I spent countless hours porting my head and also used the tall 194 / 164 valve seats etc from 12 bolt , I cut 100th off the surface , porting is power , also several other mods to use 175 rollers with guides screw-in studs I took 425th off the stud deck to get the proper rocker ratio , also smith bros had to make me custom push rods , I researched this for hours and getting advice from others , it’s my first 6 build ever ! And I’m building street n strip cars since a teen in the 1970s , no expense spared in my build , and I years work , with a 3x2 man a fre ( 3 1958 Pontiac carbs) first pull 363 HP 408 tg , but the 3rd carb cracked at shaft base , so we put the Clifford 2x4 intake with 2 new Holley 450s , made 383 HP 418.7 tq !!! All under 6000RPMs , We put an Accel coil in the DUI, HEI and picked up 5:38 race shop was impressive ,the owner couldn’t believe the power I got from a 292, 60 over , it was the first inline 6 on the dyno in thirty years there !!! The collectors ( on long tube heddders) make more power !! But there wasn’t enough room to use the collectors on the dyno , that is key for power on these hot inlinrs !!! If I had to do this again and I am , build a back up but know now what I didn’t know on the inlines , I’m confident I can build a street strip 292 , no modern crap ( I’m old school ) but the best internal parts I’m going to have a 292 making 425/ 440ish HP and 475 torque !!!! Now that I built one , it’s awesome !!!! There’s more power inside there ! I’m gonna get it , you can find some of the dyno pulls and see the car it’s went into , the car alone took 1000 hours to fabricate and built fixtures. Etc before you put a hand on it,the whole package built was and is , I had to fabricate , engine mounts And you better measure 20 times ! To get the engine at center angles , clutch linkage , the list goes on and on. !!!! But do it right , can’t be on budget , and time !!! , that new 292 build fired up in 15 seconds on the dynoy😢😮 3:50
Great video’ we do the Holden 6’s here without the lump port but Iv bought a boat with the mercruiser 250 engine and easier to keep the 6 than go to V8 like everyone else does.
Sim, eu acredito que você está certo. Também acredito que as modificações no seu Opala abriram o caminho para nós norte-americanos por décadas. É uma tendência interessante.
If you don’t have a full machine shop , but work on all your own stuff I would send the. Head to a builder and let them build it start to Finnish ! My Bridgeport took a dump so I cut and grinded the bosses out and grind the rest , it’s a pain in the ass , and you need to be precise and careful ,
I agree with outsourcing this. I cut the bolt bosses out with a reciprocating saw with a bi-metal blade and then ported it with a Dremel. I did take the milling to a fellow with the right but and equipment, but looking back, I was LUCKY it turned out as good as it did (definitely not perfect) and it was a lot of work and even got some metal flakes in my eye (yes I was wearing safety glasses that apparently should have been goggles) requiring a trip to the doctor for metal extraction. The take away is follow Brad's advice and outsource your head work, it's specialty work and few DIY garages have everything you need to do it right.
Wonderful video! Just picked up a 36 Plymouth coupe and I’m wanting to build a true nostalgia hot rod, no Jeggs catalog 350 small blocks here! I have a 250 straight six and offenhauser triple intake. I’ve heard all the old guys say you can make lots of power with the old inlines. But now I’m starting to see HOW that actually happens.
Sounds like a great project! Yeah I tried to use the "best bang for your buck" approach to power on this engine but make no mistake, you could save money on power with the Jegs 350. However you'd loose all the desired nostalgia so, in my opinion, you're on the right track. Let me know if you need any help along the way.
I’m certainly interested in tips and tricks. There’s a machine shop in sumter SC so I can have hardened seats put in. Cheap as they are i’ll run oversized stainless valves. What would you recommend for a cam as far as a street driven car is concerned? I want some pep but I’m not doing a gas guzzling race car. I’ve built a small block Chevy and a small block Buick. Straight sixers are new to me though.
Sounds like a good plan for the head. As much as I built this engine myself, I spent days in forums getting advice from people with decades more experience with these engines than I. In the end I actually relied upon the input from them and the suggested cam grind from CompCams. If you head to their site and fill out their cam form they will reply with a pre-made or custom grind and you can tune it accordingly. I'd start there if I had to do it again. My goals were the same as yours, except I knew I was turbocharging so I made some adjustments to their grind and ended up with a custom one. A picture of my cam card is on the Turbo Camaro website build sheet.
