nhuyghe

i have a 73 olds 350 motor with the big combustion chambers and valves, a 2 step over cam it is a comp 260 8h, a rebuilt set of #5 heads with roller rockers, edelbrock performer intake, and edelbrock carb. How much horse power am i looking at?

bccan

My wild a**ed guess is optimistically 260-280, maybe 300 if you have slightly higher than stock compression & headers. Really too many variables & too little info to be accurate.

cutlassefi

If I'm not mistaken, the 73 had smaller dish pistons so if you have the #5 heads on it you're around 9.5:1. Not enough cam and manifold though to really be in the 300's. I agree with bccan, 275 or so.

firefrost gold

I dont know how much hp but the 350 doesnt seem to get no respect > I now the fast guys
have them dialed in but they run some fast times I commend you for staying with the little brother . I thought bill travato's tip if you want to do some head porting on a 350 get a good 455 head and match the intake and mill the chambers and presto cheap ported heads.

Redog

I'm concour with the 260-275 number

bccan

Firefrost - I considered BBO heads on my 350. I have a setup that would probably have worked w/ them decently(3.90, 10.5:1, some cam, some stall, headers, etc). BUT w/ that kind of port volume I was afraid of making the lower rpm range too lazy. In my daily driving I find most of it is 2000-2500 rpm. I'm not an expert but do have a fair amount of experience, I don't think the intake velocity w/ the big block head would be conducive to snappy response until 3500-4000 rpm, maybe higher on a 350. You would need to maximize cam & intake to that range & above - for me that wouldn't work on the street but would probably do well on the track. A stick car would tolerate better than auto.
There are some that would be fine w/ that on the street & it certainly is cheaper than porting iron heads! One would just need to be sure of what they want outta their combo - big top end w/ big HP #'s or strong or responsive low/mid range w/ lotsa torque & "OK" HP #'s @ the top end. My experience is you don't get both w/ a 350, just not enough displacement.

I'm a small block guy, just have one of them that is a little bigger than average!

As it pertains to this thread, nhuyghe (I had to scroll 3 times to spell that!) is working w/ what I would call "the standard 350" build. Basically stock bottom end & compression w/ a little breathing modification. From a daily driving perspective, these need to be kept conservative or they become pigs in the low end. That 268H cam is pushing it on duration (218/218 @ .050) if car has AT & high gears. FWIW, in the blue car I'm running 80 more cubes w/ pretty good "support systems" and my cam is 218/228 @ .050. The red car has a 9:1(actual) .040 350, w/ big valves, crossovers blocked, manifolds w/ 2.5 X pipe, Performer w/ QJet, 3.08 ltd slip, TH350 w/ stock stall. Cam is hyd roller 202/212 @ .515 lift (IIRC). I'm doing a little wideband testing to tune the carb & this thing broke the tires loose on a kickdown @ 40 miles per hour on a dry road yesterday, forget a kickdown in the rain!

My point is that you want velocity & efficiency in the rpm range where car will be operated the most. If I had to guess, this engine probably makes about 300 hp, maybe just a trickle more but it idles damn near original & has excellent power & response in it's intended range of operation - idle to 3000 in 19 year old's daily driver that gets good mileage, runs on 87 octane & has some performance if called upon. Despite his being a pretty careful kid, I'm thinking about leaning out those secondaries so he doesn't get crossed up unexpectedly! Be careful of your combo w/ a 350, for anything that doesn't or isn't gonna get performance support from headers, gears, stall speed, etc keep it conservative, especially on the cam. If performance requirements go above that & support is there from other components - go up incrementally if you want a good combination of performance vs drivability (manners) on the street. Can you tell I'm ASSuming that is what your build will be doing?

firefrost gold

you look like you have some nice cars and I hoped after i put that post up it wasnt taken wrong my point was that sbo seem to relay run hard and every one wants to pull them for a 455 .I have only drove one sbo 71 and it was a great moter had a lot of power for a 350 two barrel carb.

bccan

Just another note. I just spent Saturday dialing in a very nicely restored 72 442 vert w/ rebuilt original 350, original owner car still has orig interior in nice shape. Engine is higher than stock compression (mid 9's) w/ a cam & roller rockers, otherwise plain jane build. I'll post cam specs Monday as they are jotted down on my blotter @ work.

