ibfurloughed

Hello, new to the forum.

I'm about to start an engine rebuild for my father. He has a '71 Cutlass convertibile with a 350, quadrajet, th350, not sure of rear gears yet but will find out. Number 7 is has very weak compression and she's burning about 2 quarts of oil per tank of gas. Heads were rebuilt and installed by some local mechinic about 8 months ago. So I'm sure it's time for a set of rings.

I'm looking at 2 options. First rebuild the 350 with higher compression pistons and a mild Mondello Cam.

Option 2, I know where a 6 year old un used 502 crate motor is and if I can get some good advice here about installing that motor in the 1971 cutlass, I'll see if I can get the guy to part with the 502. Things I need to know are;

Will it fit without any major cutting?
Will the TH350 hold together running at or close to 500hp.
Will the current bellhousing bolt on to thie 502?
Does someone make headers that will work with this combination?


Once I get option 1 or 2 figured out I know I'll have specfic questions about the project.

Thanks

panos

Hi and welcome on the site! I personally would refresh the 350 you have,you can build a fun 350 with honest 350-375 hp without robbbing a bank!The 502 is a chevy and im sure it could fit in the a-body but be prepared to do some work,the starter is on the other side so u have to re-route all the electrical ,other motormounts,headers etc,hope u get the point u cant use anything from the rocket 350 the th350 will not mount to the chebby motor without an adapter plate.And im almost sure it would blow behind that 502,the question is how much torque this motor make and not hp,torque is killing the trannys not hp a lot of people seem to forget that!I know that the 502 maybe a good strong motor that is tempting but you gonna end up spending more money and time making it work jmo.Im sure you gonna get a lot of similar replies about that,good luck whatever you decide!

Panos

captjim

Will it fit without any major cutting?
Sort of
Will the TH350 hold together running at or close to 500hp.
probably not
Will the current bellhousing bolt on to thie 502?
nope
Does someone make headers that will work with this combination?
yes

You are not going to get much help here putting a BBC into your Oldsmobile, a Chevelle forum might be better if you do decide to go that route.

If you want help rebuilding the 350, let us know. Or perhaps swapping in a 455 (VERY easy swap).

olds 307 and 403

A set of Probe, SRP?(BTR) or Speed Pro flat tops is the way to go. DON'T deal with Mondello. BTR performance, J@S Machine or Smitty at MJ or Rocket Racing will be better to deal with. They can custom grind you cams or offer decent off the shelf cams like the Voodoo line. The Mondello/Engle cams are good, but Mondello Performance, not so much.

cutlassefi

X2 except BTR uses mostly CP's not SRP's, in fact I think he's a CP dealer.

As the others will agree you have many options even if staying with your 350. You can use different rods, pistons etc. Edelbrock heads and so on. Myself and others can help with your cam selection, I sell custom grinds or off the shelf.

Anyway you look at it there really isn't a need to go to a BBC imo. You still have plenty of options even staying with an Olds, either small or big block.

ibfurloughed

Well I spoke to owner of the 502 today and he doesn't want to part with it. I think thats for the best.

SO, a 350 build it will be. This will be my second Olds 350 the first was in a '72 Cutlass, I was much younger and still learning what works with what. That car had 308 rear gears and I was never happy with the acceration of the end product, but it ran for 45,000 uneventful miles until my dad sold that car.

That car had good compression so I never got into the bottom end, mistake number one, so it ran the factory dish pistons. I put a set of number 5 heads on it and had them decked .040 (mistake number two) trying to raise the compression alittle. A Mild Engle/ Mondello cam, a roller timing chain, new lifters, a performer intake, Edelbrok 650 carb and a set of hooker headers. And a bucket of shimes to make the valve train work.

Now for the current motor. My dad has had a local mechanic working on this car for the last year. In the last 6 months the heads have been rebuilt with all the valves replaced. ( I think that's where the mechanic thought the low compression number 7 was coming from). And a Melling high flow oil pump was put in to take care of low oil pressure, Bearings all wearing out most likely. Carb rebuilt.

