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Hi there Classic Oldsmobile. I am planning to supercharge an Oldsmobile engine. I will be documenting it here and looking for suggestions on how to maximize the power i can get from what I got as well as any tips and tricks during assembly.
So what am I starting with
Car
Gold 1971 Oldsmobile Cutlass
GM 12bolt forged moser axles, Detroit true trac
TKO600 5speed
aluminum rad, dual elec. fans
Engine currently in car
461 ci Oldsmobile (+.030) with dual-quad edelbrock carbs with a low rise offenhauser intake, unknown pistons/rods, Olds "N" crankshaft, polished - possibly ported iron "G" heads w/ roller rockers, 1 - 7/8 long tube headers, msd ready to run
Other engine parts in hand
Used 671 blower already converted for gas complete w/ carb plate
front 2-pc motor plate ( Rocket Racing)
electric water pump
engine girdle (J&S machine)
what is my goal?
As much power as I can milk out of an Oldsmobile using 91 or 94 octane gas and carbs while still being able to drive it on the street. My nearest track is a 300km (185ish miles) drive away. So I am ok with giving up a little power to be reliable.
Other questions
would i consider adding Nitrous to the above? -Yes assuming it could be done reasonably safety
would you consider going LS swap? - Nope, Oldsmobile have always had a very soft spot in my heart.
would you consider going EFI? - Nope, I have seen how much easier it can make things. But I have always been fascinated my the analog-ness of old engines and would like to keep the carbs
what about programmable ignitions: - Yup that can be digital.
Other stuff to know.
I live in Canada so that means this car will likely experience the odd very cold start, also because of the dollar everything costs about 25-30% more. Also E-85 is very rare here so although there is a station near me it's one of two in a 1000km radius, that is why I am not considering using E-85. Lastly all my local tracks are at relatively high elevations ranging from 1050 metres (3445 feet) to 671 metres (2,201 ft)
So what is my plan?
Like everyone wanting to make the most of my money I am focusing my dollars on the rotating assembly and saving money elsewhere. Bottom up.
Crank
Bullet forged SCAT / Rocket Racing 4.5" stroke crankshaft (BBC rod journal size)
"N" cranks by my reading are good to 600hp, after that they becomes unreliable
Rod / Piston
Open to suggestions but thinking 7.1" BBC H-beam rods with appropriate pistons.
Compression ratio
9-1
Heads
Rebuild my current ported iron G heads - My logic is that I can't finish this build with ported aluminum heads and have money for the best in rotating assembly. I believe that it would be best to put my money there, then have heads that are great that are overpowering the rotating assembly. Plus it's relatively easy to swap heads at a later date in car if needed.
Block
Check for cracks, align hone, new main caps, full girdle
Intake
As I am sure you guys know there is no such thing as a blower manifold for an Oldsmobile engine that has been made in the last 30 years. So Dyers blowers / Hampton blowers makes them out of the low rise offenhauser Manifolds. Thankfully I already have one on the car and a local blower shop will be modding it for the supercharger.
Blower
I already have a used one converted for gas in good shape. The shop doing the intake it going to check it and swap out the current snot for one that is an appropriate length for an Oldsmobile.
Carbs
Unsure of the size but all my reading would suggest the holley blower carbs are the only carbs big enough. 750's? 950's? Definitely interested in suggestions
Cam
Definitely roller lifter. Since as far as I know there is not such thing as an off-the-self blower cam for an Oldsmobile. So if I am paying for custom it doesn't seem to make sense to go flat tappit when rollers offer more up to date.
Headers
I am planning to reuse my 1-7/8 long tubes which feed into a dyno max 3" x-pipe exhaust system. I would also install an O2 sensor in them to help with tuning.
Flywheel and damper
SFI steel flywheel, ATI damper? (open to suggestions on the damper)
Ignition
MSD programmable 6AL using my current MSD ready to run as a crank trigger
I am really interested in hearing suggestions on this build.
Not sure how much boost you’re going to run but you’ll need a full girdle (not a halo) and maybe even a bit of Block fill to hold up and do the 800 hp range with the block. The crank won’t be a problem if you go with the Scat billet.
And from there you may want to look into a different rod. I think K1 makes a BBC 7.00” H beam. That would allow you to adjust the height of the ring pack in the piston to a safer level.