*EDIT* Cam Specs 448/464 110 216/221 @ .050 Hyd Flat Tappet

Anyhoo - Cam is a little big for this car and even after nailing the carb down pretty nicely w/ wideband it is still lazy on low end acceleration. It is stock intake, manifolds & a 2.56 or 2.78 (can't remember which) peg legger. When I drove it home Friday night & it couldn't even spin a tire, carb was too rich across the spectrum, REALLY rich secondaries - 10:1 A/F readings, they didn't even feel like they were working, very little response. After freeing up the APT screw & making adjustments I got the idle/transition/cruise all tuned nicely, a friend had already rejetted it leaner than a rebuilder/tuner had guessed the combo. Had AY(.567) secondary rods - secondaries would just make a muted "woooooooooooo" sound, went to DP(.686) & mixture got much better, engine winds up much better & faster, carb wails a little now & will lay some rubber. I didn't have the next rods available today but I intend to try CG(.774) in there next time I play w/ it & I'll bet it will improve some more - by going leaner.

What I'm saying has been said many times by many people on the boards, I'm just trying to give details on what I have been involved with lately so info might be pertinent or a good guide for people that are working on something. Sometimes knowing what not to do is as important as anything.

I type all this as kind of an example that w/ a near stock 350 there is a tendency to overdue things. The cam is too big for the combo (custom cam from an Olds tuner), the carb was way over rich as guessed @ by the rebuilder/tuner (& never bothered to free up the APT screw). W/ a 3.08 or 3.23 rear end to wind this up quicker the combo will work well. BUT, it doesn't have it (at least until I try to talk owner into some mild gears) so it is a little doggy IMO. Depending on the components used, the engine needs to be built/tuned accordingly. A cam 1, or even 2 "sizes" smaller than what sounds sexy is probably the better choice, where you think the carb will be is probably too rich (or sometimes too big), etc & blah blah blah.

captjim

Man, if I had a nickle for every time I told some guy not to over-cam his 350.......

Anyway, nice posts by bccan!! Too big a cam in a heavy car with no gear and a smallish engine = no fun to drive. A little gear helps a lot. My 9 to 1 355 ran 13.9 with 3.42 gears, Performer, and a 210/216 cam (Engle 16-18). By contrast, with an RPM intake and 214/224 generic cam, it ran 14.8, almost a second slower. 60' was absurd, 2.4 IIRC. No a$$ down low. More is sometimes less, it is all about the combination and tune.

71supreme

I am really enjoying this thread, even though nhuyghe hasn't replied since August.

I have a few questions as I am reading through all of this great info. Some of them may be hopelessly elementary, so please forgive me...

The engine in question sounds like a nice base to me. The 73 used the heads to create lower compression, so the pistons should be flat, or shallow dish. Using #5 heads here should bring a nice compression increase, no?

bccan: "Cam is 202/212 @ .515 lift (IIRC)"

What is IIRC?

What is wideband?

I have read that along with over camming otherwise mild motors, big valves can be a mistake as well. Why might this be true?
With a more lightly modified motor is lift (to a degree) more beneficial than duration? Most of the lower duration cams I see have lower lift #s.

I have learned that rear gears should come first in a speed upgrade, which makes sense given that horsepower generally needs RPM to be of any value. This thread began with a warning of too much cam. With that in mind, what other upgrades should be considered before a cam upgrade will make a difference, or before the car becomes "undercammed"?

While this may seem like a hijack, it's not my intent. My purpose for asking is as much to help nhuyghe (and anyone else who stumbles here, and myself) spend money allocated for his build as efficiently as possible if that makes sense.

Thanks!

bccan

CaptJim - Funny you posted as I was thinking of you (no,not that way!) the whole time I was typing & hoped you would chime in. You have been the most vocal on a conservative approach when building 350's, you have a great frame of reference to draw from & detail it out for people.

Hell, I have a very stout 350 short block sitting in the garage waiting for a home that I replaced just because I built it the way I always built engines in the past. The problem is I hadn't discovered the Olds forums & ended up a little high on compression & couldn't get quite the balance of performance vs manners that I wanted. This put down low 13's in my car w/ a best of 13.1 @ 106, probably capable of a couple/few 10ths less w/ a better tuner or driver (or both). At least it was built w/ generous clearances & good parts so internals look so good it looks like a freshly assembled engine inside. Most people would be ecstatic w/ an engine like mine or yours in their car, some wouldn't use them for a magazine rest in their outhouse. Everybody has different needs. My new engine in the blue car still subscribes to the conservative tune mantra. I could, very easily have it in the mid 500's for HP w/ a cam, intake & porting - BUT street drivability would take a back seat. How do you think 500 ft/ lbs @ just under 3000 rpm, w/ a pretty light recip assy, pulling very high vacuum (18-19" @ idle) through a 3.90 feels if f I decide to give it the spurs? Darn toottin' pretty damn fun! And don't forget to try & keep it straight! I'm sure there were not flat tops used but I don't know the dish sizes. We all have to remember to watch compression height & dish size when using replacement pistons so we don't end up w/ 8:1 engines that were expected to be more powerful than stock!