I'm sure you could weld them, but it's just not as easy for everyone. The set screws are easy for most DIY mechanics and are unlikley to fail and result in engine damage or failure. If you didn't get the welds right, splatter or other debris could end up in your chambers and do some real damage. Set screws from the underside make a solid mechanical connection, and once the head bolts are in place, they ain't going anywhere. An experienced welder could probably just tack them in place, but not everyone has the tools or skill.
In theory I understand these and it makes sense, but how much does it really improve? What results did you see that made it worth it? Better Mpg or hp?
@@5oclock_Charlie that’s the theory but has anyone really compared to know if it’s really that noticeable? Half a HP and 1 extra mpg wouldn’t be worth the trouble or the expense. 10 extra HP and 5 extra mpg savings would.
Oh ya the straight 8's are a torque masterpiece. And fast. But then again no parts available if any.. Somewhere back east a guy has just about all the things needed. But he ain't going to let go of any of it.... Lol. One day it will be a barn find. Ha ha. Back in Missouri. You can find just about anything. Stashed away in a building or a barn. Just sitting. But they won't let it go.....
Yeah, I'd say straight 6's are just rare enough to make it interesting, while still being affordable, and possible to get decent power. Ive looked around now and yeah, if one were to acquire a straight 8 you might not want to risk turbocharging as you'd always worry about cracking the block or something. At least with the 6's spare stock parts are available. In my area they are very coveted, but if you look hard enough...
Turbo Camaro I've got a buddy who runs some CNC Machinery, I'm going to hit him up and see what we can come up with... I'll keep in touch with my results.
Hey so I have a question. I have a 250 I6 but it's the late model with the integral head unit. Where the exhaust and intake are casted in one piece. Now the question is can I take a head from another earlier engine and put it on? Btw amazing work I love the Inline 6
At 15:43 it looks like you snapped the head off of the bolt that holds the lump in place. At 16:35 it looks like you're using a bolt with the head on it to secure the lump. Which is correct?
Hey, at 15:43 I remove the hex bit from the crappy ratcheting driver I'm using. It looks like it breaks because the bit was loose on the end of the driver and kinda wobbles as I pull it out of the bolt that's already recessed in the head. At 16:35 I pull the same driver away from the head and that same silly hex bit stays stuck in the bolt head. The head of the bolt holding the lump in is actually recessed in the underside of the head so it doesn't affect the flush surface of the head when it's mounted.
Why not just leave the head of the new bolt without the lump. It should still flow much better than having that restricted post in the way. You can purchase a round headed Allen head bolt there called button head bolts. Just wondering.
You're not wrong, that massive bolt boss has to go for sure. 12bolt.com sells the lumps did Dyno tests on stock head vs bolt boss removed vs boss removed with lumps and the tests showed the best performance with the lumps. Somthing to do with the increased air flow and velocity created by the lumps. If you're going to take the time to remove the bolt boss, I wouldn't dare quote the stats without confirming, but I remember the advantage was a no brainer for the cost.
incredible work !!! the inline six is one of the most pratical engines out there and there is to few videos about it ! tank you !! keep the good work!!!
You just want to use the Mil-bit to surface the inside of the port so the new head bolt has a flat spot to sit on. I held the lump in place to ensure it would end up flush with the front of the port, as that was more important than my concern with holding it by hand. The new head bolt isn't a super tight fit through the lump so it wouldn't hold it snug there anyway.
Friend if I just do the job of releasing the intake tower without placing the piece of aluminum would be good? Where I live, I do not think I have that piece!
Removing the bolt bosses should provide a much better air flow overall, but adding the lump helps to direct the bolt up over the head bolt and toward the combustion chamber. I'd consider emailing Tom Lowe at 12bolt.com and ask what the cost of the lumps would be shipped to you. They aren't expensive, but I suppose the shipping could be.
Hey Jackson, I have no idea. I'm not familiar with the 151 and don't know off hand if the parts for the 250/292 are compatible with your motor. I know Brazil is famous for their work with the L6 so I'd be looking locally if it was me.
lump creates venturi effect, speeding up the air, increasing cylinder fill rate and at the same time reducing pumping losses and creating tumbling effect improving fuel atomization, making a more homogeneous air/fuel mixture, thus improving combustion and efficiency. Quite simple actually ;)
Diving deeper than that the directional transition the intake air must make to go from the port floor to through the valve creates turbulence that kills flow. If you give the air a larger radius to make the turn you reduce turbulence greatly, and improve flow.
