desperate help needed for 1971 Avanti II

[Quicksilver]

Here we go. I bought this car (RQ1634) in december 21. What with one thing and another, it finally got to my mechanic today.

Turns out it needs a lot more than i was led to believe.

Rear brakes, bushings, power steering pump, a/c compressor, wiring, etc. The biggest thing is the motor. the 305 in it is trash, and most likely the auto trans as well.

I had grandiose plans to fit an LS engine ad a 6L80 transmission, but according tho my mechanic, the motor won't fit. Not without a complete custom set of headers, mounts, etc. and the transmission tunnel is tight, so we need a smaller transmission.

So what have you all done? Has anyone done an LS, or later fuel injected chevy motor, and what difficulties did you encounter?

Am i best off just to find a small block 350 chevy and put an aftermarket Holly fuel injection unit on it?

And suggestions for a transmission?




 

[Gunslinger]

LS engines have been fitted but I don’t what mods had to be done.  Hopefully someone here who has done that will fill you in.

When I had a ‘70 Avanti II I bought a crate engine…350/330 hp version.  For my style of driving (I’m not 25 anymore)…I think it was overkill.  The 290hp crate engine would have done just fine plus it’s a regular fuel engine where the 330hp crate engine was premium fuel.  With a 700R4 transmission it could spin the tires in any gear.  
 

There was minor issue with the 700R4…the transmission support had to be relocated somewhat and a new neutral safety switch/backup switch assembly had to be fabricated.  No big deal but was necessary.  You could go with converting it to a manual 5- or 6-speed transmission.  I’m kind of sorry I didn’t do that but it would have cost more to do it the I would want.

A 200R4 engine would actually have been a better choice…a better spread of gears and could have been built to 700R4 strength…plus being smaller.

I also went with an aluminum driveshaft…less rotating mass and un sprung weight.  I also used lightweight composite leaf springs for less weight.

I went with an Edelbrock EFI which was trouble-free and performed superbly.  Sticking with a carburetor would have certainly cost much less but I wanted EFI.

If I had to do it again I would gone with electric power steering to get rid of all the hydraulics and hoses hanging down under the front but aftermarket electric power steering was just hitting the market at the time and I didn’t care to be a test case using it.

Overall…the best I can tell is to follow the KISS principle…Keep It Simple, Stupid.  Trying to do too much too fast can be counterproductive and expensive.  I would suggest starting with the brake system and suspension first.  Make sure the hog troughs are solid as replacing those eats up budget very fast.  Then the drive train and cooling system.  Interior and body last.

Make a plan and stick to it.  You can get into the weeds faster than you think with mission creep with any car but more so with an Avanti.

Rebuilding an Avanti is an act of love…not of reason.  

 

 

Edited April 2, 2024 by Gunslinger

[Quicksilver]

Thank you. the body, frame, and hog troughs are fine. no holes, surface rust only. frnot end is rebuilt, the engine is the big problem

[ronmanfredi]

350 with a 200R4.  If you get a high horsepower 350 then you should get a built 200R4 for it.

[Murder]

On 4/3/2024 at 12:47 PM, ronmanfredi said:

350 with a 200R4.  If you get a high horsepower 350 then you should get a built 200R4 for it.

What he said

To elaborate:

350 crate motor - pick your horsepower / price.

2004R because you want a 4 speed automatic instead of the oem 3 speed. 2004R instead of 700R4 because it is narrower and has better gear ratios. 

Edited April 8, 2024 by Murder

[1963r2]

LS motors have been installed. I'm going to attempt one soonish.

You will need motor mounts to place the engine in the right location . I believe people have used hooker headers (rear dump) to clear the steering box and you need a rear hump sump which Holley and others do.

I have heard that the gearbox fit can be an issue for some but not others so I'm not sure what to do there yet but I'm going to try a 4L60e.

If you have Facebook (Avanti swap page) there is a fellow selling his Ls swapped Avanti. Its rough looking but he might have some answers.

