LS1 Restrictor Issues

[ls168camaro]

Has anyone on here run a restrictor on their LS1?? I have one that I tried mounting in front of my MAF and the car will not pull or rev up. It just cuts out. I can kind of roll on the throttle when in neutral but if I stab the throttle it won't even rev past 2500.

Has anyone encountered this kind of issue? I ran a restrictor on a dyno last year and think it was in front of the MAF and it seemed fine then.

 

Bryan

[Dave Schotz]

Hi Bryan, I have put a restrictor on my T2 LS1 car, for CMC2....

 

We had to use a spacer behind the throttle body, and then the restrictor behind the spacer plate. I have images that I'd be more than happy to email you if you give me your email info... that show the spacer, and the plate.

 

I don't know about in front of the MAF... and how that might work... but we've had to run them behind the TB for a long time in Touring 2.

 

Let me konw how I can help.

 

Dave

 

PS What size restrictor are you trying to use?

[Glenn]

Dave, send them to me too please. i'm the one making these for Bryan.

 

the one he has now is 50.8mm.

 

[email protected]

[Dave Schotz]

Sounds great Glenn... Sending now... and that sounds right on... I think you will see just below 280RWHP, and 320 TQ...

 

We used something very close... my guy worked in inches unfortunately (we did them quickly) and I'm right at about 1.99" 2.03" ish... (Roughlyi 51mm when I did the math... probably closer to your size.

 

Pics have been sent... feel free to post for everyone, if you can.

 

Also... you'll notice one is very elaborate... and the other (spacer) very simple... I don't have pics of the restrictor plates we made... but I can tell you we used the 'simple' template... and just added two addt'l holes up top... and it worked like a charm...

 

Peace,

Dave

 

PS The restrictor plate I have a pic of, is our original SCCA T2, 58mm Plate

[mitchntx1548534714]

Dave, the spacer is needed to allow the butterfly to clear the restrictor plate. How thick is that spacer?

[Glenn]

Mitch, i forwarded Dave's email to you.

[Dave Schotz]

Hey Mitch, yeah... the Spacer is roughly a 1/4" thick... unfortunately I just dropped off the LS1 Firebird to Alan Blaine's this past weekend... and my spare restrictor, and spacer are in the glove box!

 

I should be talking to Alan this weekend... and will ask him to measure the thickness... whatever the thickness is... you'll need to add at least an 1/8" due to the hole being smaller than the size we originally ran in T2... the blade still hit my 51mm plate w/ the original spacer... so we had to make it thicker.

 

Hope this helps!

Dave

[Al F.]

Just out of curiosity...why not simply make the restrictor asymetric? The problem is the butterfly swings past the back of the TB when it opens, so why not cut the restrictor so that section is full port and then restrict the opposite half where the butterfly isnt in the way? Just thinking out loud...

[Glenn]

and then what size would you lable it?

Edited February 7, 2008 by Guest

[Dave Schotz]

Hi Al, I believe that is how Robert from Argent Lab originally did it. And I think it's a neat Idea, but measurement would be difficult.

 

I just figured that it had been done for so long in T2... (albeit a 58mm) that keeping it centered, and reducing the size would make sense, and be easy to measure w/ Calipers for confirmation etc...

 

I really think that once we figure out what the min thickness of the spacer needs to be... to say, clear even a 45mm spacer... that we should add it to the rules of the CMC2 class...

 

Meaning... that we say on LS1 Cars... where a restrictor is required we put in a min thickness of .25 max thickness .50 so that it is something that is controlled as well.

 

Peace,

Dave

[mitchntx1548534714]

and then that size would you lable it?

 

Only in millimeters ...

[TurboShortBus]

and then what size would you lable it?

 

The spacer could still measure, say, 50 mm ID, or whatever you make it.

 

If you want to stick to round openings, and the spacer is 1/4" thick, and the butterflies interfere, then you can taper the sides of the "inlet" opening with a die grinder, as long as the 50 mm circle (or whatever ID) on the "outlet" side stays intact.

 

Or, if you want to just cut a couple of ovals, and you have access to basic CAD software, then you could just draw them and measure the area, and label them that way. Then, you could compare that area to a typical 50 mm (or whatever) diameter circle. Not hard at all.

 

Mark

[FBody383]

and then what size would you lable it?

