Poor performance with 330 V8/TH350 in a 1968 Cutlass

Hello Guys,

I just wanted to get your take on this issue I have been having with my 1968 Oldsmobile Cutlass Supreme 2D holiday coupe. Previously, it used to be quite fast and even could pull off a nice burnout when promptly accelerated with what I believe to be the original and correct 350 Olds Rocket V8 (block painted gold) with 4 barrel Quadrajet carburetor and automatic 2 speed + overdrive Olds Powerglide equivalent.

As for the 350 Rocket engine, the lifters tapped and the engine has been retired to my garage until it can be rebuilt later on with performance parts. In the meantime, I have put in a 330 Olds Rocket V8 from a 1965 Cutlass and a TH350 3-speed automatic trans. I have also had to replace the carburetor with an Edelbrock to work with the new TH350 cable operated trans (The original Quadrajet lacks the bracket for the cable as the old 2-speed trans was vacuum operated).

My question is this:

Ever since I had them installed, the current engine and trans seem sluggish to shift and at freeway speeds the engine revs audibly at a high pitch. To drive it currently, it has to be accelerated slowly and evenly through the gears to let it shift to prevent the engine from revving loudly, and once on the freeway, it starts to make a high pitched series of noises, starting from 55 mph and changing at 60 mph and then switching to a lower pitched whirring sound at 65 miles an hour. Some of this may be more noticeable to me due to the carpeting and sound deadener all being removed as the vehicle is in mid street restoration, but does all this sound normal for that engine/trans/carburetor combination? Are the higher engine rev and other noises due to the lack of overdrive only or could other issues be making this worse?

Also, when I decide to put back the rebuilt 350 V8 should I try and install a TH700 or should I just get a stronger made performance Powerglide? Is the Quadrajet really that much better than the Edelbrock and did they make one that is cable operated?

I realize it may be expensive to do this but I love my rusted out 1990 Chevy Blazer K5?s 4-speed manual (with 350 V8), and as I may need to replace the Blazer sometime soon due to safety reasons with hopefully another late 80s/early 90s Blazer full size (multiple sheared off body mounts, truck spent 18 years in New Jersey before I took it over here in Arizona) and most of the Blazers came with automatics, is there any reason I shouldn?t just wait and pay the $4,500+ to switch the Cutlass over to a manual trans so that I can continue to enjoy launching a manual in first gear?

Ultimately, what do you think is the best trans to match with my 350 V8 and are there any known concerns related to my current trans/engine combination that could sap performance?

First, what is your goal? The TH350 is usually a solid transmission the one you have sounds like its worn out. If the old tranny is ok, it might be a good bet. I think that your current engine is probably over carbureted and not properly jetted. Done right, the Edellbrock has more potential than the Quadrajet, but the Q-jet is simpler to maintain in the long run.

The TH700 is probably the best overall transmission, but the gains probably won’t be worth the cost.

Thank you for your reply.

I?m not looking to make the Cutlass a numbers matching full restoration, just a nice older car with good performance and average fuel economy for the era (10-12mpg?). It would be nice if it could simply keep up with my Blazer in respect to performance, and the Blazer isn?t even as fast as my wife?s 2003 Honda Accord V6 because of the weight difference. I realize the Cutlass isn?t a 442 or H/O with the 455, but still would like to see an increase in performance and acceleration and was hoping my current setup isn?t inherently mismatched to create issues.

I would prefer it if I could stomp on the accelerator from time to time and leave a nice little path of rubber behind me, with it quickly shifting to the highest gear without belts squealing and the engine revving like it will explode while still shifting smoothly under normal steady acceleration. I realize the small block engines must rev higher to provide this kind of power, but it seems my 350 Rocket V8 was able to do it without struggling. I think I should have a tachometer installed soon as I come up with the funds so I can at least see how high it is revving in all situations; maybe it?s revving high but still within tolerance and knowing that would ease my mind a bit.