71supreme - I have to admit that I do not know the detail on that 73 piston dish. I guess it would make sense if that was the time they started using the #8 heads w/ big chamber as I would guess the engine maintained an 8.5 or so comp ratio which would necessitate a smaller dish than say 72/earlier w/ small chambers. If that is the case, some calculations would be in order to make sure comp doesn't swing too far w/ an earlier head.

IIRC=If I Remember Correctly (sometimes I do, sometimes not so much)

Wideband is a gauge that uses an oxygen sensor that "sniffs" the exhaust & can calculate the fuel mixture, they have become common & accessible, run about $200, are very accurate for us hacks w/ carbs, that prove to be pretty inconsistent anyway, & are very easy to install. Wideband refers to the type of O2 sensor (3 wire,heated) used as compared to a narrowband O2 sensor (1 wire, not heated). They are more accurate, quicker responding, & w/ a digital readout that displays to the tenth you can really see what is going on w/ mixture & what your adjustments are doing. This may be the best diagnostic & tuning tool I have, or a very close second to a timing light!

IMO (In My Opinion) I think headers & gears make the biggest immediate improvements in the performance department. Gears will be the most instantly noticeable upgrade you can make. They can completely change the acceleration ability of the car. BUT they come at a price, higher revs, less mpg on any open road, say 40mph plus in speed. The conservative approach applies here - too much of a good thing is liable to ruin your "driving usability" for most people. For example most of the late 60's/early 70's plain jane cars (which is what the majority of us start out with as opposed to a W-car) come w/ a 2.56-2.78 peg leg rear end, great for the open road but not conducive to quick acceleration & response. A move to 3.08 or 3.23 will be very noticeable & still maintain tolerable highway speed engine rpm, anything over that & it starts to become a very personal opinion on what is tolerable or not. Once you get into the mid 3 ratios, say a 3.55 w/ a 26"-28" that would be typical on these cars, you are looking @ around 3000 rpm @ 60 miles per hour. Fine for some, not fine for others. My kid's car (red one) started this exact way - w/ original you couldn't even start up from a light in the rain w/ the most gentle throttle application without spinning like you were on snow. I had an old set of 3.08's & a posi carrier so they were installed in the car - he was a little traumatized the first time he drove it on the highway w/ what to him was a screaming engine & gas gauge that seemed to leap backward! He did like the better feel for around town driving & has become accustomed to the highway revs. I wonder how he would have liked my 65 442 w/ 4.11 (w/ an M20 ) or 70 SS454 w/4.56 (w/ M22, talk about sweet around town!) when I used to drive them between Hartford & Providence going back & forth to school! Rule of thumb - be conservative, on a stock engine it is going to run out of power band pretty early anyway.

Headers - usually make a very noticeable difference, especially if engine has upgraded breathing. When I first built my 350 I had big valve heads, the cam that is in the kid's car & manifolds because I wanted the car quiet w/ no header hassles (I have had @ least a dozen cars w/ headers). Was evident that thing was breathing w/ a finger in one nostril. Installed headers, drove it to the muffler shop (done that a few times) so they could graft on my exhaust - I got reactions ranging from violent disgust, to one guy @ a light who was laughing & giving me a thumbs up! Open headers on the street made me very self conscious! When I picked it up it was like a different engine! Actually quieter except for the metallic "ping" & I swear it even idled better. I didn't even leave the parking lot before I could feel the difference, never mind once I got going. Even past SBO's that I had or worked on that were basically stock really like headers

Undercammed - Basically just is going to run out of "legs" for the engine speed. Throw some 3.90 or 4.11 gears behind a stock small block & it will take off like a scalded AND raped ape but the acceleration is going to run out pretty early in each gear's rpm range. That is why the W31 had such a big cam & frequently steep gears so that it could use the higher rev range to make horsepower, it wasn't a torquey stump puller, it was a screamer. An example using cars I am presently involved with - my kid's again. He had separation anxiety from his car when he stopped home from school for the weekend so he drove it back to school & I drove it home. On the highway, going roughly 70mph that engine was so happy @ around/just over 3000 rpm, hit the gas & it just rips because it is right in the power band of that cam. I don't know where it runs out because it hasn't been dyno'd or taken to a track rental (he had an exam when we went in Sept), I would guess it probably runs out of lungs right around 5000 rpm. Again we get back to the cam working in harmony w/ the engine's breathing ability (intake, heads, exhaust), rpm range (gears & trans) and most importantly, usage. You can lean a little more economy, efficiency or performance but it will all fall pretty much within a range on a mild small block build. Also - valvetrain comes into play. You can only have so much lift, I think appx .5" or less w/ stock valvetrain. It is only going to tolerate a moderate cam profile (not too fast a ramp rate) & springs can only control so much before upgrades become necessary which costs money but pays back w/ performance. Everybody has a line to straddle there. I also think that a lot of cam design is emphasizing additional lift in relation to duration & happily Olds does not have any critical piston to valve clearance issues well into the mid/high .500's lift range but valvetrain has to be compatible.

