Slant Six Forum :: RPM limits

I wonder why top alcohol/fuel motors don't run balancers?

What would it take to make the bottom end hold 7500-8k? Aftermarket rods and bolts? I know it'd be pushing it still on a 225, but maybe a 170 or 198 could handle it. Of course, you'd need some major head porting and a big ol' cam to get it there

Aftermarket rods. Stock rods will not last at 7500-8000.

Oh, and some new kind of head that will flow enough to support that kind of RPM and make power.

And a block that will keep the main web in at the RPM you speak of.

Also, have you guys heard of using two tops for the main bearings? You shave a tang off and that way more oil gets to where it needs to go?

Quote:

It breaks.

Well duh, but I mean why does it break? Is it just not strong enough to handle the higher revs? What exactly happens, is it actually pushing the crank out of the block? Is it harmonics or what?

I know low end is lost to gain higher revs, I'm just interested in knowing the limits of the engine. Curiosity really, is all.

A 6 cylinder crank is neutrally balanced. When you spin one at the balance shop you don't hang bob weights on the crank like you do with a V engine. In my estimation the problem with our cranks is the distribution of the mass. Because the counter weights are distributed unevenly between the throws it causes the crank to flex and tears the block apart. If one were to have a crank made with counter weights on both sides of each rod journal the crank would flex much less and live longer at high RPM.

Quote:

3. I have a Comp Cams 260H and an AussieSpeed 4 bbl manifold that I plan to install. Should I change out the valve springs? I have not decided if I want to go to the oversize valves.

I have one of the AussieSpeed manifolds with a Holley 390, it works much better than my Clifford manifold. The only problem with it is that I had to spend about 3 hours with my die grinder to get the triangle washers to fit. If you don't have a die grinder (I have 3) or the time to fit the manifold I would get a Offenhouser 4 bbl manifold for ease of fitment. The Offy manifold will work with your stock manifold, headers or Dutra duals. The Aussie speed manifold will work with headers or Dutra duals...I have Dutra duals on mine and the current Clifford manifold will only work with headers. Headers can be a pain in the rear on a slant six. I could have made the Clifford manifold work with Dutra duals but I would have needed to do lots of grinding and Tig welding on the manifold to make it fit.

I agree and diagree. I start to see what your saying and maybe I'm not understanding. The balancing is essentially taking the parts and holding them at a tighter tolerance.

Author:	slantzilla [ Sun Nov 23, 2008 7:13 pm ]
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Quote: I wonder why top alcohol/fuel motors don't run balancers? Because they would destroy one trying to drive the blower off of it. The engines have such a short life span they don't really need one anyway.

Author:	Doc [ Mon Nov 24, 2008 10:21 am ]
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Quote: What would it take to make the bottom end hold 7500-8k? Aftermarket rods and bolts? I know it'd be pushing it still on a 225, but maybe a 170 or 198 could handle it. Of course, you'd need some major head porting and a big ol' cam to get it there I have built 170 / 198 combos that rev to 7500 on factory bottom-end parts. As noted, the right cam and some good head flow is needed. I was also careful to select good crank and a nice set of connection rods, recondition the rods with ARP bolts and have everything rebalanced. DD

Author:	runvs_826 [ Wed Nov 26, 2008 7:03 pm ]
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Well, with that and talking with my Uncle I've been rethinking the need for H-beam rods. I don't need it to be a super engine, but will want it to spin to 7500rpm and somewhere around 350hp. I have small block rods that I was going to have cut into the crank, but if the rods will hold up than I won't bother. If I give a crankshop (hopefully a good one in Oregon) a picture of your cranks do you think that will give them some ideas to lighten the crank and balance the assembly?

Author:	Doctor Dodge [ Thu Nov 27, 2008 7:57 am ]
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Lightening a crank is a time consuming job, most crank regrinding shops will not want to do that kind of work. Weigh your crank and then call them and ask for a quote. Tell them you want 5 lbs off of it. To be honest, crank lightening is not worth the effort and cost. Better to simply deburr & polish off the leading edges of the unit then have it rebalanced. DD

Author:	Force Fed Mopar [ Sat Nov 29, 2008 4:44 am ]
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Quote: Aftermarket rods. Stock rods will not last at 7500-8000. Oh, and some new kind of head that will flow enough to support that kind of RPM and make power. And a block that will keep the main web in at the RPM you speak of. What happens to the main web?

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RPM limits https://www.slantsix.org/forum/viewtopic.php?t=32206	Page 4 of 4

Author:	Joshie225 [ Sat Nov 29, 2008 7:39 am ]
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It breaks.

Author:	Doctor Dodge [ Sat Nov 29, 2008 8:21 am ]
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Alot of stuff breaks when that happens... To be honest, the biggest problem I have with high RPM Slants is keeping all the bolts tight, every fastener on the thing wants to loosen-up. DD

Author:	slantzilla [ Sun Nov 30, 2008 10:38 am ]
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The biggest drawback to a high rpm motor is that you have to give away low end. 7500 rpm sounds cool, but what use is it when you have to put in a 5000 stall converter and 5.38 gears in order to run 14 teens? There are no free lunches.

