Re: Project Blown 305
 

Here's the not-so-official mock up:

http://i1307.photobucket.com/albums/...pse12l2asr.jpg

http://i1307.photobucket.com/albums/...pstlj9skzj.jpg

http://i1307.photobucket.com/albums/...pscgxb96d3.jpg

http://i1307.photobucket.com/albums/...psyxly5yzu.jpg

http://i1307.photobucket.com/albums/...pszm8kyv34.jpg

http://i1307.photobucket.com/albums/...pspouveo4k.jpg

http://i1307.photobucket.com/albums/...pshzf1ifxc.jpg

Excuse the water everywhere but it looks quite promising.

I've found a few places selling tubing that would actually just plop into place so I may just do that although moving the blower up might be cooler too.

It looks promising, the adapter is on its way and I'll be buying a blower tomorrow and the front cover.
What's cool about the adapter is it will work perfect as a template to drill the big steel chunk so I can just bolt it down and not worry about the angled bolt holes that would almost require a machinist to do.

By running an 8v92/71 I should bridge some of that gap (11" from the front of that plate to the crank balancer flange lol) they offer up to an 8" long snout so I should be able to make this work.


Meanwhile my friend donated these to the cause haha
http://i1307.photobucket.com/albums/...psd22qlhw3.jpg

http://i1307.photobucket.com/albums/...psibuzjggq.jpg

Needless to say, this is exciting.

Kind of tempted to find a 478 diesel or gas block/crank to make it that much more insane and also allow me to get started on the machine work.

Re: Project Blown 305
 

Might have to add to my list...

-478 block/crank somewhere nearby
-Scoop of some kind to match up with two carbs

Re: Project Blown 305
 

Cool stuff man! Perrty excited here to, that's gonna be sweet! :upyes:

Re: Project Blown 305
 

You are building a "Hot Rod"? Wonder why the drag racers never used the 305? Wonder why they never put a blower on one? Hmmmmm. I wonder if it's because they are so heavy? Or if they won't rev. If they were not built to rev? If they would "blow up" with a blower? I just wonder. Maybe they are good for just hauling like all the ads say. Don't know. Good questions though. Trying to completely redesign a motor is possibly a huge waste of time and money. If a person wants a hot rod motor, they are already talking Chevy. So why stay with original if it's no longer an original 305? Are you building a Chevy inside a GMC? That won't work. There will be no "HOT" in your hot rod. A Chevy 350 with minor upgrades will blow your tailgate off. You are talking more torque. Torque without revs will not produce horsepower....as in: hot rod horsepower.

Re: Project Blown 305
 

People usually don't go after certain engines because if the application it's used in is not common for being hopped up people usually don't build aftermarket parts regardless of the merit of the engines.
Typically the most often hot rodded stuff is what's most readily available which would come down to chevys and hondas. Coincidentally the owners happen to be typically the most sensitive. Wonder if there's a correlation.
I'd bet you'd love what I'm putting in my chevelle, anyways, I digress.

The common hot rodded engines aren't picked because of design it's because of ease/cost of attaining them.

At the end of the day if this thing runs and looks pretty (which there's no way it won't with an 8v92 on top lol) I'm content, to me it will be far better than any Chevy product could ever be no matter the output.

Re: Project Blown 305
 

Love'd yer comment Cuttyman,

Diesel engines don't rev, yet a 5.9 liter 12 valve cummins is easily capable of putting out 1500+ torque and 800+ HP all under 3,000 RPM. And that is with a boat anchor bottom end and heavy pistons. Yes, it has a slight cubic inch advantage.....but he only mentioned Revs. And an 8000 RPM 350 would have no stinkin chance. lol

So, someone please explain to me why a v6 wouldn't respond the same way? YES I know...this is Gas and not diesel....But:

A turbo charged 292 on 10 PSI puts out over 350 HP and 450 Torque. Different engine design, but in the Long run....quite similar.....a Truck engine.

