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Big bore boss motor do's and don't ?

15K views 32 replies 15 participants last post by  Cobolt005 
#1 ·
I'm looking to build a 323 boss motor, and putting my fox lake stage 3 heads and my bullit racing cams on it with a 10.5:1 compression. will be a turbo auto car and looking to make 1000whp. The only down side I've read was head sealing issue ? What have most done to fix this ? Just trying to get info on the swap to make sure I don't miss nothing !
thanks rob
 
#3 ·
You can run the Titan SCE headgaskets or run soft copper head gaskets and O-ring the block and heads. You can't run a full circumference o-ring on the boss blocks since there isn't enough room between the cylinders, but you can run a "figure 8" setup which I have run with no issues at all.
 
#6 ·
The big thing to remember if you want to use a Big bore block with boost is just know from the word go that you won't be able to push a lot of boost. If its a mainly street setup that you won't be leaning on much it will probably work fine.

If you want to run north of 20psi all the time I wouldn't use one.
 
#7 ·
This isn't entirely true. I run the Titan SCE gaskets north of 20psi all the time with no issues at all on my street car. With my drag car I run mid to high 30psi boost using the figure 8 o-ring setup that I mentioned above. I've never had a head gasket sealing issue on my Boss blocks. Not to say that people haven't had issues because we all know they have, but I can almost guarantee that if you want to push really high boost with the big bore motor and you run the o-ring setup, you won't have issues.
 
#11 ·
save the cubes....add 2psi....
 
#15 ·
Sounds like, as you pointed out, the ship has already left the dock, Jason. Unless you are planning on removing the engine to modify something the only thing that really remains to be done is stage and make a pass to see how it is working.

Keep us posted on how the BB build performs for you.


Ed
 
#16 ·
Sounds like, as you pointed out, the ship has already left the dock, Jason. Unless you are planning on removing the engine to modify something the only thing that really remains to be done is stage and make a pass to see how it is working.

Keep us posted on how the BB build performs for you.

Ed
As luck would have it, the engine is going to come out in the coming months to do cams. I was planning on installing the new cams and the timing components myself however, I am having some hesitancy as this will be my first rodeo working on anything internal to the engine. I consider myself to be fairly mechanically inclined, I installed the turbo kit, comfortable installing/removing trans and engine, etc.
 
#17 ·
I ran my boss block at 16 to 17lbs for about 3 years. No head gasket issues. Next build I am thinking I will do port heads and cams and keep boost 19lbs ish on e85. I am thinking this setup will live for a good while.
 
#18 ·
From what I saw the best way to put boost in one of these while retaining a conventional head gasket is to keep the compression ratio in check and use ARP2000's at 110lbft.

8:1 and 30psi boost no issues at all on a Cometic 3.750" bore gasket, and it would not worry me to put a little more in it either.

Next engine I am doing for a customer is 10:1 and I think I will have to step it up to a copper gasket and oring'ed block as suggested by Helomech74

Just my 2c

Daniel
 
#19 ·
From what I saw the best way to put boost in one of these while retaining a conventional head gasket is to keep the compression ratio in check and use ARP2000's at 110lbft.

8:1 and 30psi boost no issues at all on a Cometic 3.750" bore gasket, and it would not worry me to put a little more in it either.

Next engine I am doing for a customer is 10:1 and I think I will have to step it up to a copper gasket and oring'ed block as suggested by Helomech74

Just my 2c

Daniel
Daniel- thanks for the feedback.

I will be pulling the engine out shortly to put in some new cams. I currently and running ARP2000 studs with cometic MLS gaskets. I'm running 17psi right now but would like to up it to 22ish and shoot for 4-digits on the dyno. The engine has ~400 miles on it since the build. If I retorque the studs to 110ftlbs when I do the cams, do you think I will have a high probability to successfully keep the coolant on the wet side and the cylinders dry?
 
#21 ·
Daniel any opinion on the max overbore on these blocks running boost? 20lbs ish. I am going to be pulling mine soon and may need to clean up the cylinders. I have read some say 5 or 10 over is pushing it given that the block is already essentially max overboard as is. Any experience with this?
 
#26 · (Edited)
As far as boring is concerned you can bore the Boss block .040" without compromising the cylinder integrity, cylinder sealing between bores however will be lessened. The block is not "essentially maxovebored", it's cylinder walls are no less thick than the cylinders of a cobra block.

