'72 Oldsmobile Cutlass Supreme

Let's hear all the gory details about your car and how it became alternative fuelled.
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Helmet
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Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

'72 Oldsmobile Cutlass Supreme

Post by Helmet » Sun Jan 14, 2007 3:00 pm

Hi, my name is Willem and I am from the Netherlands.

Last year I bought a Cutlass, its pretty much a weekend cruiser.

Currently, it has a 455 Big Block Olds from a '71 Toronado in it. It can run on both regular gas and LPG.
The carb is a Holley, the mixer is an Impco 300 50/70. It has flowtech headers, followed by Cherry Bomb mufflers (yikes :shock: ).

For some reason, I want to make it faster and handle better. :?:
Sort of, or much like, Martin did too his Camaro. :wink:

I'm thinking of going with LPG and removing the gas parts. It's still a long way into the future, but a better exhaust system, ported heads, and a whole lot of other performance goodies should be fed by a big carb... or tho smaller carbs. Propane guy's 806 CFM flowing carb sounds nice, and other wise two Impco 425 will do the trick.

But I'm getting ahead of myself...

Some pics:

Image

The car, and below the hart of the beast:

Image


C3H8
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dual mixers

Post by C3H8 » Sat Jan 20, 2007 2:58 pm

Unless the motor is hopped up quite a bit and revs higher then normal a single 425 will handle it. I ran a 1977 GMC motorhome that used the Toronado engine and tranny with the 425. This thing weighs in a 12000 pounds. The power was great on it. You will find that once you go to straight fuel using the TB only on the quadrajet that the power will be significantly different.

Helmet
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Location: Holland, Europe

Post by Helmet » Sat Jan 20, 2007 4:08 pm

Well, currently its bone stock, first thing to do is preparing the car for the extra horsepower. Only then will I focus on the engine.

But yes, the plan is to hop it up: ported aluminum heads (~300 cfm flow @ .600 lift at the intake) large headers and a large exhaust system, 10.5 compression, lightweight reciprocating assembly and of course a camshaft to handle it all (there is more to it, but I don't think I would have to explain it to you).

This is just a weekend cruiser: I'd like to see how much horsepower one can make on LPG, but if it proves impractical, there is no need for me to go through with it.

Also (and this is where you'll see that I'm a rookie) is it not possible to mount the 425 straight on the intake manifold? I thought the mixer itself was capable of metering the fuel?

By the way, I don't have a Qjet, its a Holley, don't know which model.
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

Imperial73
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Post by Imperial73 » Sat Jan 20, 2007 8:30 pm

Willem, I also live in NL, feel free to give me a call 06 12 765 666 and I'll try to explain a few things in Dutch.

C3H8
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Toronado

Post by C3H8 » Fri Jan 26, 2007 1:26 am

Is the Holley a square bore (all 4 venturri the same size) or a spread bore (secondary ports larger then the primary). If its a square bore the 425 will bolt directly to the throttle body with no adaptors. The only mod required is to use a screw to actuate all the throttle plates together. Makes great power off the line and good flow at the higher end.

Helmet
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Location: Holland, Europe

Post by Helmet » Sat Jan 27, 2007 7:17 am

I don't know if its a square or spread bore, I never had it apart.
Like I said, its bonestock, with restrictive intake manifold, heads, mufflers etc.
Besides, the 300 isn't much smaller than the 425 (correct me if I'm wrong).
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

C3H8
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300 vs 425

Post by C3H8 » Thu Feb 01, 2007 1:44 am

You correct. A 300-50 series mixer puts out 428 CFM I believe and the 425 is good to 460 CFM. The difference is the restrictive nature of having to retain the carb with a 300. The added carb restricts the airflow since the air has to go through the mixer and still pass through the carb venturri after that. Sometimes this causes some power and economy losses. As long as your not flogging the heck out of it though it shouldn't be a problem. You can identify the square bore vs the spread bore by looking down the throat of the carb. On a spread bore the secondary throttle plates are about twice the size of the primary (front) throttle plates.

Helmet
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Joined: Sun Jan 14, 2007 11:25 am
Location: Holland, Europe

Post by Helmet » Thu Feb 01, 2007 10:36 am

Using my amazing deduction skills ( :lol: ), I have determined that I have a square bore Holley:
- the Toronado intake manifold is made for a spread bore Q-jet (bosses in the front are closer to each other than the bosses in the back), I can see a 1/2 inch or so adapter plate sandwiched in between the manifold and the carb. The top bosses on the adapter are the same distance apart, front and back.
- Looking at the left/driver side of the carb, I can see that the front and rear barrel are the same diameter.
Whew!
But at least I didn't have to take anything apart. :)

Right now, I'm babying it: I see now reason to put stress on the stock TH350 and the stock rear axle. I only romp on it when getting on a freeway (it puts a smile on my face).
The mileage I get is quite good for a big block: roughly 15 mpg, combined city and highway.
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

C3H8
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425

Post by C3H8 » Thu Feb 01, 2007 10:08 pm

Good news then. If you choose to go to a 425 it will bolt directly to your Holley throttle plate. The only mod you will have to do is put a small screw in the lever that actuates the secondary plates so that all the plates open together. You don't need any additional adaptors.

