cljolley

Hi Guys, I recently acquired a 71 Cutlass Supreme with a rocket 350 in it. It came with lots of receipts and records, however I am still unsure of EVERYTHING that's been done to it. I know it has a cam, roller tipped rockers, upgraded lifters, pushrods, edelbrock perf. RPM manifold, edelbrock 1411 750 CFM carb, and a ghetto rigged dual exhaust. It feels very lazy from a stop and has almost no real low end power... Once it gets to the top of first gear though, it seems like it builds substantial power, but then shifts into second bringing it back into its flat spot. What might be the issue, and what can I do to improve low end power? I do plan on rebuilding the engine sometime this or next year. Aside from the aforementioned modifications, I believe the engine is stock.

Cam specs are:
Lunati Bracket Master II
P/N: 00083

Duration@ .050: 224/234
Lift: .496/.522
LSA: 112*
Link to cam card:
http://www.lunatipower.com/CamSpecCard.aspx?partNumber=00083

I feel like th exhaust lift and duration may be too much for this engine and is robbing my low end torque?

​​​​​​​

oldcutlass

What distributor is installed on your engine and what is your dwell (if applicable) and timing set to?

I hope your bottom end is not stock with this cam.

Do you know what rearend gears are in your car?

cljolley

It has had bearings changed, but that's all I'm aware of as far as bottom end goes. Why do you say that anyhow?
It has an HEI distributor, and my timing is set at 22* Initial, and I just recurved the mechanical timing advance and total timing is right around 38* I believe.
Rear end is stock as far as I know. Maybe a 2.56 but I can't be sure. Only guessing.
I also may add, the car is strictly a street car. I'm not lookin to race it or go fast, just mainly looking for good acceleration and fair driveability.

oldcutlass

Your timing is fine with an HEI.

IMHO, your rearend gears are the limiting factor to your performance issue. This combined with the cam you listed that makes power between 2500 rpm and 5500 which is why your engine seems to come alive just before the trans shifts. Using replacement head gaskets and stock pistons your probably netting just over 8:1 in compression which only compounds the problem.

You can perform a compression test and see roughly what your up against by the net results.

cljolley

Okay, I'm afraid I'm only a beginner with these engines. I'm normally a Honda guy. If I perform the compression test I'm looking for what? Around 180 PSI? Then am I calculating something based off that figure. I'm not sure I understand what I'm looking for. Also, if I change the gears to say 3.73, or even a 3.90, can I expect better performance from a stop?
Also I'm still confused why you mentioned the bottom end, was compression ratio the only thing you had in mind, if so I do plan on rebuilding the engine with higher compression Pistons. Any other recommendations? And what compression ratio can I safely run using pump gas?

Im trying to learn as much as I can, so any advice is much appreciated. I even got the How to build max performance Olds V8 book, but I'm afraid not much of that applies as I am not looking for any ludicrous 600hp build.

MDchanic

Hmmmmmm... High revving cam + tall rear end = Dog. No mystery here.

- Eric

MDchanic

Hondas don't have compression?

- Eric

cljolley

I agree, I never thought the stock gearing was helping anything, but do you have a reccomendation as to what gear to use for a fun street car? I also plan on getting a higher stall converter as well.

cljolley

i was not implying that at all. Let me rephrase. I'm a beginner tearing apart engines, and am unfamiliar with the Oldmsmobile design altogether. I was only saying I am in unfamiliar territory...

MDchanic

A stock '71 Olds with a nominal 8.5:1 compression ratio should have about 130psi in each cylinder, with a variation no more than +/- 10%, but as low as about 110psi would not be out of place on a used engine.

With that cam, it may be lower, but I can't say how much.

- Eric

MDchanic

As far as a rear end, yes, as you suggested above, a rear end ratio in the high 3s would be much peppier.

Of course, a rear end weighs several hundred pounds, and a cam weighs about 12 pounds, so I'd change the cam first, although the point is that the engine, transmission, and rear end are all a complete system, and the entire system must be considered as a whole when making modifications - something the PO clearly did not understand.