 

If you want to stick to round openings, and the spacer is 1/4" thick, and the butterflies interfere, then you can taper the sides of the "inlet" opening with a die grinder, as long as the 50 mm circle (or whatever ID) on the "outlet" side stays intact.

 

Or, if you want to just cut a couple of ovals, and you have access to basic CAD software, then you could just draw them and measure the area, and label them that way. Then, you could compare that area to a typical 50 mm (or whatever) diameter circle. Not hard at all.

 

This presumes every inside radius yields the same airflow (horsepower/torque) and there's no current rule requirement for standard thickness, right?

 

Doesn't mean that can't be cleared up...

[TurboShortBus]

This presumes every inside radius yields the same airflow (horsepower/torque) and there's no current rule requirement for standard thickness, right?

 

Doesn't mean that can't be cleared up...

 

I don't believe that there are any rules for plate thickness, restrictor ID, restrictor shape, etc. Just go make a plate and see what happens.

 

At our level, there are no guarantees from 1 radius to another, 1 area to another, 1 engine to another, etc.

 

Mark

[Dave Schotz]

And ultimately... I'm guessing it probably doesn't matter too much... as long as when your car rolls onto the dyno... it makes the same power as on the window.

[FBody383]

I don't believe that there are any rules for plate thickness, restrictor ID, restrictor shape, etc. Just go make a plate and see what happens.

 

At our level, there are no guarantees from 1 radius to another, 1 area to another, 1 engine to another, etc.

 

And ultimately... I'm guessing it probably doesn't matter too much... as long as when your car rolls onto the dyno... it makes the same power as on the window.

 

It's back to Glenn's question of measurement and notation on the dyno sheet which is currently in the rules.

 

I don't have the experience to know the variation in output based on different radii in this application. The potential for variability may lead some to take a chance that, at the track, only the plate is measured instead of performing a dyno test.

[TurboShortBus]

For an elliptical opening in a restrictor plate, I don't see why an X and Y dimension wouldn't suffice. Granted, the shapes of ellipses can vary with any fixed X and Y dimensions, but it seems to me that the inspectors just want to make sure that you're using the same parts, and if the dyno numbers match up, then it shouldn't be an offense that gets you booted out of Nationals.

 

If you want to keep a perfectly round opening, then just use a thick enough plate that will allow you to taper the opening from, say, 60 mm ID on the throttle body side of the plate to 50 mm ID on the other. Your controlling dimension is still 50 mm, and you can sleep well at night knowing that you can call it a 50 mm plate on your dyno sheet.

 

Maybe, in order to eliminate any confusion, the rules should state that restrictor plate openings shall only be round, and cannot have any other shape.

 

Mark

[TurboShortBus]

But, somewhat back to the original question...I would never do anything to modify or alter the airflow anywhere near the mass air meter. Those things can be finicky enough on their own, and they don't need any help with a restrictor in there that causes turbulence or disturbs the airflow that they are calibrated for.

 

This is where an old-school set of SuperTrapp mufflers would come in handy...lol

 

Mark

[Al F.]

Well, thats right, the whole thing is to stay away from the maf when dramatically altering air flow. Remember how a lot of maf sensors have a honeycomb mesh in front? Thats an attempt to straighten the air flow (laminar in geek speak) and was there for a reason.

 

Remember also that the current dyno form has only one purpose: to document the parts and settings that were employed in order to attain the numbers submitted. Over the years more and more data fields have sort of been added on as people realized a lot of drivers would have common parts, and the restrictor size piece is no different...only that was added when LT1s were the only restricted cars and there was no reason to do anything fancier than round holes.

 

My point is, lets not let the design of the form drive the design of the restrictor. Lets figure out what makes most sense from a cost perspective, and if we need to adjust how we document that then lets!

[ls168camaro]

Dave-thanks for the pics and help on this issue.

 

To clarify he MAF does have a mesh metal screen and the restrictor was placed up against the screen. It caused the engine to die at idle, not rev past 2500 at full throttle etc. I did get a J1850 code.

Tried the plastic one and basically had the same issues. So lets stay away from the MAF for a restrictor. My original thought was that it would be better to restrict it in front so that the computer could compensate for the airflow. Maybe that could still be done but not right in front of the MAF.

