8V71 vs. 8V92

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engineguyBill
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Re: 8V71 vs. 8V92

Post by engineguyBill »

Am going strickly on memory, so I could be wrong, but I am thinking that the 8V71 and 8V92 engines both used the same basic blower . . . . .

I also think that an aftermarket 671 would be the best way to go, mounted to the engine on a blower manifold. Blower mounted on a tunnel ram manifold would have an ungodly long drive belt which will likely lead to problems. You guys probably already knew this, but the distinctive "whine" sound of a GMC Rootes-style blower is not the result of the blower itself, but rather the air being trapped between the blower pulleys and the wide (3 inch) drive belt.
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Re: 8V71 vs. 8V92

Post by t120r »

engineguyBill wrote: Sat Apr 25, 2020 11:40 am Am going strickly on memory, so I could be wrong, but I am thinking that the 8V71 and 8V92 engines both used the same basic blower . . . .
The 8v71 and 8v92 are interchangeable for the most part. But they are different blowers. Easiest visual way to tell is the 8v71 has a 6" wide intake flange (approx) and the 8v92 has a very wide flange that spans almost the full width of the blower. The bolt pattern on top and bottom are the same between both of them, so they can easily be swapped. For a diesel the only difference I can see is the 8v92 comes in a small bore and I have no idea how that affects an 8v71. As they aren't mean't to pressurize, it would probably work fine. BUT, there are quite a few differences for a gas conversion. Neither would be a show stopper though.
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Re: 8V71 vs. 8V92

Post by Krooser »

I have a 3N53 blower I could sell him...
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Re: 8V71 vs. 8V92

Post by 2seater »

This is loosely related to the original post but this subject is a curiosity. I have an 8V92 blower, with the turbo bypass if that matters. My intention is to use as a flowbench air source so the capacity is what interests me. I did a tracing of the lobe void area on 1/5" graph paper some time ago. As near as I can estimate, the void has an area of 4.16 sq.in. with a 3 lobe rotor length is 15.75" which my math works out to about 393 cu.in. per revolution, or about 227cfm at 1000 rpm. The cubic inch displacement at about a 2:1 overdrive would seem to be a good scavenge match to the 736 cu.in. 8V92. If the capacity is similar to the 8V71 blower, is the difference in scavenge demand compensated for by a lower drive ratio? Does my math have big holes in it?
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Re: 8V71 vs. 8V92

Post by Krooser »

2seater wrote: Mon Apr 27, 2020 2:07 pm This is loosely related to the original post but this subject is a curiosity. I have an 8V92 blower, with the turbo bypass if that matters. My intention is to use as a flowbench air source so the capacity is what interests me. I did a tracing of the lobe void area on 1/5" graph paper some time ago. As near as I can estimate, the void has an area of 4.16 sq.in. with a 3 lobe rotor length is 15.75" which my math works out to about 393 cu.in. per revolution, or about 227cfm at 1000 rpm. The cubic inch displacement at about a 2:1 overdrive would seem to be a good scavenge match to the 736 cu.in. 8V92. If the capacity is similar to the 8V71 blower, is the difference in scavenge demand compensated for by a lower drive ratio? Does my math have big holes in it?
I sure don't know... I quit school in the 6th grade because the teacher didn't want me and my Dad in the same class...
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Re: 8V71 vs. 8V92

Post by 2seater »

I sure don't know... I quit school in the 6th grade because the teacher didn't want me and my Dad in the same class...
[/quote]

Well, interesting reply but not terribly enlightening. :?

Simple question is; my figures are substantially less than mentioned 44x for the 8V71 blower, so either I measured incorrectly, or something additional is different to scavenge a much larger engine with a smaller blower?
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Re: 8V71 vs. 8V92

Post by t120r »

So all big bore 8v71 and 8v92 blowers flow the same theoretical 448cid per rev (wallace racing). The variables with the 8v92 is that there is a small bore 8v92 that flows 80% of what the big bore does. Also, the turbo bypass plate could bleed off pressure. Either way, to use that 8v92, you want to toss the bearing plates and use the 2 bolt hold down style. The angled bolts don't really hold the blower down, they are mostly used for positioning.
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Re: 8V71 vs. 8V92

Post by t120r »

I'm by no means an expert, but i have LOTS of these blowers here. I can show you the various housings and bearing plates if you think it will help.
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Re: 8V71 vs. 8V92

Post by PackardV8 »

2seater wrote: Mon Apr 27, 2020 2:07 pm This is loosely related to the original post but this subject is a curiosity. I have an 8V92 blower, with the turbo bypass if that matters. My intention is to use as a flowbench air source so the capacity is what interests me.
No help on the capacity, but FWIW, it must be a good idea, because I saw a similar setup at Smokey Yunick's shop back in the 1960's. It was being driven by the largest electric motor I ever saw. When he threw the switch, lights dimmed all around.
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Re: 8V71 vs. 8V92

Post by rustbucket79 »

I’m betting that idea died on the vine. :lol:
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Re: 8V71 vs. 8V92

Post by 2seater »

rustbucket79 wrote: Sun Apr 04, 2021 4:16 pm I’m betting that idea died on the vine. :lol:
Yep, didn't pursue it further for a flowbench, don't know about O/P. Eight vacuum motors and a single variable frequency drive works just fine, but very loud.
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