Have I spewed enough hot air for now? I'll stop now for everyone's sake! Remember - this is not gospel but things I believe in that have been learned & observed over 3 decades screwing around w/GM engines, mostly Olds & Chevy. I put it out there as I think it can help people who are trying to figure out a combo. In general the best thing you can do is to at least get advice & parts from the real Olds engine builders/vendors. DO NOT assume your local machine shop knows ANYTHING other than what a stock spec book tells them. If you are going to go it yourself, I would highly recommend Bill Travato's book for some guidance on performance builds & apply some of the machining techniques & guidelines as they suit your build. His competence is unimpeachable & it is great that he shares his knowlege w/ us instead of hoarding it, other builders on the Olds boards too.

71supreme

Thanks bccan!

My biggest reason for asking was to try to plan out a "one piece at a time" upgrade schedule. My eventual goal is right where your at with the ~13.1@106. Just a fun car I can take to the track every now and again.

captjim

Just to clarify, all 73 and later 350s had 14cc dishes. All 71 and 72 350s had 23cc dishes. 68-70 350s had 14cc for "low comp" and 6cc for "high comp" engines.

The stock 350 cam is so tame (.400/194 +/-) that even a stock engine will profit from an upgrade, just don't go nuts. An 8.5 to 1 engine would benefit from a .450/205 ish cam, IMO.

There are few (if any) drawbacks of a larger intake valve, just do a bowl blend to take full advantage. Low lift flow is very important on a driver and a larger intake will help with that, IMO.

71supreme

Thanks Jim! I did not know the specs on the dishes, just that the 71-2 used the dish to lower compression. When it comes time for me to change pistons, I will probably be looking at the 6cc's for my 71 350.

As far as the valve size, this is where I get horribly confused. It seems many variables that are good for low end torque are bad for higher rpm horsepower - Smaller valves increase VE(whatever that is), wider LSA, and shorter duration. lower lift...... Can't we all just get along?

I don't really want to open a can of worms, but I may be doing just that. My question here is, since we are talking about mild engines, or at least coming up from stock... At what point does this trade off occur. Can a mild cam (the .450/ 205ish) actually benefit from the smaller valves?

I realize I am at the point where I know just enough to be dangerous, and have absolutely no real world experience, so I will appreciate your thoughts. Thanks!

f-85

Well are you running a 260H or 268H? What size valves? What size carb? Headers? What compression? Lots of things you left out? But Comp Cams has a free desktop dyno. Google search it and download it. It will give you an idea of what kind of power it will make.

captjim

Everything is a trade off or compromise. If you run 2.14 gears in a heavy car, the smaller valves and a tiny cam MIGHT make a bit more torque, but then you are done at a much lower RPM. Engines are air pumps, the better it breathes the more power it makes. Like bccan stated, it is all about the combination of parts. More compression requires more cam requiring more gear and converter. Also, cubes rule, a mild 455 will be easier to run a low 13 than a 350 will. My advice would be to find a build that you like and copy it. My current 355 has a 227/233 Voodoo, great manners, runs strong but needs a race gas mix. I built it that way on purpose, best of both worlds, nothing beats compression.

Also, regarding rpm. Olds engines generally made good torque at a lower rpm. That is why a 350 Olds will run good with 3.42s while a 350 SBC might like a 4.10, peakier curves. My 9 to 1 355 with the 210/216 cam made best ET shifting at 4600. Yes, 4600. (I am a big fan of short-shifting heavy cars). It revved to 5500, was cool, made a bunch of noise, but that's all. Most street guys will go faster shifting at a lower rpm, especially with Olds and Buick engines. A 350 Cleveland on the other hand......

bccan

Link is to an example of what a low comp engine w/ a fair amount of "component support" can do. I think this might be well past the average cruiser/daily driver driver setup for most people w/ that cam/gear/converter. Most people would probably find it too many comprimises for good street manners, but there are those that wouldn't.