Frank
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Post by Frank » Thu Feb 01, 2007 10:49 pm

The secondary valves on my Quadrajet throttle body are progressive (OEM operation) and I haven't noticed any issues with this type of operation.

What would happen if you didn't put a screw in the lever that actuates the valves together?

franz
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throttles

Post by franz » Fri Feb 02, 2007 11:11 am

The Holley uses a vacuum secondary while the Q-jet uses a mechanical secondary linkage. When connecting a 425 to a Holley baseplate, the vacuum secondary linkage is removed, requiring an easy fix on the drivers side linkage to make all 4bbls open at once. The progressive nature of the Q-jet is easier on low throttle openings as all 4 opening at once can be rather exciting if one is not prepared for it.
On a petrol engine, you really need the progressive throttle to prevent severe hesitation, but on a vapor fuel engine, there is no problem with fuel dropout on rapid throttle action.

Franz

Helmet
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Re: 425

Post by Helmet » Mon Feb 05, 2007 2:12 pm

C3H8 wrote:Good news then. If you choose to go to a 425 it will bolt directly to your Holley throttle plate. The only mod you will have to do is put a small screw in the lever that actuates the secondary plates so that all the plates open together. You don't need any additional adaptors.
Hmm, I don't think its necessary to put on a 425. I have 28 inch rear tires, and a 2.93 rear gear. I don't have a tach, so I can't see what RPM it really turns, but I can calculate what it should turn.
In second gear at 60 mph, it makes 3200 RPM. For a 455 CID engine, at 3200 RPM and .85 VE, it only needs ~ 360 CFM.

Throttle response is also excellent: stabbing the throttle for a split second results in a squealing rear right tire (not a small tire, either).

So, I'm pretty sure my Impco 300 is more than adequate :wink:
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

stroker
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Be carefull you do not run to lean

Post by stroker » Mon Feb 19, 2007 1:32 pm

Greetings Please read the following, I have posted this, not to but there is some valuable info, If you run to lean you will toast your motor.
Hi, saw your ride on a propane forum and had to talk with someone that might have gone though the same type of high performance teething pains that I am now going through. First I built a 4x4 1 ton camper van and then converted to propane, this was 5 years ago. The motor was a 350 30 over 250 cam 1.5 rockers 9.5 compression heads mildly ported and of course balanced. I was running the largest Vaille vaporizer made, along with a 650 cfm Tecnocarb mixer. This system gave me 50,000 miles of trouble free service and I do mean trouble free, -20 +35 C easy to start, plugs were changed at 35.000 miles and was not necessary, went through air care without ever having any problems, however being a bit of a gear head wanted more. So I did my research and designed what I think is the correct motor for my application. 383 Stroker with 11.2 compression X4254H cam with 1.6 roller rockers, lift corrected to .477 / .492 / RHS Vortec heads ported to flow 260 in 184 ex at .500 lift, Along with the this I went to 0 dec height, used Beehive springs, total seal gapless rings. Now you have an idea I might have a bit of knowledge, I will tell you about the dyno and road test.

The builders suggested that I break the engine in on the dyno on gas, this produced 416 HP at 4900 RPM & 494.9 TQ at 3800 RPM however 477 TQ AT 3000 RPM. Now we hooked up the aforementioned propane system and were building good power until 3600 RPM and then just like too small a fuel pump the engine leaned out and lost power. I had a very good idea this was going to happen, so contacted Tecnocarb, drove out and picked up a new Vaporizer and Mixer. Once installed and back on the dyno the engine produced 386 HP and 452 TQ, I was happy with the results and installed in my van. Another thing I should mention is this engine developed 19.5 inches manifold vacuum at 900 RPM. The van was already running headers and mandrel bent 2.5 stainless exhausts, so just a straight forward install. I have since drove this vehicle 2000 miles and it is hard to start, vaporizer freezes at plus three C, will not idle, as in you can set idle at 900 RPM and turn engine off restart and now the rpm is 1600. I realize this sounds like a vacuum leak but I disconnected trans and brake vacuum hoses and but a plug in manifold, removed mixer installed new gasket and there was no change in the results The only thing this system does well is go fast, under full throttle pulls strong, no hesitation from stop, however if I accelerate hard and slow down to 10 miles an hour engine tries to die and I have to feather gas peddle so engine does not die. I talk with another propane guy that told me to run my old vaporizer on the front of my mixer and run the new tecnocarb vaporizer on the rear and turn the idle screw all the way in. This is not what I want to do; I will go back to my old motor and use the new motor with an injection system on a vintage ride before I do this. I am beginning to wonder whether I have a faulty vaporizer or if it needs to be electronically controlled. Okay, do you have any ideas to help steer another propane guy in a new direction to sort out this problem.

Thank You in advance for any and all thoughts
Sincerely Gerry Vass
thehook@shaw.ca

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