1G Cylinder Head Warning!

[TOONAH]

Just wanted to share my 1G Stage 5 cylinder head saga.
Got my motor running a couple of weeks ago, only to discover coolant blowing out of the
O2 bung hole. Traced it back to a small hole in #4 exhaust port bowl about 10 mm down from the valve seat. Impossible to weld. The man who did the work claimed he had a CNC program to machine the ports and bowls for better flow. He claimed he pressure tested it before sending it back. He lied to me twice. The machinist who now has the head said that all the machining was done with a dremel tool. I concur. This was the second head I sent, since the first one leaked repeatedly. It had more welds than I can remember. So $1200 and two heads later I still have no decent head for my project.
I just want to warn you that I believe that the 1G head cannot be ported with out lowering the reliability factor significantly. Just use 1mm OS undercut race valves and port match the
gasket area to the intake and exhaust manifolds.
BEWARE OF ANY 1G CYLINDER HEAD THAT CLAIMS TO BE STAGE 5, WITH A CLAIM OF 20% INCREASE IN FLOW. EVEN IF THIS WERE TRUE, THERE IS LIKELY TO BE PAPER THIN
ALLOY AROUND THE INSIDE OF THE PORTS.
Your comments encouraged.

 

[Anger890]

I had a Accuflow CNC ported head, never any issues, countless people have successfully ported the 1g cyl head casting and achieved solid gains. I would think your head porter is the problem, not the cyl head casting.

 

[lacroixdp]

Agreed. I had my first DSM's head machined by Hobbs Racing and he did a fantastic job. I never had any leakage problems.

 

[kottyking]

The 1g head can easily flow enough for 450+ hp, for most of us that is PLENTY. I would never port a 1g head, for this reason. You usually hurt more then you help.

 

[4g64fiero]

Kiggly racing uses a "lightly ported" 2g head on some of their highest HP cars.

I dont see a reason at all to even bother porting a 1g head.

 

[Rob10_99]

Dremel: 2 You: 0

 

[pj91gsx]

The cylinder head from the sexy grandma build had a hole in it. sometime it can be welded up and fixed. in my opinion the head castings dont always end up the same. some head you can port bigger and some you can. I was porting and hit a crack in the head. The head that I ported had gotten very hot before and thats why I put a hole in mine. luckily i have about 5 heads so i just grabbe another one and didnt port it as much. Ive been to 2 porting shops to learn what to do for my port work.

 

[Anger890]

Core shift is what you are referring to, which is common in castings. If the guys CNC program was developed on a head that had very little core shift and then implemented on heads with major shift I could see an issue. Most shops have the CNC machine do the roughing in and hand finish the head work to allow for this.

Properly done there are gains to be had, specifically in the bowl/seat area.

 

[300dollarGSX]

Just use 1mm OS undercut race valves and port match the gasket area to the intake and exhaust manifolds.

The throats should be blended to the seats when oversize valves are used. The machinist sometimes does this for you (depending on price and type of shop), but cutting the seats for oversize valves or installing new oversize seats will leave a step where the seat ends. Not blending or porting this area with larger valves would be like installing a larger wastegate flapper, but not porting out the wastegate hole. Yes, the undercut portion will flow a little better, but you're defeating the purpose by refusing to port at all.

 

[TOONAH]

Nice comments, thanks. I am going to have my Manley valves and springs installed in an unported
IG head (after it has been pressure tested!).
Can you give me some advice on gasket port matching? The intake is ok but my exhaust manifold has
bigger port holes than the cylinder head.
Oh! I thought that the stock seats can be cut down to recieve oversize valves. 1mm = about 0.039".
Perhaps only if they are in good shape?

 

[300dollarGSX]

Oh! I thought that the stock seats can be cut down to recieve oversize valves. 1mm = about 0.039".
Perhaps only if they are in good shape?

You are correct. In most cases, the stock seats can be cut to fit the larger valves. The problem is after the shop cuts the seats for them (or installs new seats depending on what is necessary), there will be a small step left in the throat just beneath the seat. The machine only cuts so far past the seats. The area beneath what is cut by the machine is what will need to be blended.

You can see the step I'm talking about in this picture. Look at the exhaust ports just beneath the freshly cut area.