409 vs 415 SBC

[cgarb]

My vote for the old standard 3.75x4.155 only giving up 3ci from what you want and not as much clearance issues. Still plenty of meat left in the bores if you hurt it too. Surely the rotating assembly will be cheaper and shelf pistons. Probably the difference you would pay shelf piston vs custom would cover the bore and hone.

Just figure up some exotic combo that would make 406 CI and tell everyone that's what it is.

[RCJ]

I would use the 4.100x 3.75 comb also.Are your heads 23 degree?

[tracyracin]

Yes they are 23 degree heads

[steve316]

If you go with a 3.875 stroke and a 283 ( 2"0 ) rod. you can run a standard base circle cam. the rods I use are com-star and I have .050 to .045 rod to cam clearance.

[geraldtson]

A small base circle will be necessary. I would consider a cam of 260°I/268°E at .050"tappet rise on a 106°or 108° separation installed at 102°to 104°ILC with .430" to .450" lobe lift a pretty straight forward choice. I would shoot for 14/1 c.r. I am only one engine builder, a good cam grinder talks to many , gaining input, receiving feedback, utilizing very specific knowledge and experience to give the Best advise/product. Again to each his own and happy racing!

What is considered a "small" base circle? Lunati have some cams that are .900"

I consider .850 a small base circle but you'll have a hard time finding one that small. A true .900 will work for you i also consider a small base circle. Be careful many "so called" small base circle .900s will be closer to .930.Most cam company's shy away from smaller cores because they don't have that small a core in stock to work with. They'll have to get one. Also they have more flex,not as strong and all that stuff. I've used them for years with no problem but trust me it's not what you want to do! In your application with 3.875 stroke and stock cam location your gonna be to close. Probably gonna have rod to cam contact "unless you use small base circle.900". Just grind your rods for clearance! Don't look pretty but works fine. If it were me i'd agree with most on here and resist the urge and just go with 3.75 stroke for many reasons. If you insist on small base circle i'd use Bullet. They will listen to you and produce what you want.

[tracyracin]

If you go with a 3.875 stroke and a 283 ( 2"0 ) rod. you can run a standard base circle cam. the rods I use are com-star and I have .050 to .045 rod to cam clearance.

Is it easy to check the rod to cam clearance?

[tracyracin]

A small base circle will be necessary. I would consider a cam of 260°I/268°E at .050"tappet rise on a 106°or 108° separation installed at 102°to 104°ILC with .430" to .450" lobe lift a pretty straight forward choice. I would shoot for 14/1 c.r. I am only one engine builder, a good cam grinder talks to many , gaining input, receiving feedback, utilizing very specific knowledge and experience to give the Best advise/product. Again to each his own and happy racing!

What is considered a "small" base circle? Lunati have some cams that are .900"

I consider .850 a small base circle but you'll have a hard time finding one that small. A true .900 will work for you i also consider a small base circle. Be careful many "so called" small base circle .900s will be closer to .930.Most cam company's shy away from smaller cores because they don't have that small a core in stock to work with. They'll have to get one. Also they have more flex,not as strong and all that stuff. I've used them for years with no problem but trust me it's not what you want to do! In your application with 3.875 stroke and stock cam location your gonna be to close. Probably gonna have rod to cam contact "unless you use small base circle.900". Just grind your rods for clearance! Don't look pretty but works fine. If it were me i'd agree with most on here and resist the urge and just go with 3.75 stroke for many reasons. If you insist on small base circle i'd use Bullet. They will listen to you and produce what you want.

I assume that you grind your rods down to clearance the cam before you have the rotating assembly balanced?

[cab0154]

my $.02 would be that i wouldnt try to run a small base circle and a lot of rpm. id run a 3.5" stroke and standard base circle and turn it 7600. i mean, if you can get away with a 3.625 and a standard base circle that would work.

[tracyracin]

my $.02 would be that i wouldnt try to run a small base circle and a lot of rpm. id run a 3.5" stroke and standard base circle and turn it 7600. i mean, if you can get away with a 3.625 and a standard base circle that would work.