Heres the direction I'm thinking this time around, minding that I'm on a budget. Have a machine shop check the block and crank. New rods and pistons (trying to get as much compression as the factory bottom end and heads can take and run on pump gas). Grind out the AIR humps in the heads and use what I got. New cam, I want a civil idle and just street driving no drag racing (factory torque converter and trans, don't know the rear gears yet). Factory intake, Rebuilt quadaJet. Set of headers.

Well what do you think for parts and what do think I'll get out of it.

Thanks

cutlassefi

If you're o.k. with boring it .068 over I'd seriously think about doing the Chevy conversion, meaning a SBC 400 Piston and an aftermarket 6.200 rod. By the time you have your other pistons pressed off, have the new ones pressed on, recon the rods, get new rod bolts, buy the new pistons blah blah blah, you'll be spending as much or more than doing it with SBC stuff. Just a thought.

I did one like that, turned out great, awesome throttle response cuz everything inside was a bunch lighter.

captjim

Hey Mark, just curious. SBO 350 bore is 4.057. Most 350 Olds bores will probably clean up with .003-.004 honed out, unless the block is trashed. Puts the finished bore at 4.060, which will use a 350 SBC .060 piston. Ever do that and save a bunch or boring, not to mention the 350 SBC pistons are cheap? Just a thought......

cutlassefi

Yes I'm all for trying to save the bore, I've even tried to find .080 over SBC pistons but no real luck. But a 350 piston has a 1.550 Compression distance, won't work with a 6.200 rod and the stock 3.385 stroke. You'd have to grind the crank to Small journal size, stroke it to 3.500 and use a Small journal 6.00 SBC rod.
Gotta use the 377 piston, 4.00+ bore for a 3.75 crank. it has the correct 1.425 compression distance.

Plus going to 4.125 and beyond is a cheap way to increase displacement and breathing as well.

Aceshigh

Hell, save yourself the trouble.

Wanna buy my 1970 rocket 350 / TH350 carb to pan fully running rebuilt engine now??? I'm looking to go modern with EFI.
I can even take video's of it running the street if you want. I'm pulling it this winter to clean it up and prep for sale.

PM Me if you're interested.
Not looking for alot, but a rebuild cost with the block completely done will cost you close to what I'm going to ask for this complete running setup.
Plus you can have the trans, it's of no use to me after I yank it. I've got a 6 speed going in too.
I also have a Olds O axle and SSIII rims I'm trying to find a home for.

NewEngineChrome2.jpg

ibfurloughed

I like were your heads at on the cheaper SBC parts. I think I want the machine shop to measure the bores and tell me what I'm starting with and the how much might need to come out to clean up the barrels. I'd rather not bore that much out unless I had too. I've run into problems before by not having enough meat between cylinders. Granted I have no idea whats there right now.

captjim

You still have to use Oldsmobile heads. 4.125" is only .068 over, it won't be an issue, there is pleny of meat in the block, guys have gone 4.185".

Jon69

If that block has just worn factory cylinder bores and your going to replace pistons anyway, you really cant go wrong with a .030 overbore. You will increase displacement and compression in one step.
As for making that a high compression engine and still running on pump gas, that is really an dynamic compression ratio question. And to answer that you need to know what your cam profiles will be.
I had my 69 350 reworked more than a decade ago. It was bored .030 over and I have had zero problems related to that.
However 35K miles later I'm looking at a roller cam. More money than a flat tappet, but the advantages are well worth it. Not the least of which being able to run any modern motor oil.

ibfurloughed

I got to go look at the car today. Looks like it has 2:56 rear gears, not too excited about that. Any idea how much to get some different gears put in it?

Also the car is a 1971 with a matching number s block however the heads are #7's??? Dad says when he decoded everything it was a late production 1971....could Olds have started putting #7's on early?

