Centrifugal supercharged Avanti II

[CaffeineRacer]

Just curious if anyone has done it. I've been playing around with the idea of fitting up a newer Paxton supercharger, but then painting it orange and using a reproduction carb bonnet to sort of make a resto-mod homage R2. I've been trying to figure out the best arrangement for accessories since I want to keep my AC unlike the original R2s.

Anyway if you done it and have pictures please post. Otherwise please speculate of how possible this might be and what would be involved.

[Paul K.]

There was one Avanti II a 68 or 69 model that had a supercharger. From what I have read it was modified by Altman at the Avanti II factory and its owner was the Ashtabula Fiberglass Co. president. I have a vintage road test of this car and its pretty fast for the its time.

[drat]

I would be interested in this info too for my 69 RQA

[Gunslinger]

It can certainly be done. Vortech makes a supercharger kit especially for the small block Chevy. They recommend an engine with a 9.0:1 compression ratio for best results.

Paxton does make modern superchargers but I believe they're mostly for Ford applications. That doesn't mean you can't use one on the GM engine but it will likely take a lot of fabrication.

Best of luck if you do it...and post lots of photos of the entire project from start to finish.

[drat]

Weighing my options. Single turbo and Cam? Just cam? Engine swap? I dunno. Thinking about best bang for buck, fuel mileage, reliability are all things I'm juggling in my mind

.

. It plenty fast, but I want a little more. I'd like to be around 400. But I wouldn't scoff at 450-500hp I have already done 202 heads, edelbrock manifold and 650 carb, Sanderson huggers, exhaust with flow masters and hei. It certainly made a difference but I'm a little greedy.

[drat]

Here's a question. Was the 69 avanti using the L-46? I may be close to 400hp than I thought

[CaffeineRacer]

My understanding is that the L-46 was an option on 69 corvettes and therefore wouldn't have been the engine put in Avantis that year. They usually used the base model corvette engines for a given year. Also didn't the L-46 engines come from the factory with 202 heads already? What is the block casting number?

[CaffeineRacer]

You're right that Vortech makes a kit for chevy small blocks so that is certainly a possibility. This is really just a thought exercise at this point, but I would like to do this in the future when life permits.

Does anyone know if there was a different between the R1 and R2 carbs to accommodate the pressurized system from the supercharger? Was there a system the adjusted fuel pressure in a boost dependent fashion?

The biggest fabrication hurdle would be the brackets for the supercharger. I think the way to do it would be to move the alternator down to the lower passenger side of the block sort of where the smog pump was originally. This way the PS and AC can stay where they are.

On R2s that have been retrofitted with AC, where do they put the compressor?

[Gunslinger]

There was definitely a difference between R1 and R2 carburetors. The R2 carb was sealed and some other internal differences. The R3 carb didn't have to be sealed since it was in an enclosure box so internal and external pressures balanced. The R2 used a different fuel pump as well.

Holley makes several carbs specifically for blow-through supercharging. You can check their website for the model numbers. I've been told that Edelbrock marine carbs can be used for supercharging since they're sealed but I've no idea how accurate that is.

I know that Avanti II's have been equipped by owners with a supercharger but have not actually seen one. Hopefully someone with more experience can fill you in on how it was done. I tend to think eliminating the a/c from the car helps simplify things considerably.

When my '70 was being rebuilt I considered adding the Vortech kit...the 350HO I purchased is an ideal engine for it...but decided that fuel injection was a better way to go for my purposes. I also didn't know what modifications to the engine bay may have had to be made, if any.

If you want power, it would probably be easier to either build your engine up or install a crate engine at whatever power level you want. I know it doesn't carry the panache of a blower but would solve a lot if potential issues.

[CaffeineRacer]

Gunslinger, good to know about the carbs. I figured there had to be differences between them. I like the way the carb bonnet looks compared to the box, but it would certainly simplify things in terms of the carb. Moving to Holley efi system with the blower might be another option if I decided I was really set on the bonnet.

