mffi115

Hi! New to the forum and this is my first thread. I have a motorless '73 vette project car, original big block. I have the original 4 spd and bell housing.

I've been following threads about LS conversions on the corvette forum and am leaning strongly to an LS conversion.

I have a chance to buy an LS1 w/ECM, brackets and accessories minus AC for $3,500.00. It is on EBay, but I've talked to the owner and he's close enough for me to pick it up. He claims 430 HP with apprx 100 hrs on the motor. It has a truck intake and beefed up bottom end for a supercharger that he never put on.

Any opinions / advice on buying this motor and the price???

My vette has a mechanical tach so I won't be able to run it. How do guys who do these conversions run tachs?

Thanks in advance.

Carl

67rsss

iTrader: (4)

Do you mean a mechanical speedometer? I haven't run accross a mechanical tachometer, so I am not sure how you would adapt to it, but there is a way if you are creative. The LS1 will not bolt right up to your 4 speed, you may want to consider swapping to a T56. What is the motor out of? If he is claiming hours instead of miles, has this already been a swap motor? What is beefed up in the short block? Is the block aluminum (LS) or Iron (LQ). That truck intake would have me concerned that this isn't an LS1, but rather an LQ motor. There are a couple guys on here that have lived through the swap on the 70's vette, so it can be done. THere are a couple of threads in the stickies that you would want to read, but without more info and picks I would look at passing on the motor. $3500 for an engine without a trans is a bit high unless there is documentation to support work to make it worth it. Forged internals might justify it, but you will still need to go to the car intake, you are not getting the truck intake to clear in a Vette. Pics, year, work done to it, and milage (and how it was used) would be helpful.

Rodder

iTrader: (2)

All 'vettes had a cable-driven mechanical tach from day 1 until the end of the 1975 model year. Wonder if he could use a Cable-X to drive it?

mffi115

He has receipts for the bottom end work. He says he spent $2,600 on it. The motor was in a dune buggy. I agree from the prices I've seen that it's high.

What's a Cable-X set up? I assumed that since Gen II SBC and later don't run a "traditional" distro, that I'd have to run a separate electronic tach.

mffi115

[QUOTE=67rsss]Do you mean a mechanical speedometer? I haven't run accross a mechanical tachometer,

The mech tach had a cable that attached to the side of the distro and ran to the back of the tach. I assume that I would have to mount and run an after market electronic tach. How do I hook up the electronic tach to the LS motor?

67rsss

iTrader: (4)

The PCM outputs a tach signal at 2pulses per revolution, which is the 4cyl setting on an aftermarket tach. You can also have the pulse output changed int he computer to be the 4 ppr used by most 8cyl tachs. Dakota digital makes a little box that will do the conversion also. I have never worked on vette's so that is kinda neat to learn. I will look for one. I am thinking that if you could adapt the cable for it, the cable X may work out. Using the 2ppr, you would need to expirement with the Cable-X and adapt the fitting for the tach. Does the tach use a speddo type cable? If so, this would be a pretty cool solution!

Is the computer and harness already setup to run this engine the way you plan on using it? If so, that is a great amount of time and cost saved, and the price starts to look much better. You will really want to look at the issues with that intake though, You would need an awful big cowl hood to clear it....

mffi115

(Does the tach use a speddo type cable? If so, this would be a pretty cool solution!)

I'll have to check when I get home this weekend. But, I don't think so

(Is the computer and harness already setup to run this engine the way you plan on using it? If so, that is a great amount of time and cost saved, and the price starts to look much better. You will really want to look at the issues with that intake though, You would need an awful big cowl hood to clear it....[/QUOTE])

I've decided to pass on this motor and wait 'til I get the car moved from AZ to CT this summer, settled into the new house, then start looking for a motor & tranny.

Novas Forever

The tach and speedo cables are the same except for length.

67rsss

iTrader: (4)

If that is the case, there is no reason why you couldn't set the Cable-X to do the job. You would definatley need to talk with the manufacturer about what setting to use, as the equation used to determine the switches doesn't cover this case, but there is no reason why it wouldn't work.