Now, considering the 305 v6 is low compression, Adding compression would be a way to make power without the need for more revs. Not to mention you are going to be putting in lighter pistons and lightening up the crank which would easily allow for more top end!

Back to that read up of the guy who hotrodded that 478! It would toast 454's and was capable of 5500 RPM! SO, how come the 305 isn't capable of toasting a 350???

Any engine can be improved, already it's well known that a 500 cfm 2 barrel and dual exhaust is a nice improvement......so a few pounds of boost won't hurt a thing.

Cuttyman, how much boost will that supercharger put out?

Re: Project Blown 305
 

I don't really have a goal output for the SC, probably just 5psi to start and see how well it works.

Kinda depends on a few factors cuz if the bores aren't in too bad a shape I may try to clean it up and run it stock on boost to see what it can do/handle.

If all else fails I'll grab another and start over.

http://i1307.photobucket.com/albums/...psjpphq0cm.jpg
Here's what's coming out once the v6 is ready.

http://i1307.photobucket.com/albums/...ps2rbo0rnw.jpg
Here's the trucks clean side lol

http://i1307.photobucket.com/albums/...ps3ezfzorz.jpg
And the other side.
I'm hoping the blower won't be forward enough to require me to remove the 56 Chevy hood emblem.

http://i1307.photobucket.com/albums/...psgppytxnv.jpg

Planning to keep the exhaust like this but more than likely I'll upsize the rest of the tubing (2.5" straight from the long tubes)

Re: Project Blown 305
 

You kids have fun now. Don't eat too much ice cream. Chat it up some more, it's cute.

Re: Project Blown 305
 

I agree. I'm going to aim for 50 percent underdriven as I'm still learning the ins and outs of these big blowers.
When I get the whole thing together and it runs smooth I might try pushing it a bit more.

When i get to a fully built setup I'll try for more to see what it can do. The joy of the big blower is I can spin it slow and still make a good amount of boost.

Either way I stoked. The blower is on its way as is the front plate and adapter.


Also I'll probably still the main plate for the same pattern as the top of the blower so I can plop the dual quads on for a startup setup so I can get it running without the complications of the blower.

Re: Project Blown 305
 

What are you gonna use for the dual quad setup?

Re: Project Blown 305
 

It's too bad that this thread is starting to degenerate.

Everyone has a point, however it boils down to what each individual wants out of what they are building. There is nothing wrong with a high reving small block NOR is there anything wrong with a boosted low speed engine, gasoline or diesel.

Over the years, I've done it about every way it can be done, but my favorite is boost. I've boosted sixes up to big block V8's and I've fooled with the diesels too. As my first turbocharged engine was in 1976, that's where my preference lies. Does that make me right or wrong? NO. It's what I prefer.

I love the idea of a supercharged 305. I also like high speed small blocks. One is no more right or wrong than the other. It's what the owner builder wants, not what someone else thinks is right in their eyes.

On the subject of GMC blowers, the 8V92 blower moves about 736 cubic inches of air every revolution. For every other GMC blower, multiply the first number by the second and it will give you the approximate airflow per revolution. Your 305 will breath 152.5 cubic inches per revolution (at 100% VE), so figuring out which blower at what drive ratio is easy depending on your boost requirements.

Personally, I think it is a neat project!

Re: Project Blown 305
 

Yeah, to be honest until one dude popped up I felt this was one of the best mod useful forums.

Im from the same thought process. Anything can make power, it's more a matter of withstanding the forces applied.

I'm going to say at 50% under I should be making a decent amount of boost. I get different answers each time I search on specific blower info. Some say 8v92 was the cubic inches of the diesel it came on and the 8v71 was the same blower almost but mounted to a different engine id noting slight mounting changes(I hear its taller than the 71 due to the top flange being taller) but overall flowing the same amount and having roughly the same case dimensions.

I'm excited for this, I'm glad there's a few others who are as well. This group overall has only made me more excited as it's pushed me closer to my goal.

