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Hot Rods BORE NOTCHING

Discussion in 'The Hokey Ass Message Board' started by Rcraft, May 1, 2019.

  1. Stueeee
    Joined: Oct 21, 2015
    Posts: 305

    Stueeee
    Member
    from Kent, UK

    Will you be doing the bore notching yourself? it's the kind of job that most machine shops (over here anyway) aren't keen on doing -probably the reason that I get to do so many.
    [​IMG]
    The notches are much simpler to machine on blocks (like this old Austin race motor) where the valves open at 90 degrees to the block face -which of course isn't the case with an SBC motor. As said earlier in this thread, keep the bottom of the notch well above the top piston ring to stop the ring land getting burned.
     
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  2. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,217

    ekimneirbo

    OK, thanks for letting us know what you are attempting to do and what you have to work with. Here is my opinion.
    If you notch the bores you will have to disassemble the engine to do it properly and not end up with debris inside the engine. If you try to do it by hand without disassembly, you will probably screw it up. The canted valve big block engines have the valve opening on a canted angle so they only need to miss the cylinder wall at the top. Your 2.02 valve will open on an axis more perpendicular to the piston and will probably need to clear the cyl wall further. If you get the notch too deep you will lose not only compression ratio, but possibly compression past the top ring. You stand a lot better chance of screwing something up by attempting to do this just to use the wrong heads for the engine. Whatever heads you use, you need to insure that they have good valves, seats and guides ($). I know this is not what you want to hear,but I think the majority of the experienced people on this site would not do what you are trying to do. In the long run it will cost you far more money than doing it the right way. Thats just my opinion....but its based on first hand experience of trying to make something work and spending more money in the long run. Good luck whatever you decide.
     
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  3. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Somebody should tell @402BOSSMAN that he's wasting his time building a 283....

    https://www.jalopyjournal.com/forum/threads/breathing-life-into-a-283-jr-fuel-destined.1085889/
     
  4. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,217

    ekimneirbo

    The fellow building that 283 is obviously a talented machinist who can perform all his own machining at no cost to himself. Much different situation than someone who is going to have to pay for the work and is trying to get by "on the cheap". Your example is being built for amatuer racing using aluminum rods,hard block filler, and splayed aftermarket 4 bolt main caps along with specific aluminum heads to work with the Pistons he has. For the type of racing he plans to do, there will probably be limited competition, with minimal $ invested. So he is NOT wasting his time. He knows what he wants and how to go about it.
    Building a 283 with minimal $ is basically a waste of time and effort if someone is looking for good street performance. S10s could be bought with 262/4.3 V6 engines that were basically a small block with two cylinders removed. So for all the effort he will have marginally more power. Since it's no harder and basically no more expensive, using a larger displacement small block would be a better option. Since it's apparently not a currently running 283, why throw any money into something that will have mediocre performance? On the other hand, if someone has no money and just wants a daily driver with peppy response, then you use what ya got....that's how old hot rods used to be built.
     
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  5. CNC-Dude
    Joined: Nov 23, 2007
    Posts: 1,031

    CNC-Dude
    Member

    As has been suggested already, stick a head on the block and flip it over to look at it from below. That will tell you all you need to know. Notching the cylinders is done more for unshrouding than actual valve clearance issues. I've cut valve reliefs in many NHRA Super Stock 283's and the intake valve pocket is fully in the piston top and never extends off of the top of the piston.
     
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  6. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    People build cars for themselves, not for others. You don't have to understand or agree with it. This may be hard for you to understand, but some folks just like 283's. Some folks like Ford flatheads and will spend a lot of money building one that won't make a lot of power. Nobody needs your understanding or approval. The OP certainly wasn't asking for it.
     
  7. lumpy 63
    Joined: Aug 2, 2010
    Posts: 2,603

    lumpy 63
    Member

    I love small sbc's 302's 283's and so on....But honestly if the Op isn't planning on revving this thing to the moon with 5.57 gears and a crapload of compression whats the point? Notching the cylinders just to make 2.02s fit doesn't make a lot of sense when a set of 1.94s or 305 heads would perform a lot better. It would be a better decision to sell the big valve heads and buy something more suitable for the application . Not being a dick just saying that having raced everything from 283's to 427 small blocks you gotta realize the bang for the buck.
     
  8. Deuces
    Joined: Nov 3, 2009
    Posts: 23,757

    Deuces

    You better delete that^^^^^ before the mods shut down this thread.....
     
  9. A 283 is a sweet little engine,,,
    Just throw 1/2 of the treefiddy thinking away and think like a small cube engine, treat it like a small cube engine, build it like a small cube engine, gear it like a small cube engine ,,,,
    I’m sure you get the idea
     
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  10. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,603

    Johnny Gee
    Member
    from Downey, Ca

    C10 S10 no problem!
     
