Hi Everyone,

My 455 in my '68 is in need of a rebuild. I drive my car everyday in the Summer (8-10 mpg and $3.30 gal for premium is no fun!) and due to the current and future state of gas prices, I'm entertaining the idea of going w/ a Pontiac 6 cylinder engine. Since I know little about them I was hoping you all could help.

1. What kind of hp/torque could one expect to get out of a 6 that will need to be reliable but fun?

2. How much do they weigh vs. a Pontiac V8?

3. What would be involved in swap from my current V8 to 6?

4. I currently have a T400 trans. Will the 6 bolt up or should I have a dif. trans?

5. What Gear ratio should be used in a fgf for all around driving?

6. Expected gas milege?

7. What should I expect to pay for a rebuilt engine?

Thank you all for your advice!

DONT. If your # crunching by the time you buy all the things needed to do this swap that you dont have. Im sure that will off set the $ saved on gas. In the long run. Besides when that punk kid pulls up next to you with that 6 cyl.in your car you'll have to turn away. Yes there are some high torquing 6s out there but theres the $ thing again. Keeping it real. .02 BIll

I gotta agree - keep your engine in there, or maybe, maybe look for a 350 (if that's what originally came in your car, since the 455 isn't original). You can look to change the tranny out to a 4 speed - 7004R maybe? Or look into a manual overdrive system that can save you some gas with your TH400. But in the end, these cars suck down gas, and will never get close to 30mpg that ecomony cars easily acheive.

Oh, and $3.10/gal is pretty cheap, compared to the east coast prices.

Maybe drive the bird less?

you can ,for numbers crunching excercize email Quenton at
Q.Olson@PrimatechMotorsports.com he can probably get you an idea on what a nice 6 cyl cost you....but as said before...you can get a lot of gas for the difference in cost plus R&R of engines...

Thanks for the plug, Bjorn.

Here's a thread on the Pontiac OHC-6 site that discusses the MPG you might expect from an OHC:

OHC Mileage

The change-over to an OHC from a V-8 is a little involved. The TH400 will physically bolt to the block, but the list of stuff you need for the conversion is pretty extensive, including some parts that are almost impossible to find, like OHC motor mounts.

I'm not saying that this conversion is the right solution for you, Vic...but Bill, don't knock the OHC-6! This engine has earned my true respect as my Le Mans did some serious pavement pounding at the Dream Cruise this year and a lot of pleasant (and economical) cruising all summer.

A Pontiac 350 would be a bolt-in replacement and would give better fuel economy than what you are getting now.

You don't need more than a 3.23 gear for all around driving. Mine is considerably milder and yet returns good performance.

Thanks for all the great responses. I have some thinking to do. There are some "out of the box" options to consider but discussing them here might cause some heart attacks! This is a great forum and we're all lucky to have all of you who contribute.

Thanks again.

I second Vikki on the 3.23 gears. That's what I've got and it seems to be a pretty good compromise gear. It revs kind of high on the freeway but not too bad.

Gas should be coming back down soon or else I'll start believing the Big Oil conspiracy theories. Crude oil is down below pre-Katrina levels and gulf coast refineries should be coming back on line.

"gulf coast refineries should be coming back on line".....
they will ,just a matter of time , todays paper had a list of the 'down ones', it was long!

you know the saying 'what goes up comes down'...its true ,but we`re not sure for how long though....I`m sure they would like for us to get used to pay $3.00/ gal, so well think $2.35 is cheap!
last year this time I was happy to find a few stations with $1.65......
but after visiting Sweden w $6.00 /gal gas ....$3 doesnt seem so bad ,except when you fill up! lol

I remember filling up my 68 bird for $3.25 in 1969....!! its all 'relative' ......
as in "relatively" expensive...LOL

Don't give up so easily on that 455. Tell us what your engine combo is now (carb, intake, cam, heads, exhaust). I'm sure during the rebuild and with some proper tuning you can eek out a few more mpg.

Vikki No way I was knocking the OHC6. I said there are some high torque 6s out there but you'll pay for it. Thats great your Lemans has your respect with the OHC6. Wondering if you'd feel the same if it came with a 455? My bird originally came from the factory with the ohc 6. When I bought it it had a 283 chevy. I had no quams putting in a big V8 over a OHC 6. No matter how high gas gets mine is a MUSCLE car not a sunday buggy. This Email along with the first was not to stir anybody up. twofirebirds asked for this boards .02 and I gave mine. This has to be the longest e-mail ive written on this board. Sorry if I offended you or anybody else. Bill

I know that I'll probally get some flack for this but downgrading the transimssion to a 350 turbo will save gas by weight reduction; also, it takes less energy to rotate the internal mechanisms of a 350 compared to a 400. You will get identical performance from a turbo 350, the difference is that it isn't as durable as the 400. (The tranny rebuilder who built my previous 350 and a professional drag racer/drag racing car builder bot agreed that for engines >500 hp, a turbo 400 is a waste of engine power. They were running turbo 400, but their cars exceeded 500 hp, and a 350 wouldn't live that long married to such engines.)

Smitty is running a lock up tranny. I only drove his car through a residential neighborhood, and a short run on a 35 mph highway, so it wasn't like a real test run. Even so, it was enough to get a small taste of 1-3 shifts. It seems like a nice set-up, and his transmission would be my selection as an upgrade.

As Bob is running, my car has a 3:23 screw. That's about as loose of a screw as you want if you want to consider the car something you can drive other than to the gas station and the strip.

