Porting sbc heads?

[SoCalDave]

Cast iron heads are a pain, so maybe start work on the intake bowls already. I practiced on the stock 993 heads from my Nova and it takes a long time to remove material.

[steve cowan]

Can you post photos of cylinder heads if possible, chamber etc

[88bluestar]

Will have to clean them up first.

[mag2555]

Just for the record, your not getting anywhere near 290 cfm@28” out of any iron head that ever came out of GM / the factory
bolted to a production block.

Max ported with a 1.94” valve getting 260 cfm is a large challenge and had better have a flow bench at your disposal!

[Bill Chase]

Stock heads only. Vortecs not allowed. The 991 is what I have to work with. Porting allowed, chamber can be smaller so decking it to a certain degree is ok. I had planned to run a -5 flat top with them. 6.0 I beam stroker rods.

what about the 128/113 castings from the 86-91 corvettes? aluminum, easier to port. can be found pretty cheap now days, you would need a dich piston to keep compression down due to their 58cc chambers, but if the class allows chamber work you can probably get them up to 60-62 cc just unshrouding the valves.

[mt-engines]

Just for the record, your not getting anywhere near 290 cfm@28” out of any iron head that ever came out of GM / the factory
bolted to a production block.

Max ported with a 1.94” valve getting 260 cfm is a large challenge and had better have a flow bench at your disposal!

[Dave B]

And to clarify-
383 cubes needs 290cfm @ 6000rpm before anyone loses there mind.

And if engine was designed correctly a 383 would have 290 cfm at .450" lift .Unless you have something against making good hp or like messing with 60 yr old junk. Last I looked it's 2023 and the modern day grocery getter SBC comes with over 2.150" valve .It idles in traffic and pulls cleanly to over 7000 rpm and comes with a warranty.Im amazed people still play with 60 yr old technology that belongs on a sewer tanker truck or a half running farm truck with snow plow attached.

[Dave B]

Just for the record, your not getting anywhere near 290 cfm@28” out of any iron head that ever came out of GM / the factory
bolted to a production block.

Max ported with a 1.94” valve getting 260 cfm is a large challenge and had better have a flow bench at your disposal!

Why couldn't he?
We have heads laying here from 1970s that were factory production and raced in back then.Those heads had ports moved around and filled ,different valve sizes etc.They flowed over 290 then and still do.You think those guys had 1020 benches or cfd to work with then? It amazes me people waste their time with dinosaur parts when current tech will run circles around this stuff.Every day I see guys on here that have 383 or whatever that run 10.50s .We have a stock headed LS Vette that runs 9.60s @3500 plus so far with no flow bench ,no cfd blah blah. We don't have slicks or race tires or weenie bars, Just factory LS stuff and parts from jegs. I see Chad put all this effort into ancient tech that guys have beat to death for years.Why try to run a 60 yr old head design that guys go as fast with at 290 inch that you can with chads 358. I guess I don't understand living in the past or constantly going backwards.There are so many ways to polish a turd and it's been tried all ready, 1000s of times.Look up guys like Randy Wilson who ran mid 9s with this old tech and he did it years ago.He had iron gm bowtie heads,same port sizes,same epoxy blah blah.He ran lb per inch.So if he ran a 296 he weigh 2965 or so at 10 lbs.Like I have stated other times my father had these same small engs ,same dinosaur parts in 70s and made over 600 hp then.So what so exciting about doing the same now ,50 yrs later ? Same bat shit ,same bat channel..Some of you guys need to lose your 1950 tech reports and let your boys life mag subscription go!

[88bluestar]

If it were easy to move to an LS I would. They allow stock 5.3 only, cathedral head only, zero mods allowed aside from MSD ignition, Holley intake, adapter and 4412 stock carb. Stock or CT525 cam allowed but again no mods so power wise it still comes up short on power compared to the stock older engines where you can port etc. weird rules but that’s what we have here.

[rebelrouser]

seen posted 290cfm should be the goal and I would agree with that number. Also agree hard pressed to get a stock SBC head to 290CFM. So just to throw this out there, when I do a head, first thing is to flow it stock, then start working on it. So how much increase do most of you guys get? I usually find more than 20% improvement is really pushing it. And I find while you may not get the 290cfm, I look real hard and the speed over the short turn, and keep the velocity below 400 ft per second at 28 inches and then I flow at max lift as hard as my bench will pull most heads 35 inches just to make sure they don't back up. I have been doing a lot of sbc jet boat engines, mild cam and hand porting the heads, 400 to 425 HP with 220 lift cam .520 lift hydraulic rollers, and they idle pretty at 17 inchers of vacuum. My bench says around 250 cfm to 260 cfm the 260 cfm is if I use a better valve like a manley.

[steve cowan]

My reference was 290 cfm at 6000rpm for a 383.
Depression will be higher than 28" @ 6000rpm.

[steve cowan]

Just for the record, your not getting anywhere near 290 cfm@28” out of any iron head that ever came out of GM / the factory
bolted to a production block.

Max ported with a 1.94” valve getting 260 cfm is a large challenge and had better have a flow bench at your disposal!

Why couldn't he?
We have heads laying here from 1970s that were factory production and raced in back then.Those heads had ports moved around and filled ,different valve sizes etc.They flowed over 290 then and still do.You think those guys had 1020 benches or cfd to work with then? It amazes me people waste their time with dinosaur parts when current tech will run circles around this stuff.Every day I see guys on here that have 383 or whatever that run 10.50s .We have a stock headed LS Vette that runs 9.60s @3500 plus so far with no flow bench ,no cfd blah blah. We don't have slicks or race tires or weenie bars, Just factory LS stuff and parts from jegs. I see Chad put all this effort into ancient tech that guys have beat to death for years.Why try to run a 60 yr old head design that guys go as fast with at 290 inch that you can with chads 358. I guess I don't understand living in the past or constantly going backwards.There are so many ways to polish a turd and it's been tried all ready, 1000s of times.Look up guys like Randy Wilson who ran mid 9s with this old tech and he did it years ago.He had iron gm bowtie heads,same port sizes,same epoxy blah blah.He ran lb per inch.So if he ran a 296 he weigh 2965 or so at 10 lbs.Like I have stated other times my father had these same small engs ,same dinosaur parts in 70s and made over 600 hp then.So what so exciting about doing the same now ,50 yrs later ? Same bat shit ,same bat channel..Some of you guys need to lose your 1950 tech reports and let your boys life mag subscription go!

We all know you are "THE BEST EVER" because you keep telling us

[mag2555]

Assuming the OP is a somewhat novice at porting you find me one that will get 260 cfm out of a 1.94” valve the first time around, you other folks taking about blowing out the port walls and having to then weld, then is that what you think the OP is willing to do , really!?

[mag2555]

Hey Steve, please dig up a post on here where I ever eluded to being anywhere near the best ok?

There all stored on here to be looked back on so you find one, and until then stop your comments ok?

[HQM383]

Hey Steve, please dig up a post on here where I ever eluded to being anywhere near the best ok?

There all stored on here to be looked back on so you find one, and until then stop your comments ok?

He was responding to Dave B and defending you.