The comments below explanation is right on ! These lumps have been around since the 60s , they would use brass and braze lumps in , now they are a cast insert , I can’t say for sure who’s is best but it works well when you flow test them , you put my head on any stock 292 and I bet you will pick up 75+ HP
Hi, I see you plugged the egr holed on the exhaust ports. Did you remove the little tubes that protruded into the exhaust ports? How? I am trying to remove them from my 292 head. Thanks. 🙏🏼
Hmm, I plugged the holes with the bolts as seen, but mine didn't have little tubes into the exhaust ports. As long as they are plugged and don't pertrude into the ports too much I wouldn't worry about them.
Wasn no kit when we did this to holden 6's. We used countersunck screws and didn't fit a lump, we just left the countersunk screws pretty flush with the top of the port
Yeah, the fast forwarded video is good for time saving but I should of considered swapping the audio out. Ahh well. It's still neat to see this head get some attention.
Are any aftermarket heads available for the inline engines. ??? I was starting to look for them and came across the hump/lump. Thing. There's a vwhole market open out there for massive improvement and it barely exists. Engine covers and a few manifolds. .??? So much could be added. The inline engine has been out there longer than any other to include the straight 8. And God's big 426 & 503. They could make monster horse power. But mope nothing out there.......
Yeah, a handful of custom accessories and billet dress up items but performance parts are few and far between. No after market heads that I'm aware of. These engines have a big performance market in Brazil, but I'm not sure what they do for cylinder heads there. I'd bet the most cost effective upgrade for airflow is going to be the bolt boss removal followed by the lump install. It does make a significant difference if you can source cheap machine work. Those 8's would be fun to work with but I'd bet the performance costs for them are even higher.
Good question! The lump kit came with the bolts and I'm fairly certain they were fine threaded. Also by looking at that tap I'm pretty sure it's a #8 fine.
Yeah the basic idea is a little odd. However, there's actual flow rate tests that show removal of the bolt boss has a massive improvement over stock and then the installation lumps changes the shape of the port and increases velocity which has better flow than just removing the boss. Check out this link: www.12bolt.com/65279inline-cylinder-head-flow65279.html
If you weren't interested in the lumps you could still cut the boss out, use the shorter capped head bolts and then thread in some plugs. If you want to avoid machine shop work all together you could port and slim the bosses, but the added flow would be minimal in comparison. Consider the size of that bolt boss and what fraction of the port it consumes. A terrible design for flow but certainly accomplished the "bomb proof" intention they had for it.
Tony thompson: Big hole doesnt mean huge flow. Air/fuel mixture velocity drops if port is too big. That causes fuel to separate and form drops. But it would be best to shape that boss a bit and forget that sawing and lumps.
I agree with the first part, it's not just about the size of the hole, but it's natural flow. If you take a look at 12bolt.com they conducted actual dyno results on airbflow, with this head: stock, ported, ported without lumps and then with. Lumps had the best flow as they create the most ideal path for the air to move with the design of these chambers. Any attention you give to this head is good as it's stock flow is horrible.
I spent countless hours porting my head and also used the tall 194 / 164 valve seats etc from 12 bolt , I cut 100th off the surface , porting is power , also several other mods to use 175 rollers with guides screw-in studs I took 425th off the stud deck to get the proper rocker ratio , also smith bros had to make me custom push rods , I researched this for hours and getting advice from others , it’s my first 6 build ever ! And I’m building street n strip cars since a teen in the 1970s , no expense spared in my build , and I years work , with a 3x2 man a fre ( 3 1958 Pontiac carbs) first pull 363 HP 408 tg , but the 3rd carb cracked at shaft base , so we put the Clifford 2x4 intake with 2 new Holley 450s , made 383 HP 418.7 tq !!! All under 6000RPMs , We put an Accel coil in the DUI, HEI and picked up 5:38 race shop was impressive ,the owner couldn’t believe the power I got from a 292, 60 over , it was the first inline 6 on the dyno in thirty years there !!! The collectors ( on long tube heddders) make more power !! But there wasn’t enough room to use the collectors on the dyno , that is key for power on these hot inlinrs !!! If I had to do this again and I am , build a back up but know now what I didn’t know on the inlines , I’m confident I can build a street strip 292 , no modern crap ( I’m old school ) but the best internal parts I’m going to have a 292 making 425/ 440ish HP and 475 torque !!!! Now that I built one , it’s awesome !!!! There’s more power inside there ! I’m gonna get it , you can find some of the dyno pulls and see the car it’s went into , the car alone took 1000 hours to fabricate and built fixtures. Etc before you put a hand on it,the whole package built was and is , I had to fabricate , engine mounts And you better measure 20 times ! To get the engine at center angles , clutch linkage , the list goes on and on. !!!! But do it right , can’t be on budget , and time !!! , that new 292 build fired up in 15 seconds on the dynoy😢😮 3:50
Great video’ we do the Holden 6’s here without the lump port but Iv bought a boat with the mercruiser 250 engine and easier to keep the 6 than go to V8 like everyone else does.
