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How to make it drivable?


Nick H.

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Hey guys, it's been a while since I've been here. I finally convinced Mom to sell me Dad's Monte Carlo. It was a father-son project car for many years, and we enjoyed working on it together from when he purchased it in 1993 until his death in 2010. It still isn't finished, but I know when Dad built it, he wanted it driven, not just stared at and wiped down every few weeks in the garage. . . Which seems to be what has become of it.

 

Anyway, when we rebuilt the new engine, we went a little over the top with it, and it is a bit less street-friendly than I'd like. It's got a 468 BBC 4 bolt main block, 12.5:1 CR, with closed-chamber heads and a big lumpy cam. Holley 850 double pump carb, Offenhauser intake, Hooker headers, with true duals through Flowmaster's, 3" all the way back. The car is an absolute beast, always starts on the first turn of the key (2 pumps of the gas pedal, turn the key, fires right up, no choke), and scares the bejeezus out of me. Roasts the tires under light acceleration (thanks to a big converter), and averages 2MPG city. I'm not kidding, you read that right. I drove it 36 miles in 2010, and it took 18 gallons of Turbo Blue leaded 110 octane race gas to do it.

 

I'd like to get this thing to run reliably on pump gas, and double-digit fuel economy would be fantastic. My question is, would a set of open-chamber heads and thicker head gaskets lower compression enough that it could be run on Premium No-Lead pump gas? I'm also seriously considering new rear gears and possibly a trans swap down the road to improve mileage, but right now, I'd really love to be able to put gas in it at the gas station down the road, rather than having to load up 4x 5 gallon gas cans and drive 15 miles to get Turbo Blue, drive back, pour it in, and make it to the corner before I have to do it all again.

 

Anyway, what all would I need to do to get this thing running on pump gas? How much could I drop compression with open-chamber heads and thicker gaskets? I'm thinking my target CR is around 10.5:1, which SHOULD allow me to run 93 octane. Your thoughts?

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I have a 9 1/2:1 454 with 3.73 gears and can barely get 10 MPG on prem unleaded with a 750 double pumper carb

you will have to change pistons to get it to run on pump gas, trust me, I had a 12:1 468 before this motor, your converter is killing your MPG big time too!

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I have a 9 1/2:1 454 with 3.73 gears and can barely get 10 MPG on prem unleaded with a 750 double pumper carb

you will have to change pistons to get it to run on pump gas, trust me, I had a 12:1 468 before this motor, your converter is killing your MPG big time too!

Not opposed to swapping converters, but my plan is to eventually go with a T56 6-speed behind the 468. If I can't accomplish decent drivability through the 468, even if I do change pistons, I'll go with a standard small block. The car currently isn't driven, it's seen the road maybe 50 miles in the last 10 years. I just want to be able to drive it to car shows, go for the occasional sunday cruise, and have some fun with it every once in a while. It's not going to be an everyday driver, I just want to be able to get gas for it locally, and make it from gas station to gas station without running out. haha

 

I LOVE the torque of the Big Block, but the car was originally a SBC car, so I'm not opposed to swapping out. If I could get this thing to hit 18-20mpg highway, I'll be happy. City mileage isn't as much of a concern, as it's only going to be driven maybe 250-500 miles a year tops. Heck, at 2mpg, that's still only about $1500 a year in fuel. . . lol

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I would consider it, but this one has some sentimental value, if you know what I mean. Dad's gone, and this is the engine that he and I built for this car. If I do anything with the car, it's likely going to be a mild SBC with a 6 speed manual behind it. Even then, the car is unlikely to be driven much. I'm not sure how many miles are on it, but I know it's low, and I'd like to keep it that way.

 

The car was originally a 350 SBC car, Dad bought for $500 from a junkyard. Southern car, no rust, fantastic shape, but showing it's age. He drove it for 2 years, then blew the motor. We took it down to bare metal, fixed every dent, ding, and crease in the metal the old fashioned way, and it was repainted. He bought a 4 bolt main 454 truck block for $650 in 1996, and we built the engine over the next 2 years. Those 2 years were probably the most influential in my education about the mechanics of the internal combustion engine. By the time I was in 5th grade, I could look at a part from inside a BBC, tell you what it was, where it went, what it did, and what other parts were connected to it.

 

This is the engine that I learned how to build engines with, I don't think I could bring myself to sell it.

