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Guest Message by DevFuse

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spfi vs. n/a mpfi cam with ported SPFI

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10 replies to this topic

#1 MilesFox


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Posted 07 February 2006 - 10:06 PM

i am porting a pair of carb heads(no cracks and 135,000 mi) for a 101,000 mi spfi block

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

#2 idosubaru


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Posted 07 February 2006 - 10:23 PM

i checked into bigger valves for the XT6 a month or two ago. got no responses here or elsewhere. the local aluminum head specialist that i always use could not source any through his suppliers. maybe there are suppliers he doesn't deal with, but he couldn't find anything with a quick search. two 6 cylinder heads cost $175 for a complete valve job, pressure test, maching the heads, new valve stem seals, everything. they charge less for 4 cylinder heads but i forget the break down. someone else i know paid $200 for the same thing. i'd expect no more than $150 for a 4 cylinder 8 valve EA82.

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.

#3 MilesFox


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Posted 07 February 2006 - 10:54 PM

as far as having the machine work done i already have the valves off the head, and a seal set. i suppose they will need the valves to grind them but i can put them back on once the job is done

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!

#4 idosubaru


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Posted 07 February 2006 - 11:18 PM

cam swap aint that hard for sure. wonder if the machine shop might measure the cam lobes for you, two different ones to see if there is a difference? have them with you when you drop the heads off and see if they'll have a look?

how would you test? feel or compression test?

#5 MilesFox


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Posted 10 February 2006 - 09:10 PM

i will go by driving the car. swap arpund cams and exhausts to see what i get.

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

#6 Tycho


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Posted 12 February 2006 - 07:08 AM

On my SPFI build I had .005 taken off the deck to bring the quench height (piston to head) down to .035 or so. I also had .010 taken off the heads, although the increase in CR was negligible. If you want to increase the CR, do it by decking the block FIRST (reducing quench height). .035" piston to head would be a good limit to observe. On smaller bore engines (82 mm bore) I've gone .030" without problems, but piston rock in these huge bores is going to be a bigger factor. The tighter your quench is the more knock resistance you'll have. Shaving the head will not help the already bad knock situation that these engines have (due mainly to their large bores).

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.

#7 MilesFox


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Posted 19 February 2006 - 03:47 AM

i have been using a dremel tool withthe flex extension. works rather well withthe variable speed and has torque

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?

#8 MilesFox


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Posted 19 February 2006 - 10:33 PM

f*'n A yeah!:banana:
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

#9 nicky nighteyes

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Posted 20 February 2006 - 12:49 AM

lets see a pic of the engine paint job. sounds hot Miles

#10 MilesFox


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Posted 21 February 2006 - 12:34 AM

i got on the dual chrome harley mufflers. pulls pretty good on the low end, torquey plus low range!(vs pushbutton:eek:)

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

#11 85Sub4WD


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Posted 21 February 2006 - 11:53 AM

i wonder if one could install a SPFI throttle body on a setup with MPFI N/A heads, with a MPFI turbo/early MPFI NA intake manifold (not spyder), and MPFI NA cams (pref later, 87+ ones)

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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