If you have a mill, just mill it. It’ll probably be easier and more uniform. Saws are for carpentry.
@@richardbilbruck7241 Very true. I do not have a mill. I borrowed someone's for the lump port install video but sometimes a sawzall's ya got 😅
Caramba parece ser o mesmo cabeçote do nosso querido Opala, muito top
Sim, eu acredito que você está certo. Também acredito que as modificações no seu Opala abriram o caminho para nós norte-americanos por décadas. É uma tendência interessante.
@@TurboCamaro67 show 👏👏
Very nice work friend
Cómo de llama en argentina esa rampita ?
If you don’t have a full machine shop , but work on all your own stuff I would send the. Head to a builder and let them build it start to Finnish ! My Bridgeport took a dump so I cut and grinded the bosses out and grind the rest , it’s a pain in the ass , and you need to be precise and careful ,
I agree with outsourcing this. I cut the bolt bosses out with a reciprocating saw with a bi-metal blade and then ported it with a Dremel. I did take the milling to a fellow with the right but and equipment, but looking back, I was LUCKY it turned out as good as it did (definitely not perfect) and it was a lot of work and even got some metal flakes in my eye (yes I was wearing safety glasses that apparently should have been goggles) requiring a trip to the doctor for metal extraction. The take away is follow Brad's advice and outsource your head work, it's specialty work and few DIY garages have everything you need to do it right.
Wonderful video! Just picked up a 36 Plymouth coupe and I’m wanting to build a true nostalgia hot rod, no Jeggs catalog 350 small blocks here! I have a 250 straight six and offenhauser triple intake. I’ve heard all the old guys say you can make lots of power with the old inlines. But now I’m starting to see HOW that actually happens.
Sounds like a great project! Yeah I tried to use the "best bang for your buck" approach to power on this engine but make no mistake, you could save money on power with the Jegs 350. However you'd loose all the desired nostalgia so, in my opinion, you're on the right track. Let me know if you need any help along the way.
I’m certainly interested in tips and tricks. There’s a machine shop in sumter SC so I can have hardened seats put in. Cheap as they are i’ll run oversized stainless valves. What would you recommend for a cam as far as a street driven car is concerned? I want some pep but I’m not doing a gas guzzling race car. I’ve built a small block Chevy and a small block Buick. Straight sixers are new to me though.
Sounds like a good plan for the head. As much as I built this engine myself, I spent days in forums getting advice from people with decades more experience with these engines than I. In the end I actually relied upon the input from them and the suggested cam grind from CompCams. If you head to their site and fill out their cam form they will reply with a pre-made or custom grind and you can tune it accordingly. I'd start there if I had to do it again. My goals were the same as yours, except I knew I was turbocharging so I made some adjustments to their grind and ended up with a custom one. A picture of my cam card is on the Turbo Camaro website build sheet.
Muito bom os vídeos onde consigo comprar essas peças para fazer no .eu cabeçote
I bought all the parts from 12bolt.com, thanks for watching!
Thanks for watching all the way from Brazil! I got the lump port parts from 12bolt.com
Brasil 2020 👊✌️✌️ 6inline❤️✌️
Directionality?
Sorry, you lost me. Did I say that in the video improperly? Or were you looking for some specific information?
why not just weld the lump in on the inside instead of using the set screws?
I'm sure you could weld them, but it's just not as easy for everyone. The set screws are easy for most DIY mechanics and are unlikley to fail and result in engine damage or failure. If you didn't get the welds right, splatter or other debris could end up in your chambers and do some real damage. Set screws from the underside make a solid mechanical connection, and once the head bolts are in place, they ain't going anywhere. An experienced welder could probably just tack them in place, but not everyone has the tools or skill.
In theory I understand these and it makes sense, but how much does it really improve? What results did you see that made it worth it? Better Mpg or hp?
It squeezes the air and makes the velocity go up, this makes the CFM of the port go up, increasing both power and mpg.