Hyd roller would be fine, I can help there if you like.
And buy a wideband O2 to tune it. Don’t rely on your ear or reading plugs. An O2 will give you a good initial reference point if nothing else.
Best of luck in your project.
Welcome to the site Earl! I like the sound of your blower project outline, and the fact that you want to document the build here at C.O. There are a number of engine build specialists who contribute regularly, and are always willing to share their knowledge and expertise. Myself, I'm not a builder by any means, but will be doing my own rebuild in another couple years or so. I read and follow all the build projects and soak up all the opinions and knowledge. When I'm ready to pull that trigger, this is where I'll start
Good Luck with the project - I'll be following along.
I recently sold my 23T with a 351 Cleveland and an 8-71 Dyers blower, 2 Holley 750 blower carbs, with a toploader 4 speed . I have assumed you are going to run 2 carbs. On the carbs, two 750 Holley BLOWER carburetors would be perfect. 950 CFM carbs on a 6-71 seem too big for me, if you had an 8-71 or 10-71 and were thinking of running considerable boost then yes, remember you still have 1,500 CFM to play with. Make sure you buy blower carburetors, a regular carb will not work. Blower carbs have a vacuum connection on the primary metering plates to get vacuum to the power valves, if you run a regular carb you would need to eliminate the power valves, up your primary jet like 10 sizes and it will run pig rich on the street. There are blower carbs that come with mechanical chokes, but running 2 chokes would be kind of a pain, I guess it can be done, I have never tried it.
Cold start in winter time, LOL. This is a blown motor. It will start but you will need to warm it up before you can get going.
Not sure how much boost you’re going to run but you’ll need a full girdle (not a halo) and maybe even a bit of Block fill to hold up and do the 800 hp range with the block. The crank won’t be a problem if you go with the Scat billet.
And from there you may want to look into a different rod. I think K1 makes a BBC 7.00” H beam. That would allow you to adjust the height of the ring pack in the piston to a safer level.
Hyd roller would be fine, I can help there if you like.
And buy a wideband O2 to tune it. Don’t rely on your ear or reading plugs. An O2 will give you a good initial reference point if nothing else.
Best of luck in your project.
I have heard that the Scat billet has become unavailable for now. So my plan is to use the Rocket Racing one. Which I assume would be equivalently strong?
I have the J&S full girdle and was considering a bit of block fill. I believe that with Canadians relatively cool weather I wouldn't have to worry about oil temps too much.
I have heard that the Scat billet has become unavailable for now. So my plan is to use the Rocket Racing one. Which I assume would be equivalently strong?
I have the J&S full girdle and was considering a bit of block fill. I believe that with Canadians relatively cool weather I wouldn't have to worry about oil temps too much.
The Rocket Racing cranks are made by Scat.
Use an oil cooler if you’re using block fill. And again you have the block girdle or halo? Big difference.
I have the block Girdle. The one that bolts to the pan rail and to the caps where you need to cut a notch in the oil pan.
As for running a cooler would I need a check valve or anything to prevent the oil from draining back after then engine has sat for a long time?
👍 on the girdle.
The oil cooler would need to be mounted and plumbed in a way where it doesn’t drain. You never want to have any flow hesitation once you fire it.
The car is in the garage and I am slowly starting on pulling the engine.
But before I started that I took the car to a local shop for a dyno day. 265HP! This engine has lots of room for improvement and is I believe an excellent example of what building an engine via parts catalogue can go wrong. The parts just don’t work together. I am personally interested to open it up and confirm what is inside. Any guess if the low compression, heads or cam is the reason for max power being at 4800 RPM?
Dyno sheet and cam specs below.
To the engines credit it has survived 80,000km of driving from me and however much the previous owner put on it. Engine was built around 2000
If that is rear wheel horsepower it is really not too bad. If the timing is right with decent gas, and the af ratio is on, this is really good for a low compression 455, especially if it has manifolds and not headers. This equates to probably 330 at the crank. My guess is sub 9:1 compression.
Has anyone here ever mounted a power steering pump with a front motor plate on a Big Block Oldsmobile. I tried search around and could find anything. I am looking for suggestion because I am going to need to weld up my own brackets. My current though is is move the Alternator to passenger side mount and then maybe use the old driver side mount as a starting point to weld something together for the power steering. Any thoughts on were to start would be appreciated.