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  11. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Sorry, no hostility intended. It's just that the OP was asking a technical question, and what he got was a long winded personal opinion. I don't think his plans are wise either, but that's not what he was looking for.
     
  12. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,217

    ekimneirbo

    My apologies too.....Just meant to help !
     
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  13. Ericnova72
    Joined: May 1, 2007
    Posts: 595

    Ericnova72
    Member
    from Michigan

    All the guys basing on bore notching have obviously never done, it, don't fully understand why you do it, and don't realize the advantages to it. We do it on 4.030-4.060" bore 350/383/395 SBC's to allow better airflow when using big 2.08-2.10" intake valve heads. The valves will clear the bore without the notches, much like they do on the 427/454 Hi-Perf Big blocks with the notches....they are there for airflow reasons.

    If the OP needs the clearance for the bigger valves notch the bore, it's not some big deal that is going to lead to some huge engine problem or failure. added bonus, maybe now his 283 can take a little more advantage of the airflow provided by the bigger valve.

    Seems like an awful lot of Nervous Nellies and drama queens with opinions but no experience or facts in this thread....
     
  14. Back it up
    Just the drop in compression from those heads will castrate the 283... no matter what valves it has. That would be a drop in torque.

    The big valve would help air flow over 8000 rpm and leave the other in the dust. However, Below that rpm the port velocity and volumetric efficiency will be dismal. A drop in velocity equals a drop in torque. A drop in volumetric efficiency equals a drop in torque.

    With a 283 the very last thing you want to do is make less torque.

    Higher compression
    Higher velocity with smaller ports
    Higher volumetric efficiency
    That’s how you build torque.

    That small bore can run 10.+:1 on premium pump gas. Why would anyone want to drop compression to 8.?:1

    Of course none of that had anything to do with bore notches right, not one word.
     
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  15. AngleDrive
    Joined: Mar 9, 2006
    Posts: 1,145

    AngleDrive
    ALLIANCE MEMBER
    from Florida

    I dropped mine on my 283 and added a 4-71:D
     
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  16. :D:D:D
     
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  17. Fordors
    Joined: Sep 22, 2016
    Posts: 5,373

    Fordors
    Member

    Earlier the OP did mention domed pistons as a reason for wanting to use the 64cc heads. We don’t know how much those domes displace but it’s possible he may still wind up with a decent compression ratio, even after the bore notch.
     
  18. Missed that
     
  19. Fordors
    Joined: Sep 22, 2016
    Posts: 5,373

    Fordors
    Member

    It may seem fool hardy to some not to build a 350 but he has a lot of parts already. And is he looking for maximum performance? Or does he even care? Stop light drags, really??
     
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  20. Ericnova72
    Joined: May 1, 2007
    Posts: 595

    Ericnova72
    Member
    from Michigan

    He already stated he had the compression ratio angle covered....and at most you'd be removing 2-3 cc, about a 1/3 point compression loss.

    Not everyone wants a 283 set up to trudge around at low rpm in grandma's 4-door Impala. a 283 is never going to have TORQUE, building for it is just foolish...rev it up and enjoy the rpm rush.

    A big intake valve does not automatically equal a velocity or volumetric loss, you can only hurt those when you enlarge the port to go with it. A larger valve on a small port with the proper bowl blend and valve job can increase volumetric efficiency at low lift as the valve is coming off the seat due to increased curtain area.
     
  21. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,217

    ekimneirbo

    While I realize that its being done for airflow purposes, BUT the valve must also have a mechanical clearance to the cylinder wall and the piston top. From the information provided, I don't know that the valve will or will not mechanically clear both of those things. The OP stated that he had clearance problems. He also stated that the heads were 62 cc which suggests that the heads have been milled some time in their 50 year history, and that the bore size was 3.915. So its been bored too...which should help with wall clearance.
    The OP "did not want to have to buy anything". That suggests he doesn't want to disassemble the engine to have the bores notched. Since the 283 is such a small engine, differences in bore notch sizes, if not properly done will have a major effect on compression ratio and cause differences between cylinders. Read what Jeff Smith has to say about the critical nature of small differences in a 283 as opposed to larger displacement engines.
    https://www.onallcylinders.com/2018...rmance-upgrades-283-chevy-small-block-engine/

