Head porting experiment (gone wrong)
Thread Starter
12 Second Club
Joined: Dec 2017
Posts: 1,030
Likes: 219
From: San Antonio
Head porting experiment (gone wrong) I just wanted to share a little experiment I conducted on a set of "junk" heads. In case anyone has thought about adding "dimples" to a cathedral port head, I advise against it. Here's why:
TECH Resident
Joined: Mar 2012
Posts: 858
Likes: 402
From: Texas
Are you sure that there wasn't some kind of calibration error when testing the dimpled port? Those numbers seem damn low for what was done.
I remember about 15 years ago, there were some people talking about port dimples/ grooves, and how it was supposed to help fuel atomization...
And nothing ever came of it. To this day, all of the big names in port development still have smooth walls.
It kind of reminds me about grooved pistons/ cylinder heads back in the mid '00s. Supposedly a groove in the piston head or cylinder would drastically increase octane tolerance and decrease BSFC.
Lots of guys SAID they tried it with great results, but no one could give any concrete numbers.
https://garage.grumpysperformance.co...grooves.11674/
I remember about 15 years ago, there were some people talking about port dimples/ grooves, and how it was supposed to help fuel atomization...
And nothing ever came of it. To this day, all of the big names in port development still have smooth walls.
It kind of reminds me about grooved pistons/ cylinder heads back in the mid '00s. Supposedly a groove in the piston head or cylinder would drastically increase octane tolerance and decrease BSFC.
Lots of guys SAID they tried it with great results, but no one could give any concrete numbers.
https://garage.grumpysperformance.co...grooves.11674/
Thread Starter
12 Second Club
Joined: Dec 2017
Posts: 1,030
Likes: 219
From: San Antonio
I normally don't touch the short side. I only put the dimples in the first half of the "short side", but I stayed far away from the "short turn". The area where I put the dimples is supposedly slower. I was trying to increase air speed in those areas.
I saw an Eric Weingartner video where he dimpled a FloTec casting LS3 style head. I have been wanting to test this on a cathedral port head every since then. The dimples actually helped on the LS3 head. The theory behind this is that the dimples effectively "shrink" the port. Since the LS3 ports are so massive, it actually helps to make them smaller. Shrinking the ports increases air speed, which increases air flow. Since the cathedral ports, especially the 706, are so small already, the dimples hurt air flow. Making the 706 ports smaller seems to restrict airflow instead of helping it. Now that I know that, I won't be putting dimples on any cathedral port heads.
Here's the video I was referring to:
I saw an Eric Weingartner video where he dimpled a FloTec casting LS3 style head. I have been wanting to test this on a cathedral port head every since then. The dimples actually helped on the LS3 head. The theory behind this is that the dimples effectively "shrink" the port. Since the LS3 ports are so massive, it actually helps to make them smaller. Shrinking the ports increases air speed, which increases air flow. Since the cathedral ports, especially the 706, are so small already, the dimples hurt air flow. Making the 706 ports smaller seems to restrict airflow instead of helping it. Now that I know that, I won't be putting dimples on any cathedral port heads.
Here's the video I was referring to:
Thread Starter
12 Second Club
Joined: Dec 2017
Posts: 1,030
Likes: 219
From: San Antonio
The dimpled and non-dimpled ports were flowed back to back. There were no changes to calibration or any other factors. The first flow sheet I showed was from over a year ago. That head is on the 5.3L engine I built and sold last year. I just pulled out that sheet because that head still had the swirl ramp. I was curious if the swirl ramp would change anything, and it didn't look like it did. Other than the swirl ramp, the head from the first sheet and second were ported the same.
Anytime you commit to an experiment and you can acquire solid data from that, it didn’t go wrong. (talking about your title here) Data is data, no matter which way you or I hoped it would go. I’ll say this about what you’ve done…dimpling has its place, but as you’ve seen here, it’s not going to help a fast port. I’m super excited to see testing like this here on Tech!
Trending Topics
TECH Fanatic
Joined: Jul 2007
Posts: 1,802
Likes: 331
From: Wilmington, De
Anytime you commit to an experiment and you can acquire solid data from that, it didn’t go wrong. (talking about your title here) Data is data, no matter which way you or I hoped it would go. I’ll say this about what you’ve done…dimpling has its place, but as you’ve seen here, it’s not going to help a fast port. I’m super excited to see testing like this here on Tech!