Re: Project Blown 305
 

Whoops double post.

I'll snap pics when I get the blower here.

Definitely excited for that!


So since I ordered an adapter for the top to fit on the steel plate I have I'm thinking I can drill 6 holes to mount the dual quad plate directly on that to run NA first, then when the motor is sorted I can slap the blower on, move that plate up to on top of the blower and off I go.

https://www.ebay.com/itm/181486211512

Re: Project Blown 305
 

If anyone's chasing these parts to do your own it's all on eBay through a few vendors.

The running total will prolly be under 1500 for the blower related stuff which I feel is really good.
I'm waiting for the next swap meet to find a test belt and gears.

Re: Project Blown 305
 

There used to be two, one was finally banned. Yer gonna get those folks who think that what they say without proof actually matters. Both told me that the 4 barrel mod I did was a big waste of time and that I was dumb and ignorant for doing so because...Oh that math says blah blah blah....Who gives a darn? REALITY says it works and works well. lol

Anyhow, $1500 for boost ain't a bad start! :thumbsup:

Re: Project Blown 305
 

Yeah, some people just really only think an SBC is all that works...

It's kinda a shame we don't have a company that produces the flanges cuz we could prolly easily make a nice 4 barrel intake that takes a bit more advantage of flow with a more stand up intake.

It's a shame it would take a lot to convince edelbrock or someone to create the part.
A simple 4 barrel medium rise intake would bump performance and also offer better fuel mileage since a big 2 barrel doesn't have a small set of primaries to do the low speed stuff.

Yeah I don't think it's bad at all.


I did a bit more searching. 8v92 was the diesel it was under, the 92 was the cubic inches per cylinder equating to 736 ci. The blower is needed because it's a two stroke and it doesn't make enough compression or something
I'm going to need to find more info on how much air the blower pushes at a specific rpm so I can somewhat calculate the psi of boost.

Re: Project Blown 305
 

Detroit Diesel's nomenclature is the first number is the number of cylinders and the second number is the displacement in cubic inches per cylinder. Where a "V" is between the two numbers indicates it is a V type engine.

As these particular Detroits are two strokes, they aspirate every revolution. The reason for the blower in the first place is not for any supercharging, but to aspirate the engine as a two stroke does not have a dedicated intake stroke. Pressure to charge the cylinder must come from an outside pump.

The 2 stroke Detroits have been around since the late 1930's, so it didn't take very long for someone to figure out their blowers would make great air pumps to supercharge 4 cycle engines.

You really aren't going to need an 8V92 blower to pump up the 305. A 6-71, 4-71 or even a 6V53 would do the job. The smaller the blower, the faster you will have to turn it for any given amount of boost on your 305.

A few things to remember about the GMC blowers. The bigger they are, the more power they'll need to turn. Also, for any particular blower, the faster you turn it, the more power they absorb. (double blower speed, and the power requirement increases about 4 times depending on the internal leakage) Also, the GMC blowers become less efficient as you try to extract more boost from them.

I'm thinking a 4-71 (284 CI) or a 6-71 (426 CI) blower will give you the boost you want without absorbing to much power or becoming less efficient. Not to mention they are smaller and will probably package better on a narrow/shorter engine like the V6.

B&M used to make a couple of blowers, one was I believe 144 cubic inches for mildly boosted 350 sized engines and the other was a 177 incher for mild big block sized engines. Both of those were of smaller capacity than even a 4-53 GMC blower (212 CI) and they were of a nice small size easy to fit in most applications.

In theory, a blower providing 305 cubic inches of air per revolution directly driven at crankshaft speed would make 15 pounds of boost on a 305 cubic inch 4 cycle engine. In reality, the charge heating would probably reduce intake charge density to the equivalent of about 8 pounds of boost. If I recall, the maximum efficiency of the GMC roots blower is about 45 percent.

Between your engine size and boost desired, for any given blower size, you'll be able to easily calculate the needed drive ratio. I'm sure there is plenty of information and probably graphs of the various outputs of the many blowers out there, including the GMC's.