@@5oclock_Charlie that’s the theory but has anyone really compared to know if it’s really that noticeable? Half a HP and 1 extra mpg wouldn’t be worth the trouble or the expense. 10 extra HP and 5 extra mpg savings would.
Oh ya the straight 8's are a torque masterpiece. And fast. But then again no parts available if any.. Somewhere back east a guy has just about all the things needed. But he ain't going to let go of any of it.... Lol. One day it will be a barn find. Ha ha. Back in Missouri. You can find just about anything. Stashed away in a building or a barn. Just sitting. But they won't let it go.....
Yeah, I'd say straight 6's are just rare enough to make it interesting, while still being affordable, and possible to get decent power. Ive looked around now and yeah, if one were to acquire a straight 8 you might not want to risk turbocharging as you'd always worry about cracking the block or something. At least with the 6's spare stock parts are available. In my area they are very coveted, but if you look hard enough...
Turbo Camaro
I've got a buddy who runs some CNC Machinery, I'm going to hit him up and see what we can come up with... I'll keep in touch with my results.
Roger Marshall yeah please do! I'm always curious about how eveyones projects have turned out.
Going to be doing this on a 292... eeek
+Thanos that's the ideal 6 to do it all on! Good luck to you!
keep us informed on how it turns out.
I always assumed that the head bolt held those in place
Hey so I have a question. I have a 250 I6 but it's the late model with the integral head unit. Where the exhaust and intake are casted in one piece. Now the question is can I take a head from another earlier engine and put it on? Btw amazing work I love the Inline 6
Yes, it's no problem to use an early cylinder head on a 1975-84 engine that originally had an integral head.
At 15:43 it looks like you snapped the head off of the bolt that holds the lump in place. At 16:35 it looks like you're using a bolt with the head on it to secure the lump. Which is correct?
Hey, at 15:43 I remove the hex bit from the crappy ratcheting driver I'm using. It looks like it breaks because the bit was loose on the end of the driver and kinda wobbles as I pull it out of the bolt that's already recessed in the head. At 16:35 I pull the same driver away from the head and that same silly hex bit stays stuck in the bolt head. The head of the bolt holding the lump in is actually recessed in the underside of the head so it doesn't affect the flush surface of the head when it's mounted.
@@TurboCamaro67 Got it. Thanks. Looking forward to watching your head work.
Why not just leave the head of the new bolt without the lump. It should still flow much better than having that restricted post in the way. You can purchase a round headed Allen head bolt there called button head bolts. Just wondering.
You're not wrong, that massive bolt boss has to go for sure. 12bolt.com sells the lumps did Dyno tests on stock head vs bolt boss removed vs boss removed with lumps and the tests showed the best performance with the lumps. Somthing to do with the increased air flow and velocity created by the lumps. If you're going to take the time to remove the bolt boss, I wouldn't dare quote the stats without confirming, but I remember the advantage was a no brainer for the cost.
Good working installing the lumps. I have the lumps in mine.
incredible work !!! the inline six is one of the most pratical engines out there and there is to few videos about it ! tank you !! keep the good work!!!
We've got plans for a lot more inline 6 videos. Thanks for watching!
Why not put the head bolt in to hold the lump while you are drilling for the capscrew?
You just want to use the Mil-bit to surface the inside of the port so the new head bolt has a flat spot to sit on. I held the lump in place to ensure it would end up flush with the front of the port, as that was more important than my concern with holding it by hand. The new head bolt isn't a super tight fit through the lump so it wouldn't hold it snug there anyway.
Friend if I just do the job of releasing the intake tower without placing the piece of aluminum would be good? Where I live, I do not think I have that piece!
Removing the bolt bosses should provide a much better air flow overall, but adding the lump helps to direct the bolt up over the head bolt and toward the combustion chamber. I'd consider emailing Tom Lowe at 12bolt.com and ask what the cost of the lumps would be shipped to you. They aren't expensive, but I suppose the shipping could be.
@@TurboCamaro67 Thank you very much friend! I will send the email to know the price of the shipment to Venezuela! Congratulations on your videos!
nice job , i have 151 2.5L 4cyl iron duke brazilian opala ! where i can fine some parts for my engine ? thanks !
Hey Jackson, I have no idea. I'm not familiar with the 151 and don't know off hand if the parts for the 250/292 are compatible with your motor. I know Brazil is famous for their work with the L6 so I'd be looking locally if it was me.