    Here is what David Vizard has to say in his book "How to Build Horsepower"
    "When larger valves are installed, shrouding can often be reduced by grinding the combustion chamber or top of the cylinder bore. If shrouding is not reduced to the level that existed with the original valve size , there may be little or no increase in flow--and in some cases larger valves can actually reduce low and mid-lift flow.
    (My comment: 283s need all the low and mid- lift flow they can get because of a lack of torque)
    Vizard further says "Another reason to consider using larger intake valves is that any power gains are not necessarily accompanied by noticable tradeoffs in other areas. But obtaining these benefits on some heads require more than just simply unshrouding the valve. These cases entail a lot of time developing flow bench modifications. A prime example of this is the early Chevrolet performance heads that use the 1.94 inch intake valves. Installing the larger Chevrolet 2.02 valves without any other changes, will reduce flow. It takes a considerable number of minor modifications in both the combustion chamber and the port pocket to obtain the desired increase in flow; and its not just a question of grinding but of knowing where and how much to grind"

    Now the questions that needs to be answered are; how does the OP plan to machine the notches without "buying anything" ? Will the pistons clear the larger valves ? How will the OP verify piston to valve clearance, and check the compression ratio which changes if he uses the 461 heads with larger chambers (per Jeff Smith). If he has to modify the pistons for clearance then the engine will need to be rebalanced. Do the 491 heads have good guides so the valves don't wobble ? Will his pushrods be the right length since the heads appear to have been milled? Will his intake manifold line up properly and not leak if the heads were milled ? Etc......

    Personally I see a lot of things to consider besides just a simple possible increase in airflow. I'm a firm believer "that if a job is worth doing.....it's worth doing right" , especially when it comes to engine assembly.
     
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  22. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    One of the draw backs to L heads the shrouding of the valve. Big valves can do this in a over head also. Question just how much valve does a 283 cu inch engine need? Ford found that out in the Boss 302. they backed down the intake size in 1970 and it still was over kill.
     
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  23. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,603

    Johnny Gee
    Member
    from Downey, Ca

    Ask a question and in return...
    [​IMG]
     
  24. clem
    Joined: Dec 20, 2006
    Posts: 4,190

    clem
    Member

    This is the only sentence in this whole thread that I actually understand.......
    .......please carry on......
     
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  25. David Chandler
    Joined: Jan 27, 2007
    Posts: 1,101

    David Chandler
    Member

    Personally, I wouldn't chance doing the block. I say that because there is no way to undo it, if you don't like it. Different heads however can be swapped, if you don't like the results. While 305 heads can and will work, they are not the be all and end all. That area under the studs creates it's own drawbacks from the flow disruptions they create. But they are cheap and available. So if infinite amounts of horsepower are not the end goal, they are worth considering, if one is on a very tight budget. Certainly for a street engine, they would be adequate. I have run them on a 350, with 1.94 intake valves, and unshrouded chambers, and some port work. All things considered, they did all I hoped they could do. For a 350, I probably wouldn't do it again, unless I was broke and had lot's of free time to work on the heads. A 283 will never be a torque monster. No offense intended. The stoke is too short. But they will wind up like nobody business too. When I was a kid everyone wanted one, that could get one. 327's came out later, and were not available at the time. That said, they were a VERY good running engine, and I wouldn't walk away from one, that was worth saving.
    Good Luck!
     
  26. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 2,872

    427 sleeper
    ALLIANCE MEMBER

    ^^^^^ VERY well said!
     
  27. 41rodderz
    Joined: Sep 27, 2010
    Posts: 6,540

    41rodderz
    Member
    from Oregon

    Being on a budget = working smart.
     
  28. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    So, we're talking about bore notching for valves that were intended to fit a 4.00" bore, and the bore is 3.915"?

    That's 0.085" different in diameter. In other words, the cylinder wall is 0.0425" closer to the valve edge than it should be.

    There is likely not an off-the-shelf gasket to do this, you would likely be stuck with a custom gasket, like dead-soft copper, or otherwise.

    Keep in mind that you would be removing material from the first and third block webs between cylinders, on both sides! of the web Once you get done doing that, your head gasket will be very narrow in that area.

    If you overcame that hurdle, and managed to free-up some flow on the bore side, you would need to hit 7500-8000 rpm to use it. And, even at that, the gain would not be huge.

    Now, ask yourself if this is worth it. And, if you still answered yes, remind yourself that you have a transmission, that depending on the model, has either one, or two overdrive gears, which have the intended purpose to keep the RPM DOWN.
     
    Last edited: May 6, 2019
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  29. Gary Addcox
    Joined: Aug 28, 2009
    Posts: 2,528

    Gary Addcox
    ALLIANCE MEMBER

    A .040 overbore gives you a 289 cu. in block. I've seen a few bad-ass running 289's out of a sbc eng.
     
    Deuces likes this.
  30. Thank you, you got the idea
     
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