Figure you get two complete revolutions of the crank everytime your distributor makes one revolution. Also assume you get one pulse every time the distributor turns. That is a base of .5 ppr. That would mean (lets assume that everytime the distributor rotates, the cable makes one full rotation) that your tach is displaying a value twice what the distributor is turning. When the distributor shows 500rpm, the crank is going 1000rpm.

If we compare that ratio with the 2 pulses per revolution (of crank) output from the LS1 PCM, that means that the 'distributor' is rotating once for every pulse.

This means that your tach is actually looking for one turn of the cable for every two revolutions of the crank. What we are getting from the PCM is (pretend a pulse is a turn on the cable) two turns of the cable for every turn of the crank. This means four turns of the cable for every two revolutions of the crank (to go back to original wording). Therefore, if the engine is idling at 1000rpm (crank), putting out 2000 pulses per minute, you would want the stepper motor in the Cable-X to spin at 500rpm.

That means the cable-x needs to be a divide by 4. I don't know if it can do that (it appears to be set up for multiplication), but I think a quick call to Abbott would find out. You could always adapt the number of pulses as well either in the PCM or using an adapter box like the Dakota Digital tach adapter. Using this method to mutliply or divide the ppr signal from the PCM will add a little delay, but should remain accurate, assuming whatever you use to drive the cbale to the tach is accurate.

Based on this thinking, I do think you could find a way to use a Cable-X to run your mechanical tach.

mffi115

Thanks 67rsss. That's great info. It will be a while before I get started on this project, but I'm looking forward to the challenge and will be coming back with more questions. BTW, I've gotten some good advice on the Corvette Forum for the T-56 shifter mods and motor mount and tranny adapter brackets.

mffi115

Thanks, Novas Forever. It is starting to sound easy...and it does scare me!

Novas Forever

I understand

joelvette

iTrader: (11)

amazing how 1 little statement about a mechanical tach can show our age. those who don't know and those who do. sometimes i miss the old days when you could sit on the rad support with your feet on the ground to troubleshoot only 2 or 3 wires, 1 or 2 vacumn lines, etc. nowadays we need a computer to control the same old gas, air, and spark.

Rodder

iTrader: (2)

Nope, it doesn't show your age, just what you've worked on. I'm betting 67rsss is older than me

67rsss

iTrader: (4)

Ah, I have seen some pics on your site Rodder, and I bet we are pretty close in age. I just never cared for vettes until the C5 showed up. This last few years, we both have started to appreciate cars we never would have given a second thought in our 20's. I am no Ford or Mopar fan, but have learned to appreciate several of them for what they are. Starting to find some of the history of these cars fascinating, and the next thing you know, even Ramblers can be kinda cool.

Rodder

iTrader: (2)

I've always liked Mustangs, I just don't like working on 'em . Still don't have much use for a Mopar unless it has a Cummins under the hood. I was mostly into rice until my 2nd year of college when I built my first small-block Chevy.

67rsss

iTrader: (4)

Never believed in rice, and I drive an 07 LBZ Duramax. More power, and better manners. The Allison sure runs slick. I absolutely love it. The power is incredible, but I really need to learn a lot more about diesels before the warranty expires. Never worked on them, and only sorta understand how they work. Mustangs never did it for me, and there are several Mopars I appreciate now that I still don't want to work on. The Daytona and the 'bird really are the begginings of overt aerodynamic influence in long distance racing, and I have to respect that. The 429 Cobra Jet really was a beast, and the O-rings used to put the heads on were way ahead of their time. There is a 62 Galaxy driven locally, and even though it isn't my taste, it makes me happy to know someone is taking care of it. I guess I have grown more sentimental, and less controversial over the years, but I really want my grandkids to get a chance to see some of these cars in person, even the ones I don't like. When was the last time you saw a Cord? How about a Kaiser Fraiser? My kids have never seen a 58 super chief or even a 54 Chevy. There are a lot of cars dissapearing forever...