- Eric

cljolley

​​​​​​​okay, so when I rebuild and use a higher compression ratio, this should mitigate some of the negative effects the cam may have on the engine? How does one go about determining a compression ratio to aim for when rebuilding an engine?

cljolley

Yes I understand that the whole assembly needs to work together to function the way I want. I would like to try to retain the cam that is in it now if it is not too radical.( Simply because it's just more money in the build) Are you suggesting that it isn't a good cam for the street? If I raise compression and change the gears, would it then be acceptable? I guess what I'm trying to say is I would rather work around it rather than change the whole setup. The specs are actually nearly identical to the recommended specs from Edelbrock for that particular intake and carb combination. So if I just raised compression and gearing, it would seem as though it's a good starting point wouldn't it?

oldcutlass

One other thing to check. With the engine off, looking into the carb have an assitant hold the gas pedal to the floor and ensure the throttle is opening 100%.

cljolley

Allow me to outline my plan before further discussing anything:

I am building the car mainly for the street. I do not care about top speed, but mainly driveability, and quick acceleration. This is a budget build.

I plan to to rebuild the engine with a conservatively higher compression ratio for use with pump gas only.
*New pistons, maybe .40 over
*Retain cam that's in it now if well suited for street application.
*Roller rockers (already installed)
*Upgraded lifters (already installed)
*Upgrade valve springs
*Retain stock heads with minimal machine work/porting
*Edelbrock Perform RPM intake mani (installed)
*Edelbrock 750CFM carb (installed)
*HEI ignition (installed)
*Possibly upgrade cooling system.

As far as drivetrain, I plan to keep the transmission relatively stock aside from a shift kit, and a higher stall converter; maybe 2800-3000 RPM stall.
*3.73 or 3.90 rear end gear (any higher reccomendation?)
*B&M Megashifter
*Upgraded Trans Cooler

I think that's about it. I don't suppose I have a HP or TQ goal as I am unfamiliar with V8 engines and have no idea what I can reasonably expect this all to yield.
Im sorry if I sound like a complete newbie idiot, but I am always eager to learn and welcome constructive criticism.

cljolley

​​​​​​​i will certainly do that as the throttle cable is all janky from the rig the PO set up.

oldcutlass

Since the car is new to you, before throwing parts at it with assumptions, why not verify what you have now? Do a compression check to see what the numbers are and if they are consistent. Verify your current gearing. Go through your receipts and see if the PO already installed a torque converter or check to see where this one flashes.

cljolley

I have gone through records, unfortunately many of them are very old and there are large gaps in the timeline. I do however believe the converter is aftermarket as it is bright blue, but I already tried testing it and the tires break loose at very low RPM. Probably around 13-1500 RPM. I understand what you're saying about checking compression, and current gearing, but if I plan to rebuild and change things what is the point other than just sheer curiosity?

MDchanic

Remember: Cam cheap and light, Rear expensive and heavy.



That strongly depends on how you want the car to feel when you drive it.
This cam essentially has nothing below 2,500 RPM.
So, if you have a manual transmission, you will need a darned low first gear, and be spinning it up over two grand every time you stop at a stop sign, or, if you have an automatic, you will need a converter with about a 2,500 RPM stall speed.



Again, that depends on what you want.
Higher compression is another piece of the puzzle, and is always helpful (until it's not), but that's not even a secondary issue for you right now.



Which is your choice, but, really, you want to start with a conceptual blank slate when you do this, then decide what you want, then figure out what you can afford, then figure our where to compromise.



Again, the intake and carb are light and easy to change, the rear end less so.
If you want a high revving setup, you will need a different rear end ratio.
That is your choice in the end.

- Eric

cljolley

I do appreciate all the input, but it seems like you're trying to tell me to shy way from the cam I have simply because it is a higher revving top end set up. Is there really anything wrong with this if I have the proper gear and stall speed to suit it?
I know I'm coming off as argumentative but I'm really just trying to understand the reason you think changing the little stuff is better than just working with what I already have and "finishing" what the PO started which is a seemingly higher revving build.

