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spfi vs. n/a mpfi cam with ported SPFI
Posted 07 February 2006 - 10:06 PM
i am porting with a dremel and flex extension and a putting the final touches on the job.
i have a 2 part question
1. shaving the heads
there is a volkswagon shop behind the local napa MOFOCO if you have heard of them , i was thinking about having my heads achined there. what i want to know what would be a recommended amount to take off. .010, .050???? i am using spfi block and intake
i do understand if i go too far the intake wont match the same, but it shouldnt be any different than putting a gen1 ea71 intake on an gen 2 or ea81, as far as that goes i can slot holes and whatever. i am more concened about valve clearances
also what would i get for compression ratio starting with 9.5:1 and then shave the heads whatever amount
what should i expect to pay including a valve grind? what are the options for bigger valves? the heads are from an 87 carb
2. spfi vs mpfi-n/a cams
i have either the cams original to the block or a pair from an 87 xt mpfi non turbo. is there a difference withthe cam profiles? i know that mpfi yeilds a little more HP so i wonder if the cams will make advantage with ported heads and dual exhaust, and valve clearance
opinions? once i get a sharper dremel bit and another days time i will be ready to torque the heads on
Posted 07 February 2006 - 10:23 PM
watch your intake manifold gaskets. they are huge and overlap into the intake ports anyway. you'll want to trim them down and match them to the intake and/or heads. i posted before and after pic's at xt6.net of how far they protrude into the ports, it's quite a bit.
i posted questions about cam differences awhile ago and couldn't seem to get a consensus answer. "yes their different, but no they aren't" sort of thing. wonder if delta cam would know, they've seen enough of these cams to know if the spec's differ.
so what about the valves/piston clearance miles!!! you'll have the only interference EA82 around! got a junk head lying around you could mill and see how far you can go? the shop might even be able to tell you, i think they have specifications from the rebuilders associations, or whatever there sources are for the maching spec's when checking thickness, warpage, etc, they should be able to tell you the limits based on that.
Posted 07 February 2006 - 10:54 PM
i guess i will have to go with my gut or trial and error withthe cams, i guess physically compare them, but it wont be hard to swap the cams on a running motor to compare!
Posted 07 February 2006 - 11:18 PM
how would you test? feel or compression test?
Posted 10 February 2006 - 09:10 PM
good idea about having the cams measured. i'll see if they can grind them for me.
now only if they can calculate what cam profile would be best compared to stock numbers and if i have my heads bench flowed(this would be good to match them withthe port job)
i guess i will have to go do some hollerin'
meanwhile i am in the middle of taking the old motor out of the sedan. my dual exhaust is caved in on one side so i may do other exhaust ideas this time
Posted 12 February 2006 - 07:08 AM
To find the exact CR increase you need to CC your combustion chambers. Since I was taking a mere .010 off I didn't even bother to check it. On some other builds where I've taken .030 off or more, I always CC the chambers before and after (I'm usually re-working the chamber anyway so it gives me the opportunity to match them all within .1 cc). If you know the engine stroke, bore diameter, piston protrusion above deck, compressed headgasket thickness, and chamber CC, you can find your CR. finding the change in CC per amount shaved...well these chambers are pretty simple, so you could probably just measure the average depth, assume the chamber area is the same from deck to valves (it's not, but it's reasonably close), and estimate the reduction in chamber volume per amount shaved.
If you want to alter the heads in a meaningful way a die grinder and carbides are the way to go. I worked the SPFI heads on the aforementioned build with a Milwaukee 12 amp grinder running off a VARIAC to allow low speed operation. Long shank double cut and alumacut carbides are your friend. The short turn radius is a key area to watch on these heads. It's absolutely terrible no matter what you do with it, but you can improve it a good deal with minimal work.
Posted 19 February 2006 - 03:47 AM
i have been using high speed cutting heads "made in germany" then finishing with a stone and sanding drums
i wore through on the exhaust port to the dead space around the ports so i crammed some jb weld in the dead space to reinforce that area
so far the motor is together withthe m pfi n/a cam s, which definately appear to have more duration
hopefully this motor is good for 100-105 hp with the cam, and ported heads, ,along with dual exhaust
i wonder how possible it would be to make a dual spfi?
Posted 19 February 2006 - 10:33 PM
runs and drives. havent gone too far yet but lots of free flow at least how it sounds with the dual exhaust.
i anaged to remove the vacuum manifold and the vacuum solenoids for a stripped down spfi:banana:
now that the motor runs(fired up on the first try) the geraic engine paint should bake on. i painted the block orange, the heads are natural, and the cam towers black. the valve covers are black and the SUBARU is sanded down to shiny. the cam mpulleys are orange and yes, open belts
cant wait to get a pair of cherry bombs!
tizzle i like your avatar:headbang:
john, this is a 300 dollar loyale i picked up here in wisconsin. still got the sedan. just put a fresh m otor in with n/a mpfi cam s and ported heads
Posted 20 February 2006 - 12:49 AM
Posted 21 February 2006 - 12:34 AM
got to get it on the highway yet but the mufflers help out a lot. drives almost like an ej 18. now to fix the dented 90 bend and fit an o2 sensor bung.
i'll have pics soon
Posted 21 February 2006 - 11:53 AM
it would probably make more sense to go the whole MPFI N/A route, but SPFI computers, parts and such are much easier to find
That would DRAMATICALLY improve flow into the engine, because you have two ports per head (one per cylinder), and the potiential for porting it further is greater too - of course, you would have to block off the fuel injector places, but I do see potiential there, if the SPFI throttle body would fit - the coolant sensor would also be an issue, but that would be easy to resolve
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