When I was young, I didn't care much about cosmetics, just had to have a powerful & nicely sorted out drivetrain & something like this would have been fine, now in my almost 50 yr old phase I would enjoy it for about 15 minutes and/or a drag pass or two, then back to something smooth & quiet. Not putting it down! He is getting some good performance out of it.

https://classicoldsmobile.com/forums...ger-350-a.html

Jharken

https://classicoldsmobile.com/forums...ger-350-a.html

I was just trying to get the most out of the junk I had laying around.

The most important part is getting the rpm's for everything in the same range.

The most average power down the track runs the quickest.If you are over camed and cross the stripe 1000 rpms under peak you left wheel tq on the table and ET.

Quote from captjim
Man, if I had a nickle for every time I told some guy not to over-cam his 350.....
Anyway, nice posts by bccan!! Too big a cam in a heavy car with no gear and a smallish engine = no fun to drive. A little gear helps a lot. My 9 to 1 355 ran 13.9 with 3.42 gears, Performer, and a 210/216 cam (Engle 16-18). By contrast, with an RPM intake and 214/224 generic cam, it ran 14.8, almost a second slower. 60' was absurd, 2.4 IIRC. No a$$ down low. More is sometimes less, it is all about the combination and tune.

Street car will always benefit from the conservative approach.

Torque rules on the street that is why 455 are so appealing.You can run almost any gear and the car will perform.Don't need a lot of stall to crutch low end torque because the motor will do the work for you.

This is just my opinion for what its worth build a 455 if torque is #1 priority and cost.There is no way a 350 will ever be able to compete in low rpm torque that can pull a heavy car and street gearing.

Build a small block and cam it and gear it and let it rev.

As Oldsmobile enthusiast we should be steering all street torque type builds to the king street thumper the 455.

bkeese

This is an interesting thread, but it has caused me to ask what about the W31. In stock form didn't Hot Rod say that the W31 could out run the W30 in the 1/4 mile? Was that because of better gearing, 3.90s in the W31 and less in the W30, which it should like (torque monster)? What ETs would you expect from a stock W31 built with quality parts. This includes stock exhaust, intake, carb and 93 octane?

I've owned sbc all my life and my 1st car a 62 vette with a 327/365 loved the 4.11 gears, 3000 rpms @60 mph. I even turned 8000 rpms in 4th once, damn near didn't get it slowed down in time. Do the math! I do have a W31 now and wonder what makes it roar, couldn't some of these guys clone the W31 to accomplish what they want as long as they have gears?

BLACKCADDY

I got a black 86 caddy fleetwood brougham... The 307 oldsmobile been fulling rebuilt with every thing stock in it that comes with the building kit....unfortunatly, i am not satified....so i am asking what do i need to do as for more horse power with the same engine 307?

Rickman48

Interesting thread - in total agreement with the answers and explainations given.

As far as the Cadillac goes, I, personally would rather change a motor, than a cam while in the car! Turbo or nitrous would work, maybe twice!
Being a 'boat', the Cad needs cubic inches to move it - I'd go for a 350 or 403, but I don't know what trans is in there, or if it'll hold up!
Unless you can find a Cadillac guy that'll install a 500 inch motor and a 400 trans!!
Someone did that with a '79 CDV and ended up winning everything in a Hot Rod Real Street contest, a few years back!

KustomRocket88

@ BLACKCADDY I got a black 86 caddy fleetwood brougham... The 307 oldsmobile been fulling rebuilt with every thing stock in it that comes with the building kit....unfortunatly, i am not satified....so i am asking what do i need to do as for more horse power with the same engine 307?

I would say go with headers and rid the cat converter, and do duals, so at least it will have better breathing. I found some Edelbrock Carbs and a pretty good set of headers I'm thinking about installing in my 307. The edelbrock is big bucks though, you may be looking into a carb between $200 and $600. In terms of the headers, these aren't bad...just like $140 and they are made for all the small block engines including the Oldsmobile 307. Depends how much money you wanna dump into the 307. They'll bolt right on:

http://www.summitracing.com/parts/BIG-11152FLT/

By putting in 373s in the rear end that'll help quite a bit in terms of acceleration, although your mpg would go down. I'm thinking about lower gears in the rear end as well in the near future.

Good luck, I hope this helps!

Timothy26

I have a stock 71 cutlass 350 rocket.....It feels so POWERLESS....What can I do to wake the engine up?

cutlassefi

Put a gear in it first.

captjim

Keep in mind that most of those comparisons were done using bias ply tires, which the 455 would fry. Take a LOT of that old hp and performance info with a grain.

Guys, if you really want good answers, you will do better starting new threads.