I just built a new engine for the car and it makes plenty of useable power. This is more about making a "resto-mod" avanti II that pays homage to the original R2s. When I did the engine I followed all the original studebaker paint scheme with the semi-gloss black motor, orange/red fan, and chrome bits. I'd never want to seriously modify an original Avanti R2 as they are a true piece of history, but an Avanti II is more of a modified vehicle to begin with so I see less of a problem as long as the design remains the same. Plus the chevy power plant is much more user friendly. So adding the blower is not about adding power (though that's certainly a plus) or any other real practical reasons. Just for kicks.

Hopefully someone who has done this will chime in.

As for the AC, it's hot in Texas so that will definitely be staying.

[Devildog]

This is a good idea, I have thought of doing something similar. On my 75 with the 400 SBC, I installed a PowerJection III EFI which functions nice. I would like to go to a bonnet on the EFI throttle body and use an induction tube with filter mounted for cool air source. Is there aftermarket bonnet for the EFI/carb body ???

Since these 400 SBC are only 8.5 CR, they are a good candidate for supercharging. I have not run the calculation, but with a mild 3-5 psi boost, the engine would probably increase from 200 hp/330 ft lb to 300 hp/400 ft lb. If don't go crazy with psi, it should not be big bracket to mount a Paxton blower. I replaced the old A6 A/C compressor with a modern Sanden, that bracket is tons smaller that the original. I would think a Paxton operating at a mild 3 psi would not be much more torque on a mounting bracket.

A low psi Paxton with the PJ3 EFI should be reliable and have good driveability. The 400 SBC with EFI and 700 R4 tranny performs well; however, a Paxton would add a wow factor and yield lots of style point while bench racing.

We need to do this.

Joe

[Devildog]

You're right that Vortech makes a kit for chevy small blocks so that is certainly a possibility. This is really just a thought exercise at this point, but I would like to do this in the future when life permits.

Does anyone know if there was a different between the R1 and R2 carbs to accommodate the pressurized system from the supercharger? Was there a system the adjusted fuel pressure in a boost dependent fashion?

The biggest fabrication hurdle would be the brackets for the supercharger. I think the way to do it would be to move the alternator down to the lower passenger side of the block sort of where the smog pump was originally. This way the PS and AC can stay where they are.

On R2s that have been retrofitted with AC, where do they put the compressor?

I believe they mount the A/C compressor top-center on R2 289s

Joe

[drat]

caffeine racer, in talking to my dad I figured out the heads that were on it when I was given it by him a few years ago aren't the stock heads.

My mom blew the engine in 77. It sat for 20 years? He paid a local shop to rebuild it ground up... Looks like they just put 194 ? donor heads on it instead of rebuilding the stockers. So Without a build sheet I guess I don't know what heads it came with. I thought the engine block code comes back a 1968 crate motor (replacement corvette motor) and not an actual corvette motor. But I could be wrong. Lemme double check the number.

[drat]

Well having a hard time reading the number. It's in front of the passenger head under my AC pulleys right?... I'm nursing a broken hand after having surgery on it. So the combination of old peeling paint oil, and pain killers isn't helping... Here's my best guess

240 5 1 V08308 B0

[CaffeineRacer]

Devildog (Joe), do you know what sensors the efi system you have on the car uses? Depending on things there might be some adjustments made for something like a MAP sensor so the positive pressure doesn't make things out of whack. I wonder how tuneable those efi systems are as I'm sure a custom tune would be required.

The 8.5:1 CR is perfect for a SC and you could probably safely run 5-8#s boost and not worry about hurting anything thing. 3#s might be a little on the low side. I believe the original R2 engines they ran about 5#s of boost.

Right now I'm trying to mock up (on paper) how I might do this with my carb as I think the pressurized box method might be easier as its just designing some mechanical linkages rather than the bonnet method which would require some fancy carb modifications to make sure everything was seeing the correct relative pressure. I'd love to keep my Q-jet for this, but I can always fall back on one of these off the shelf blow-through carbs.

I'm going to email Paxton and see if I can get some dimensions of the supercharger so I can start figuring how things might fit in that engine bay.

[Devildog]

Devildog (Joe), do you know what sensors the efi system you have on the car uses? Depending on things there might be some adjustments made for something like a MAP sensor so the positive pressure doesn't make things out of whack. I wonder how tuneable those efi systems are as I'm sure a custom tune would be required.

