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LOL. When I ran the numbers, it was something like 7000#. That's plenty of safety factor. I'm an EE, not an ME, so I wasn't going to get cute and cut it close. :-)
You know how often I run into EE's that are surprisingly mechanical and ME's that are surprisingly electrical? it's uncanny.
I'm a Chem E, which really just means I have an uncanny ability to make things burn.
This thread is really interesting to me as I'm thinking of doing a Mamo build on my LS3 C6. Want more power for the street and track duty. The go to head seems to be the MMS260 AFR casting but I'm more interested in power under the curve, I like torque, so I was thinking of doing the cathedral 220's or 235's myself. Of course I'm wondering how much power under the curve will this gain and how much up top you're giving up. There are some dyno sheets using the 260 head but I haven't seen one yet with the MMS cathedral port so I'm really hoping those are forthcoming here. Thanks everyone.
This thread is really interesting to me as I'm thinking of doing a Mamo build on my LS3 C6. Want more power for the street and track duty. The go to head seems to be the MMS260 AFR casting but I'm more interested in power under the curve, I like torque, so I was thinking of doing the cathedral 220's or 235's myself. Of course I'm wondering how much power under the curve will this gain and how much up top you're giving up. There are some dyno sheets using the 260 head but I haven't seen one yet with the MMS cathedral port so I'm really hoping those are forthcoming here. Thanks everyone.
From what I have learnt and experienced is that a dyno does not tell you how the car will feel and perform on the road.
Under the curve power is very important for a street car.
Have you read my thread in this section? Im using Mamo's 250cc head for my 434.
It seems to me that you are after the same type of driveability with strong part throttle response where you don't have to nail the throttle to go fast.
The AFR LS3 head is also a good choice and will drive better than an OEM LS3 head however if you want the best driveability with great throttle tip in and really hard hitting torque you need the cathedral setup.
If you don't plan on turning the LS3 into a 416 cid engine stick with the 220 head for ultra crisp throttle response and an explosive power delivery.
This head is rated to be able to support up to 408 cubes.
You will also need a fast 102mm intake to compliment it too.
Ready to install ... These show the crane and the low rider engine cart I built for doing this. You can go in thru the driver fenderwell and not have to lift the car. But it's so light in front with no engine I sometimes just pick it up by hand and have my wife add some more blocks to the front stacks.
I only have to raise the front air dam about 6 inches to slide the engine under.
You can see a little bow in the cart. It's a sheet of 3/16" steel, IIRC. Any stiffening I add would likely raise the cart, and this works. It *barely* drags on the floor, still easy to slide around. The important thing is ... the headers don't drag.
I primed the oil system in mine today.
Engine is in the car. Took about 20 minutes with a custom priming system that recirculated oil from the pan to the external pump to get all the lifters pumped up.
Tom Wong in Vancouver did it last time. I think I will do a lot of idle tuning, steady state tuning, driveability stuff over the winter, and take it to him in the Spring for power tuning. The clutch will be broken in by then, and it'll be in the ballpark. Not like I can use "power" mode in the wet Northwest winter, anyway. I do drive it, but very carefully. :-)
Tom Wong in Vancouver did it last time. I think I will do a lot of idle tuning, steady state tuning, driveability stuff over the winter, and take it to him in the Spring for power tuning. The clutch will be broken in by then, and it'll be in the ballpark. Not like I can use "power" mode in the wet Northwest winter, anyway. I do drive it, but very carefully. :-)
Good approach. I know Tom. We graduated high school together back in 73.
From what I have learnt and experienced is that a dyno does not tell you how the car will feel and perform on the road.
Under the curve power is very important for a street car.
Have you read my thread in this section? Im using Mamo's 250cc head for my 434.
It seems to me that you are after the same type of driveability with strong part throttle response where you don't have to nail the throttle to go fast.
The AFR LS3 head is also a good choice and will drive better than an OEM LS3 head however if you want the best driveability with great throttle tip in and really hard hitting torque you need the cathedral setup.
If you don't plan on turning the LS3 into a 416 cid engine stick with the 220 head for ultra crisp throttle response and an explosive power delivery.
This head is rated to be able to support up to 408 cubes.
You will also need a fast 102mm intake to compliment it too.
Thanks for the advice Bortous, reading your last 2 threads now. Very interesting so far.
Well, it turned out that both of the clearances I was worried about are going to be OK ...
The hood closes completely
The new intake means I can't run my strut tower brace ... but there's contention whether this does anything on a Miata, anyway. So that's 4# of bloat off the front end. :-)
The sway bar brackets are slotted, so I just slid them forward to clear the damper bolts. I have .125" of clearance. The lower radiator hose still clears the sway bar, so it's all good.
Dang you got at least 1/8" between the dampener and sway bar! It actually looks up top like a lot of room. Is it tighter than it looks? Nice not having that damned cowl I bet...
Dang you got at least 1/8" between the dampener and sway bar! It actually looks up top like a lot of room. Is it tighter than it looks? Nice not having that damned cowl I bet...
It looks like more, but a sheet of 1/8" aluminum that touches all 3 damper bolts is "pretty close" to the sway bar.
Hey, I'm *happy* with 1/8" ... for this car, that boatloads of clearance. I tried in the first interation a couple years ago to get by with about a credit card thickness ... that didn't work. The engine moved enough fore/aft to have the damper make wear marks on the sway bar, so I changed to a sway bar that has a bend in it to move the middle further from the damper.
To change the starter probably means dropping the trans ... you can't extract the passenger side header when it's in the car. I *think* you could extract the driver's side, but not sure, and you'd have to pull the steering column first, it runs through the header tubes.
I think the top of the intake manifold might be 1/4" from the bottom of the hood.
I can't put a larger engine in the car, because the extra stroke would require the front of the pan to be deeper, and that would hit the steering rack, and I don't want to change the delicious Miata steering geometry because it's a f***ing sports car, not a drag racer. So 6.2 is all I get. :-)
This whole thing is a collection of almost non-existent clearances. I'll take the 1/8" in front of the damper and feel awesome about it. I considered losing the front sway bar and upping the front spring rate, that would take 20# off the nose of the car, but I think the ride (it's 99% a street car) would suffer for it.
Last edited by grubinski; Aug 3, 2020 at 09:06 PM.
Just the opposite actually....the short travel Johnson's properly set up run very quiet relative to most performance LS engines (and their infamous sewing machine reference).
Stock lifters are twice as loud and that's due to all the sloppy internals that doesnt exist with the premium Johnson's which have much tighter internal tolerances among other internal perks of the design (the reduced travel another huge benefit).
They are about as close as you will get to an SR without the need to ever adjust anything and they will also turn big RPM if you pay attention to the valvetrain details (stiffer pushrods, lighter valves, lightweight roller rockers, the correct spring with ideal seat and open pressure and spring rate).
Details....details....details.....LOL
Mike (OP) your pushrods are ordered....email me to confirm you received the email I sent you regarding the lengths I grouped for you
Cheers,
Tony
Oh, so the sewing machine noise after my upgraded my heads, cam and lifters, can be solved by going with the short travel Johnson’s on my new 408 build.
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