Lower compression and Gasket Choice

[bronco78idi]

Hey all, I just dropped off my pistons after talking with each manufacture about the makeup of the piston. I am now looking for input. How low should I drop the compression and where should I mill down parts to achieve the best possible compression and still have a daily driver with a turbo and achieve max boost (not going crazy). Also who’s head gasket should I use?

 

[Devon Harley]

Denpends on what turbo an what you wanna do. I would leave it alone an coat the pistons instead. An victor reins an fel-pro seem to be good. Your gonna need ARP head studs if you want max boost. Nothing crazy doesn't mean much. 15 isn't crazy an that's stock. 20psi doesn't need milling niether does up to 30psi. But it would be good to do but like I stated cryo treat it an that would help more

 

[tanman_2006]

My 2 personal favorite ways of lowering compression is to polish the area around the valves and improve flow.

Number 2 for me is to have the center of the pistons machined out leaving a good thick ridge to protect the rings.

 

[idiabuse]

Purchase a camshaft that reduces the cylinder pressure and you wont have to worry about compression.
My new 7.3 is all stock with turbo pistons Victor Gaskets and studs, using a intercooler makes it possible to
use the engine as a workhorse and survive. It makes 15 psi and reaches up to 900 EGT wich is completely safe.

If I decide I want more boost I will then purchase a camshaft to lower cylinder pressure, better than wasting coin on
cutting pistons.


Javier

 

[riotwarrior]

Actually...the correct method would be to assemble the engine..less rings...then measure the amount that each piston rises above the deck surface, then mill each piston individually to acheive a balanced deck height so each piston is exactly the same deck clearance and if you need to lower comp there is a safe limit but I don't recall that dimension, then have piston tops ceramic coated and sides moly coated. and cryo treated too....

That's the best method..just milling willy nilly off the top without regard to making each piston the same height out of bore is not worth the effort IMHO....


Al

 

[88 Ford]

When you say max boost, what are you aiming for? Also what are your plans with a turbo? And like Idiabuse said a cam is a good way to do it as well. I'm not sure if the Typ4 cam lowers compression (Russ can weigh in on that) but the RD cam and the J2 cam both drop compression a lil bit. The J2 has a more significant drop but it is more of a high rpm cam.

 

[88 Ford]

Actually...the correct method would be to assemble the engine..less rings...then measure the amount that each piston rises above the deck surface, then mill each piston individually to acheive a balanced deck height so each piston is exactly the same deck clearance and if you need to lower comp there is a safe limit but I don't recall that dimension, then have piston tops ceramic coated and sides moly coated. and cryo treated too....

That's the best method..just milling willy nilly off the top without regard to making each piston the same height out of bore is not worth the effort IMHO....


Al

Agreed. Doing it this way takes into account more of the tolerances.

 

[icanfixall]

Miling anything of the top of the pistons and then ceramic coating them is a good thought. But remember to balance the pistons after this. Otherwise you will have vibration you don't want. I balanced my complete rotating elements down to 1/4 to 1/3 gram each. When the engine is running you hear it but don't feel it.. Kinda an odd thought. We don't spin these engines up past around 3500 to 3800 rpm so they can live well with some out of balance pistons. Actually the factory engineers at Mahle told me they can run very well for many hundreds of thousands of miles with a piston weighing as much as 14 grams differant from all the others.. I do not subscribe to the train of thought no matter what degrees they have. 14 grams is plenty of weight to be throwing around... All of my pistons were milled and ceramic coated. Then balanced as a set. They all stick up out of the cylinder 24 to 26 thousands with a factory spec of 31 thousands max...

 

[hesutton]

If you are not planning on more than 15 psi and the head decks on your block havn't been machined..... then no reason to lower compression at all.

If your block's head decks were machined to return them to flat and square, just run pistons with lower compression height (like those offered by Mahle).

