I'm not a TPI guy, but I came on this and thought it might be useful to you. I looked around but didn't notice a prior post, if you all have seen this, then I apologize. http://www.geocities.com/softtailduece01/

Yes it has been done. If I remember correctly Madmax was the first one to try it and post his results. That was a while back though. It might be an article by now. I know there is an article on siamesing the runners.

I siamesed the runners and plenum and gained about .10

Did you ever end up using the L98 cam for your rebuild? Or did you go with something else?

I didn't do a rebuild and yes I stuck with the L98 cam.

Ran a best of 13.34@103 MPH in ideal conditions, but usually run 13.6@101MPH in normal conditions.

There was still some tuning to do as well, I got my wideband but the new house took up my time towards the end of the season so I didn't get to the track often.

This winter I do plan on doing a cam swap, maybe the LT4HC...but I'll see.

I want the car to go solid 12s so I need a cam, to install the SLP runners I got and a Vigilante. That should do it.

Why u asking?

There are two recent threads on siamesing the intake manifold. One recommends against it the other recommends for it. The applications however, are different. I am a little confused. I am considering this for my set up and would like some advise. Soon I will sit down with my mechanic and discuss this. I have a 5.0 litre TPI engine with a Comp Cam and Headman Headers. The catalyic converters are gone with an improved exhaust system. An MSD distributor and coil were recently installed. I am considering porting the plenum and runners and having the intake manifold ported or siamesed. I have read the two articles on this procedure. Is it worth it to go to the intake manifold or stop at the runners? I have decided not to port the heads or buy new heads. Thanks for your advised.

Personally the idea of siamesing the base is faulty IMO by what I have read. Since you will be siamesing past the entry point of the injector, in other words the a/f mixture is already begun you risk of running lean in the cylinder 7 as previously mentioned on this board.

Cylinder 5 and 7 are paired together and after 5 is finished firing, its scavenging from the overlap of the cam, taking with it possible air and FUEL from the next cylinder to be fired, its neighbor #7. I guess depending on your cam profile is what effects this would have.

I think siamesing the runners and plenum is all that should be done, it seems to risky to siamese the base IMO.

Also you must not forget that you want to maintain good velocity and smooth flow, so over porting your intake can cause you to create turbulance, slow down the intake charge and result in less overall power with possibly more peak power in a higher RPM range but overall the package may be slower. Porting is as simple as everyone thinks it is, its a science and art.

You arent siamesing past the entry point of the injector, the injector sits almost in the head. Depending on how far you go, you're ~2-4" behind it. About the same as a miniram.

On a 305, your first step is to port the intake base as is, pay special attention to the middle of the runners where the cross section is smallest and open that area up but be careful not to break through. Work on the transition from the runner to the base, as cast its a total joke. Last you can match the port exit of the base to the head, just make sure the intake manifold side is the same size or smaller than the opening in the head. You dont want the air coming down the intake through the base and running into a wall at the head. Do that first, I think you will be happy with the outcome. Fortunately the 305 doesnt want as much air as bigger engines do.

yeah I realized that looking at some pics after I posted!

Well put! The last previous thread was about porting a 350 with a Super ram, of which you have neither. Do what Madmax has stated or spend $400 for the already ported out Accel base. Fror a 305 though I would just port the stock base.