Engine and transmission in now out. From the outside the engine is looking good for the age. Oil leaks seems to be mainly from the valve covers and rear main. Next step is to start taking the engine apart.
This may be a dumb question, but why not use the factory style motor mounts? I solves a lot of issues & my feeling is you are creating a problem with the front plate instead of making any real improvement.
Save the plate for a tube chassis car that does not have motor mount provisions.
It's pretty common to crack the olds block in the area of the two motor mount bolt holes when dealing with 800+ ftlb torque. So a motor plate or a cable restraint to the head is required if you are doing real racing type power in an olds. We don't have a 3 bolt mount on the side of the block like a chevy or pretty much every other engine.
where have i seen a yellow engine like that before ? probably on here but im sure ive seen a yellow one before I dont think yellow engines are to common?
That’ll be the least of his worries if he doesn’t do the right things in the bottom end first.
I am going to be paying a lot of attention to that bottom end.
Plan is
-Scat / rocket racing 4.5" crank, forged rods and forged pistons
-block will be possibly 1/2 filled? (open to recommendations)
-J&S full gurdle
-front motor plate
Previously you mentioned an oil cooler plumbed to prevent the oil from flowing backwards. To keep it from draining back would I need a check valve of some sort? When I look at kits they seem to just be the adapter, rad and hoses. I am on board with why i should have one just unsure of what the install should look like to prevent drainback.
I am interested to see how your whole build, engine, and blower drive setup turns out.
My $.02....
Boost Power potential - depending on the head airflow numbers, and the low-profile intake manifold airflow numbers, the cam timing, compression ratio, and the cylinder head chamber condition (polished or stock cast, iron or aluminum),as well as which spark plugs you run, and how good your fuel quality really is, will all determine how much power you can really make on pump gas. It could be 450hp or 700+hp.
Rotating assembly - Run a shorter stroke 425 crank or a billet crank(4.00 or 4.250 stroke), and the lightest, strongest rods you can find/afford. I don't truly believe there is anything but disadvantage when going to a long stroke, long rod Oldsmobile Engine with limited airflow heads and limited RPM capability. I think it just puts more strain on the block and rotating assembly. With a blower and the 5 speed, I don't know what your gearing and tires/chassis setup is like, but you will have an even harder time hooking up a blown, stroked BBO, and it will run out of breath sooner on the top end with stock or mild heads.
On the heads, a well developed, properly machined set of G heads can still push a lot of power. Go with longer valves than stock, and custom intake valve seats. I would recommend a 2.12 or a 2.14 intake valve, and a 1.6 or 1.625 exhaust valve.
There is a fine line here of spending more than just freshening up the valve job and assuring the springs are right for the cam, and not spending more than a decent set of aftermarket aluminum heads will run...
Block - larger head studs and going with cometic head gaskets as a minimum, or stepping up to solid copper head gaskets and cutting the block and heads for O-Rings and receiver grooves.
Sorry but I disagree with a good part of this.
The more you can make on just motor the less boost you’ll need. If you’re running out of intake flow you can always up the boost to a point.
The Scat BB Stroker crank happens to be fully counterweighted, that’s a huge plus. Couple that with the fact that the rod ratio on the Stroker kit is about the same as a stock stroke 455 and that’s a non issue.
And no need for bigger head bolts/studs unless you’re getting into major boost, same with the having to use Cometics. Mr Gasket for instance makes a composite head gasket that’s good to 14.0:1 compression etc.
Spend your money on the bottom end first, get a wideband or schedule dyno time to tune it right. You’ll be fine if you do these things
Last edited by cutlassefi; September 6th, 2019 at 04:57 AM.
Mark, I agree with upgrading to a fully counterweighted aftermarket crank no matter what stroke it is, but I just don’t see any advantage in adding more stroke to an already undersquare engine with a wheezy head design that noses over around 5,000 rpm with most builds.
Adding boost can obtain the end goal either way, but I would think that less piston speed with a stock stroke, much better flowing heads/good cam design, and less boost pressure would be an easier, less detonation-prone combo for pump gas.
These blocks don’t like big rpm, UNLESS you’re running really light internals, WHICH you really can’t do on a boosted application. See where I’m going with this? It’s a catch 22 to some degree when using a stock block.