As for the old 2-speed trans, it was quick but it would hesitate to shift as well, but with less gears there are less shifts so it wasn?t as noticeable. Also the overdrive made freeway speeds much more enjoyable and less noisy. My current setup was always meant to be temporary so I could enjoy the car in the meantime but all the noises at highway speeds cause me concern and makes it hard to enjoy coasting on the freeway when I am paying attention to every little sound to try and identify its source.

Also, the TH350 had been rebuilt (It was given to me for free by the auto body shop and required a rebuild due to water damage if I remember correctly) a few months ago when I had both it and the 330 V8 installed, and I was told the 330 V8 had been rebuilt a few years ago when a friend of the body shop I had my Cutlass painted at bought a 1965 Cutlass, and the 330 V8 was removed only to put in a 425, so the 330 had been stored at the shop and didn?t require any major work to get up and running again.

I have seen in Year One Speed Catalog that they sell overdrive units and if I remember correctly they can hook up to an existing transmission? Would that be more cost efficient at around $2000 and work well with both the 330 V8 and 350 V8?

Over carbureted? Not jetted? I am unfamiliar with these terms, and a google search didn?t yield many results as to a clear explanation of these terms. What does this mean? I would like to add that the Edelbrock carburetor was purchased brand new by the independent shop and that the mechanic said he had ?softened? and adjusted the shift when I brought it back after I first test drove it and it was shifting too late. It is much better now under a slow and steady acceleration but still shifting late under a quick acceleration.

If you have a vacuum modulator valve, change it. If transmission fluid leaps out of the hole, you had too much in the transmission.

"Is the Quadrajet really that much better than the Edelbrock and did they make one that is cable operated? " Yes and yes. The Edelbrock is just a copy of a Carter AFB.

I never heard of a Powerglide with an added overdrive. Burn rubber?? Not.

Do I have this right,you have installed a “temporary” engine and transmission so you would not be deprived of the joy of driving your 1968 Olds? the one with no carpet? A temporary engine?

You could have applied all the effort you are expending on the temporary engine towards getting your perment engine ready.

Are you saying you want to put your Blazers 4 speed in your Olds? The Blazer has the compound low first gear? this would not work out well in the Olds.

OP here,

It could be 5-10 years before the other engine is ready as my wife will no longer put up with my project keeping us out of a house (though my timing certainly saved us from being upside down on a house payment) so I wanted to just drive it around as is for a while and save up slowly for the rest of the interior while I consider the engine options I really want. It?s fully painted and bodywork/trim is done and it really is a beautiful car to cruise around in, and the incomplete interior doesn?t really bother me.

To get it moving right now, the 330 itself only cost me $500, the trans was free but the rebuild cost maybe $600, the carburetor somewhere around $600 + labor for everything to the tune of $4,500 or so in total if I remember correctly. I wasn?t paying much in the way of bills at the time so it didn?t hit me as hard as it would now. I planned on keeping the TH350 but now I?m not so sure, it depends on if it can be adjusted to give me the kind of modest performance I want out of the 330/350.

I don?t plan on taking the rusty 4-speed out of the Blazer as I use the Blazer as a daily vehicle, I just like how it drives and was wondering about an equivalent manual for the Cutlass, or whether I should stick to automatics that could perform as well as the manual does with the 350 V8. As I would need a clutch pedal assembly and a variety of other bits to put a manual in, it would be an expensive conversion, so I was hoping to hear I could expect to achieve similar performance with an automatic. I was also entertaining the option as I will really miss the Blazer?s manual when I ultimately get rid of it because the rust is so bad.

Optimally, in the short term I?m looking for a relatively inexpensive fix utilizing my existing 330 V8/TH350 setup (a few thousand dollars or so) to improve shifting whether I am accelerating smoothly or need an extra burst of speed as well as lowering RPMs on the freeway to improve MPG and performance. My thinking is an overdrive unit but I?m not sure what the downsides may be to installing an aftermarket overdrive unit onto the tail end of a trans that never had overdrive (particularly its effect on lower gears).