The 8.5:1 CR is perfect for a SC and you could probably safely run 5-8#s boost and not worry about hurting anything thing. 3#s might be a little on the low side. I believe the original R2 engines they ran about 5#s of boost.

Right now I'm trying to mock up (on paper) how I might do this with my carb as I think the pressurized box method might be easier as its just designing some mechanical linkages rather than the bonnet method which would require some fancy carb modifications to make sure everything was seeing the correct relative pressure. I'd love to keep my Q-jet for this, but I can always fall back on one of these off the shelf blow-through carbs.

I'm going to email Paxton and see if I can get some dimensions of the supercharger so I can start figuring how things might fit in that engine bay.

The PJ3 EFI is set-up to do turbo/supercharge engines in the software. It is a quite easy point and click input software. The mass flow sensor is built in the throttle body so mass of incoming air is computed plus O2 ratio on the feed back loop from exhaust.

I have found the EFI software is smarter than I am, just set the broad parameters and it is closed loop feedback and will 'learn' on its own better than me tinkering with it. just set the the A/F ratio and it w do the rest.

Joe

[CaffeineRacer]

Twin Paxton supercharger 1963 Avanti. http://www.paxtonauto.com/article.php?id=5

Was this factory? If so awesome!

[CaffeineRacer]

Devil Dog, does the distributor on your Avanti have a vacuum advance? If so what is the vacuum source for this advance and will it be effected by the supercharger?

[Avanti83]

JMHO but why use EFI if the computer is not controlling the timing, particularly in a blown engine? If the EFI can't handle that important criteria then it's the wrong EFI.

[CaffeineRacer]

I think one of the big reasons is cost. Those kits cost enough, then add in a brand new computer controlled distributor and the installation of a knock sensor and you've just added another $500 to the price tag.

I agree that having the computer control the timing is nice, but there are still some nice benefits of having fuel injection. Car starts quick on hot days, cold days, and everything in between, fuel mileage goes up, as does engine efficiency and likely horsepower.

I have a CCC quadrajet on mine and I thinks its the bees knees when it comes to street car carburetors. I get great mileage and performance when I need it. These systems also controlled the timing although the early system like in my car does not have a knock sensor so the computer really just has some preset timing advance curves based on engine temp, throttle, rpm, and O2 sensor input.

Edited September 26, 2014 by CaffeineRacer

[Devildog]

JMHO but why use EFI if the computer is not controlling the timing, particularly in a blown engine? If the EFI can't handle that important criteria then it's the wrong EFI.

These second and third generation throttle body add on EFI's do not control ignition timing (it is not designed to be a complete engine management system) you can buy the 4th generation EFI's that will interface with an electronic controlled ignition system.

Controlling ignition timing is nice, EFI to maximize A/F ratio is a much bigger bang for the buck (performance and economy).

If one wants to really do it right, probably for $15,000 buy aftermarket add-on DIGITAL ignition, EFI, etc. then your $9,000 Avanti will perform more like a ZO6 Corvette.

$2,000 EFI on my Avanti is fun and makes run a bit more dependably in Houston's hot weather. I actually like tuning the old carbs which work just fine, but stink and have hard vapor lock start occasionally. It is all just fun and the challenge of make old junk run

Joe

[Avanti83]

We'll agree to disagree. My 355 SBC in my 83 has a Holley Avenger EFI setup. With the carb/ vac. dissy setup it just wouldn't perform as well as it should throughout the RPM range even after numerous carb and timing changes. I bit the bullet and put on the Holley Avenger. It will use the small SBC HEI distributor (less than $75).

Right out of the box, it was much improved over the old system and still runs great.

I downloaded the timing and a/f curves and there is no way any standard (carb-Dissy) setup would control like the EFI does.

If I were to add a blower, the $500 (less on an SBC) would be cheap insurance on a $3000 blower system and unknown cost of the engine.

I guess I could spend $500+ on a dyno session but that would only let me know I was optimum at that time.

