"gee.... you did a fantastic job home porting. I am sending my $$ to you to port my heads right away. "

 

You're not helping.

 

Hey, I've been "lurking" in this thread since the beginning and I think we all applaud your ambition to do your own port work. Not all may agree with the outcome or the theories behind your work, but most will admire the effort. Speaking for myself I know how much of a pain in the a$$ it is to R&R heads on our cars...so I didn't want to venture into uncharted waters (ie porting myself and risk having little or no gain to show for all the work)...I left it to those who specialize in this field, and who have spent years honing their craft...and the way my car performs is a direct result of their efforts and worth every penny to me...

Again, I applaud your efforts...now its time to strap those things on and see what we see...I'm not a big fan of numbers as those who have followed my dyno rants probably know...You have to see how it works in the real world...Good luck with what you are trying to accomplish...

--Alan

 

agreed.

 

I admire that you took the time to port you own heads, but I don't think you're going to get the answers you are looking for here. The reason is because very few people ever set out to attempt to reach the same goals you are. I don't think you'll get much more flow from the heads leaving the runner volume at 180cc. With home porting them, that is. If I were in your shoes, I'd open them up a bit and try and help the .400" and .500" flow. Try to sacrifice as little velocity as possible, but get some more cfm in those lift areas. I'm not a head porter, but from what I understand, you have to sacrifice to get what you want (low end torque, high rpm horsepower, or a good mid-range). If you want to make a ton of torque down low, then you can't have the heads flowing rediculous flow numbers all the way around with huge runners. You need that port velocity. Now, pick the rpm range you want the car to perform in, port the heads and select the cam accordingly. If you going to spend most of your time driving around town and cruising on the highway, I'd say the heads you did would be fine. If you want something that will scream if you want it to, then you're going to have to sacrifice some low-end torque to get it (port velocity). I could be completely off of the map, but this is what I understand.

If the low end torque is what you want, bolt the heads on the car and take it to the dyno to see what kind of torque and horsepower it makes and where it makes it. That is going to be the only way you can tell what you did and if you reached your goal.

 

Thanks for the helpful posts Sweetred95ta, ABA383, sam and Kevin Blown 95 TA. About half the posts in this thread are flames of varying intensity by a few people, in my opinion. Don't expect everyone to agree with me and don't see why anyone should get their skirt blown up if I or anyone else questions their post, it's logic, or it's intent when malice is obvious. I just expect people to disagree in an intellectually honest fashion instead of saying anything to win an argument. Generally if I'm working with someone who has a lower level of understanding I try to share what I know. I don't really feel all that superior by putting someone down or degrading them because they asked me a question that I know ( or in some cases only thought I knew) the answer to.

For those who are interested in home porting or even porting in general read on.

After talking to a few competent head porters who have seen my ports and thinking things over I feel pretty solid in guessing that the unmodified short side radius is responsible for both the very strong low/mid lift flow and the choking affect somewhere above .400" lift. The port velocity has picked up a good bit from stock and this increased velocity is starting to show the stock short side radius as the weakest part of the port at higher lift/higher velocity. From my experience I'm not convinced that a peak flow 16% higher than stock is a big horsepower handicap with a cam in the 220 duration range but since this cam lifts .570" I am going to tweak things just a little to try to stabilize or slightly increase the flow rate at .5" lift and up.

Here's what I think is happening above .400 lift: The port velocity has climbed high enough that air is separating from the floor as it tries to make the turn over the short side radius. This kicks in once the valve has lifted enough to let the velocity exceed some certain max. stable speed. The lower pressure air at the port floor gets fast enough at high lift that it can't make the turn into the cylinder without "running off the road" and colliding with the bulk of the flow along the port roof. This disrupts the airflow across the top and sides of the bowl headed down into the port and causes some turbulence. This turbulence over the short side radius heading down into the cylinder is probably the primary restriction in the current port's form. The port obviously works great up until .400" lift but to get higher high lift flow rates the stock short side radius will need to be modified, at the expense of some of the low/mid lift flow.

I made a tool today to measure the port wall thickness on either side of the head bolt between the intake ports. It will also measure the thickness at the pushrod constriction. Did a little grinding to decrease the radius at the sides of the port floor over the hump of the short side radius ( made the flat area of the floor wider for more volume in the floor over the hump and less velocity here. Also widened things as much as possible by the head bolt to give more volume on the port sides, this should decrease the velocity there some and help the high lift numbers.
The flow is very promising from .2" to .4" lift so I wanted be conservative and hopefully pick up a little peak flow while not dropping too much of the mid lift flow.

I hope to get them finished over the weekend and retest the flow next week.

People with information or opinions that don't have a malicious intent are welcome to post anything helpful or critique the logic here. Just trying to decode the puzzle with a little help where I can find it. Is that a crime? Seems like it is to some people.

Later, Michael

 

Had some new flow tests done today, got to actually assist the tech in getting the numbers and setting things up.