Re: Project Blown 305
 

Thanks turbobill

The harder part seems to be finding info for non 71 style blowers in terms of cfm and displacement.
I don't believe the 8v71 and 8v92 are different blower wise but are from the diesel they came off of but I'm having trouble finding anything on the blower itself. As for what I should use, the 8v92 is already on its way and is new so I'm sticking with it.

Something to note, I may have a handle on 2 478's and a 401 so I may be stepping up the cubes in that way.
JE said they can produce a 5.125" piston so then I'd just need to machine the crank to fit a rod that matches a decent compression height.

Re: Project Blown 305
 

If the 8V92 and 8V71 blowers turn out to be the same, in your search for info, you will probably find that it is driven faster on the 8V92 engine. I'm sure there is a Detroit Diesel forum out there for the guys that love 'em. Such a forum may also be linked to an page for old GMC trucks and buses. The Antique Historical Truck Society forum has a few guys that know the old Detroits well, so maybe they can tell you.

Scour ebay for old Detroit service manuals for both the 71 series and the 92 series. They may also have the tech info you're looking for. I have one from my military days, but it is buried somewhere lol, and it was on the 71 series. That was before the 92's came out.

I have a 478 that I'm going to boost with a turbo. That particular truck currently has a turbocharged 468 Chevy big block, but I've always wanted a 478 for it. Took well over 10 years to find a nice one and I've had it now 17 years so I need to get started. Retirement is less than two years away fortunately.

Also laying around is a 478 Toro-Flow and a few 305's. At least one of those will eventually wear a turbo too. (maybe both) Don't know what I'll use them in as I already have over 20 vehicles and really don't need any more lol. Guess I could always put them on display and run 'em now and then!

Re: Project Blown 305
 

Haha nice!

I'm curious the differences in block and internals on the diesel 478's.

I'm only stating that as that's all I've found differentiating the -92 vs -71.... some say it's bigger bearings etc.
I would agree there's probably a bump in speed that the blower is spun at.
I haven't dug through the diesel forums because differentiating between the blower they use and the engine itself is difficult based on the blowers not having a name/number themselves.

Re: Project Blown 305
 

And I know the feeling, I'm at 9 vehicles... all projects (either because I turned them into a project or they started that way) at 28 so I def understand the thought there haha.

Re: Project Blown 305
 

The block is a bit different on the Toro-Flow as it has a balance shaft on the left side just above the oil pan rail and the assorted gear train to turn it.

I believe the rod/main bearings are the same size between both and the cylinder head bolt pattern is also the same. The bellhousing and rear of the engine looks the same.

Some gaskets are the same and I wouldn't be surprised to find the rods and some of the valve train may be the same too.

Re: Project Blown 305
 

Interesting, I wonder why they have a balance shaft if it's the same everywhere else?

I wonder if the block was reinforced further than the gas variants?

Would be neat to investigate.

Re: Project Blown 305
 

I doubt I'll have both of mine apart at the same time so I won't be able to help lol. I wouldn't dare pull the heads of the Toro-Flow as I have yet to see any available anywhere.

Re: Project Blown 305
 

The ToroFlow engines did use crossbolt mains, so they were a 4 bolt main vs 2 bolt main for gas engines. In 1973 GMC had redesigned the bottom end of the block only on 478M gas engines with much larger main journals as well as more beef in the main saddle area and much larger main caps & bolts but still a 2 bolt main. When I get a chance I'll take some pics of the newer main caps vs the older main caps and post it.

Re: Project Blown 305
 

That would be awesome, the mains in these aren't too terribly large from what I've seen.

I almost think a big diesel block would be a good foundation if not better than the rest since it's setup for 4 bolt mains although I don't plan to rev this hard, just make the blower work early and stop at 4K.
The hard part will be making the truck work on the freeway unless I adapt an nv4500.