I saw that Weingartner video on the dimpled port, and partially dimpling the port showed a gain of about 3-5 cfm while dimpling the entire port showed a loss of 3-5 cfm. The partial dimple was done in areas where airspeed would be the slowest and the larger 5 cfm gains were seen at .600 and .700 lift points. I think the ultimate question is if the labor involved with dimpling 8 ports is justified by the benefits.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
TECH Resident
Joined: Jun 2011
Posts: 936
Likes: 472
I saw that Weingartner video on the dimpled port, and partially dimpling the port showed a gain of about 3-5 cfm while dimpling the entire port showed a loss of 3-5 cfm. The partial dimple was done in areas where airspeed would be the slowest and the larger 5 cfm gains were seen at .600 and .700 lift points. I think the ultimate question is if the labor involved with dimpling 8 ports is justified by the benefits.
Also, the airspeed differences at lower vacuum levels could be more pronounced, allowing better throttle response and driveability. On a purely strip-use vehicle, not really important, but for street use, can be a benefit that wouldn't show up on a dyno. On an actual engine, the goal is to get the air accelerating as quickly as possible during intake opening, not necessarily worrying about a peak velocity, but it's a decent way to differentiate port flow.
Last edited by 68Formula; Oct 30, 2023 at 09:03 AM.
Anytime you commit to an experiment and you can acquire solid data from that, it didn’t go wrong. (talking about your title here) Data is data, no matter which way you or I hoped it would go. I’ll say this about what you’ve done…dimpling has its place, but as you’ve seen here, it’s not going to help a fast port. I’m super excited to see testing like this here on Tech!
Thread Starter
12 Second Club
Joined: Dec 2017
Posts: 1,030
Likes: 219
From: San Antonio
I saw that Weingartner video on the dimpled port, and partially dimpling the port showed a gain of about 3-5 cfm while dimpling the entire port showed a loss of 3-5 cfm. The partial dimple was done in areas where airspeed would be the slowest and the larger 5 cfm gains were seen at .600 and .700 lift points. I think the ultimate question is if the labor involved with dimpling 8 ports is justified by the benefits.
Thread Starter
12 Second Club
Joined: Dec 2017
Posts: 1,030
Likes: 219
From: San Antonio
Anytime you commit to an experiment and you can acquire solid data from that, it didn’t go wrong. (talking about your title here) Data is data, no matter which way you or I hoped it would go. I’ll say this about what you’ve done…dimpling has its place, but as you’ve seen here, it’s not going to help a fast port. I’m super excited to see testing like this here on Tech!
The machine shop said they have seen dimples in heads before. It worked on some heads, but not others. He mentioned the GTR and some Honda heads, but I don't remember exactly which one it worked on.
TECH Resident
Joined: Oct 2006
Posts: 993
Likes: 173
From: Euless, TX
A flow bench is a helpful tool but more flow does not always equal more power. A back to back dyno test would give better information here. I have also wanted to see setups pulled from ~1,000 to say 4,000 rpm with 1/4 throttle opening. Every dyno pull you see is 3,500+ rpm and WOT. I would also find BSFC and torque output at say 10% throttle and 2,000 rpm interesting.
I would also wager that dimpling the bowl was the flow loss, not the dimples in the port. You added turbulence to the side that should be flowing at the highest velocity, thus inducing turbulence. I bet that port was screaming too. Up for a test just dimpling the port floor on the manifold side at the entry of the port? The dimples in theory act much like adding epoxy to the slower flowing areas of the port.
I have also seen it said by an Engine Master participant and winner that year state that the ideal port would flow ZERO until ~0.300 lift. Flow under 0.300 is mostly lost to reversion.
I would also wager that dimpling the bowl was the flow loss, not the dimples in the port. You added turbulence to the side that should be flowing at the highest velocity, thus inducing turbulence. I bet that port was screaming too. Up for a test just dimpling the port floor on the manifold side at the entry of the port? The dimples in theory act much like adding epoxy to the slower flowing areas of the port.
I have also seen it said by an Engine Master participant and winner that year state that the ideal port would flow ZERO until ~0.300 lift. Flow under 0.300 is mostly lost to reversion.
Last edited by Fast355; Oct 31, 2023 at 12:58 AM.
Staging Lane
Joined: Sep 2022
Posts: 67
Likes: 18
From: Mississippi
My experience with dimpling the iron block ls heads is that even if done flawlessly, you won't gain anything more than maybe 6cfm, if that, and for the amount of time that it takes to do a good dimpling job, it's nowhere near worth the trouble. One way to look at it is how much is YOUR time worth an hour. Then figure up how much time it takes to do a really good hand-porting and dimpling job, and when you come up with your final "cost" figure, I guarantee you'll come up with a dollar amount that would pay for a nice set of CNC aftermarket heads.
I love to see that you gave it a try though, and I'm even more glad that you came here and shared the results with everyone. It's stuff like this that made me fall in love with this forum to begin with!
I love to see that you gave it a try though, and I'm even more glad that you came here and shared the results with everyone. It's stuff like this that made me fall in love with this forum to begin with!