Author:	Force Fed Mopar [ Sun Nov 30, 2008 12:17 pm ]
Post subject:
Quote: It breaks. Well duh, but I mean why does it break? Is it just not strong enough to handle the higher revs? What exactly happens, is it actually pushing the crank out of the block? Is it harmonics or what? I know low end is lost to gain higher revs, I'm just interested in knowing the limits of the engine. Curiosity really, is all.

Author:	runvs_826 [ Sun Nov 30, 2008 2:03 pm ]
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http://www.allpar.com/corporate/bios/ha ... rview.html Many of you have probably read this, I just reread it this weekend and it reinforced my postion to switch over to the 170. The 170 was the performance motor out of the slant sixes. The others were afterthoughts like dodge seems to do. The longer stroke 225 seemed to cause torsional issues for such a small block, as well as others. That is why I believe that supercharging a 170 is the way to go. The 340 used to be the small block to have back in the day and in my opinion the 360 was a truck motor. Nowdays you can turn this truck motor into a performer with aftermarket parts and other tricks, but let's not forget what engine was orignally built to perform. Yes, for more rpms you give up a certain amount of bottom end. I explain it to my dad with choosing camshafts that on a spectrum your engine makes so much "power" and you can shift the power up and down on the torque to horsepower scale. My uncle is paying big bucks for a small block that is stroked and can spin 8000rpm. I argued originally that he is giving up some torque for this privlege, but with gears you can keep the rpms up past the first two second of the race which is what is killing me, I got no top end! So with this I'll keep the ball rolling. Also, have you guys heard of using two tops for the main bearings? You shave a tang off and that way more oil gets to where it needs to go?

Author:	Charrlie_S [ Sun Nov 30, 2008 2:52 pm ]
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Quote: Also, have you guys heard of using two tops for the main bearings? You shave a tang off and that way more oil gets to where it needs to go? Actually it is easier to renotch the main cap. "Once and done". When removing the tang you have to make sure you don't have a high spot, and need to do it every time you replace the bearings. But that doesn't help the mains caps or the web. It helps the rod bearings.

Author:	Joshie225 [ Sun Nov 30, 2008 7:05 pm ]
Post subject:
Quote: Quote: It breaks. Well duh, but I mean why does it break? Is it just not strong enough to handle the higher revs? What exactly happens, is it actually pushing the crank out of the block? Is it harmonics or what? I know low end is lost to gain higher revs, I'm just interested in knowing the limits of the engine. Curiosity really, is all. A 6 cylinder crank is neutrally balanced. When you spin one at the balance shop you don't hang bob weights on the crank like you do with a V engine. In my estimation the problem with our cranks is the distribution of the mass. Because the counter weights are distributed unevenly between the throws it causes the crank to flex and tears the block apart. If one were to have a crank made with counter weights on both sides of each rod journal the crank would flex much less and live longer at high RPM.

Author:	Force Fed Mopar [ Mon Dec 01, 2008 8:51 pm ]
Post subject:
Quote: A 6 cylinder crank is neutrally balanced. When you spin one at the balance shop you don't hang bob weights on the crank like you do with a V engine. In my estimation the problem with our cranks is the distribution of the mass. Because the counter weights are distributed unevenly between the throws it causes the crank to flex and tears the block apart. If one were to have a crank made with counter weights on both sides of each rod journal the crank would flex much less and live longer at high RPM. Ok gotcha, thanks. That's the kind of info I was looking for.

Author:	AussieSpeed [ Tue Dec 02, 2008 4:19 am ]
Post subject:	Re: RPM limits
Quote: Quote: 3. I have a Comp Cams 260H and an AussieSpeed 4 bbl manifold that I plan to install. Should I change out the valve springs? I have not decided if I want to go to the oversize valves. I have one of the AussieSpeed manifolds with a Holley 390, it works much better than my Clifford manifold. The only problem with it is that I had to spend about 3 hours with my die grinder to get the triangle washers to fit. If you don't have a die grinder (I have 3) or the time to fit the manifold I would get a Offenhouser 4 bbl manifold for ease of fitment. The Offy manifold will work with your stock manifold, headers or Dutra duals. The Aussie speed manifold will work with headers or Dutra duals...I have Dutra duals on mine and the current Clifford manifold will only work with headers. Headers can be a pain in the rear on a slant six. I could have made the Clifford manifold work with Dutra duals but I would have needed to do lots of grinding and Tig welding on the manifold to make it fit. Just want to add my 2 bobs worth here, The AussieSpeed PP&R hurricane should not need 3 hours of grinding to fit. Did you not get the instruction sheet on grinding the triangles rather than the manifold ?.. I will put up the sheet in a new thread..

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Author:	440_Magnum [ Thu Dec 04, 2008 10:40 am ]
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Quote: I agree and diagree. I start to see what your saying and maybe I'm not understanding. The balancing is essentially taking the parts and holding them at a tighter tolerance. No, balancing has nothing to do with tolerances at all. Tolerance is how precisely the parts fit together, not how well they are balanced by other parts moving in the opposite direction. Josh was right as far as his statement went- balance has NOTHING to do with the stress seen on the connecting rods, rod bearings, and bolts because those stresses come about solely from the mass of the piston reversing direction twice per turn of the crank, not how equal those forces are from piston to piston or how well they are balanced by the crank counterweights (in a v8, that isn't done in an inline six anyway). But good balance DOES drastically reduce the loads imposed on the main bearings and the block itself. Even the crank may see less flex loading with proper balance.