 

10mpg on pump gas is a LOT better than 2mpg on race gas. If it's going to take an LS engine to make this thing streetable and economical enough for an occasional weekend cruise, I'll see what I can find for a 5.3 or 6.0 truck block to rebuild. I will say, a twin turbo 5.3 LSX backed by a built T56 would be a pretty fun drivetrain, but it kind of defeats the purpose of selling off all of my LT1 vehicles to get back to my old-school roots. . .

 

Arrgh, why does this have to be so darn complicated?

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you can drop the compression by going to an open chamber head....if you have the funds use an aluminum head as they are more detonation resistant. You can take a little of the lumpy cam out by advancing it a couple of degrees or just swap it out for something a little tamer. You should be able to run 10 1/2 to 1 on premium if the ignition and intake system are right... wink

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you can drop the compression by going to an open chamber head....if you have the funds use an aluminum head as they are more detonation resistant. You can take a little of the lumpy cam out by advancing it a couple of degrees or just swap it out for something a little tamer. You should be able to run 10 1/2 to 1 on premium if the ignition and intake system are right... wink

Will compression drop by a full 2 points with just a head swap? What will the gas mileage be like? I'm liking the idea of an LQ9 build, since it will make power, have a newer engine that's proven reliable, and it will get much better mileage. I'd rather be able to enjoy driving the car without stopping at every other gas station, but if I could see double digits out of the big block, I'll just go that route.

 

Any idea what kind of cost I'm looking at for heads?

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If you're going to the expense of doing an engine swap, and everything is set up for the big block, why not just rebuild the 468 with new pistons, camshaft, heads and intake/carb? You get to use your motor and you get to rebuild it again to remind yourself of those memories with your dad. The machine work is done, it's just the parts and your labor. Everything else is done already (front springs, exhaust, etc.).

 

I know you can make killer small blocks and I love the Vortec in my Camaro, but big blocks belong in first gen montes. There's just so much engine compartment there. JMO.

 

Definitely think about putting a 5 or 6 speed in there. You'll love it.

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If you're going to the expense of doing an engine swap, and everything is set up for the big block, why not just rebuild the 468 with new pistons, camshaft, heads and intake/carb? You get to use your motor and you get to rebuild it again to remind yourself of those memories with your dad. The machine work is done, it's just the parts and your labor. Everything else is done already (front springs, exhaust, etc.).

 

I know you can make killer small blocks and I love the Vortec in my Camaro, but big blocks belong in first gen montes. There's just so much engine compartment there. JMO.

 

Definitely think about putting a 5 or 6 speed in there. You'll love it.

 

Yeah, but how will the mileage be? I live about 2 1/2 hours from where the car is kept, when I go home, I'll be driving the Monte Carlo almost exclusively, only on nice days. If it got good enough gas mileage that I could drive it home for a week and drive it to work until I go home next, I would do it. I know a BBC isn't going to get great gas mileage, but I'm hoping for better than 10MPG on pump gas. I don't beat on the car, because honestly, it scares the crap out of me. It's the fastest car I've ever driven, and it simply roasts the tires off without even trying. I've never gone full throttle in it, I've never raced in it, I've never gone over 55mph in it. It's simply too much engine for what I intend to do with it, which is just cruise around and think of all the memories of working on it with Dad.

 

Another consideration, this engine is brand new, has less than 100 miles, and was designed and broken in by 2 people, one is well-known in the local racing community, and the other is a retired GM engineer who specializes in engine development and research. Top-Shelf parts were used in the build, the break-in was done properly, and I have receipts for everything, including the block. I could easily sell this engine for $3,500-$4,000. That would more than cover an LQ9 with all the wiring and ECM, as well as a used LS1 T56. Sell the built TH400 for another $800-$1,000, which would cover the other incidentals, like engine mounts, trans mount, tuning, driveshaft, etc., and I'm not going to any expense at all, I'll probably have some money left over, to be honest.

 

A 6-speed, however, was something we had discussed before he died, he thought it was a great idea, so I plan on doing that, but it'll cost me at least $2k for the parts, plus I'll need a new driveshaft, trans crossmember, and a way to convert the speedometer to electronic, unless there's a way to convert the T56 to mechanical. . .

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My girlfriend has a 1971 pro street ventura. The motor is a 498 BBC (645hp 655tq) with a hydraulic roller, 10.5 comp, 950 Quick Fuel, 5 speed tremec, 3.50 rear gears and a 29" tall tire. We got 15.5 MPG on the highway cruising at 60 mph.

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My girlfriend has a 1971 pro street ventura. The motor is a 498 BBC (645hp 655tq) with a hydraulic roller, 10.5 comp, 950 Quick Fuel, 5 speed tremec, 3.50 rear gears and a 29" tall tire. We got 15.5 MPG on the highway cruising at 60 mph.