In the long term I?ll be considering engine/trans options that will really give it power, and being unable to really test drive my options until they are in the car I wanted to hear your thoughts and suggestions.

I will also keep pleasedodgevan2?s suggestion in mind; maybe I can ask my mechanic about it this weekend and see if this may be an issue.

The TH350 is a good transmission but it’s possible this one could be slipping.
You can perform a converter stall test very easily. Shift into LOW, hold the brakes, and try to rev the engine quickly. The engine should stall around 1800-1900 RPM and rev no higher. Allow the engine to idle for a couple of minutes.
Repeat this process after shifting into SECOND. Allow to idle.
Repeat in DRIVE.

If the engine revs up into the 2400 RPM range, give or take, the transmission is on the way out.

To me, there is no wrong answer on the carburetor. Both the Edelbrock and the QJ are great carburetors. The Edelbrock has the advantage of fewer parts and simplicity; that’s about it. Yes, the QJs can be had with cable operation.

Given the choice between an aftermarket overdrive, PowerGlide, or a TH700R4 I would take the latter with a twist.
The 700 is basically a Chevy transmission which uses a different bellhousing bolt pattern than the Olds/Pontiac/Buick/Cadillac engines. The BOP/Cadillac transmission would be the 200R4.

My reasoning for the 200R4/700R4 would be simplicity, better driveability, and improved fuel mileage.

As to lack of power that may have something to do with the engine. My book shows 2 different 330s available for that year.
One is a 2 barrel rated at 250 HP and the other a 4 barrel rated at 315 HP.
So the question would be if someone has thrown a 4 barrel onto a lower rated engine in the past in which case you may have a more anemic engine with a muscular look.

If you can dig up the block, head numbers, etc there may be some info in one of my other books to verify exactly what you have.

Thank you!

I can try and look at the engine tonight to see if I can find any engine codes and post them later. I didn?t know that they made two different versions of the same engine for a 2 or 4 barrel carburetor; I thought they used the same engine and the 2 barrel carburetor simply restricted more air to limit performance. I trust the auto body shop as they never steered me wrong, have excellent customer service and were always willing to talk to me, even asking me how my Cutlass is doing when I bring my rusted Blazer in for a safety check, and the owner?s friend that sold me the engine absolutely loves Oldsmobiles and is even restoring a 1974 H/O, so it would seem strange to me that he would not mention if it were the 2 barrel carburetor engine. I?ll give them the benefit of the doubt but still try and post the codes. I seem to remember a number across the top of my 350 hidden by the air filter, is this where I may find the number on the 330?

As for the stall test, I found the following article noting the process:


It mentions chocking the wheels and holding down the breaks as you said and includes further detail. I unfortunately do not yet have a tachometer installed so I cannot record the stall point RPM, so is this something I could ask an independent shop to perform? Do many shops have a tachometer available to test this on different vehicles? If not I could probably wait until I have one installed since I plan to put one in anyway but that would be after I put a little more money in my coffers. You mention shifting into second, how would I do this with an automatic?

I?ll look more into the 200R4/700R4 and determine which one I may prefer. I?ve got plenty of time to pick one out but a list of what to look for never hurts. Thanks again!

I’m curious, Why didn’t you just go for the ubiquitous Chevy 350/350 combo instead using the 330? Chevy 350’s are 12 for 10 cents in practically any junkyard.

A quick look at my engine book shows there were 3 basic versions of the 330; a 250, 260, and 315 HP with the latter being a 4 barrel. The 260 was not offered by the factory in the Cutlass model. There were also various sub-versions but the HP ratings remained the same. The difference was in model applications. There were also 3 or 4 versions for export so these should be irrelevant.