Heath

 

[bronco78idi]

Thanks all,

My goals are, it will starts in all weather, Good performance on the highway meaning 65 to 70 Great low end pulling power. I am not sure about the Turbo at all. I never had a diesel and have no clue as to what is normal psi to Max PSI. I was told that the turbo would improve MPG and hill climbing at higher altitude. I am willing to spend the money to make this the Best engine I can mechanically. This is the last engine I want to build for the Bronco.

What I really want to know from this forum is What is the BEST Rings and main bearings to use, Best Gaskets, Valve Springs, Rockers, CAM, etc. If it was your build who’s parts would you use. Please give the manufacture’s name so I can look it up and order it.


Also I am looking at inner coolers and water/methanol injection kit.

I really would like to hear thoughts on the water/methanol injection kit.

I am going to send my pump to the MOOSE!

Robert

 

[Devon Harley]

PM Heath he is more than willing to share all his info on his recent build as he has with me an he got the good stuff! At affordable price an I would put a waste gated turbo on there either a 093 factory ford turbo or a hx35 the Hx will require more work but has a higher performance without going crazy an from what your wanting to build or the willing for good internals it can handle it easily an give more power. Also a cam typ4 for what your doing would be best. Good low end bronco power from it lol. Almost forgot towcat on the board knows where to get gapless rings.

 

[IDIBRONCO]

I hope you have fun with your Bronco. I did. If I remember right, when I was in the business, we used Clevelite bearings, Sealed Power rings, fel-pro gaskets, but I can't remember what rocker brand we used. I don't know what brand lifters we used. We got them in a box of probably over 100. Our machine shop got them for us. I trust them because they bulit several race engines a year. Some even went into Pro Stock NHRA cars.

 

[bronco78idi]

The machine shop I am using is a Great guy, but I think this is his first real diesel build.

 

[tanman_2006]

Actually...the correct method would be to assemble the engine..less rings...then measure the amount that each piston rises above the deck surface, then mill each piston individually to acheive a balanced deck height so each piston is exactly the same deck clearance and if you need to lower comp there is a safe limit but I don't recall that dimension, then have piston tops ceramic coated and sides moly coated. and cryo treated too....

That's the best method..just milling willy nilly off the top without regard to making each piston the same height out of bore is not worth the effort IMHO....


Al

measuring the amount the pistons protrude should be done on ALL engines prior to assembly.

It's a good idea to ceramic coat the pistons after cutting into them. Cryo treating might not be the most effective way to modify pistons. A good coating can go along way in most common applications.

Leaving a thick ridge on the edge of the pistons helps to keep from adding pressure to the rings.

 

[hesutton]

The machine shop I am using is a Great guy, but I think this is his first real diesel build.

That scares me a bit. These are NOT just large versions of a small block Chevy and if the machine work isn't done properly, it could ruin your heads/block and your build. If he doesn't know about these IDI's and hasn't done them before, I'd honestly look else where for machine work. It is a very vital part of rebuilding these IDI's correctly........ and if done wrong, can be a nightmare.


As far as parts and their cost....... here is the list of stuff I did/used on my 6.9 rebuild.

The final tally of parts and their cost, here's the list (it's a little scarey):
Machine work and installation of new cam bearings $1100 ($220 of that was balancing work)
Gasket set and valley pan (Victor Rienz) $250
Clevite 77 rod and main bearings $314.25
Mahle reduced compression pistons with rings, pins, clips $550
"typ4" cam $200
New Ford lifters $90 (eBay find)
Intake vavles (Perfect Circle) $75
Exhaust valves (EngineTech Stelitte face) $105
Comp cam 910 springs $81
Rear main seal with repair sleeve $42
Head work (had to be redone, 1st shop didn't do what they said they did) $410.26
ARP head studs $215
7.3 PSD intercooler $200
Intake hat $66
Intercooler piping/boots $194
Moose pump $689
Moose injectors $1085
Water pump (new Ford) $95
Head dowels $12.50
New 7.3 rockers (Melling) $95.92
Rodney Red Radiator $750
-------------------------------------------------------------
Total = $6619.67


Heath