Is it a risk to run 8k or 8200 with a small base circle cam? I definitely need some sort of reliability cause I can only do this once this season LOL

[geraldtson]

What is considered a "small" base circle? Lunati have some cams that are .900"

I consider .850 a small base circle but you'll have a hard time finding one that small. A true .900 will work for you i also consider a small base circle. Be careful many "so called" small base circle .900s will be closer to .930.Most cam company's shy away from smaller cores because they don't have that small a core in stock to work with. They'll have to get one. Also they have more flex,not as strong and all that stuff. I've used them for years with no problem but trust me it's not what you want to do! In your application with 3.875 stroke and stock cam location your gonna be to close. Probably gonna have rod to cam contact "unless you use small base circle.900". Just grind your rods for clearance! Don't look pretty but works fine. If it were me i'd agree with most on here and resist the urge and just go with 3.75 stroke for many reasons. If you insist on small base circle i'd use Bullet. They will listen to you and produce what you want.

I assume that you grind your rods down to clearance the cam before you have the rotating assembly balanced?

I assemble and check then disassemble and grind as needed. Can grind before (preferably) or after balancing. Never had a balance issue grinding after rotating assembly had been balanced. If you're gonna use 4-7 swap might want to clearance with both firing orders in mind. I only grind rods that need to be ground. If you're gonna be swapping cams later in car you might want to take a little off each rod to gain clearance for different cams. Might save a motor down the road somewhere. Still i'd go with 3.75 for many reasons in you're circle track. Be more clearance everywhere and more durable which is what you need.

[RCJ]

There will only be a few hp difference in any of the bore stroke combo mentioned.If you aren't required to run 23 degree heads that is where I would spend the money.When I went from 23 to -12 brodix It didn't extend the rpm range much, it put a lot more torque and hp under the curve.For reliability and budget I would limit myself to 7800.

[geraldtson]

my $.02 would be that i wouldnt try to run a small base circle and a lot of rpm. id run a 3.5" stroke and standard base circle and turn it 7600. i mean, if you can get away with a 3.625 and a standard base circle that would work.

Is it a risk to run 8k or 8200 with a small base circle cam? I definitely need some sort of reliability cause I can only do this once this season LOL

Yes its a risk compared to larger base circle. Weaker all the way around especially for circle track " think durability". Real small base circle leaves lifters sitting much further down in the hole which also means extra long pushrods.For drag racing you'd be fine but for round dee round it'll cause you problems. For higher rpm and durability you'd want fatter cam and shorter pushrods!

[engineguyBill]

4.100" is not a popular bore size at all. You would be much better off running a 4.155" or 4.185" bore size - much easier to find pistons and rings in these sizes . . . . . .

[pdq67]

If you go with a 3.875 stroke and a 283 ( 2"0 ) rod. you can run a standard base circle cam. the rods I use are com-star and I have .050 to .045 rod to cam clearance.

Is it easy to check the rod to cam clearance?

Use a long piece of heavy lead solder, "wire", that should be right at .100" in dia.

Just thread it along each rod and turn the engine over by hand watching the pinch between the cam, rod and solder wire. Remove and mic the pinch to give you the clearance amount.

Works like a charm.

pdq67

[Reef]

Randy at Race Tec pistons will be very helpful. They have no problem with bore size mods.If you need the pistons right away just ask they will do it. I like pdk67 method for cam to rod check , never done it that way but great idea, I have long feeler gauges I have also cut a long strip of cardboard about the width of a lobe. Might as well grind before balancing IF you end up needing to grind be sure to finish nicely. I have a shot peener to final recompact the surface glassbead would be an ok alternative, not the end of the world if you can't do either just nicer. You will not have a reliability problem just get a .900"B.C. it's done every day in engines that last 20+ nights going round and round at 8200rpm and more . I try and keep as much base as possible but sometimes you deal with the parameters in front of you.