S.J.S.

K guys...(Vince, Phil, Lloyd, John G.). As you know I'm doing my heads.(going on 30 hours). The two things I wanted to know was how much did you take out of the exhaust ports?

I know you said they flow pretty well already. I was just thinking of taking some of the guides and just smoothing it out and polishing it.

As for the intake runners. On the push rod side.....did you take a lot off that wall or any? I was just gonna smooth out the casting lines.

thanks guys....

O'ya one more.. will it make a big difference if one intake flows more than the other???

NightTrain66

As far as "CFM" and getting results on a "FLOW BENCH", the larger this area is, the more the heads will flow. Since the engine works different than a flow bench, it is sometimes discussed what the best size of this area should be. Cubic inch and RPM could possibly tell you what size this needs to be if you were to ask the right person. I feel that you will not get this area too largewith out welding the push rod walls and using offset rockers so here is my opinion "as right or wrong as it may be". . . . .

you want this are to be as large as possible so raise the roof and widen them as much as possible while being able to make them all the same size. You will have to grind from the pushrod walls AND the center divider wall to achieve this.

Hope this helps, maybe others will chime in and tell you their opinions.

NightTrain66

Buttercup

I did just as much work in the exhaust bowls as I did the intake and also raised the roof a little bit. Everything was polished from there.

I'm no pro but I didn't concern myself with widening in the purshrod area at all. The airflow is straight and relatively slow in that area compared to the bowls and seats. If it's not a restriction why put much time into it? I did resurface the whole port. If anything I removed material high on the wall and roof adjacent to the next intake port, since most of the active airflow is going to be high and on that side. I just blended straight down into my somewhat canted bowls from there.

You want the ports as identical as possible! If one port flows more than the other how can you get the fueling right??? These EFI systems only measure bank to bank, not cylinder to cylinder. Not to mention that you want all ports to flow their best to make the most power.

97Z-M6

well i took alot out of the the push rod area and thats why i have to ge them welded. i personally think you should widen them. but im no pro. to me it looks like it makes the path straighter to the bowl. but what do i know, im by far no pro.

now the exhaust... this needs to be done carefully, this is a big weakness on our heads. i did everything on the exhaust as i did the intake. i straightened eveything out. and open the port up to match the gasket. but dont match the gasket on the floor of the exhaust port, the lip helps stop reversion. because the engine does not flow a constent flow of air like a flowbench, it comes in very fast pulses, and the lip left on the port floor helps to keep those pulses of air from coming back in the port, some say its not important, some say it is. maybe loyd can elaborate. hopefully loyd will flow my heads for me, when they are complete.

Buttercup

I don't touch the floors either. They are low flow velocity areas and lowering them could actually encourage reversion.... like you mention a "lip" can also help diminish reversion. Same goes for the intake. Also keep in mind that the coolant passage is fairly close to the exhaust port floor and you wouldn't want to break into that.

FastZinTennessee

I took a lot off the guide on the exhaust side. I also took a good amount of material out around the guide. Other than that I smoothed out the whole exhaust side, and enlarged the runner slightly.

John

Ai

Regarding the PR area, it's almost impossible to make it too big with an LT1 casting IMO.

However, if the rest of the port wont move but so much air because of your shape etc, then you can technically make it larger than you may need.

As far as port to port flow, everyone I've always learned something from has gone for equal flow. Generally I can get within a half percent port to port, but so long as youre close I wouldn't be terribly worried. That's probably not going to make or break whatever you're doing. Still.. be as consistent as possible

S.J.S.

So Phil....your saying that I can take a lot off of the runner wall on the PR side? Just not punch through right. What about the exhaust ports???

GA93FORMULA

Final cc numbers on my LT1 exhaust ports were 75cc. Stock LT1 exhaust ports are 60-65 cc (not sure) prior to porting. So basically I removed 10-15 cc of material from each port. Most of the material came from the roof and both sides of the valve guide boss (still the roof). I also introduced additional port bias on the cylinder wall side of the exhaust bowls to improve swirl. I simply cleaned up the floors. Leave the floors alone (both intake and exhaust ports). My final intake port volumes were brought up to 185cc each. Like someone posted earlier... the pushrod wall side at the intake port entrance is really thin and I went through 3 of these (easily repaired). Apparently the intake port entrance on the LT1 is narrrower (in general) than some of the other performance GM castings. As such, this narrow cross-section can negatively affect high lift (>.500) flow numbers. I left a 80 grit finish on the intake ports and 150 grit on the exhaust ports, followed up with polishing on exhaust ports only. I put in approximately 80 hours on my own heads. This time includes cc'ing all ports and chambers to equalize volume, plus the multitude of measurements required to maintain proper port form/shape from one port to the next. Very time consuming, but worth every second