71 Cutlass

If you want a faster car, just drop in a 455. If you decide to stick with the 350, use big block valves. Most important item, DO NOT go above 10:1 compression, or you will pay for it on today's gas. My CR is slightly above 10.5:1 and I get the "milk bottle rattle" from time to time b/c I over did it. I can't run any vac adv. from the dist. or it's detonation all day long. So be sure and know what the CR will be. Here's my 1971 350 build below. I think I could have gone up one step on my cam, b/c my tires spin too much off of the line and take way too long to finally gain traction.

Edelbrock Performer RPM intake manifold
Edelbrock Performer Carburetor (600CFM 4 barrel).
Edelbrock carburetor insulator gasket (0.320")
Edelbrock True Roller timing chain
Comp Cams Camshaft XE262H(Duration @.050 218/224 Lift 475"/.480" LSA110)
Forged flat top pistons/rings (by Diamond) from Dick Miller Racing
W-31 stainless steel valves (2" intake, 1.625" exhaust)
Head porting (pocket) 3 angle valve job, tear drop valve guides
Sanderson Headers (Part # 0351—shorty type)
3.42 Posi track (originally 2.56 open)
TCI Torque converter 2400 stall (Breakaway # 241100)
Transgo shift kit #2
MSD Pro-Billet Distributor and MSD Blaster 2 Ignition Coil
MSD Super Conductor spark plug wires (8.5mm)
Walker Dynomax turbo mufflers/dual exhaust (originally single)
Spectre Performance Air Filter w/ K&N X-Stream Air Filter lid
Bored 60 over, 10.5:1 compression ratio

captjim

#7 heads are correct on a 71. #6 for 1970, #7 for 1971, and #7a for 1972.

Depending on geographical location and whether upgrades are planned, gear swap is $650 +/-

michael hilsabeck

i got a cam from summit it was supose to be a step up from stock but when i got it the valve lift was .496 this is a big cam i bought new push rods and rocker arms. after putting the cam in my car the rocker arm had all kinds of play in them so i my mild rocker arms 6000 and now my valve lash is fine but now im haveing to put valve springs in it and i instaled a oil presure gange and i have low oil presure so now im thinking i have to rebuild my motor. my question is how much problems im i going to have with this cam sense i don't have ajustable rockers so should i go back to stock this is the first oldsmoble i have worked on i want it to run good can eany body help

cutlassefi

I have a guy here in town that does great rear end work, reasonable too.

71 Cutlass, you can get rid of alot of your problems by changing cams. The Comp aggressive stuff isn't the best choice with stock heads, ported or not. I can explain why later.

michael hilsabeck

is it better to go back stock or keep bulding arownd this cam

71 Cutlass

Cutlassfi,
change to what cam? give me specs. I also used the Lunati, with virtually the exact same specs as the Comp and John Stolpa at Rocket Racing personally chose the cam for my build... he sold it to me in fact. Ran my cam choice by Dick Miller to confirm John's choice and he also said the cam was fine for my build up. I'm curious to hear what cam you have in mind.

michael hilsabeck

some came close to stock for i dont have to change my heads from stock i already have 15000 in this car the cam they sold me has rpm range 1500-6500

michael hilsabeck

i am looking for a mild cam that work with my motor with out chaning every thing

michael hilsabeck

the cam they gave me duration at .006lift intake290 exhaust 300 duration at .050 lift intake224 exhaust234 lift at cam intake.310 exhaust.325 lift at valve intake .496 exhaust.520 timing at .050 lift

cutlassefi

Here's the deal, when you use a Comp Xtreme or a Lunati VooDoo if you already have alot of compression it'll make it worse. You need more off the seat time, especially with OE heads, they just don't flow like the new stuff nor do they typically flow well at lifts above .525 or so.

If you truly have 10.5:1 comp you'll need some thing in the 230+ @ .050 range and/or something on a tighter lob sep.
Try to stay away from the Edelbrock/Generic stuff as well. They're just too lazy and ground on the wrong lobe center for your combination. I'm surprised Dick miller and others recommended that cam, too small for 10.5:1 comp.