Basecle is the some size of parts 6cc and 4cc 151L and 153 L , that diferente just 2cc last ,I have one Chevy Opala ss !
why put the lump in? you have more of an opening without the lump.
lump creates venturi effect, speeding up the air, increasing cylinder fill rate and at the same time reducing pumping losses and creating tumbling effect improving fuel atomization, making a more homogeneous air/fuel mixture, thus improving combustion and efficiency. Quite simple actually ;)
@@fsouzajr Thanks ,in very simple terms sort of a funnel effect?
Port floors reduce flow.
So by blocking the port floor you raise flow.
Diving deeper than that the directional transition the intake air must make to go from the port floor to through the valve creates turbulence that kills flow. If you give the air a larger radius to make the turn you reduce turbulence greatly, and improve flow.
The comments below explanation is right on ! These lumps have been around since the 60s , they would use brass and braze lumps in , now they are a cast insert , I can’t say for sure who’s is best but it works well when you flow test them , you put my head on any stock 292 and I bet you will pick up 75+ HP
Hi,
I see you plugged the egr holed on the exhaust ports. Did you remove the little tubes that protruded into the exhaust ports? How? I am trying to remove them from my 292 head.
Thanks. 🙏🏼
Hmm, I plugged the holes with the bolts as seen, but mine didn't have little tubes into the exhaust ports. As long as they are plugged and don't pertrude into the ports too much I wouldn't worry about them.
Wasn no kit when we did this to holden 6's. We used countersunck screws and didn't fit a lump, we just left the countersunk screws pretty flush with the top of the port
Yeah I'm fortunate kits are available as it sure made it come together nicely. A worthy upgrade no matter how you accomplish it.
nice job
It sounded like you picked up some paranormal chipmunks on audio
Yeah, the fast forwarded video is good for time saving but I should of considered swapping the audio out. Ahh well. It's still neat to see this head get some attention.
Are any aftermarket heads available for the inline engines. ???
I was starting to look for them and came across the hump/lump. Thing. There's a vwhole market open out there for massive improvement and it barely exists. Engine covers and a few manifolds. .??? So much could be added. The inline engine has been out there longer than any other to include the straight 8. And God's big 426 & 503. They could make monster horse power. But mope nothing out there.......
Yeah, a handful of custom accessories and billet dress up items but performance parts are few and far between. No after market heads that I'm aware of. These engines have a big performance market in Brazil, but I'm not sure what they do for cylinder heads there. I'd bet the most cost effective upgrade for airflow is going to be the bolt boss removal followed by the lump install. It does make a significant difference if you can source cheap machine work. Those 8's would be fun to work with but I'd bet the performance costs for them are even higher.
You tap the lump with "a regular #8 tap" - would that be a regular #8 fine or a regular #8 coarse ?
Good question! The lump kit came with the bolts and I'm fairly certain they were fine threaded. Also by looking at that tap I'm pretty sure it's a #8 fine.
Mucho trabajo pero eso no se le hace a una Tapa Gm lo mejor es comprar hemisferica , entubar o 12 bocas.!
Boy that's a shitty designed head.
So removing the original casting just to plug up the port with something else. ?????
That just doesn't make sense ????
Yeah the basic idea is a little odd. However, there's actual flow rate tests that show removal of the bolt boss has a massive improvement over stock and then the installation lumps changes the shape of the port and increases velocity which has better flow than just removing the boss. Check out this link: www.12bolt.com/65279inline-cylinder-head-flow65279.html
@@TurboCamaro67 How about just "porting" the original boss, streamlining it to improve flow?
If you weren't interested in the lumps you could still cut the boss out, use the shorter capped head bolts and then thread in some plugs. If you want to avoid machine shop work all together you could port and slim the bosses, but the added flow would be minimal in comparison. Consider the size of that bolt boss and what fraction of the port it consumes. A terrible design for flow but certainly accomplished the "bomb proof" intention they had for it.
Tony thompson: Big hole doesnt mean huge flow. Air/fuel mixture velocity drops if port is too big. That causes fuel to separate and form drops.
But it would be best to shape that boss a bit and forget that sawing and lumps.
I agree with the first part, it's not just about the size of the hole, but it's natural flow. If you take a look at 12bolt.com they conducted actual dyno results on airbflow, with this head: stock, ported, ported without lumps and then with. Lumps had the best flow as they create the most ideal path for the air to move with the design of these chambers. Any attention you give to this head is good as it's stock flow is horrible.