I am porting a set of 243 heads. Using a GM exhaust gasket to mark the area to "raise the roof." Why does it look like I need to open it up so much? What am I doing wrong?

 

The stock exhaust gasket is actually much larger than the stock exhaust manifold so double check that you don't raise the roof too much.

 

I don't have a flow bench so I don't have any first hand experience. After watching countless video's on porting 243 heads I pretty much came to the conclusion that there isn't anything to be gained by opening the exhaust port.

 

So what gasket is this guy using? Basically trying to do what's at 3:50. My gasket seems giant compared to his? Thanks

 

243 cylinder head that I raised the roof. This set of 243 heads will go on a C5 and should wake it up nicely. The pictures is not the best still it should show that I raised the roof and still left plenty of material.

 

I'm not sure, but I'm using the exhaust gaskets that came off my '01 Camaro.

 

Ok, I get the idiot award for the day. 4:20 answered it lol Like you said also...

 

It's actually easier to get better results as a percentage on the exhaust ! Stock port is going to flow low 180s ........ good hand port 210 cfm when compared to top cnc programs !

 

I'd wager a bet that if you had a flow bench to quantify your results you'd hurt way more than you'll gain by porting without the aid of a flow bench. Bigger is not better.

 

I'd have to search for the video, I'm not saying there aren't gains to be had overall. The video I watched they did step by step port work and put it on the bench with each change. Bowl blend was a good gain as was working the swirl ramp and guides on both intake and exhaust, Good gains with a good valve job and back cut valves, Unshrouding the valves and port matching were smaller gains but still an improvement if done correctly and can actually hurt flow if taken to far or done incorrectly.

 

Yes agreed , there are no gains in simply hogging out the port exit or just belling it out behind the guide boss .This being op first set , focus on the areas that will net you the biggest gains A good valve job and bowl blend will net you 70% the results with minimal amount of work .

 

Often a smaller port will have better velocity than a larger port.

 

I would think just knocking off the rough, raising the roof some and smoothing the exhaust chambers would improve performance. Some good videos on the subject from StreetKillz Video Chronicles

 

Remove lumps and bumps, size reduce obstructions like the guide boss, blend the bowl to valve seat and if your really feeling it, blend the valve seat to the chamber so the transition there is seamless. Don’t make the port bigger, not really necessary. Most bang for the buck is bowl work.

 

If you want to know the theory behind head porting David Vizard has a few videos and some books on the subject. On Youtube HeadflowInc and David Vizard have the most useful information as to the reasons you should make certain mods to cylinder heads.

 

I would not recommend his videos as guide for a novice for a number of reasons .His terminology is not accurate , there is no real benefit in removing the hump behind the valve guide boss if a novice starts digging there he could break through real quick and so on !