I'm getting ready to start the installation of the Holley Stealth Ram that Bret modified for me, and I'm seeing a possible problem. The Stealth Ram has hole in the front of the plenum for the IAC air as shown in this picture. However unlike the LT1 manifold, it does not have an IAC channel to distribute the air evenly to all the cylinders. The air just enters the main chamber of the plenum, basically right into the front four intake runners. I'm forseeing problems with the air distribution at idle. I had a problem with this with my stock manifold and BBK throttle body until I made some modifications to the throttle body.

My idea is to introduce the IAC air into the middle of the plenum. My original plan was to block off the IAC in the throttle body and install a remote IAC, and I may still do that. However I was thinking there may be a way to modify the stock IAC to work. Here's my idea. If you look at this picture you see that the air enters one hole, goes through the IAC motor and exits the other hole and in to the intake manifold.

I'm thinking I can block off the hole in the throttle body and then drill a hole in the IAC block like in this picture then on the other side insert a fitting and run a hose from it into the middle of the plenum between the two intake tunnels.

I guess my question's are: Am I right in assuming that if I just let the IAC air enter the front of the plenum I will have problems? And if this is true, will my idea work or am I over thinking this?

Oops. I just realized I put this in the advanced tech forum. Sorry. If one of the mods feel the need to move it, that's fine with me.

 

Remove the electrical part(black) fab you a plate to go over the hole, drill progressively larger holes in plate until it idles.
Just an idea.


I dont think you will any air problems with the way it is setup now.

Is that lid lower than the stock stealth ram plenum? If so how much?

Buddy of mine installed one with only trimming the metal under the windshield.


David

 

Which car are you installing this on? Was this intake shortened at all to fit underneath the cowl/hood of a 4th gen? I dont think you will have idle problems with this manifold as compared to an LT1/4, like I am having. I have tried every IAC trick under the sun to get the IAC to draw evenly from all of the intake ports, and no matter what I try, it still throws the 02's for a loop, pushing air past them and making the car run rich at idle. I think having 240+ degrees intake duration doesnt help either, but it would be interesting to know if using a HSR, or modified version of one would help the situation any. I think having the IAC in the stock location, as part of the throttle body would work fine in your application. My AS&M throttle body was pulling air from the plenum instead of the IAC passage cast under the plenum, and it idled fine. Modifying it to draw air from the IAC passage made no difference for me.


Nick

 

I'm not anticipating problems getting it to idle.


When I talk about air problems, I'm talking distribution not volume. The problem I had before was that my BBK 58mm throttle body let the IAC air into the plenum instead of the IAC channel on the stock manifold. Whenever we pulled the plugs they showed it to be progressively richer from front to back. I assumed that that was because the front cylinders were scavenging the incoming air from the rear. After I modified the throttle body like this, the plugs looked much more uniform.

My thinking is that since this intake doesn't have the IAC channel to distribute the air evenly to the indivuial cylinders I will experience the same problem. I thought that if I could introduce the air in to the center of the manifold, like between the intake runner tunnels, instead of the front this would help. I don't know maybe I'm barking up the wrong tree.



The intake is only slightly lower than it was when stock. Bret milled off the fins which lowered it maybe 1/2 inch. I will be cutting a notch out of the cowl, but since it's on my race car, that's not going to be a problem.

 

Mike,

Try the way that Holley has it setup now. The LS1 cars have a IAC setup very similar to this and they work fine even when the IAC inlet hole is reduced in size.

Bret

 

I'm definitely interested in this intake for my LT1. When I saw your pictures, Bret did an outstanding job modifying it. I cant' to see what kind of numbers you will post. Keep us in the loop........

Johnny

 

Any results yet, Mike?

I've been wondering lately, when much of the tuning/idle/reversion/low RPM drivability problems when running a healthy cam are often blamed on the LT1 intake, if replacing the intake with one that has significantly longer runners won't minimize many of these problems. Maybe eliminate the need for the whole IAC circuit all together?