Built up my first small block in high school. Have worked on a few of them over the years, though I have never had the opportunity to work on an LT1/LT4. While I was in the corps, I earned a bit of beer working on cars, and even built 3 Ford 390's during that time and modified a Ford AOD. The first one didn't go as planned, the distributor is a 180 degrees wrong, and it took me the better part of a weekend to figure out why that beast wouldn't fire. I have rebuilt and tuned many Quadrajets, and still feel they are the best running factory carb out there. Once you have it working, it stays working. I have never owned a 427, but always have an eye out for a reasonable SS427 (Z24) 67 or 68 Impala. I have never, ever worked on a car with a mechanical tach, but I am going to keep my eye out for one. I would really like to see how that is setup.

Rodder,
How did that run on natural gas? Did you get a decent torque curve? Detonation issues? How high could you have pushed the CR? That is a pretty neat project.

Rodder

iTrader: (2)

I've had Mustangs as my daily drivers since '97... requirements were 2+2, RWD, V8, manual trans with overdrive, under $30k, and didn't look like a Geo Storm. Only car that fit was the 'stang .

I started out building junking lawnmower engines, then old Honda motorcycles, and then my dad gave me his dead '79 RX7 when I was 15 and paid for parts to rebuild it. Went through a couple of other rice burners in highschool, and eventually got sick of bending suspension components anytime I looked at a pothole wrong and got a new Jeep Wrangler--biggest pile of ever owned.

We never got good dyno numbers from the NGV truck. The only chassis dyno we had access to was rated for 250HP. The #1 purpose of the competition (and 1/2 of the total points) was for emissions, so we made a lot of compromises for emissions and then tried to pickup power any way we could outside of FTP75 conditions. The Vortech didn't start making boost until about 3000 rpm, the big blower cam didn't squat below 3000 (but zero overlap was good for HC and NOx), the manifold liked to run above 2500, and the torque convertor was stalling about 1600 rpm. It didn't have enough torque to spin the tires off the line, but roasted them right as the tach swung past 3000. By 3500rpm, the air valve on the CV-style natural gas carb was slammed wide open and from there up it got lean--26:1 by 6000rpm. Fortunately it's the rich side of stoich where you burn pistons with natural gas. It tipped the scales at a little over 5000lbs and ran the 1/4 a little over two seconds faster than stock/gasoline, and a full second faster than anyone else in the competition. The only other truck that was faster than stock was Texas Tech's--they were running a 305 stroked to 334, stock heads, smaller cam, 10.5:1, and a B&M set up for 5psi. We had a prototype Banks Dynafact in it (predecessor to the GTech) and I saw it read 275HP at 5000rpm (at about 22:1 AFR). We didn't have any detonation issues when I was there... we were consistently getting 120-125 octane natural gas from the local gas company, and it was 123 the day I tuned the spark maps to be 2deg before tripping the knock sensor. I heard later that they got some bad gas (~115 octane) and blew the headgaskets. I don't remember exactly how much timing I was running, but I do remember having to set the distributor at 20deg instead of 0 (because I was topping out the advance in the ECM at low-MAP high-RPM). More static CR (or more boost) and less timing would have made more power. There were a couple of schools with milder heads/cam running 14.5:1 normally aspirated, but I can't remember if any of them passed NOx emissions.

It would have been interesting to see what it would have done with dual carbs and 3500 stall convertor. Unfortunately never got to try... I got kicked out of UT for grades a few weeks after the competition, and the next generation of students converted it back to a stock gasoline engine and sold off all of the hi perf parts.

Novas Forever

While working on my neighbors '67 Vette he had me fix his factory tach that was not working. I unscrewed the cable from the side of the distributor (looked like a speedo cable) and the gear that drove the tach was spripped. Went to the dealer got a repair part. Took the old cast iron distributor apart and the tach drive was a lot like a mechanical speedo drive. To check the tach itself I just spun the cable and the tach needle jumped. The mechanical tach is just like a mechanical speedo only it measures engine revolutions. Electronics and computers that fire the plugs will banish the mechanical tachs .

mffi115

I asked the same question on the price of the LS2 in the corvette forum and some guy contacted me that he has a LS6 long block, minus oil pan, w/70k miles and Thunder Racing Mild cam for around $1,800. Fair price?

Will an LSx bolt to a '73 bell housing and 4spd? I might use the stock tranny until I can buy/make mods for a T-56.