Thread: LIM Modification

One thing that has troubled me since I first saw the inside of a LIM is how its designed. first, the outlet is not centered so flow to the cylinders Im sure is not equal nor optimum (Ive wondered if this may contribute to KR) and then the ridge that runs down the middle of the LIM. It seems the idea of it was to split the air flow, but the ramp is so steep that I highly doubt that it does even that effectively. Looking down at it it looks like the air would be coming out at such a velocity it would just bounce off the bottom of the LIM and then just brute pressure and velocity would force some of it to the cylinders rather than it being guided there with minimal resistance.

So I would like to know if anyone has experimented with any internal LIM modifications that would improve air flow? No offense to anyone, but please dont post and just say it wont work or you dont see how it can be done. The whole purpose of this is to see if it has been done, can it be done and whether or not there would be any real benefits.

So if you have modified the LIM with this, then can you either post up what you have done, pictures would be a HUGE bonus, or PM me if you dont want to post it in the open forum.

If you dont think this will work then I would much rather you post up WHY it wont work with any supporting information.

I have some working ideas and am working on some mock ups, but I would like to get some input from anyone that has attempted this.

do you have a pic of the LIM. im just kinda curious as to what exactly your talking about.

I truly feel that if you could put some type of inlay in there that would organize the air flow better then velocity would go up significantly. I have long personally question why there is only a 40hp difference between the NA cars and the Supercharged particularly in comparison to other supercharged vehicles on the market that see much more gains. I am nearly convinced that the largest reason is the way the LIM is designed. It does not promote good air flow at all.

Theres not much you can do with centering the outlet due to the way the supercharger outlet is, but I feel channeling the air flow is very possible. I would be really curious to how badly the #5 & #6 cylinders are starved compared to the rest of them since the placement is more biased to the first 4 cylinders.

blowfish, I dont have any pics of the LIM here with me. Ive got some service work to do after work but if I have time I'll post up a couple.

Okay, I borrowed an image from the classifieds:
I forgot already who the owner was, but if you dont want me using the image just let me know and I'll take it down.



Blowfish, if you look in the square area you will see a ridge down the middle. That is the splitter I was referring to. But if you see one up close, you can tell it does not angle the air flow much if at all and does little more than just split the air flow. And the square area is slightly forward of the middle cylinders so the #5 and #6 cylinders, I believe, probably dont get the air flow that the others do. There is little more, as I mentioned, than vacuum and brute force of the air flow that gets the air into the cylinders.

The easy solution is just to put some type of metal strip in there that would provide a more gradual ramp with perhaps some type of grooves or something to bias the flow to the cylinders. You're not going to be able to fit anything in there like full fledged channels and such.

I would like to have the resources, machine equipment and such to extend the ports to the heads up to the square area. Some tubes as it were extended up to the opening of the LIM so that when the supercharger was bolted on it would be sitting directly onto the the ports to the cylinders. But you would still need some type of splitter in there and I dont know how practical all of that would be.

The outlet of the supercharger is so small in comparison that I think at this point its more practical to just split the air better, angle the split better and put in some bias to each cylinder.

ahhh okay. WOW that does not look very effective at all!! and i see how the 5 and 6 cylender is getting starved. now that i look at it that looks like a very poor design. might just be me not knowing anything (shut up tdc) but it deff looks like it could be better. does anybody make an after market LIM???

deff very intrested to see how your research goes

Im kinda at a stand still with putting the Grand Prix back together until I can get some more money together so Ive been looking at stuff like this. This is what happens when you miss your car and start looking for things to do that dont cost a lot to concieve or try out.

Originally Posted by SyntheticShield

Im kinda at a stand still with putting the Grand Prix back together until I can get some more money together so Ive been looking at stuff like this. This is what happens when you miss your car and start looking for things to do that dont cost a lot to concieve or try out.

haha i deff agree with that. question. isent boost messured by the amout of air built up?? so going down into the lim after the supercharger the air is just being stored in there before it gets used??

ON my engine when I built it, all I did was gasket match it to the LIM gaskets, port the inlet for the GenV and port and polish the intake runners, and make them smooth as a baby's butt and added in a quick polish job through out the entire inside of the LIM its self to get rid of the rough casting marks.


Oh, and tapped, plugged, and JB Welded the plugs into the coolant ports of the LIM to the bottom of the supercharger.


Back when I was doing these for other people, some of them had me make that hump down the middle of the LIM into a sharp blade to "split the air" to each side of the LIM.

Nobody knows if any of that was useful or not, but they wanted it, they got it.

~F~

Regarding the injector location... Everything I read points to the L36's location being the most optimal as the fuel has the most time to atomize and mix before entering the cylinder. The reason GM moved the injectors to the heads for the L67 was that the blower didn't allow much room on the LIM to maintain the proper injection geometry. To maintain that geometry without modifying the blower a lot (though ZZP seems to have found a way to clearance the blower case) they moved the injectors to the heads.

Originally Posted by Sabrewings

Regarding the injector location... Everything I read points to the L36's location being the most optimal as the fuel has the most time to atomize and mix before entering the cylinder. The reason GM moved the injectors to the heads for the L67 was that the blower didn't allow much room on the LIM to maintain the proper injection geometry. To maintain that geometry without modifying the blower a lot (though ZZP seems to have found a way to clearance the blower case) they moved the injectors to the heads.

when I was talking with james, he stated the opposite, and that the in jector placement on the L67 was better, but angling the injectors has a huge effect on the atomization, there is only like .5 inch difference between the two injector mounts

thats why if you were ever to tap you lim for some alky, youd need to add two more on the 5 and 6 cylinder side. without those youd get uneven distribution. im not sure this would have anything to do with your car knocking, but it definately doesnt help with flow issues.

no one that i know of has done anything to remedy this. but then again, no one has found anything wrong with how it works either.

well if air is built up then i see it hard for cylenders to be starved. air is going to be on tap when it needs it. after i thought about it i was like wait....

well i was just throwing out the starved theroy. there is always room for better air flow.

Intense racing offers a ported L.I.M for $199. I don't know how effective the porting they do is but they do hold quite a few 3800 powered records.

It is in the induction section on their website but they don't reccomend them for stock heads. theres a bunch of pics showing the difference between stock.

These BRAND NEW lower intakes have been professionally ported to match our INTENSE™ Stage 2 and Stage 3 heads. They willl help increase airflow and horsepower gains even further with those heads. We do not recommend these for those with stock heads as air turbulence will occur causing reduced laminer flow and a reduction in performance.