Ignition timing, cam timing, etc. is the same on all but my book does not give the camshaft specs. Odds are the HP difference on the 4 barrel model is likely due to a different cam profile and dual exhausts. Duals on the older cars really made a difference; not so much on late models.
The lower HP versions had 9 to 1 compression ratios; the higher HP version had 10.25 to 1.

Block codes are behind the water pump near the oil fill tube. The lower HP versions will be coded, T, UL, or U. Higher HP versions will be coded TG or UG. Cylinder head codes are above the center exhaust ports.

Just some info to verify if someone has taken a 2 barrel model and converted it to a 4 barrel. This conversion won’t increase the HP that much and even then, only at wide open throttle.

The stall test could be done with an aftermarket tachometer. Some shops may be leery about even performing this test though although it’s not harmful at all if done properly. Don’t abuse the process basically.
With the TH350 you should have a place on the shifter mechanism for 2nd gear. If not (since the old trans was a 2 speed) then you just shift into LOW and then move up a notch.

Your friend may not be trying to pull anything on you at all. So many of these engines were modified way back when it’s anybody’s guess as to how they came from the factory. I’ve even tweaked a lot of them myself; changing heads, manifolds, etc. around in an effort to squeeze a bit more out of them.

The 330 was sold to me by the friend of a trusted body shop owner so I could reasonably expect that the engine I received would run without needing a major overhaul, and for $500 it didn?t seem to me a bad deal. I also reasoned that the Olds Rocket 330s and 350s were similar enough to warrant the fewest hassles in a switchover, and while I did need a new water pump and had to replace many other accessories anyway, the only thing I needed because of the engine switch itself was a belt pulley to accommodate my existing AC compressor with the 330 if and when I decide to have an AC kit installed to replace the existing system.

Also, my Olds is less common (I?ve seen many more Chevelles and Impalas than Cutlasses from the late 60?s), and even though I recognize that the more common Chevy engines also have the most aftermarket and OEM support, I wanted something a little more unusual and loyal to the Olds brand.

Thanks, I will try and take a look at it the next few days and post back with what I find regarding engine codes. Fingers crossed!

As for the stall test, I?ll have to hold off until I can order the tachometer and have it installed, I?m thinking of getting a Sunpro Super Tach II Tachometer to match the Sunpro oil/temp/batt gauges already mounted to the bottom center of the dash. At $45 or less they seem fairly inexpensive so I could maybe get one sooner rather than later.

My Cutlass also came with dual exhausts and still has them from the old 350. I?m thinking of having a new exhaust system installed for under $300 when I can scrounge up the cash as the old pipes are ancient and when I had new tips and pipes mounted from the old mufflers to the back of the car to pass emissions here in Arizona (the old tips pointed down under the differential which wasn?t a problem in California, no emissions testing), the muffler shop tech showed me that someone had welded a crude patch over the bottom of one of the pipes leading into the engine to repair damage, likely before we even owned the car. I?m thinking Flowmaster 40s may be a nice upgrade as well.

One question, where may I find the center exhaust ports?

In regards to the exhaust ports, I mean the area of the cylinder heads where the exhaust manifold attaches in the middle.
My book shows the head numbers should be facing up outside of the valve cover and should be pretty visible.

The price for that 330 doesn’t seem that bad to me for a date coded older engine.
Even if you go back to the Olds 350 later I would either hang on to that 330 or put it up for sale. Run across someone needing a date coded 330 to return a car to original and they may be willing to pay a premium price for it because how many 65 Cutlass 330s are out there anyway? Very darned few I’d bet.

My reasoning for the 200R4/700R4 would be simplicity, better driveability, and improved fuel mileage.

I agree there with the exception that he will need to rig up the TV cable and adjust it properly. Not a super big deal but I’ve seen more than one guy stumble on this aspect.

You mentioned the 455 HO 442. Believe it or not, the 4 barrel version of the 350 was faster. The 425/455 was better suited to the heavier vehicles and towing trailers than to racing.