Here's a compilation of flow bench results from today's two tests and my original that was posted a few weeks ago. These are home ported LT1 heads. Version 1 at the right was the original test for the first port job. The stock column near the left is the stock port. Version 2 and 3 were made today with a slight revision to the short side radius between tests that took less than 5 minutes.

Here are port flow numbers for Version 2 and Version 3 porting, both at about 185cc's port volume:

Version 2

.2"- 132cfm .3"- 182cfm .4"- 225cfm .5"- 253 cfm, .6" lift 262cfm

Version 3 numbers ( after very small change to short side radius)

.2"- 133cfm .3"- 185cfm .4"- 228cfm .5"- 235cfm .6"- 239 cfm



Average flow from .3" to .6" lift ___________average flow from .4" to .6" lift
combined

Stock:_____ 195 cfm________________ stock: _____204 cfm___
V 1 port: ___224 cfm__15 % impr.____ V1 port: ___231 cfm ___13% imp.
V 2 port: ___231 cfm _ 18% impr. _____V2 port: ___247 cfm ___21% imp.
v 3 port:___223 cfm __14% impr.______V3 port: ____235 cfm__ 15% imp.






The version 2 numbers were taken with slight changes to the version 1 porting, the top of the pushrod constriction was widened as much as possible, the area on the cylinder wall side of the intake guide was widened as much as possible considering the head bolt location between ports, the guide was narrowed down more. Also the floor of the short side radius was widened and the last 3/4" of the radius before the valve seat was blended and layed back a little bit.

Version 3 numbers were recorded at the same session this evening after talking with one of the porting techs who reviewed the just recorded version 2 flow chart. He said that smoothing out an area of the hump in the short side radius by around 1/8" and radiusing it about 1/2" either side to blend would pick up the mid flow numbers some. I was pretty happy with the first numbers and skeptical about improving them. I took less than 1/16" off the most abrupt part of the radius ( where the port floor peaked and turned into the short side radius.) Very, very subtle change that took about 4 minutes to complete. The helper said he would do a lot more before retesting but I exercised my veto and decided to retest with about the most subtle change that I thought might change the port flow a measurable amount.

Boy did it change, the low/mid numbers came up just a little but the .5" and .6" lift numbers went in the toilet. Since the numbers from .1" to .4" were actually a very slight improvement we thought it might be a leak that developed between the head and the fixture on the .5" and .6" numbers on the version 2 test we ran today. Since we'd already torn it down we couldn't really repeat it though we tried. Another guy mentioned that if you run the bench very long it can heat up and affect the accuracy. We did notice one time when he tested the same lift three time for about 10 seconds apiece in a short time span that the flow number dropped by about 6 cfm and then 10 cfm. Don't really know if this accounts for the unexplained drop of high lift flow in test version 3.

So anyway, the version 2 numbers were remarkably high at high lifts. If something wasn't awry with the bench or the setup for attaching the head then I was onto something really good here. The % improvement jumps through the roof at .5" and .6" lift with peak flow of 262 cfm.

Since I setup the head on the fixture for the last tests I wondered if something had been changed between test version 2 and 3 today that was shrouding the valve at high lift and killing the high lift numbers. We ran the exhaust again and got the same numbers as a test of the bench consistency, then had the guy who set it up the first time set it up again from scratch to get the same numbers.

Overall I'm pretty pleased with the version 3 numbers, a 16 and 17% improvement in flow at .5" and .6" compared to the stock port with a peak of 239 cfm compared to 203 stock. The version 2 numbers were nearly identical to version 3 numbers from .1 to .4" lift so I think there's a good likelihood that test error crept in and drove them up. I'll probably put about a half thimble of epoxy back to replace the metal I removed and retest just so I'll know



I'm inclined to say that the last sublte mod. to the short side radius wouldn't have choked off 12 to 15% of the flow, if a change this subtle is the difference between 239 cfm and 262 cfm then it would be very difficult to hand port with any consistency at all.

Like I said, I may throw a dab of epoxy in their and retest to see if the 262 cfm peak comes back. If it does and the numbers weren't a fluke I should be able to get them all in that range. Who knows?

later, Michael

 

you found your restriction.
NOW GET TO WORK!

 

It isn't always a restriction in the usual sense. You grind away at the short side radius cause it makes sense that you are opening up the port, but then the air on that side travels less distance than the air on the other side and you have uneven flow and it can cause turbulence which can hurt filling of the cylinder.

 

I'm confused....

I thought the head porter was the guy at the dealership who brings you home when your car is being fixed?

 

The take on "Professional Head Porters" in this thread is pretty interesting. It's as thought they are a few chosen Zen masters or something. There is no magic in airflow, and with the SBC... well, it's all been done. Nobody is blazing new trails these days on stock castings.

I can understand why a good head porter is a rare thing if the rule is you have to spend years sweeping the floors first. Your best and your brightest would never even start. They would just wind up being lawyers, accountants, and engineers... that are into DIY head porting for fun on the weekends .

BTW- Grammarman, I agree with you on the whole DIY philosophy, and I port my own heads. If the goal was guaranteed success, well I can certainly afford to buy proven off-the-shelf goodies, but where's the sport in that? Just try not to be such a tool.