MDchanic

No, I am trying to get to what you are really after, so that you don't make the same kinds of mistakes that the PO made.

Also, some of our posts have crossed.

It sounds like you want a higher-revving setup, which is fine, it's just very different from the stock design, which some people don't really understand.

I think your ideas for a rear end ratio are good, and that this will all fall into place well, but I would recommend considering all of the parts, including the cam, from scratch, so that you get a car that runs the way you want it it to.

I would talk to Mark (CutlassEFI) about final cam choices, as he is very experienced in that area, and tends to be willing to help.

- Eric

cljolley

[QUOTE=MDchanic;1008869]Remember: Cam cheap and light, Rear expensive and heavy.
[QUOTE]

Okay for comparisons sake, what cam specs do you have in mind? Carb reccomendations? Intake manifold? I just want to compare to what you think is "right"...

cljolley

Okay, I'm not really trying to re-invent anything. Nor am I really after a higher revving setup, I just wanted to work with what I already have for my wallets sake. If that ended up being a top end horsepower build then so be it. If I had the time, and money to invest though I would prefer something with low end torque..I do see your point now though. I really was just curious if someone thought my plan seemed like it would work well or not.

if I was starting from scratch though, and wanted a lower revving build what would you change about my plan I previously outlined? What would you do differently?

cljolley

I suppose of it all boils down to just replacing the cam with a different spec one to move the torque curve down, that would be a better option. But wouldnt either application benefit from the mods I've listed such as a higher gearing, higher stall speed converter, 750CFM carb, etc...?

oldcutlass

You cam is 2500 - 5000, your manifold is 1500-6500, your carb is a 750 on an engine that should have a 600-650 cfm. Your saying your running stock gears with an unknown torque converter. I would say your combo is not working together.

cljolley

To be fair, the Edelbrock cam with the same specs as mine has it listed at 1500-5500. I tend to agree about the carb though even though Edelbrock lists the 750 as the recommended option.

olds 307 and 403

For your motor get the LF2321 .030" oversize Speedpro 6cc dish forged pistons or contact Mark Remmel, Cutlassefi on here, he is bringing a modern 8cc dish forged piston for the Olds 350. Either piston will give you low to mid 9's for compression. Put 2.07/1.625" valves with bowls opened up in your #7 heads, if you are doing a full rebuild. You are actually probably under 8 to 1 with 24cc dish pistons used in 1971 350's, horrible for that cam. Mark also does custom, mine is on the way and has off the shelf grinds for your motor. Also take that Edelbrock 750 cfm and throw it as far as you can, they are junk. Either a Street Demon 625 or 750 cfm or the Quick fuel Slayer in 600 or 750 cfm carbs will be a massive improvement. Also a 2500 stall torque converter is necessary with that cam and a minimum of 3.23 gears. If you don't drive on the highway much, go 3.55 or 3.73 for gearing.

cljolley

Why do you say the Edelbrock carb is junk. I feel silly saying this but I feel somewhat attached to it. If I replaced it with the street demon, how do I decide the CFM I want?
​​​​​​​also what do you mean "open up the bowls?"

MDchanic

I will note here that since clj has been a Honda guy (But we all know that that's all in the past now... Right? ), he may not have a "feel" for what it's like to drive an American V8 car with 3.73 or 4.11 gears on the highway, and might benefit from finding someone with a car that's set up that way (whether Olds or not) and taking a drive in it to see whether he likes it.

- Eric

cljolley

I'm afraid I will always have an appreciation for all cars. But I can tell you, even though my Cutlass is a turd, I still love zipping it around town. I'm sure I would love the car with higher gearing.