By over carbureted, I meant that the carburetor opened up so wide that flow through the venturis slowed down to the point that the fuel didn’t atomize correctly. The question here is do you have vacuum secondary throttle plates or straight mechanical. A lot of people would remove the vacuum linkage and go straight mechanical which is OK for a manual transmission or an automatic with a high stall speed torque converter. This isn’t good for a stock automatic especially if you punch it from idle. It will just bog down.

Vacuum linkage to the secondaries prevents the secondaries from opening if the manifold vacuum is below 3"hg. This keeps the engine from bogging down.

As for the different HP ratings. I’m not sure about this particular engine, but the typical GM V8 of the era had three versions, a low compression 2V (barrel) that ran on regular gas, a high compression 2V and a high compression 4V. A lot of people would convert either of the 2V versions to a 4V for better fuel economy.

The 4 barrel got better mileage because most of the driving was done using only the primary barrels, which were smaller than the two barrels of the 2V carb. The two primaries were also located a little further forward on the engine and that turned out to give it a better cylinder to cylinder fuel balance because of the backward tilt the engines were usually mounted in. A little extra power was just a bonus.

When I was young, I had a 66 Pontiac Catalina with a 389 4V that got about 15 mpg. My dad had a 64 Catalina with the high compression version of the 389 2V that only got about 12 mpg.

As for the transmission, I would avoid the 200/700 series transmissions. They were built for economy, not power. My first choice would be the TH350 if it isn’t slipping. I don’t remember any 2 speed with a lock up torque converter in 68, the lock up converters didn’t come into vogue until after the gas crisis of 73. If it does exist, then it would probably be a good option with a good running 350. BTW, the Olds 350 was a much better engine than the Chevy. The Chevies were good, but the Olds was better.

If there is a way to put a lockup torque converter with the TH350, and I think a few were made in the mid 70’s, that might be a real good option.

For now, if the current transmission is slipping, put the old 2 speed back in and then take your time with the 350. You could slowly build up the 350/350 combination and when ready put it in.

One more thing, you might have a leaking diaphragm on the vacuum advance of the distributor. It can cause bogging down on hard acceleration and can affect the shifting of the transmission. If your 330 engine came from California, it might have one of those state required aftermarket smog devices that blocked the vacuum advance of the distributor. If so, remove it, it never worked anyway.

Thanks for all your help and advice!

I finally had a chance to take a look under there and this is what I found (please forgive any misuse of terminology):

When facing the car, on the left side of the engine near the oil fill tube and A/C bracket, on the shaved section just below the valve cover is the stamped code T 687932. The letter in front was difficult to read but the number was very clear.

Also on the engine block was the raised number located near the oil filler tube at the center of the engine just behind the water pump, and the code is 1381917. The engine block and valve cover appeared to be painted Gold, though there were discolorations in other areas that made it difficult to identify a single color (The valve covers appeared to be light blue in some areas and gold the rest). The valve covers have decorative raised lettering that says ?Oldsmobile.?

On the section of the engine that the carburetor bolts onto near the front of the engine under the air cleaner was the following:

16(or 8)2

This part of the engine appears to be bright blue in color. Do these numbers coincide with the 250HP version of the 330? I found the following information at http://www.442.com/oldsfaq/ofeng.htm#Engines:

?Code is stamped on the right cylinder head. Unfortunately, this only applies to what was originally the driver’s side head. This code consists of a prefix letter (330 V-8=T (1964-65) or W (1966-67), 400 V-8 = V), then a production sequence number, followed by a suffix code letter (L = Low compression, E = 2-bbl export, G = High compression, H = 4-bbl export). A 2-letter code on the oil filler tube identified the engine.?

I didn?t have the foresight to identify any codes on the oil filler tube, but does this information coincide with what you have found? If this is the 250 HP version how significant a drop would that be from a 4 barrel carbureted 350?

Thanks again.