I bet the biggest detractor from the fuel mileage in this car, besides the high compression, is the stalled TH400 behind it. . .

 

Is there an easier 6-speed to swap in that can handle the power output of the BBC, or is the T56 about the only one that can do it? I had considered a Richmond 5 or 6 speed, but I don't know much about them. I know the T56 can be built to handle upwards of 800hp, which is why I was going to go that route.

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I have a tko 600 behind my 750hp 582 BBC in my Monte. It has been upgraded to withstand 900hp.

Thanks, I'll look into it. Any idea what it would cost? I'm guessing I'm probably around 600-700hp right now, but the car has GOBS of torque, and I really don't want to try launching just to hear the trans grenade on me. The TH400 was built to handle the power, but 3 gears isn't doing it for me, as far as gas mileage is concerned. Once I drop compression and get everything set up right, I think I should still be around 500hp, and still have gobs of torque, but at this point, keeping the BBC in place is going to limit my budget, as the cost of the parts was going to be determined by what I was able to sell the whole drivetrain for.

 

Any ideas on the compression issue? Can a set of open chamber heads and some thicker head gaskets really drop the compression by 2 points? Seems like a bit more than you'd expect, but I guess the open chamber heads really are that much different. Just want to make sure before I spend the money, you know?

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Liberty's Gears did my trans and you can go to their site for trans info. Mine was around $4000 with shipping. I would take Crazy Davey's lead on the open chamber heads.

Before I sink money into heads, I just want to make sure they will solve the fuel issue, as I would hate to spend the time/money on them, only to find out that I'm still in race gas territory, and it won't run on pump gas.

 

Dropping the compression like that, would I need to replace the carb as well? It has a Holley 750 double pump carb on it now, would that be too much after dropping the compression to 10.5:1? It would need re-jetted obviously, but would it be too much carb for the engine at that point?

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Do you know what the casting number of the current heads are? It would be good to know to determine the approximate CCs of the chamber. Were the chambers CCed during the build? Do you have the piston part number? This info would help to determine final compression.

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Hey Nick, I was under the impression you didn't want to sell the motor, so if it would just be sitting and doing nothing, I thought it might be better to rebuild it. I think you could make a nice motor and replace your torque converter for $3500, and you could sell some of the parts you pull from the motor.

 

Open chamber heads will drop the compression and solve some of your gas problems. If you do it, make sure you check the piston to head clearance. I remember doing that to a 396 once upon a time and the dome of the piston was just catching an edge of the combustion chamber. I have a feeling that band aids like a head swap aren't going to make you happy. That engine and drive train were designed for racing, not cruising or gas milage.

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Do you know what the casting number of the current heads are? It would be good to know to determine the approximate CCs of the chamber. Were the chambers CCed during the build? Do you have the piston part number? This info would help to determine final compression.

 

I'm going to look through my records and see if the head specs are in there. I'll also grab the cam card, and see if I can find out what pistons are in it. I was trying to figure out the final CR last night, and I just don't have enough of the information to figure it out. Are the casting numbers under the valve covers? Or are they elsewhere on the heads? I just want to know if I need to pull the covers to figure out what they are.

 

Originally Posted By: ripleydale
Hey Nick, I was under the impression you didn't want to sell the motor, so if it would just be sitting and doing nothing, I thought it might be better to rebuild it. I think you could make a nice motor and replace your torque converter for $3500, and you could sell some of the parts you pull from the motor.

 

Open chamber heads will drop the compression and solve some of your gas problems. If you do it, make sure you check the piston to head clearance. I remember doing that to a 396 once upon a time and the dome of the piston was just catching an edge of the combustion chamber. I have a feeling that band aids like a head swap aren't going to make you happy. That engine and drive train were designed for racing, not cruising or gas milage.

 

I agree, which is why mileage isn't my primary concern. Well, it is, and it isn't. I want better gas mileage, but only because it costs me so much to drive the car. If I could get around 10-12mpg on 93 octane, I'd be happy. As the car sits, it costs FAR too much to drive. After running the numbers, it comes out to $3.83/mile just in fuel costs alone, assuming the current price of $6.99/gallon for 110 Leaded fuel, and the cost to drive 50 miles each way in my daily to purchase fuel. Add to that the fact that a FULL 19 gallon tank of fuel in the Monte Carlo will only get me 38 miles during city driving, and it's a ridiculously impractical car.