ELY442

This cam is similar to a Mondello JM20-22 cam. I have this on my 455 with a Torker manifold, QJet, TH400 w/2400 stall and a 3:08 gears. This cam is a great street cam.

olds 307 and 403

Many have issues with the Edelbrock carbs. Supposedly Edelbrock got the booster size wrong on the 750 cfm. The Street Demon carbs are heavily based off the Carter Thermoquad in an all new improved castings 3 barrel design . I know the guys on here who have ran the 625 cfm Street Demon carb say it jetted for a motor like I am telling you to build. The 750 cfm has larger primary bores and richer jetting no doubt.

cljolley

So much information to take in. So this carb is a 3 barrel? And my question still is left unanswered. How does one choose the size of the carb when building an engine? I don't want to under or over-carb and then have to buy another new carb.

MDchanic

Remember that unless it's completely built to race standards, an Olds V8 will have a practical top RPM of about 4,500 in regular driving (yes, it may be able to redline at 5,500 when accelerating, but you don't drive it around at 5,500).

With a 2.73 rear end, you will be turning about 2,000 RPM at 60mph, 2,500 RPM at 75mph, and about 3,000 RPM at 90mph.

With a 3.90 rear end, you will be turning about 3,000 RPM at 60mph, about 3,750 RPM at 75mph, and about 4,500 RPM at 90mph.

If you're cruising at 3,750 RPM in one of these cars, you know it. It's darned near 4,000. It's not like running a Honda or a BMW at 4,000 RPM.
You can do it, and it's got its "cool" points, but you should make sure you actually like it in practice before you spend several thousand dollars making it happen.

- Eric

Fun71

As said already, that cam with the very low 1971 compression ratio (8:1 maybe), factory stall RPM, and pathetic 2.56 rear gears makes for a very mismatched combination that won't perform well.

If you are planning to rebuild the engine soon, then there's no need to swap the cam - go forward with the rearend gear swap as you will need that in the future anyway.

If there will be some time until the engine rebuild, swap the cam for something milder and the engine will be a lot peppier and the car will be much more fun to drive, even with the 2.56 rear (been there, done that in the 1980s). My 350 with a .435 lift, 204° duration cam and the factory 2.56 rear was quite impressive back then.

edit:
Something I forgot to mention is that unless those are custom forged pistons, .040" over (and not .40 over) will be cast pistons that are short on compression height, which means the final compression ratio will be much lower than expected. I don't know why, but all cast piston manufacturers make their pistons about .020" shorter than the factory pistons whereas the forged pistons are the correct height.

Jamesbo

"What we got ere is failure to communicate"

I'm with the Eric [1&2] Plan your work and work your plan. If all of the components don't work together properly you will end up worse off than you are now. And unhappier with your car with less $$$

cljolley

Cool, yeah I did mean .040 over. Oops. Do you have any opinion on the Efelbrock carburetor? I would really like to keep it as I have already studied it and familiarized myself with it. I plan to rebuild it soon also.
I think I will keep the cam, get my carb rebuild done, and then proceed with the rear end change and engine build. Anything else I should take into consideration?

oldcutlass

If you like Edelbrock and its working well for you keep it, it may work well once you get the bottom end fixed up. Its not a bad carb. Carb opinions vary as much as what oil type to use.

cljolley

It does have a bit of a stumble from the get go, but I'm working on it. I have jets to match it to the 1407 performance setup. Mine is a 1411 set up for fuel economy. I got jets and metering rods to basically clone the 1407 as well as larger accelerator pump squirters. I'm hoping that, cleanup, and the rebuild kit get the carb working as it should.

olds 307 and 403

Yes, a 3 barrel to fit on square and spreadbore manifolds. Any carb will need to calibrated to YOUR motor. The Qjet, Street Demon and AVS all have the air velocity secondaries, making it much harder to over carb. Plus both have multi step metering rods, like your Edelbrock and triple stacked primary boosters, unlike your Edelbrock. The 625 cfm is fine if you never plan to run above say 4500-5000 rpm, if you want more like 5500-6000 rpm, the 750 will be better suited. I would buy a calibration kit for either. Good luck getting rid of the stumble on that Edelbrock, some have tried everything with no luck.