A friend ran a boss big bore block for a couple years at mid 20psi, no 0-rings. Never had a problem. Others have pushed mid 20s without 0-rings and also not had problems. It's all in the prep as it with any forced induction block.

If wanting to tq the head studs to 110 I recommend tq'ing the tq plates 110 during the honing process.
 
#22 ·
No but I went 0.005" on this build as the block had a little wear in it, I would bot be concerned at 20lbs, most important is use the ARP2000's and up the head clamp with a higher torque setting IMO (I know some disagree, but its effective and I have yet to see a downside in the iron block)

Daniel
 
#24 ·
For those reading this thread please remember the torque specs Daniel is speaking about are for the iron 3.700 bore BOSS 5.0 block. If you, for example, have an aluminum block like a Teksid or Aluminator that you put the 3.700 bore Darton MidSleeves or even try in standard bore condition when you torque the heads to 110 ft/lbs you will most likely damage the block. The iron BOSS block responds decidedly better to the high torque than it's aluminum cousins do. Daniel has done considerable investigative torquing in this particular area. :)


Ed
 
#25 ·
Thanks Ed yes I probably didnt make that very clear. Cheers

Ill delete a few PM's... I have 2000 storage on Australian Ford Forums and thats always full too.... I hate to delete stuff!

Daniel
 
#30 ·
Hello I am as well looking into doing a big bore block build and I see some talk about using the SCE ICS Titan Head gaskets P/N: S46754.
Now I know maybe a stupied question but better to ask questions before laying out the cash. On the SCE ICS Titan gaskets it say's for a bore opening of 3.750" and well the big bore block is 3.700" wouldn't that 0.050" larger dia. matter? Would like to know as I want to go with these over the Cometic MLS gaskets.
Also whats everyones view on MMR 3000 Head Studs besides the price! I know OMG :what: I just dont want head gasket issues with boost but I want the cubic's.

@Eatualive281 I am interested how lightly used we talking about.
 
#31 · (Edited)
The 3.750" bore of the gasket is the correct size for the 3.7" bore BOSS block. The stock bore gaskets are 3.625 for a 3.552 bore, so no need to worry.

How much boost do you plan on running? If you're going to be pushing into the high 20's and above, it would behoove you to look into having the figure 8 O-ring done. This will all but eliminate any chance of pushing a gasket. I have total confidence in the SCE ICS Titan gaskets into the mid 20 lbs or so of boost, but if I were doing another engine today, either for the street or the track running high boost and I was using the BOSS block, the Figure 8 O-Ring and dead soft copper gaskets would be a the top of the list to be done.

Just use the ARP 2000 studs, no need to spend the money on those MMR studs when 2000 studs will work perfectly fine.
 
#32 ·
+1 on everything Jim said^.

A little additional commentary on the use of specialty studs. I have seen ARP 2000, custom ARP 625+, and custom ARP2000 step studs. Like Jim said the ARP 2000 studs are more than adequate. The ARP 625+ studs are off the charts clamp force wise and significantly exceed the ARP 2000 studs which are more than adequate. The ARP625+ studs end up being about a $3,000 proposition if I remember correctly. The custom step studs, I believe also made by ARP, either step from 1/2 inch to 11mm (stock is 7/16" to 11mm) or they step from 9/16" to 1/2 inch.

The OEM 7/16" to 11MM only has a 0.004" difference in diameter which is for all intents and purposes the same diameter. The step studs have a 0.062" diameter difference between the two ends. The step studs I have seen usually put the entire difference at one end go the stud. What this does is concentrate the stress from the torque spec for the large end in one small and localized area.

A chain is no stronger than its weakest link, no matter how big all the other links are. Same thing with stud type fasteners. When you use a step style stud all the strain is localized at the point the stud changes diameter. This localized stress is similar to putting a scratch in a plate of glass. That is where the break will occur. The step stud can be no stronger than the diameter of its narrowest diameter.

ARP2000 is more than adequate. If yo want to spend a lot of money on better studs the answer is ARP 625+ studs. Iron blocks are a bit stronger in some ways than aluminum blocks. An ARP 2000 stud over 110 ft/lbs of torque can break a brand spanking new Aluminator block. There is no reasonable application for higher strength with aluminum. Properly built and assembled there is no reason the ARP 2000 studs will not work correctly for iron blocks.


Ed
 
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