In my garage is a 2013 Impala that get 303 HP from 3.5 liter V6. It doesn't get there without timing control so it must be an improvement over previous technology. I understand that timing is only one factor in the engines performance but optimum performance depends on accurate timing control.

Not to be argumentative as I'm just an old guy that believes in the newer technology for maximum performance.

Bob

[CaffeineRacer]

Well Bob, its on like Donkey Kong now. Just kidding, but for the sake of a lively discussion.

So I just read through the Holley Avenger manual and I see what you are saying about the distributor and timing control. What are the inputs it is using to determine the timing? It seems like the only consideration for the timing is engine speed.

In a blown application like we are talking about and your reference to the electronic spark timing being a sort of insurance I'm not sure if this type of system would be much help in preventing detonation and damage to the engine. It specifically states that the kit doesn't use the knock sensor connector (although I don't know why then they put it in the wiring harness). So without a knock sensor the system doesn't know that it should retard the timing if the engine starts knocking under boost. It'll certainly keep the A/F around 14:1 based on the O2 sensor readings, but with the boost they usually seem to tune the engine to run a little rich at higher RPMs.

With the avenger can you make custom A/F maps? It would be awesome if you could using the engine speed input to also map out a richer fuel mixture so that way as the boost came on you'd be able to prevent leaning and potential detonation that way.

Also old guys are supposed to be stuck in their old ways. lol

I'd love to pull out all the stops to have an Avanti that ran like it just came off the 2015 assembly line as well, but I also derive enjoyment from working with some of these obsolete technologies like carburetors. There is a real mechanical beauty to them.

[Devildog]

We'll agree to disagree. My 355 SBC in my 83 has a Holley Avenger EFI setup. With the carb/ vac. dissy setup it just wouldn't perform as well as it should throughout the RPM range even after numerous carb and timing changes. I bit the bullet and put on the Holley Avenger. It will use the small SBC HEI distributor (less than $75).

Right out of the box, it was much improved over the old system and still runs great.

I downloaded the timing and a/f curves and there is no way any standard (carb-Dissy) setup would control like the EFI does.

If I were to add a blower, the $500 (less on an SBC) would be cheap insurance on a $3000 blower system and unknown cost of the engine.

I guess I could spend $500+ on a dyno session but that would only let me know I was optimum at that time.

In my garage is a 2013 Impala that get 303 HP from 3.5 liter V6. It doesn't get there without timing control so it must be an improvement over previous technology. I understand that timing is only one factor in the engines performance but optimum performance depends on accurate timing control.

Not to be argumentative as I'm just an old guy that believes in the newer technology for maximum performance.

Bob

Bob, we are not disagreeing. I was saying the 2nd and 3rd gen add-on EFI's like my older PJ3, your Holley Avenger is what these guys call a 4th generation that can use timing. If you ever need any help with that Holley, the guy that designs and develops for Holley in Bowling Green is Doug Flynn. Doug is just a wonderful guy and has stayed at my house a couple of times while doing testing at SAM in Houston.

If I was buying an add on EFI today I would go for the timing interface such as the Avenger. The MSD, FAST, Edelbrock, PJ, etc all makes a pretty good bolt on system now days that can interface, even control timing. I am the great enabler and love to help my buddies buy high tech stuff for their old cars that they really do not need but just have to have.

I am one those old guys also that loves this stuff available now days. I tell the young guys if you really want to understand ignition and timing effects on performance, drive a Model T with spark advance on the steering column. The driver is the 'ignition computer', inputs are your butt and ears

Joe

Doug is a real car guy as well as smart engineer, has low 9's sec (maybe into 8's now) big block Nova with all the neat stuff.

Edited September 26, 2014 by Devildog

[Avanti83]

Doug

Not my intent to sell the Holley unit but to use my experience to point out that computer control of timing is an important part of the engine control parameters. It's impossible to find a new vehicle that does not have control of all parameters in the engine with the ECM so my conclusion is the best way to control engine parameters is with the best electronics available.

I won't contest the advantages vs disadvantages of the available systems but to note that if I were to spend a ton of cash on a blower eguipt system I'd research the heck out of the available systems and pick the one that was best for my application. I will guarantee it would control timing.

JMHO, Bob