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Dont give away any RPM. Your right thats power thrown away. As far as a girdle, I dessagree, a girdle will strenthen things a lot. It will also hold down vibration and allow the engine to rev smoother. The Jeep 4.0 went to a girdle from the factroy & you wouldnt believe how much it helped.
It could be a simple girdle that just tied all the mains together, but one that went to the oil pan rail would help even more, but would be harder to fabricate. Look at the factory 4.0 Jeep girdle, it would be easy to dulicate for the slant.
I think so too... I even think that going thru the trouble of machining new main caps that crossbolts thru the blocks would be worth the shot.
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Also, its a funny think that the /6 has the same main jurnals & caps as a big block 440 Mopar. You might even be able to add some ductile iron main caps from a Big Block. People think of these kinda things as overkill or only for durability, but the truth is, it helps make more HP.
That's why I don't like the idea of stroking the crank and fiddling with the main and rods journals. Slant six is the engine that has the biggest con rod journal and biggest main journals. That's why other makers had to use 7 mains and threw con rods like popcorn.
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Crank stroke, I am not sure I wouldnt use the 198 crank.
do these come in forged steel? Also we never had 198's so I'd have to import one crankshaft from up there (Expensive! A while back while I was depressed and just wanted out of finishing my car, I looked into how much shipping would be so I could send the 906 to doug, and it was a lot of dough.)
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The head does not flow enough to feed a engine of this size. This will make it peak low in the RPM's on HP no matter what cam you run. That is why I think the 198 crank would work better. The engine will rev better, and it will not be so big that it out flows the head. If you run 250 plus CID, it will peak at around 4800 or lower depending on how big the engine is. And like I said, it will not matter how much cam you put in it, its just not going to make power above 4800rpm, it cant , it cant breath enough. Now with a 198 crank, it could peak at 6400 rpm and be shifted at 7000rpm.
Mmmhh... I really need to measure that head and pass the measures up so educated folks can do the math. I remember this little rascals turning 10k (with 11k valve float) on a 93mm bore 170 stock stroke. And that was with carburetion and other class limitations. Bowls are HUGE, so are ports. I think I can stick 2 of my big fingers down the in port, wich I can't do on a stocker.
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WHY, Simply because of the Head. With the big bore, the head will flow more, but not enough to feed big CID displacment. Long strokes Do Not Make engines peak at low RPM, its all in the Head Flow & Camshaft. On the Big Block engines we run 4.250 & 4.500 stroke cranks & still peak on HP above 7000RPM's. But these engines have the head to flow what is needed. If we take one of these 500 plus engine's and run a factory iron head on it (limited on flow) they peak real low in the RPM's also.
I was jumpin' to say that slant six heads are only outflowed by hemi heads, but then I recalled that this statement is true on stocker heads on 170 CID and you're talking about aftermarket hi tech heads...
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Run a shorter stroke (does not have to be a 170, 198 would do it), as big a bore as you can, and turn the most RPM you can. You will make more Horse Power than anyone else has with a N/A /6 engine at compairable Compression.
With a 93mm bore, and the 4.125 crank(225 crank) you have around 260 CID. That is to much for the /6 head flow. And it will peak at 5000rpm or below. With the 198 crank & the 93mm bore, you get around 229cid. The head will flow enough to let that engine turn 7000RPM or more.
I'm not really shooting for a "big cubes" motor, but a combination between something around 4 litres and a good useful range of rpm. If you peak around 5k but you continue to pull strong up to 7k I'm fine. I'd use the largest cam I can match to this combo. Lumpy idle? who's idling?
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One thing that I like about slant six is although they peak lower than your average built V8, the power and torque curves flatten out more gradually after peaking. Your typical SB or even BB would peak and then die (as in hearth attack die) your slant would peak and then continue pulling less and less (as in "wounded" during the peak and passing out quietly at home later) (pardon my dark comparissions!)
I want "maximum area below the curves" since this would be street'd. I can live with high gears, with a little bit bitter lower end, with lumpy, "nervous" idle, but I don't want this to be a circle track tuned engine.
so maybe I can settle around 250 cid and still have plenty of live left on the heavy wall casting block with a bulletproof bottom end just in case some of the gearheads that are secretly developing the long longed aluminium head can come up with a better head with raised ports and all.
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Its something to think about. This is all with around a 210cfm flow on the intake port in the /6 ( and thats more than most heads flow with oversize valve & full port/polish)
You would need 240cfm (minimum) for the 260 CID engine to turn 6500rpm.
Jess
IIRC mike had created even better breathing heads? (better than 210)?
All of this considerations is what has been holding me back thru the years, I really appreciate all your input here.
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Seems like 300HP should be no problem if you get all those ducks in a row. You could use a bigger cam maybe??
Lou
biggest cam that would make useable power on this combination.