And with only decent flowing heads a BBO will make power well past 5000. Its been done many times. Add a blower to that and it raises that potential even more.
Maybe he can install some 2.73 gears so he can utilize 1000ft/lbs of torque and 550 hp.... and a max of 5,000rpm....
After seeing all the stroker Big Block builds, I just don’t see a significant power gain that doesn’t truly come from the heads/induction path on these engines, not from increased cubes. Like you said, let the boost make the power.
To the OP, I wish for the best possible outcome on this cool project!
The other move would be to spend the $5k the blower costs and put that toward a Rocket Racing Block, bore and stroke that to be a monster start of a build, and save up for better heads later.... with the big bore capability, and block strength, you would literally have a base engine that could handle anything you ever wanted to do with it.
Then you could supercharge, turbo, or spray nitrous to your heart’s content.
The other move would be to spend the $5k the blower costs and put that toward a Rocket Racing Block, bore and stroke that to be a monster start of a build, and save up for better heads later.... with the big bore capability, and block strength, you would literally have a base engine that could handle anything you ever wanted to do with it.
Then you could supercharge, turbo, or spray nitrous to your heart’s content.
If that was in the cards budget wise I would do that. However, being here in Canada that block would be $7k or more after shipping, exchange and taxes. Which is less than the full intake, supercharger, carb assy. since there is guys here that make manifolds locally.
As for Batten Runner comments he is right, this build could be 450HP or 700HP+. Obviously aiming for the higher number. Looking around there is very few 671 / 871 blower builds and even less well documented ones. Same goes for turbos. So as far as I can tell there is not a well established path I can work from like I could if it was an N/A build. That is why I think the back and forth BattenRunner and Cutlassfi are having is good. When the engine is done and I have some performance numbers someone wanting to do a similar build could go back and go "yup doing X was in the end not the best way" or "yup doing X is what I need"
As for short stroke or long stroke my thought process was because this is a blower application getting air into the cylinder will not be an issue as it will have lots of help from the blower. Getting it out might be an issue. If this was a turbo engine a shorter stroke (455 or 425) I would think would be advantageous. For turbos a higher reving engine seems to be a plus.
But since this is not a turbo and the engine I'm not expecting to rev super high, then my thought would be for all the displacement I can get and focusing on re-enforcing the block as much as I can. I've heard 700-800crank HP is the point at which BBO need help. With the plan to use a SCAT/rocket racing bullet crank and forged pistons I will definitely be open to suggestion on those. My feeling is this build will live or die based on the crank/rod/piston selection in combination with the block prep and re-enforcement. I haven't bought the crank yet so the exact engine specs are still open.
I’ve already given my recommended recipe. The biggest issue in my experience is bottom end stability.
Best of luck in your build. Let me know if I can be of help in any way.
I've always ran limited strokes with forced induction for longevity.
When you have an engine with limited bottom end strength, the last thing I would do is add a longer stroke to stress it further....
This also applies to some extent to the charger as well, but I would pick one, not both
I know it;s tough when you are spending money on a good crank, as its not a huge difference in cost to stroke it.
... but when something fails, it all turns to junk & wasted money in a hurry.
Typically boost helps to overcome flow restrictions so use it you your advantage & run a significant amount.
Considering you plan to run factory heads, you are already flow limited.
A longer stroke will likely just shift your curve to a lower RPM, trading peak HP for more torque (keep in mind, I'm saying this as you are flow limited), whereas the charger will increase power it across the board as well as improve your RPM range by a few hundred.
A good example... I built a blown 350 Chevy for a guy, stock bottom end with good heads, mild cam & 8# boost.
He later wanted to increase power so we built the bottom end with good parts so we could crank up the boost.
Added a stroker crank since we were replacing it anyway & ultimately made it a 383. Upon testing the engine with the same top end & supercharger drive ratio, it made almost 2# less boost but nearly the same power. Where 38 cubes should add roughly 50 HP, so does 2# boost on this engine.
The difference here was I now had enough strength to run 15# boost & I could rev the engine higher than I previously could on stock parts, adding over 150 more HP in the end.
Last edited by Lonnies Performance; September 7th, 2019 at 07:51 AM.
A good example... I built a blown 350 Chevy for a guy, stock bottom end with good heads, mild cam & 8# boost.
He later wanted to increase power so we built the bottom end with good parts so we could crank up the boost.