 

Looks like I will have to get after Robert to get the spacer plate and restrictors finished. They will be behind the throttle body. This should richen up the car and maybe help with my knock sensor codes that I have been getting but could foul out the 02's.

Dave do you run o2's with the restrictor or have any issues?

Thanks for all the help.

Bryan

[Dave Schotz]

Hi Bryan, your car's fuel trims will stay identical... We run the O2's with no problem... because the restrictor is behind the throttle body... and your throttle body is doing the 'sucking' your MAF is only getting 'sucked' through the less air... we hooked up a Fuel Trim sensor before and after, and the trims were identical... so however your car is set... it will remain the same.

 

I'm confused about your knock sensor codes? Your front two should always be fine... it should just be your rear two giving a code due to no cat's (so no different in exhaust temp/trim) but doesn't affect power.

 

If you are getting fuel trim/02 sensor codes from the front two... something isn't quite right... and since we can't tune these cars in CMC2... I'd say get another computer... and Maf, and 02 Sensors... Because something in that mix isn't right (again only if you are getting the errors from the front O2's.

 

Take Care,

Dave

[ls168camaro]

Thanks for the info.

 

I had 2 codes when I had the restrictor in place. P0101 MAF or VAF and P0161 02 Bk 2 Snsr 2.

After a session or two I would get the knock sensor codes. I didn't write down what the specifics were for which group or bank. Though there were always 4 codes. The scanner I was using would also give me a code J1850 before it would scan for the rest of the codes. I think the J1850 said VPWM but not sure???

 

One thing is I still have a set of cats immediately after the exhuaust manifolds in the Y pipe before it goes into one exhuast pipe.

 

I also felt like there was a decrease in power once the codes were set but don't have confirmation. Some have said the knock codes would cut power as the computer is sensing knock. Phil on Frax stated that the computer would go to a low octane table which would pull alot of timing down low and some up high in the rpm band.

 

Dave-is the fuel trim sensor the same thing as an air/fuel ratio monitor or something different? The guys running the LT1's with restrictors complain about how rich the car's run. There plugs don't look great, one has discolored the rear of the car, and the oil gets contaminated with gas. Have you experienced any of these issues in T2 with the restrictor?

 

I assume turning off the knock sensors in CMC2 is illegal but I don't see it would matter.

[Dave Schotz]

Hi Bryan, yeah that is strange... especially when you say you have the cats in place... the only thing I can think is... since you had it infront of the maf... or possibly not sealed perfectly... you were getting the codes...

 

We have never receieved any codes when going from restrictor, to without restrictor, and vice versa...

 

Yes, Air Fuel Ratio Montior... same thing... we removed the rear most pass side '02 Sensor... inserted the Air Fuel Ratio Monitor (Some people just use tail pipe insert as well). And Dyno'd the car... Same Air Fuel with Restrictor as without... so once you get the plate behind the Throttle body... you should be ok.

 

LT1 cars... I'm not sure about... I'd guess their computers, and mapping aren't quite as sophisticated... and maybe that's why their A/F Ratio changes.

 

But LS1 cars should not change. And you shouldn't get the knock sensor code either... you can always dump 100 Octane in there... and see if that fixes it... but I think you need an afternoon on the dyno...

 

If it were my car... I would pull the plate... and put new O2 sensors in... reset the computer... and do 3 pulls... (and to be safe put 100 Octane) make sure your car is still good... with no codes... if you get a code... then fix the issue at that time.

 

Then... install plate... reset the ECU (dump the battery)... and do 3 more pulls... A/F should stay the same... and you shouldn't recieve any 'new codes'.

 

Good Luck, let us know what you find.

 

Dave

[ls168camaro]

Dave I got the knock codes without running a restrictor. Same thing happened last year. I need to check and make sure they are correctly hooked up. I don't know how sensitive the sensors are and if it picks up knock from the chassis somewhere instead of the engine.

 

Good info that the a/f ratio stayed the same. That was something I was concerned with.

 

Bryan

[Dave Schotz]

I'm not sure if they changed on certain years, but I believe the knock sensors are located underneath the intake manifold on the LS1 cars...

 

You could make an attempt at replacing them... the knock thing has me a bit confused... we've never had to turn them off on our race cars.

 

Good Luck!

Dave