Pb

[Quicksilver]

On 4/8/2024 at 6:40 PM, 1963r2 said:

LS motors have been installed. I'm going to attempt one soonish.

You will need motor mounts to place the engine in the right location . I believe people have used hooker headers (rear dump) to clear the steering box and you need a rear hump sump which Holley and others do.

I have heard that the gearbox fit can be an issue for some but not others so I'm not sure what to do there yet but I'm going to try a 4L60e.

If you have Facebook (Avanti swap page) there is a fellow selling his Ls swapped Avanti. Its rough looking but he might have some answers.

Pb

good afternoon. did you ever get around to doing the LS conversion? How did it turn out

[1963r2]

Not yet, still working on my original car first. Hopefully I will get a chance soon. Have you made any progress?

[Zedman]

Hi Quicksilver- Interesting you say you have a 305 cid in there for that vintage of car.  BTW What transmission do you already have?   My slant on this is to ask a question about two things.... how much do you want to spend and is horsepower an issue...     If it's a horsepower issue, by all means follow the suggestions you've been given by the knowledgeable souls so far (up engine, OD transmissions, EFI etc).   I also promote the KISS principle- I'd wonder whether just rebuilding what you already have would be the route best travelled.  I have just rebuilt my 305 SBC and also the TH350C (lockup torque converter  trans) - it has cost me very little and is DONE. I even had the transmission test run on a dynomometer to check its operation after I rebuilt it. Thing is you ought to drive this Avanti- not spend a lifetime working on it

Just my humble opinion, mind...  🫡

 

[Randy Atkin]

I assume you know a '71 would have come from the factory with a 350 and 4 barrel Rochester Quadrajet carb.  The transmission was a Borg Warner 3 speed automatic, basically the same trans Studebaker used.

 

Edited January 10 by Randy Atkin

[Mark63Avanti]

On 4/2/2024 at 5:05 PM, Gunslinger said:

Rebuilding an Avanti is an act of love…not of reason.

A fella really should have this tattooed on his body, somewhere you can see it every day.  But if you fall in love with the Avanti (or Studebaker or any other car) then you're in for a treat.

[Quicksilver]

Ac previous owner put in the 305 from a Monte Carlo. The car still has the original automatic. With some health problems i've had we haven't really started on the car yet.

I was just offered a deal on an LS 6 litre with a 6l80 transmission, tested and running. It is actually cheaper than a number of 350's that i have found. It even comes with an adapted wiring harness.

However, paying attention to what you have all said, i will likely go with a built 350 and a 700R transmission, and top it off with a Holly Sniper fuel injection system.

Any advantage one way or the other between a 200R or a 700R?

[Gunslinger]

Go with a TH200R4 as it has a better spread of gears.  It can be built to take prodigious amount of power.  I had a TH700R4 in the ‘70 I owned and it was shifting into 2nd gear almost immediately and chirping the rear tires without trying to.  
 

Another thing to consider…think about getting an aluminum driveshaft as it reduces rotating mass and weight which is always worthwhile in an Avanti.  

[Zedman]

22 hours ago, Quicksilver said:

Ac previous owner put in the 305 from a Monte Carlo. The car still has the original automatic. With some health problems i've had we haven't really started on the car yet.

I was just offered a deal on an LS 6 litre with a 6l80 transmission, tested and running. It is actually cheaper than a number of 350's that i have found. It even comes with an adapted wiring harness.

However, paying attention to what you have all said, i will likely go with a built 350 and a 700R transmission, and top it off with a Holly Sniper fuel injection system.

Any advantage one way or the other between a 200R or a 700R?

Whilst I'm no expert on this subject, research into my TH350C led me across a number of sites... I believe you may need a device to substitute for the Computer Controlled Shifts/Torque Converter lockups with either of these transmissions. I have recollections of the 200r4 being a more convenient swap, and the 700R being able to take more abuse.  Food for thought.