Bill, definitely no offense taken. This forum is all about expressing opinions. My 'bird has a still stock 400/TH400, so I am also a V-8 fan and like to run my horses hard. The Le Mans is my first inline cammer, and for the first thousand or so miles I put on the odometer, it was simply a very well-mannered, nice driving street car with better than average acceleration compared to today's cars. The Dream Cruise brings out the devil in me, and since I was driving the Le Mans at the time I had to find out what was under the pedal. So I did...and a bone stock '66 Sprint is no slouch in a 3330# car, even with the 2 speed auto. So now I enjoy the 18 mpg, quiet operation, and the nice road driving, with the knowledge that I don't have to be hesitant about putting my foot to the floor, but a 200-4R would really make it a quicker car and give it a few more mpg!

I'd keep a V-8 in it. Too much trouble in the long run, IMHO. Find a decent running 350 & then rebuild your 455. 3.23's would be a great gear all-around for any V-8 you go with. The T-400 trans would be a bit too much with the 6 cylinder, it will pull down the power a bit. The T-400 is a heavey duty trans & would be overkill on the 6. Too many things you would have to change & alter to go with the 6.

Steve

Keep the V-8! Amervo is right, the 700-R4 (or 200-4R!!) would be a big fuel saver. I can easily predict 15 mpg with your 455. With a 350-4, my record so far is 23 highway but I can easily get 18 to 20.

For tips, click on the 700-R4 link in my signature. http://www.bowtieoverdrives.com is a great resource too.

Wow,

I didn't mean to stir everyone up. Here's my current combo. 455 .30 over, Performer Intake, 6x Heads, Comp Cams XE268 Cam, Lifters, Springs, H.E.I., 800 CFM Edelbrock 4bbl, 400T trans (converter a little over stock), 2:56 rear, Flowmaster 2 1/2 dual exhaust w/ traverse muffler. Currently I'm running 14" Rally II's w/ close to stock size Goodyear ST's.

The bottom end was rebuilt in 1989. The engine was built for street racing when I got it (In a '78 GP that ran low 12's in the 1/4)and was way too radical to run on the street. In 2000, the heads, cam and top end were done to make it more driver friendly.

The engine runs excellent and always starts immediately. The problem lies in burning oil upon acceleration. It's now burning oil at a rate of 1 Qt per 2 tanks of gas. I can't tell you how much it bugs me to see the blue trail of smoke behind me. Especially leaving from a stop light.

My car is driven 3-5k per Summer and enjoyed. Car shows and drag strips are no longer in the equation. If anyone has an idea I haven't thought of, please feel free to let me know.

Thanks

The first thing I would do, just for the sake of gas mileage and performance, would be to put an OEM Q-Jet on the car. (Jon can take it from here.)

As far as the burning oil is concerned, is it burning in the engine or on it? In other words, is it leaking onto the hot headers and pipes? Or is it actually burning in the motor so that evidence shows up on the spark plugs? Or has someone following you said it's coming from the tail pipes?

I agree with P.M.I USA. A 800 cfm squarebore carburetor is not going to help fuel economy.

Other than the carburetor, your system seems setup such that you should be doing better than 8-10 mpg.

Once you determine whether you need the lower end rebuilt or the heads rebuilt you could try the following:

1. I'm not familar with the Edelbrocks, but most carbs have a way to delay opening of the secondary valves. I'd try to add more delay to the secondary opening (make them come in later).

2. General purpose carbs are not calibrated for your specific application. They are usually "rich" from the factory to be conservative.
Step 1: Adjust your idle mixture until you read the highest manifold vacuum.
Step 2: Drive the car at 2000 rpm. Record the vacuum reading at that engine speed. Lean the primary mixture in increments until highest vacuum reading is achieved or you feel a "surge." Sometimes the vacuum will drop, but as you continue leaner it will come back up. So don't be afraid to continuing leaning it out. Since you are only adjusting the cruise mixture, you shouldn't damage the engine going to lean (it will just surge).

3. Finally, make sure your timing is set properly. Have it all in by 2800 rpm (mechanical). Crane makes a great adjustable canister and spring kit. Try connecting to manifold vacuum instead of ported. Some engines run better this way (especially if they have moderate to aggresive camshafts and low static compression). When connected, your idle speed will increase. Adjust it back down to where it was. The benefit is by adjusting the throttle opening more closed to reduce the idle speed back to normal, you will be using less air (and thus less fuel). Almost everyone I work with that has a classic happens to have set their cars this way. I tried it connected to ported, and then manifold, and found manifold vacuum advance worked better in my case. Since you are adding advance the mixture will probably richen, thus you can redo setting the idle mixture again and lean it out even more.

Let us know how it turns out.

To answer PMI's question on burning oil, the plugs are very oily and the blue smoke exits out of the exhaust. The engine has no leaks. Unfortunately, I can see the smoke covering the car behind me when I take off from a stop light.

Mike, your 2nd step has already been done. The only thing I haven't done w/ the carb is change metering rods (edelbrocks version of rejetting). I'll attempt step 3 and see how it goes.

I appreciate the advice.

If your compression and leakdown tests give good results, it might be something as minor as bad valve stem seals. It's worth a look, anyhow. Also make sure you have the correct (or correctly calibrated) dipstick, to be sure you're not overfilling your engine.

A Pontiac with no leaks? What's your secret?

Almost forgot. If it does turn out you need a rebuild, dropping your compression under 9:1 should allow you to run on 89 or even 87 Octane. This won't improve fuel economy, but the gas itself would be cheaper. Have the block zero-decked and remove any sharp edges in the cylinderhead combustion chambers.

I know Vikki! In 25 years, it's the 1st Pontiac engine I've ever had that doesn't leak. But to put your mind at ease, the trans does leak when it sits for a while!

My 'bird leaks, but a lot less than when I bought it. It's pretty much only the rear main seal, differential cover and oil pan gasket now, instead of everything. The Le Mans doesn't leak a drop.