Supermiata S1 build - Vegas
10-10-2018, 01:07 AM
#261
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I guess I just don't react well to the didactic tone as if from an expert. Once someone has established some sort of credibility, I'm all ears. I just get tired of the peanut gallery telling me how to do stuff. To be fair, most of you don't live in my world in in that regard.
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10-11-2018, 03:07 PM
#265
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I dunno, seemed Emilio's response was par for the course. Guy shows up and starts making suggestions, nobody knows who he is nor does he provide a theory or explanation behind his suggestions. It was a pretty useless post.
Kinda like mine
.
Kinda like mine
.
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10-18-2018, 03:07 PM
#269
Lost a head gasket
If anyone is curious how much boost a stock head gasket will hold, apparently around 27psi. 83.5 pistons, EFR6258, BP6D, stock cams, E85, ARP suds and around 20.5° timing.
Many variables that affect actual cylinder pressure so some BP turbo builds might let go at below or above that value. I imagine only a few brave souls have tried to sneak up on 30psi with the stocker though.
Coolant overflow tank went bloosh like a geyser. Shot the expansion tank cap across the shop. Very exciting.
It was fine when we made few less psi last year. Switching to a Cometic 84mm x .040 gasket and putting in a fresh set of ARP head studs. That should give us the little bit extra clamp load we need.
Many variables that affect actual cylinder pressure so some BP turbo builds might let go at below or above that value. I imagine only a few brave souls have tried to sneak up on 30psi with the stocker though.
Coolant overflow tank went bloosh like a geyser. Shot the expansion tank cap across the shop. Very exciting.
It was fine when we made few less psi last year. Switching to a Cometic 84mm x .040 gasket and putting in a fresh set of ARP head studs. That should give us the little bit extra clamp load we need.
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10-18-2018, 09:07 PM
#270
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We have run 30+ psi a few times reliably but we are only running the whole 30 at redline, more like 20 in the midrange, torque around 320-330 ft lb.
In my experience, if the 6 speed CAN survive so will the head gasket.
Dann
In my experience, if the 6 speed CAN survive so will the head gasket.
Dann
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10-18-2018, 09:39 PM
#271
25~27psi from 4000-7500. 390 lbs torque.
Not sure what your redline was but assuming 7000rpm and stock cams (VVT?), the VE, thus cylinder pressure, would likely be lower than 27psi at 5000rpm torque peak with VVT.
In any case, your data point aside, we have no need to further explore the limits of the stock HG
We will upgrade it and move on to the next task.
Not sure what your redline was but assuming 7000rpm and stock cams (VVT?), the VE, thus cylinder pressure, would likely be lower than 27psi at 5000rpm torque peak with VVT.
In any case, your data point aside, we have no need to further explore the limits of the stock HG
We will upgrade it and move on to the next task.
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10-18-2018, 11:32 PM
#273
Yup. That's why I shared the data point. I have heard rumors of a few other people getting closer to 30psi and others having them pop in the low twenties, so the variables are important.
I think it's safe to say if you're going to go much beyond 22psi or so, it's wise to use a Cometic sized for your bore. We called Cometic and they suggested upping from the OEM .027 to the .040 for the extra material. The just slightly lower compression ratio is not a problem with all the boost we are running of course.
I think it's safe to say if you're going to go much beyond 22psi or so, it's wise to use a Cometic sized for your bore. We called Cometic and they suggested upping from the OEM .027 to the .040 for the extra material. The just slightly lower compression ratio is not a problem with all the boost we are running of course.
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10-19-2018, 01:16 AM
#274
Are you entering the territory where some kinda mechanical locking grove is necessary?
On the extreme side I’ve machined aluminum rings into the head/block to seal things. On a mild side I’ve machined o rings into the head to apply additional pressure around combustion chamber.
Research options. IMHO you may have crossed a threshold where a better head gasket alone will not suffice. At extreme cylinder pressures the head dances on top of the block. It even shuffles around a bit. Can’t stop it. You can just deal with it in other ways.
On the extreme side I’ve machined aluminum rings into the head/block to seal things. On a mild side I’ve machined o rings into the head to apply additional pressure around combustion chamber.
Research options. IMHO you may have crossed a threshold where a better head gasket alone will not suffice. At extreme cylinder pressures the head dances on top of the block. It even shuffles around a bit. Can’t stop it. You can just deal with it in other ways.
Last edited by k24madness; 10-19-2018 at 02:47 PM.
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10-19-2018, 03:37 PM
#280
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Squish has to be adjusted in the block deck surface, not the head. The measurement is between the head and the piston, so if you machine the head, you're dropping the overall height of the head, but not where it matters (at the corners of the CC). You have to either lift the piston compression height or drop the surface of the block to account for the extra HG thickness. It's sort of a pain in the ***, since the "right" way to do it is to assemble the bottom end, measure the piston height in the deck, disassemble the entire bottom end, mill it to set squish, and then re-clean and re-assemble everything all over again.
On a fresh bottom end, well worth doing. On an already-broken-in bottom end? Not sure I'd hassle with it. Just make note and adjust on the next rebuild.
On a fresh bottom end, well worth doing. On an already-broken-in bottom end? Not sure I'd hassle with it. Just make note and adjust on the next rebuild.
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