If you're still interested let me know, I'll give you more info.

michael hilsabeck

so if i understan your saying it two small i though it was to big is that way my rockerarms lose

71 Cutlass

C-Fi,
The builder also said the cam was perfect. Obviously I'm confused, but on forum boards there's never 100% agreement, so such is life. Problem I envision with bigger cam as you are suggesting is that it would not really be in my power band (ie. starts off at 1800-6200 rpm) It's my everyday driver street car, not sure I'll be any where near 6200 rpms on my next trip to the grocery store. Also, greater lift will mean valve train geo. will be off without having to do modifications to stock parts b/c lift gets to be in that .525 area, (could be wrong b/c I've never tried it). All this plus I want decent vacuum at idle without having to worry about power brakes,etc. The next step up in the Comp cam that I have is 224/230 at.050. lift is 485/490. I have no objection to that. If I go up one more, it's 230/236/ .520/.523. (the range I think you are suggesting) is where I think problems/changes ensue. Clarify if you need to on this. Any and all advice welcome. Sorry to hijack thread, perhaps mods can move it and rename it?

michael hilsabeck

my name is michael hilsabeck i am a newbe i bought a cam through summit and when i bought te cam i told them that i just wanted a cam that wood work with stock parts and they toid me it wood work but if i had worn parts so i bought push rods and rockers then i goht the cam and put it in my rockers had all kinds of play so i use a filler gage on the valve and the rocker arm i came up with 60.000th so i got the pice in side the rockerarm mild the rockers fill better i dont think that it is col binding but now i am putting in springs for the cam this cam did not work like they said the cam is edelbrock corp #7112 duration atlift .006 intake 290 exhaust 300 duration at lift.050 intake 224 exhaust 234 lift at cam intake .310 exhaust.325 lift at valve intake.496 exhaust.520 after installing this cam i dont have verry good oil presser so i figer i better rebild the 350 my heads are#6 1969 oldsmoble cutlass supreme convertible this is my 1st oldsmoble i dont know if i should keep going with this cam or go back stock cam i am not that good with engine can you give me some advice

cutlassefi

O.K. let's take a step back here. First of all if your rocker geometry is off it's off, whether you have .400 lift or .600 lift, although more lift can exaggerate any problems.

Cams- you're still not getting the point. If you go bigger but with the same pattern you're not really addressing your problem. IMO you need something with a different pattern, not necessarily a lot more duration. You have a good problem, too much compression, most don't have enough. It'll be easier to fix that than not having enough compression. Also your carb is too small, that's contributing to your problem. You actually need a bit less velocity, filling the cylinder a little less efficiently at low rpms. That will reduce cylinder pressure and consequently less chance of detonation.

Michael- if your valvetrain is worn then it'll be that much worse. Cams have certain base circles, if that changes then when you use a stock valvetrain any variance will show up, you can't adjust it out. And if your engine needs to be rebuilt then do it. Then you can match everything around the cam of your choice and vice versa.

I believe they told you that cam was fine, just an oversight I guess. Again IMO you need someting with a bit more advertised duration and/or a different split.

Lastly everybody, don't call Summit or Jegs, most of them don't have a clue. Call the cam company directly, not the mail order warehouse.

71 Cutlass

C- Fi,
Going to have to be specific with what cam and what specs you are recommending. Also, plugs show that carb is running as a perfect match for motor. Again, carb (600 CFM) was recommended by all three previous individuals mentioned. You never addressed lift problem or powerband issue. As far as calling the cam company, the tech there also recommended the cam/carb. (I emailed him the list of parts above (except for cam of course) To be honest, I would need very detailed specifics before I would ever consider a cam and carb swap at this point.

cutlassefi

If jetted right an 850 will have correct color plugs, that has nothing to do with the right size carb. Having a Dual Plane you could have easily gone with a 750. I had one on mine with a less radical setup, worked fine.

More lift will typically give you a more broad power band. And regarding a potential cam change, my guess would be more exhaust duration and maybe an LSA change. I'll talk it over with my Erson contacts and let you know.