but will leave a cloud of unburnt fuel at every stop sign/light. Apparently, the Cosworth doesn't flow as easily as the stock lower plenum at idle. Larry is suggesting the problem may involve the velocity stacks and the inherent design. It may not be a bad plenum, just will need some re-tuning to work.

The Million Dollar Question:

Has anyone encountered any aggressive re-tuning adjustments as a result of changing to a Cosworth Plenum?


Looking for any information that would contribute to this thread.

 

hood clearance blah blah blah... you know you bought cause it looks pimp/baller. i have yet to install my cosie knowing full well it will need to be tuned.

 

Nice car dude.. Watched the video on youtube...

 

Well from an aftermarket plenum to another aftermarket plenum, I really didn't think the difference would be so great. It might be as much as 30% adjustment in fuel. (Just a rough 'guesstimation' based on o2 multiplier and AFR #'s observed via CAN Gauge)

 

Did you remove the rag from your intake tube?

 

Most definitely. The install was only about 90% complete at the time of the pic. But the car would not even hold an idle if I had left the rag in there anyway.
Rest assured it is not stuck in the intake.

 

No - there was no big change in idle and I also went from a Crawford to a Cosworth. You must have an air leak. I used blue loctite and those carbon fiber cap screws still came loose, spraying methanol everywhere! After a good retightening, it fared better, but I think I have to redo it all completely with new O rings (few drops after a hard run oozing out).

What is your vacuum at idle compared to before?

 

Vacuum is -18 as it should be with 272 cams.

Didn't use locktite on plenum end caps, but will reconsider when I get into it again. So Raj, yours was a simple swap with no retuning necessary? WOW. Gotta check things out again.

 

What are the afr's while cruising, still rich?

 

Cruising it's still in 10's.

 

That vacuum is solid. If it's rich all the time, something is seriously wrong and it's nothing to do with the manifold. Did you by chance play with the rails, injectors or harness during the install? Could you have bumped the FPR setting? Fuel pressure is the same? Does it ever normalize while driving to where it should be? Where is your MAP reference tapped for the ECU? Can u confirm the MAP reading on the ProEFI (via CAN gauge) reads the same as your boost gauge?

 

No unnecessary tinkering. Had no reason to. This was supposed to be a simple plenum swap. The only thing I did that someone would consider 'extra' was to clean up the vacuum lines by utilizing a vacuum block rather than 'T'ing the vacuum lines. Which served as an improvement because due to the previous set-up my Boost gauge only showed boost and no vacuum. I have since corrected that. I also had a chance to re-vamp all of the vacuum lines, replacing most of them with new hose. This also served to shorten a good number of hoses.
The vacuum block is fed by 1 of the 3 ports at the back of the cosworth. The 4 port block provides a vacuum source for the following:
1) Boost Gauge
2) BOV
3) Emissions device on pass side of plenum
4) To boost Controller ---> wastegates

 

When I installed my new motor and Cosworth plenum I started up the car fine with my previous tune with no issues (Going for a retune since it's a new motor and different cams).

There is a Vacuum under the Cosworth in the rear that is meant for the Brake booster make sure you have that connected. Are you throwing any CELs? Check to make sure no coil pack plugs might have come undone

 

The original plan was to mount it here in this fashion.



But after test fitting the throttle body, I came to find out it was interfering with the TB, so I had to improvise a vertical mount. It was getting kind of late and I was losing daylight, so I was a little pressed for time. This dark camera phone pic was the best I could do.



Again, with all new vacuum hose and all of the fittings got liquid sealant so it can be air tight.

 

And yes, I did put a fitting in the curved underside neck of the plenum that feeds the brake booster.

 

I'm going to bet that something you did there messed up the MAP reference that the ProEFI was seeing... You either got to fix it or get a complete retune. How does the ProEFI read boost? Is your boost gauge separate from the CAN gauge? If so, compare the readings.

 

The MAP sensor feed is a separate SS line that goes direct from 1 of the ports in the back of the plenum to the actual MAP sensor feeding signal to the PROEFI. I'm gonna have to wait until Sunday before I can get back into the car. Unfortunately due to work schedule.
I'll have more info then.

Here is a pic of the 3 ports that come standard in the back of the Cosworth Plenum.


Problem is that I needed 6 vacuum ports...hence the vacuum block.

 

Raj,
If you refer to the very first pic in this thread you will notice under the stock OEM curved hose that feeds the brake booster a SS hose with blue fittings that is rather thin, but is equipped with -4AN fitting on either end. I used this hose to provide the vacuum signal to the ProEFI. Due to the new port location at the back of the Cosworth plenum vs. the side from Crawford, I had to cut my own slightly larger bore SS hose again with -4AN fittings. Do you think the variation in hose size could be giving the ProEFI sensor a slightly different reading?

 

You can see the hose I am referring to more clearly in this pic:

 

No - the hose size should be fine. Check for a kink though. Or a leak. If the MAP sensor is reading atmosphere all the time, the ProEFI will keep dumping fuel...

I also run a vacuum block, but the MAP reference is directly off the manifold, just as you have it. My GM 3 bar map sensor is literally right behind the firewall, less than 6 inches away - with a little rubber hose connection.

When you get a chance, compare you're CAN gauge to your boost gauge. If they are spot on then it's something else.