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I hate watching technical Youtube videos when the guy on the video really doesn't know what he's talking about. Today, I may be that guy. The Bernoulli equation as it relates to intake ports is a complicated subject and I do not pretend to understand much of it. With the help of some guys on...

With a snap gauge and micrometers my intake is 1.658” and exhaust is 1.711”. That’s with 100,000 miles.

You think he’s using that finish on the throat and SS as well? That would be a real reset in the ‘it makes sense to me’ category. Edit: I'm referring to the top of the throat, as in the bottom angles directly beneath the seat angle. Surely the first couple of bottom angles are still smooth.

I sure would like to see this quantified with before and after TQ and HP curves and BSFC numbers. Speier, Morgan and the upper echelon of engine builders will spend a crazy amount of time to gain 2 HP.

Stock it's around 1.625. That's with a tape measure.

I believe that is the consensus of most of the resident racers and engine builders that responded here. Got to get the right size and shape. Then do not smooth it out much, if at all.

Post a picture. Sounds like a great set-up.

Here's a post to clean up a few loose ends from yesterday. Included is a picture of my plywood entry plate and how I use clay to blend any mismatch with the head. Also included is a picture of my manual valve opening jig. I've found it to be quite rigid and repeatable. There are countless...

And when you sink the valves, the valve stem ‘gets longer’, the valve spring is less compressed, the vacuum can suck the valve open a little bit and you can gain low lift flow. For a while it seems like you just hit the jackpot and found a bunch of flow - until you realize what really happened.

No way can this machine (a Superflow 300/600) accurately determine 0.1 cfm. I'll stick to my 1/2/3 cfm story from before. If I were to run back to back tests within a few minutes of each other, I would expect 2-3 cfm of repeatability. There are so many factors that can influence results. Air...

You're killin' me Smalls.

You're right. Or, looking at it another way, don't let me touch your ports with a cartridge roll!

Here's the final two tests just for fun. First, sand entire port with 60 grit cartridge roll. Second, hand sand the SSR only with 180 grit cloth backed sandpaper. The 180 grit hand sand made a difference. I got similar results a few months ago when I hand polished the SSR. As was mentioned...

You are correct. That made me think of an somewhat related experience on the bench with the Speedmaster head. PBR told me some months ago about the importance of flow around the shrouded side of the intake valve. So now, quite often when I make a change to the head I will flow it with the...

It is a borrowed head from a 318. I don't own it. It would be a more fair way to compare ports however.

What I did this morning with the cartridge roll took 15 minutes for 1 port and was almost foolproof. Sandpaper is just not that aggressive. If Joe average put a little Gorilla tape over the valve seats to protect them and was careful with the sander, there is no reason a 60 grit or 36 grit...

Valve job is factory. My disappointment with this head is the large volume (199cc) and the large throat (93% on a 45 degree seat). The throat was the shocker. I think it's losing a lot of flow throughout the range because of that.

Here's my understanding from some Darin Morgan videos: Intake manifold for dry flow in a MPFI system would be smooth. Downstream of the injectors needs to be rough, 60 grit or rougher. The interesting thing is that upstream of the injectors (for some distance I can't remember) needs to be...

That is my understanding as well. Really hoping these guys with dyno/track and engine building experience want to share. I have some thoughts on how rough is enough and other thoughts on roughness in specific areas, but my knowledge is mostly based on the flow bench and reading.

This topic came up in another post so I'm just starting a new post on this topic. The question was asked by @dusterbing the peace if testing had been done comparing a CNC ported ribbed finish to a smoothed/sanded finish. Here's one initial test on a factory CNC'd Speedmaster intake port. As a...

Starting a new thread for the CNC mill mark removal.

I'm glad you brought this up. I hit me that I have a single Speedmaster CNC head that I bought on Black Friday just for the purpose of flow testing. I was so disappointed with the head that after one flow test I've put it up and tried to forget about it. This is the perfect opportunity to...

If anyone is interested in the Bernoulli principle and how it explains the 350 fps flow bench velocity number and the 146 cfm/square inch theoretical flow limit let me know. I'll start another post.

Good question. Hopefully one of the experts will jump in here.

Here's the results of the 318LA vs 318 poly flow tests. Both of these heads were old, came off of 100,000 mile engines and look to be bone stock. This test proves nothing, but it is a fun comparison. Notice how the superior breathing capability of the poly shows up at higher lifts. This is...

I've never heard it stated that way before. Thanks. I've been testing on the same port for months. Make changes, try things, epoxy the throat and seat back up and try again. I've seen 20 cfm swings from one valve job to the next, but never really thought of it in terms of port speed. Good...

You are correct and there is a perfect explanation for it. I know you like numbers and math, so do this: Read up on Bernoulli's principles in articles such as this...

Now that is redneck engineering at it’s finest. I love it. For those who have never tried to get a silicone port mold out of the port - it can be tough. Like 15 minutes of hard work tough. I use a Jorgeson woodworking clamp to push it out, but your method is way better.

There needs to be a big asterisk beside that 308 number. As I mentioned early on, I have used all the cheat tactics that I could come up with to get that number. For instance, the combustion chamber has clay covering the spark plug and sometimes covering the whole exhaust valve. This creates...

Push Rod Pinch