Added a stroker crank since we were replacing it anyway & ultimately made it a 383. Upon testing the engine with the same top end & supercharger drive ratio, it made almost 2# less boost but nearly the same power. Where 38 cubes should add roughly 50 HP, so does 2# boost on this engine.
The difference here was I now had enough strength to run 15# boost & I could rev the engine higher than I previously could on stock parts, adding over 150 more HP in the end.
You do know why it made less boost, all else being equal right?
And you kind of contradicted yourself here on the longer stroke theory.
Here’s the deal, he’s trying to use off-the-shelf parts. As stated the Scat stroker crank is fully counterweighted, and on an application like this I don’t care what the stroke is, that will be a huge jump towards longevity.
Thanks.
Last edited by cutlassefi; September 7th, 2019 at 10:03 AM.
As a side-note. What would custom crank for Oldsmobile run on USA, totally new forging/billet. 2.5" mains, Chevy-rod big-end width ( the usual rods used on small-block, difference wasnt huge), stroke of your choice, and fully counterweighted?
As a side-note. What would custom crank for Oldsmobile run on USA, totally new forging/billet. 2.5" mains, Chevy-rod big-end width ( the usual rods used on small-block, difference wasnt huge), stroke of your choice, and fully counterweighted?
My SB Stroker cranks (4.00”) are $1695.00. They’re not fully counterweighted but they are knife edged, 5140 Billet with SBC Rod journals. It’s $300.00 extra for fully counterweighted.
My SB Stroker cranks (4.00”) are $1695.00. They’re not fully counterweighted but they are knife edged, 5140 Billet with SBC Rod journals. It’s $300.00 extra for fully counterweighted.
Thanks.
Wow, they are cheap across the bond even if you count taxes and freight. Def. keep you in mind if i ever have problems with my current crank/ upgrade.
You do know why it made less boost, all else being equal right?
And you kind of contradicted yourself here on the longer stroke theory.
Here’s the deal, he’s trying to use off-the-shelf parts. As stated the Scat stroker crank is fully counterweighted, and on an application like this I don’t care what the stroke is, that will be a huge jump towards longevity.
Thanks.
I didn't contradict myself at all... I was responding to your comment of making more engine HP & running less boost. This was a valid comparison to that.
The engine would have made 40-50 more HP, on engine alone, but with the same overall air flow from the charger, boost went down & power remained virtually unchanged.
That actually supported what you previously said. It shows there are 2 ways to arrive at the same goal.
So, if using off the shelf parts, Scat makes a 4.25" & 4.5" crank. A strong crank is a good option, but my vote was to stay with the shorter stroke since breathing is already limited.
Boost will better serve to push air through a weak set of heads. If you wanted to spend a lot on fully worked aftermarket heads & the block will support the stress without failure, then I would be more inclined to go with more cubes.
Took my current engine more apart today. Cylinder heads have definitely been ported, com cam roller rockers don;t show any signs of wear. It appears my intake gasket failed at some point an oil has been getting into the intake. Some of the closed intake valves had a little puddle of oil sitting on top of them. Pistons appear to be speed pro pistons. Just need to clean one off a bit more to get the full part number. Cylinder walls are nice and smooth. I don't feel any ridges at the top of the cylinder. On the bad, there does seems to be a white sand like metal on the top of some pistons and some exhaust valves. I wonder if the engine tried to melt a spark plug at some point?
before disassembly i placed the on the engine just to see. Back exhaust valves are very white this intake was clean this one seemed to have oil leaking into it
Wow, cool looking at the parts as they are disassembled, and that Blower sitting up there sure is some great encouragement!!!!
Do you have someone nearby who could do an airflow test on the heads as they are now and check the condition of the guides and runout of the valve seats?
They look like some work has been done for sure. Are they good aftermarket valves? I have seen that hard white stuff happen from the residue of burnt fuels before.
Looking forward to your build and hoping the best for you.
^ that is an excellent idea. There is a place about a 1.5 hour drive away that can do that for me. Next time i am heading that way for work I will have them do it. They will flow one of the heads and check combustion chamber column.
The car has BMR upper and lower control arms. Moser axles 3.73 gears Detroit true trac limited slip dif. The suspension will need to be dialed in but I plan to wait until after the engine is in so I know weights.
July 2nd, 2019, 08:52 PM
