I see you got a South Bend clutch, is it the one rated for 425hp/850lb-ft or some other clutch adapted from another application? Also what all was done to your ZF5? Just a stock rebuild?

Any updates on the build as well?

 

Yes, I got the 425hp/850lb-ft clutch kit, it finally came in... AFTER 7 MONTHS OF WAITING! AS for the ZF, it was a stock rebuild with bearings and synchros.

UPDATES! YES. The me and the engine builder have FINALLY come to an agreement as to what is going to happen, AND I have ordered the parts from R&D, awaiting shipping. As for the motor, ARP head studs, new bearing and bushing, new pistons, Inconel exhaust valves, head job.. basically everything that would entail a new engine rebuild. To lower the compression ratio, my builder has told me the best way to do it would be a thicker head gasket (even though I don't see why I cant just shave the piston heads bout 0.025 thou). Surprisingly, the bore was only worn out .020 thou, not bad for 570,000km. My R&D order was basically one of EVERYTHING... girdle, stage 2 turbo, RD4-150 pump, cam, intake, etc. uhh... that's about it. As for paint, I'm thinkin CAT yellow with black detailing.

Any other specific questions, go ahead and ask

 

How many miles is that? My cylinders are .004" over after honing, but is a low mileage engine.

 

Hairy
354 k

 

My engine build is cat yellow and black as well! I'm still waiting for my parts from r&d also. I ordered my studs a month ago but I guess they're backordered from his supplier. He's shipping the cam and pump with the studs as soon as he gets them in. I guess I gotta keep waiting.

 

Thanks for the update! How long do you estimate until its on the road again?

Also what turbo are you going with again?

 

If your building a performance engine with a bigger turbo and more fuel you should take advantage of this opportunity to lower the CR a little bit... As far as I know there isn't any "thicker" gasket available.. The new cam dose bleed a bit of CR But Not Enough in my opinion. If I where building another Engine I would Cut At least .025 off the Pistons and then balance the weight of all eight again before Balancing the rotating assembly. If your Engine Builder doesn't understand this you have the wrong Engine Guy.. Look up the difference between Static compression and Dynamic compression and the affect Turbo boost has on it... You will soon understand why it is so important to lower the compression ratio on a Engine that will be using more than 10PSI Boost. The more Boost and fuel you add the lower the CR needs to be.. You just need to stay above the Lowest CR that the Engine will still start well... Engine's with 17 to 1 still start ok and will take 30PSI Boost with no problems.. In my application I was shooting for 18.5 to 19.5 to 1 running 20PSI Boost Max so I cut my pistons .030 with stock gaskets. You Can't go wrong with R&D parts so Don't cut corners on the other simple performance mods you can do along the way.... Just my 2 cents...

 

Justin has some 2.8mm prototype Reinz Extreme decompression gaskets but they have not been tested yet. Stock gaskets are 2mm. Depending on how much they compress it could be equivalent to .025"-.030" piston shaving. The stock thickness prototype gaskets are being tested in Smogie now...

 

Why?
I understand that the more air you shove into an engine(via boost pressure), the higher the cylinder pressures are. If I put in 24 PSI of boost, my cylinder pressures should be around 3X stock. As long as the head studs can handle the peak pressure, it sure seems like higher CR + higher boost is good, as it means just plain more air in the cylinder.
If you're running into pressure limits(i.e. bending connecting rods or lifting heads), then yes, you obviously need to lower the CR. As long as you are below that point, though...

 

^^^This is exactly what I would like to know also. I have read until my eyeballs were falling out but I have yet to find any good science on decompression. Like you said, the only tangible benefits I can find are less stress on the head gaskets and engine internals, and it does lower EGT's. Beyond that it seems like a lot of guessing to me. The math I have found to show how much you have to decompress to run X psi additional boost (and maintain the same cylinder pressures) looks ridiculous. Boost is only the air side of the equation, and the whole point of boost and fuel is to get higher cylinder pressures = power. I'm not saying decompression does not have its place here, but I'm just not finding any good scientific justification for it, or rational guidelines for how much. I have also not seen a comparison of otherwise equal engines where the decompressed one made more power. Right now I am heavily leaning toward re-thinking my build and keeping the stock compression. Maybe I am reading all the wrong stuff, if anyone has a better resource on this topic please share it!

 

That's what I did. If you're talking 300HP range and 30 PSI or less, it should work fine. If you're talking more than that, you might shave the pistons /slightly/, but more important is going to be using PS rods. Remember, rods seem to be the limiting factor here, as Justin found out.

 

Same here. Couldnt convince myself it was worth the cost to drop compression, if anything i raised it lol, .010 off block, .010 off heads, 1.94" compression height. Going to run the 110 and s362 and beat on it, maybe more later.

 

Keep us posted, I'm following this and want to know how it comes out.

 

I'm doing a 150cc and stage 2 turbo. Very similar to what Justin had going on in his Bronco. His was the 180cc, but with stock-ish inlet pressure which made it more like 160cc output. He bent rods but he also had 20 gph 60% water meth. He says that's not what killed it, but I've read that water meth and high compression don't play nice. I won't be using water meth, and I have IDIT rods. So I am thinking I could get away with stock compression. I'm just not thinking it is necessary, and there are very real drawbacks besides cost..

 

Based on what I've seen, I'm thinking that the key is going to be using very strong valve springs. I mean, Basically everything that happened to him upper end wise(bolts came loose, bent pushrods) happened to me, at lower levels. And he had shimmed 910's. I'm betting that if you increase the seat pressure a bit from where he had it, things will work a /lot/ better, bent rods or not.

I haven't told anyone this, but I've noticed that my engine seems to rev a bit smoother under heavy load. It used to get a bit rough sounding and feeling up in the 3200+ range; I figured it was timing related, but didn't really worry about it because it still made power.
It smoothed out some since I swapped these new springs in, so it may have been floating valves all along(perhaps holding them open just a slight bit longer), but not enough to bend the pushrod until I got a ton of backpressure in there.