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pistons the great delema (help)

pat3

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ok i just need some opinions


im am running the folowing


aeromotive a1000 fuel pump
aeromotive efi bypass fuel pressure regulator with a 1-1 boost refrence
custom fuel rails
ford racing 60# injecters
granitelli 90mm maf
p+p intake uper/lower
p+p heads trying to get custom valves made
acufab 80mm throttle body
t 56 turbo
type r bov
60mm wast gate
melling hp oil pump
comp 422 cam and comp valve springs
accel coil
tailer wires
pace setter headers

still need to buy


arp head studs
arp main studs
arp rod bolts
realy good rockers


still need to find

bad a** head gaskets
valves for heads
custom intake


need opionion

im boring the block 30 and cant decide on flat tops or dish
any one know any thing about thease rocker spacers. Do i need them
 
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FIND

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That does sound like a dilemma. Since you are gonna go with FI, keep your compression down, it will make it easier for you to tune. Therefore, dish.
 
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Brandon96

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What heads are you running?

If 95TM's, you could go with 2nd gen style pistons, Keith Black makes them, which had the deepest dish on the 4.0's.. though I still can't get an exact number on them, to keep your compression down to around mid 9's:1 :dunno:
 
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pat3

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What heads are you running?

If 95TM's, you could go with 2nd gen style pistons, Keith Black makes them, which had the deepest dish on the 4.0's.. though I still can't get an exact number on them, to keep your compression down to around mid 9's:1 :dunno:

what are 95 tm's. mine are ported 93's i guess if your refuring to the year of head
 
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Brandon96

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Oh, 95TM is the Cast ID from Ford.

I may have some of this info wrong, but;

'91-'94's had the 90TM cast (I've seen it referred to the 93TM as well)

'95-'97's had the 95TM cast heads (I've also heard about a 97TM which may have been for the first SOHC's)

'98 and up at the 98TM cast


The 95TM's were known for their strength and air flow, 93TM's, which you have, are very prone to cracking, I'm not sure they'd be a good match for your boosted application. However you will get a lot of back and forth feedback on that.

Since you have the 93TM's with the larger 60cc combustion chamber, I would not go with 2nd gen pistons, as they are dished too far and may give you too low of a compression ratio. If you keep the 90TM heads, go with the first gen style pistons, which will keep you around mid 9's:1, or the SOHC's flat tops, which may get you above 10:1, but there's no way to be sure until you do the math :/
 
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pat3

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Oh, 95TM is the Cast ID from Ford.

I may have some of this info wrong, but;

'91-'94's had the 90TM cast (I've seen it referred to the 93TM as well)

'95-'97's had the 95TM cast heads (I've also heard about a 97TM which may have been for the first SOHC's)

'98 and up at the 98TM cast


The 95TM's were known for their strength and air flow, 93TM's, which you have, are very prone to cracking, I'm not sure they'd be a good match for your boosted application. However you will get a lot of back and forth feedback on that.

Since you have the 93TM's with the larger 60cc combustion chamber, I would not go with 2nd gen pistons, as they are dished too far and may give you too low of a compression ratio. If you keep the 90TM heads, go with the first gen style pistons, which will keep you around mid 9's:1, or the SOHC's flat tops, which may get you above 10:1, but there's no way to be sure until you do the math :/

ok but the way i see it is im buying pistons so i realy could care less about what stock ones are so the 95 heads are higher compresion so i need to buy dished
 
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Brandon96

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I would go with dished, yes, especially cause your going boosted.
 
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pat3

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I would go with dished, yes, especially cause your going boosted.



do you happen to know the cc diffrence in the heads i can get three sizes of dish
 
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jd4242

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Are you keeping your heads,first question and second what compression do you want to run?
 
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pat3

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Are you keeping your heads,first question and second what compression do you want to run?

well if the 95's are better then ill get those and im thinkin aroun 9 pounds of compresion
 
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jd4242

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In stock form they are but if your having them ported and polished most people like to start with 98tm,they have smaller but more round ports.you have to run 95-98 tm pistons with those heads to get 9:1.
 
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tweakedlogic

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As i understand it, the 90tm heads are the ones prone to crack. the 93tm heads eliminated this. The 95tm heads are also higher compression (if you use the first gen pistons, you will have about 10:1). But they do flow better than the 93tm. 98tm heads have smaller chambers still, but do slightly out flow the 95tm.

If you are going forced induction, I strongly recommend getting the biggest dish possible. the block, any head gasket, and head bolts are not designed for boost and will fail. Also, flow is not as big of an issue with boost. depending on the amount of boost, you will want your compression to be about 8:1, 9:1 is pushing it.

http://www.therangerstation.com/tech_library/4_0_Page.html

http://www.therangerstation.com/tech_library/4_0_Page.html
 
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Ronin8002

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no need to go down to 8:1 unless the OP plans on doing a lot of boost, i.e., over 12 PSI. 8:1 will just hurt your off boost performance but it will allow you to run high boost with pump gas.

I ran 9-10 psi on stock 9.3:1 compression and was fine with stock type headgaskets and no detonation.

You could always have the block and heads wire O-ringed and run copper head gaskets if you are worried.
 
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jd4242

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As i understand it, the 90tm heads are the ones prone to crack. the 93tm heads eliminated this. The 95tm heads are also higher compression (if you use the first gen pistons, you will have about 10:1). But they do flow better than the 93tm. 98tm heads have smaller chambers still, but do slightly out flow the 95tm.

If you are going forced induction, I strongly recommend getting the biggest dish possible. the block, any head gasket, and head bolts are not designed for boost and will fail. Also, flow is not as big of an issue with boost. depending on the amount of boost, you will want your compression to be about 8:1, 9:1 is pushing it.

http://www.therangerstation.com/tech_library/4_0_Page.html

http://www.therangerstation.com/tech_library/4_0_Page.html

Some of this is not true.95tm do flow better than 93tm but 95tm flow better than 98tm.95 and 98 have the same CC the only difference is the exhaust ports.98tm have smaller but rounder ports.9:1 is fine for boost.he has a remote turbo and probably wont be running alot of psi so i would even go 10:1!!
 
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FIND

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no need to go down to 8:1 unless the OP plans on doing a lot of boost, i.e., over 12 PSI. 8:1 will just hurt your off boost performance but it will allow you to run high boost with pump gas.

I ran 9-10 psi on stock 9.3:1 compression and was fine with stock type headgaskets and no detonation.

You could always have the block and heads wire O-ringed and run copper head gaskets if you are worried.

Indeed. Boost is just in effect, just like increasing the compression ratio of the engine. Only difference is air/fuel is precompressed, then compressed normally. Only reason to not use boost with high compression in most cases is because the engine just can't handle the pressures or temperatures. But, if you are just lowering the compression a whole lot, you are getting rid of the benefit you gain from boosting, and you are making a worse engine off boost.
 
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jd4242

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pat3

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i was aiming for 8-10 pounds for the sand drags and probly 5 on the street the truck is not a daily it is the show peice for my shop (sky high customs)


i build v8's a lot of the conceps are the same but iv never got this deep into a v6 and this is only my second explorer and just bought my thrid so i am asking opions sice you guys are familer with these engins


can any one tell me the compresion with tm 95 heads on a stock 91 block
 
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jd4242

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10:1
 
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pat3

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yea thats what it was lookin like i havent taken the heads off are the 91-94 blocks flat top pistons
 
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jd4242

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No they are dished
 
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