 

At 10mpg on 93 octane no-lead, which is currently $3.89/gallon, it would only cost me $73.91 to fill the tank, and I'd have a range of 190 miles/tank. It's a no-brainer.

 

Not to mention, from what I've read, open-chamber heads are MUCH more free-flowing than the closed chambers that are on the car. My only objective is to make the car run on pump gas, any increase in fuel economy is merely a bonus. At 2MPG, I'll still drive it to shows, cruise around town when I'm at home, and enjoy the car, but at 10mpg, I'll do the same, further away from the garage. haha

 

 

And I will admit, I have a lead foot. It's not just going to be "cruising" all the time, I'll take it to the strip to see what she can do, go on "spirited" drives, etc., but by and large, I simply want to be able to enjoy the car.

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Cam Specs are (posting as shown on cam card)

Lift: Intake @ Cam: .3334 @ Valve: 567

Lift: Exhaust @ Cam: .3468 @ Valve: 590

Rocker Arm Ratio: 1.70

Advertised Duration @ .0136 Tappet Lift: Intake: 314 Exhaust: 324

 

It's a Crane Cams CC-314-2. The card describes the cam as: ROUGH IDLE, MODERATE PERFORMANCE USAGE, GOOD MID-RANGE H.P.

 

I'm not sure what the actual CR is, Dad always referred to the pistons as "12.5:1 Pistons", so I'm sure that is just the static compression ratio. I'm probably going to try to take it to a tuner to have everything dialed in, and find out what kind of fuel was required. I've been told 105 is the lowest I could safely run in the car, but honestly, I really have no idea how accurate that statement was. It may already be able to handle 93 No-Lead, but I won't know unless I pay someone to figure the engine out.

 

I'll post the head casting #'s when I go home a week from Tuesday. I'll likely be tossing another $50 worth of Turbo Blue in it just to get it moving around the driveway again, get the shift linkage adjusted, and start reassembling the engine compartment.

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The good thing about using what you already have as a base is that everything fits and you won't be hit with tons of hidden costs. Changing motors means changing exhaust, pulleys, brackets, mounts, fuel delivery (for an LS), etc.

 

Maybe consider aluminum open chamber heads with a compression of 10.5 - I have 10.6 and run 93 octane no problem. You need to get the part number of the pistons, with the cc of the dome, and plug it into the compression calculator and see what your C/R is with a 116 or 119 cc head.

 

Open chamber heads, a dual plane intake, 750 carb, 2200 converter, and a 3.23 gear would be a cost effective solution. That mechanical cam would need to be toned down, too. A more street friendly hydraulic would fit the bill.You would still be able to roast the tires at will.

 

Or, keep the rear gear (what is it?) and the TH400, but add a gear venders overdrive. Not cheap, but you will save the cost of a gear swap.

 

You may have better luck selling your stuff while its on the car in running condition.

 

Good Luck!

Mike

 

 

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Well, I went out to fire the car up today, put a new battery and cables in it, and got her to fire up without doing anything but cranking and pumping the gas pedal a few times.

 

Bad news: Passenger side header primary on cylinder 3 (or 2, not sure which side is #1) has a rust hole in it about the size of a dime. Time for new headers. I'll get them ordered after new tires go on, I found some hooker full-length ceramic coated headers for $400 (same as what's on the car, but coated rather than uncoated). Need a new battery tray also, can't find mine. Found a new stamped tray, with hold down, tray support bracket, and bolts for $75. Probably get that ordered too.

 

Also, I mentioned before in another thread that I needed a new left quarter glass, as someone broke mine out. . . Well, I popped open the trunk, and what do you know, there's a full set of factory glass at the bottom of the pile of body trim and moldings! I already had the glass!

 

Heading back home this morning, should have a few days next week or the week after to continue parting out my Firebird, and I'll make some progress on the Monte. Starting to get excited!

 

 

Also, I had a guy offer me a set of ported oval-port iron heads for $300, he says they have larger valves than stock, and are ready to bolt on. I'm waiting on the specs, but is there any reason why I should shy away from iron heads, aside from the weight?

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I like the idea of the gear vendors overdrive, essentially turning the 3 speed TH40 into a six speed with .78 overdrive ratio. . .

 

Hard pill to swallow though, that's almost half what I paid for the car. Worth considering though, and I will look into it.

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Nick - the drawbacks to iron heads is the weight and detonation. If you truly have 12.5 pistons, not sure you can throw on the iron heads and not ping. You will have to do the math. Aluminum heads will allow you almost a full point higher compression, without pinging - so you would be able to keep your bottom end.

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