Hi everyone. This is my first post on this forum so I'll give you some background on what I'm working on. I am at the beginning stages of rebuilding a '94 LT1 TA motor and 4L60E that will go into a '79 ELky. I have the top end of the motor off and will be replacing the valves with Manley raceflos (stock diameters). I would like to know if there any recommendations for seat angles and widths as well as valve angles and widths to achieve the best flow. I have flowed the heads and I will post the numbers here now. To start with I used a SF110 flow bench so I have converted all the numbers from 10" to 28" using a factor of 1.67 as recommended by Superflow. The exhaust numbers are taken with nothing attached to the head and the intake numbers are taken with the stock LT1 manifold attached. Of course all remaining holes other than the openings for the throttle body were plugged to simulate the actual flow. This will give me a good baseline to see what if any improvements are made with a good competition valve job. Keep in mind that although I say competition the motor is going into a street car. Even though I initially flowed these heads with a nicely shaped inlet adapter on the intake side I ended up using the manifold because I found that I picked up flow by doing so. I came to the conclusion that my adapter didn't give me a straight enough shot at the valve. This adapter is the same one I use on other 23deg heads and it has always worked well but not on these guys! All help would be appreciated:


.100" 62.8I 51.8E CFM
.200" 127.4I 96.7E CFM
.300" 171.5I 127.5E CFM
.400" 192.9I 150.0E CFM
.500" 204.0I 156.6E CFM
.550" 204.0I ------- CFM

I will post the numbers again after the machine work is finished and I will also make up my mind as to whether I want to do any gasket matching in the intake area at that point in time. Not sure it would really make that much difference. I have no plans for bowl work as this is primarily a street motor. Mostly just want to see how much power I can drag out of this guy without ruining the bottom end torque.

 

Sounds like fairly routine LT1 tech.... moving the post to "LT1 Engine Tech".

I assume those flow #'s are for the unmolested stock head? That's what they look like.

 

There would be no difference from any other 23 degree SBC head as far as what constitutes a good valve job. You seem prettyf amiliar with heads, so I am not sure what I can add. Every head guy has a slightly different idea. For example, especially on the exhaust side, some builders like a little wider seat to promote heat transfer and even more if the motor is for nitrous or forced induction. This may slightly inhibit flow but keeps the valve cooler, and so on.

Will you be grinding the valves yourself or sending it out?

Rich Krause

 

No, I will be sending it out. I've read somewhere that some machinists are using dedicated seat cutters. I'm thinking that I would get a better job going that route instead of stones but not sure.

 

Well, I am still not quite sure what you are asking. You can do a good valve job with stones, but dedicated cutters are going to be more consistent. As far as what specs to aim for, like I said, this is a matter of debate among engine builders. The "typical" 3-angle valve job includes a 70-degree bottom cut, a 60-degree intermediate cut between the bottom and the seat. This will smooth the transition from the valve seat as well as narrow the valve seat. The seat itself is cut at 45-degrees, while a 30-degree cutter machines the transition from the top of the valve seat to the combustion chamber surface. The accuracy of the valve job exerts a significant influence over performance because it affects airflow, as well as the quality of the seal between the valve face and seat. Some engine builders vary intake valve seat width according to application but most people use a .060" wide intake valve seat. The general preference for exhaust seats is .080" wide for street applications, .060" wide for racing, and back to a wider seat to promote heat transfer for nitrous or forced induction (as noted in the previous post).

Rich Krause

 

Here's a pic: http://www.automotiverebuilder.com/a...ts/119854i.jpg

Rich

 

Hey thanks Rich. I need to check this forum more often. It took me awhile to find this thread this morning! Your post says 70deg bottom cut and the picture shows 75. Which works best for these heads? The exhaust valve is what you show in the picture with the single cut on the valve? Then the typical 3 angle cut on the intake valve? Last question. Are the intake and exhaust seats cut at the same angles?

chris

 

You are welcome!

A typo on my part, I meant 75 degrees.

Rich

 

If someone were to give me a choice of 4 angles, you could keep the 75*, and give me a 15* instead.