Anyway, it'll be interesting to hear your results.

 

You'll be fine without going thru all of this. The cylinder balance issue with LT1's is the "as cast" IAC channels in the factory intake. Just cut up a intake on a band saw and look at the lack of consistancy. Some engineer in powertrain thought he had a "great idea" to improve idle balance...not.

 

Hot Rod Hawk is completely right. converted one about 3 months ago and have no, none for the idle problems. The gained nice power and all and all makes for a very nice driver. Hopping to get it on the dyno and see what happens this spring.

 

so all in all what r the steps to do this? and if u could email me them at bojbp@hotmail.com, thanx

 

Unfortunately, I believe you are.

AFAIC, has little (if anything) to do with runner length per sa. It is about distribution of the air, during conditions of low rpm. Runner length, by itself, will have little to do with air distribution.

How did you arrive at this conclusion? I take it, it involved A/F ratio checks at idle, monitoring all 8 cylinders for uniformity? The design of the IAC circuit recognizes airflow characteristics, in regards to air path priority in the ports, of the oem intake, are different than they are at higher rpms. I've seen worse engineering, with regards to priority ducting, of home heating systems. BTW, I see you are from Mi. Not to tough passing emissions testing there, I understand.

Power is not the issue in this thread. It is idle quality. What are you referring to, in regards to "idle problems"? Again, a MI. native. Idle quality would therefore not be one of your major concerns. Am I correct on this?

 

Arnie, you believe I am what? Going to have the same problem, or barking up
the wrong tree?

This is a race car, so emissions are not a problem.

With all due respect Hawk, I didn't see it that way. The problem I had with cylinder balance went away when I modified my BBK throttle body so that the idle air went through the IAC channels instead of into the main plenum.

Have you pulled any plugs? My problem wasn't getting it to idle, it was getting the idle air distributed properly.

 

I was referring to the tree.

That (and the emissions compliance responsibility) is precisely my point.

 

Clean Idle control and drivability is 85% of my tuning time in my state of mind, tho that it is in "Michigan". Why wouldn't someone in Michigan want a clean Idle free of excessive fuel distribution issues?. If your not running a "lean cruise" fueling strategy [sp?] your just not worried about things like "quality drivability" and if you can't figure out the lack of "quality" fuel/idle balance issues in the LT1 intake design by the injector offset tables values take three steps backwards...
...Cheese heads too .
Those IAC channels are not of consistent dia at the point of entry into the intake port floor which I see as an attempt to feed all of the cylinders the correct consistent supply of AIR since the mounting location of the throttlebody is inherent too imbalance in "air" distribution in the LT1 plenum and that IAC tract is not favorable.
It's quite odd when you switch to another type of intake on a LT1 that funny split BLM issue strangely has exited the datalog info once you take that funky "profile" the injector balance tables are loaded with, but that's another topic.
No I don't have O2's in each head pipe though I wish I did cause reading plugs and targeting 15.3 idle afr [wb verified in collector]would be spot on for sure. Excessive hydrocarbons sux and it don't take a cat for a cleaner idle either, though it helps.

Don't be a hater cause I've spent time living in the "Motorcity" with industry leading tuners and insiders employed in the ee field and fuel mangement labs at GM. Tho it is unfair being able to acess to them and "pay them $$" for consulting on this subject back in the early days of 1994~96. You know before we had LT1 edit and had to use mastertune or have acess to a cams machine to tune, or be involved in aftermarket code hacking as the gunnie pig guy .
FUN DAYS and very informative days but it was in "MI"

When packaging a powerplant in a chassie that dictates it's "airtract" you have short comings.

:EDIT:
big cams above 250@50 duration can be driveable, get good MPG, and be "somewhat" friendly in a "driver" errrr racecar errr what ever label fits, that depends more if I'm driving on a public road or track.
:/edit:

 

Agreed, the same here for me and every LT1 or LT4 I've ever tuned.