Porting 350 Heads..how?

Discussion in 'Small Block Tech' started by MrSony, Oct 19, 2017.

  1. MrSony

    MrSony Well-Known Member

    I want to try porting my 350 heads at some point, maybe as a winter project. I'd be porting my '76 heads which I understand are thicker and leas prone to cracking that 74(?) and older heads. What I want to know, is what in the intake and exhaust ports do I address specifically, or just try and smooth out what I can? If anyone has some deeply detailed pics...maybe a thread link, that'll help a ton. Plus any input on kits or tools to buy would be cool.
     
  2. hugger

    hugger Well-Known Member

    "Smoothing" does nothing, you have to remove metal to get gains, valve guide boss, bowl, throat, short turn and chamber are where the improvments are made
     
  3. MrSony

    MrSony Well-Known Member

    What is the "bowl", "throat", "short turn (radius?)" of the port? I've heard these terms a lot, but have no idea what they mean. I know what the VG boss is though.
     
  4. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    The term 'smoothing' can be misleading. If by this you mean removing texture, it can actually harm performance, especially on the intake side which needs the texture to improve the quality of the laminar flow and its effect on a wet flow.

    If 'smoothing' means removing casting imperfections, irregularities and sharp edges, and generally creating a more direct flow path, then 'smoothing' will indeed improve performance and CFM gains without affecting the CSA or original engineering intent of the iron head casting. Doing this in addition to making sure your valves aren't shrouded at the seat, and you'll see improvements.

    I'm not a professional head porter, but I have done some of my own work. Others here will have additional information regarding this.
     
    Last edited: Oct 19, 2017
  5. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    The bowl is the area around the valve stem where it protrude from the head, just after the Cross Sectional Area and prior to the throat, which is the area leading up to the valve head transitioning from the bowl to the seat area. The short turn radius is the curve at the base before the bowl where the intake runner makes its sharpest turn.

    My semantics may be off. I'm sure others will correct any mistakes I make. :)
     
  6. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    There's some threads here on the forum already with others detailing some of their work. I haven't done any searches lately, but the search engine on this new version of the website is supposed to be a lot better.
     
  7. alec296

    alec296 i need another buick

    I'm not a pro porter . But the throat or opening just under valve needs to be opened up or blended , there is a flat spot between the intake and exhaust valve that can be shaped and the valve guide is a huge block and can be contoured and thinned down. This is about 25-30 minutes with a stone grinder and a few kinda dull die grinder bits. That included taking valve out.Just polish the runner towards the intake manifold side as that port is huge and time consuming to "gasket match" for very little gains at this level. You shouldn't have to spend hours on each port.
     

    Attached Files:

    Gary Farmer likes this.
  8. alec296

    alec296 i need another buick

    Be careful around valve seats. Don't want to gouge them. I put layers of tape on them . You should get a valve job done afterwards. There are ways to cut valve and polish to help flow. If you gouge seat it's not gonna sway from a lap job
    Also don't think you can grind heavy in one spot to really open things up as you never know how thick casting is. Take it down in layers. You can grind a hole into a coolant jacket
     
    Last edited: Oct 19, 2017
    ceas350, MrSony and Gary Farmer like this.
  9. Alssb

    Alssb Well-Known Member

  10. alec296

    alec296 i need another buick

    Last edited: Oct 19, 2017
  11. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Don't polish the intake runners, leave them rough that will help aide in mixing the air fuel mixture.

    DO NOT gasket match the intake ports either, that will hurt flow more than help it!

    If you want to do the runners then one of these would help to be able to measure the runner to make them all the same;

    http://www.ebay.com/itm/Spring-Insi...110973?hash=item1c3985237d:g:YYIAAOSwPcVVpdCp

    Use the inside calipers to see where the pinch point is, meaning the narrowest point in the port because the heads will only flow as much as that smallest point. After finding the smallest of 8 set those calipers another 1/16" of an inch bigger and open up the areas of one side of the port so the caliper fits in while still lightly touching the port walls.

    After all 8 are done with the above step, open up the calipers another 1/16" an inch and repeat doing the opposite side. The spots that the calipers don't touch don't worry about those areas because they are still bigger than the pinch point.

    Use the gasket to outline the top of the port and DO grind the top to that line and just taper that down to the valve guide. DO NOT take the bottom of the port lower at all! For the bottom of the port just grind it some what uniform taking the least amount of material off the bottom of the port as possible.

    Being a beginner you should probably not mess with the short turn radius unless you look up some of the porting threads with pictures of cylinder head cutouts that explains how to remove the material there.

    If you had a bare block you could mount the cylinder head on it so you could scribe a circle where the cylinders line up with the heads. Having that reference line would allow you to do some unshrouding in the chamber, a lot of potential flow just doing this. If you can get those reference lines you would grind to the line making sure to save the line tapering down to the valve trying to follow the radius of the intake and exhaust valves.

    Seeing how a sbb 350 head's flow maxis out in the lower lift, having the valves back cut helps with lower lift flow so if there is any $ left in the budget you might want to consider having that done. Seeing how the sbb 350 heads flow is basically all in the lower lift range this should be a good addition to have done.

    With the mentioned bowl work in one of the above posts from Andy, the above mentioned equalizing the runners out, getting the valves back cut and unshrouding the valves should net you around another 20 to 40 CFM maybe even more if you get the short turn radius right?

    The exhaust just needs the imperfections ground smooth and you can polish the exhaust runners, that will help them flow better. You don't need to get carried away though because they will eventually get covered with carbon, not as bad as your valves though. GL
     
  12. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

  13. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Not to be a wet blanket here, but if you're not familiar with head porting or metal contouring, you're better off leaving the heads untouched, or pay someone with experience to give you some minor work. Price could range from 300 to 500 bucks for some simple work that would show worthwhile gains.

    Otherwise, have yourself some spare heads in case you mess up.

    It is possible to make the heads flow worse if you port them wrong.

    My advice is to just 'smooth' over the runners, bowls, etc. as I described earlier. It's simple and effective, and you won't have to worry about removing too much material and mess anything up.
     
    sean Buick 76 and MrSony like this.
  14. EasyCompany7

    EasyCompany7 Semper Fi

    alec296 likes this.
  15. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    It's been said that simply unshrouding the valves along with a good valve job is good for 15-20 CFM, with nothing else done...that would be worth some power right there.

    Add in some contouring (with little metal removed) of the guides and a bowl blend (not too complicated), and you'd see some good numbers from a 'clean up' job.

    Hell, untouched earlier heads flow 198 CFM and later heads 188 CFM. This is better than a lot of Chevy heads.

    A novice or hobbyist could see well over 200 CFM with practically no effort, and numbers in the 215-225 (for earlier heads, and 205-215 for later heads) range wouldn't be too unrealistic.

    That's a foundation for some good power. (relatively speaking)
     
    Last edited: Oct 20, 2017
    8ad-f85 likes this.
  16. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Those numbers would be @.400 lift with no gains above this lift, but using a cam with lifts in excess of this lift would leave the valve open longer in the 'sweet spot' range, making good power with cams having .425-.475 lifts. Make the durations to match the powerband you want and keep the ramp profile not too stressful on a flat tappet cam, relative to the lifts.

    Cams such as a Crower level 2 or 3 and the TA 212 cam (or any cam similar) would fit this profile nicely.
     
    MrSony and 8ad-f85 like this.

Share This Page