Re: Project Blown 305
 

I think you'll be fine up to 4000 rpms, sounds like a fun project and you're doing something that nobody has attempted:thumbsup:, pay no attention to the nay sayers:notrolls:

Re: Project Blown 305
 

Thank you! I'm very excited about it.
I'm hoping I can come up with a way to grab the 478's and toss one in for the time being and sell the 305 to build the other.

I'll have a bunch more coming very soon when the blower shows up with the adapter plate and front cover!

Re: Project Blown 305
 

If you toss in a 478 just know you have to have the correct 8 bolt flywheel that has offset weight on it since these are externally balanced engines. A 401 may be a better choice, most 401's will accept the 305 flywheel as long as they don't have the 8 bolt crank flange.:thumbsup:

Re: Project Blown 305
 

Didn't know that, maybe I'll start with the 401 then and build on both of the 478's haha.

Weird they would go internal and external balance on the different sized engines of the same family

Re: Project Blown 305
 

The 478 has a longer stroke than the other V6's, hence the reason for external balance in this case.

Re: Project Blown 305
 

I see no reason why a gas 478 block couldn't handle lots of boost. Mine will only handle 11 pounds or so and I'm not worried at all. With it, came a Clark VO 285 transmission with a .83 overdrive. My cruise RPM at 60 will a little less than 1900 RPM.

Re: Project Blown 305
 

This thread has been cleaned to bring it back on track. Remember Gentlemen, we have rules in this forum.

Stay on topic. Cutty, good luck with your project.

Re: Project Blown 305
 

It's absolutely impossible to internally balance the 478 crank, I requested the balance shop to see what they could do and the end result was they put as much weight as they could to the crank but still needed a good amount of weight on the flywheel and front pulley. The only internally way to fully internally balance one is to stroke it and increase the bore, the end results would be 523 cubic inches.

Re: Project Blown 305
 

The Clark is a five speed. If the nomenclature only had a letter, it's a non overdrive. An O after the letter indicates overdrive. For the other larger truck transmissions, I'm not sure how they denote it in their nomenclature.

I was lucky as this is the transmission that was behind my 478. My truck is also a 4 X 4, but it has a divorced transfer case so it is only a simple matter of fabricating a shaft between the transmission and transfer case.

Re: Project Blown 305
 

Finding a Clark 280 or 285 overdrive is not going to be easy. I have been searching for one the past 6 or 7 years for my Ford to no avail.

My plan is to just use the large truck adapter plate and flywheel and run an overdrive tranny with an SAE bellhousing pattern. The Spicer/Tremec 6+1 seven speed has been turning my crank of late but any Fuller 5 or 6 speed would work fine.

Re: Project Blown 305
 

I figure if I shed serious weight off the 478 rotating assembly by stroking and aftermarket parts that aren't giant I should be able to internally balance it.


Shoot! there sure are a lot of options, I just need something OD to make it streetable and something that bolts up since my engine combo is gettin more exotic haha.

What would you recommend for an OD equipped trans that's relatively readily available for a reasonable price??

Re: Project Blown 305
 

Are there big truck transmissions available that have a married transfer case and OD?
Would they fit in the run of the mill c20's?

Re: Project Blown 305
 

No, but custom adapters have been made to couple 6 speed fullers to married transfer cases.

http://www.4btswaps.com/forum/showth...-Transfer-Case

Re: Project Blown 305
 

I don't know of any as even the big stuff years ago used divorced transfer cases.

I would find a NP205 divorced style out of a 70's Dodge 4x4 P/U or International light line 4x4. Both had the front drive coming out of the right side if you are using a 60's to late 80's GM front drive axle.

Ford also used the 205 divorced style through about '77 on the F250/350, but it drives on the left, so you'd need a Ford front drive axle.

The 205 is all gear drive and is the strongest of the light truck models. I converted my truck (a 1965 Chevy) after the naturally aspirated 454 chewed up the original Timken T221. It has held up under the turbocharger since 1986.

Are you wanting a manual transmission only or are you also considering an automatic?