[307GT]

I own a '70 Opel GT and I wanna put a small block chevy motor from a '71 Chevelle. It has about 250 or so horsepower and about 200 ft lbs of torque. Does anyone have any comments on this swap. I plan on using a turbo 350 trans. Has any completed it. Any comments on what rear I should use and if I have to full frame the car. and what to do about the rad support. Will the Opel radiator cool the small block.

 

[johnbran]

From the consensus I've read in here, most would not advise this swap, but everyone has their opinions on it. If you haven't read it yet, check out the post in here called "frame augmentation". It might give you some of the info you're looking for.

Best of luck!!
John

 

[chuckspeed]

The short answer?

Don't do it.

Assuming a stocker 307, the HP rating (I can look this up) was SAE gross in 1971 - to get to SAE net, multiply by 0.73. This gets you close to SAE gross - about 180 HP. To get this to dyno flywheel HP, multiply by 0.80 - this gets you down to 146 HP, which is pretty close to reality for a small-valve, non blueprinted 307.

To get this big hunk o'meat in the Opel, you're gonna have to cut A LOT of metal away - metal in areas where your feet go. You'll also have to:

a) Reinforce the crap out of the substructure of the car
b) re-design the cooling system to reject the V8's heat load
c) have a custom rearend made to accomodate the additional torque.
d) skip headers - there's no room
e) upgrade the braking system to handle the extra heft
f) ditto for suspension

Where you're done, you'll have 500+hours in the swap, a good $4000, and a design compromise. Meanwhile, a guy following Rally Bob's advice will take the same $4000 to build a stock-block Opel in less than half the time that handles better, and;

Is faster than your V8 opel.

Many moons ago, I used to street race here in Detroit (won't say where) and this discussion helped finance my way thru college. It's all about power-to-weight; when you make the move to the heavy V8, you start the dread weight spiral. In the case of the V8 Opel, you have to make another 30HP to be at par with the 145 HP 1.9 liter...

I took this discussion to the street with a 2.3 liter Pinto. Eventually got tired of the argument (Yes, it IS a four cylinder) and raced folks with the hood off and a velocity stack on so they could easily see it's not a V8. They still raced - and lost. This includes the guys who stuffed 302's into Pintos.

Read Rally Bob's stuff, and spend the time/money there. You'll be faster, handle better, and have a car that retains its value better over time.

 

[307GT]

would a ford 302 fit more easily than a chevy 307 and the distributor would be in the front which would help

 

[chuckspeed]

If you're still asking about a V8 inna GT...you're missing the point.

It's not distributor location - it's motor width and weight.

It's not worth it - The best application an Opel owner can possibly find for a V8 is as a mooring point for his/her pontoon boat.

 

[307GT]

All i've ever wanted to do was put a V8 in a small car and i finally got a cool car(for free by the way)the GT. So i think i am going to do it

 

[mjustice]

I hope you have boatloads of money!!!!
There are many numerous modifications which will need to be made to even consider doing this swap! You'll need a new rearend (of course). The body will need to be strengthed...Subframe possibly, cage more likely (not sure exactly). The suspension system will need to be revised (weight increase, weight balance different). The firewall will need to be cut out and rebuilt (you think you dont have any footroom now...wait until you cram a V8 in there!). The braking system will also need to be redone, because of more weight. The Tach and Speedo will need to be replaced. You'll need a new larger radiator....you'll probably have to have one cusom built to get it to fit. And when you get it done, it's going to handle like crap and won't be much faster than a built opel motor. Just think....all this money going out the window. I hope you're rich or have a rich father. Because it won't be worth anywhere near what a totally stock one will be in ten years. I think you need to get yourself a Pinto and leave the Opel alone. But then again, the less original Opels on the road, the more mine is going to be worth! HMMM......maybe you SHOULD do it!

 

[Paul]

Hey 307GT

These guys aren't just trying to blow smoke at you because they don't want to see an Opel get butchered. They're really giving you good advice. Several on this list have made the same mistake. There's a whole lot more work than meets the eye and you stand to gain nothing. So, it looks like this project would be a very poor investment of your time and money. Who knows, maybe you're a gifted machinist and steel fabricator with a complete shop at you disposal. Given the right talents, engineering knowledge, financial resources and fabrication facilities, the right person MIGHT be able to pull this project off and have something WORTH driving. Chances are slim, however, that a project like this will ever get finished, much less correctly. For my investment in money and time, I'd pick a different solution. But this is America and everyone is entitled to their own view point.

If you actually attempt this feat, we'll wish you good luck. However, I for one, hope you pick an Opel project that will leave you as a SATISIFIED Opel owner, and not as someone who is a disgruntled Opel previvious owner who has a butchered GT shell in the back yard.

Thanks and Good Luck.
Paul

 

[chuckspeed]

307-

I've done whatcha said.

I've broken rear axles.

I've blown transmissions.

I've broken windshields banging off 2nd gear.

I've twisted the car so bad the passenger door pops open on the shifts.

The long and the short of it is this is a project that is best left to the drawing board - honest.

After restoring and building a fair # of cars, I'm tellin' ya -

THE CAR IS THE CHEAPEST PART OF THE PROJECT. Don't care if you got a free driveline and car - the deal wil STILL take 500+ hours and several thousand dollars to get it done.

Still - your choice. Good luck.

 

[opelbits]

The ONLY V8 worth trying to put in an Opel would be a BOP 215 (early 60's GM) or the Rover 3500 (Same motor, they bought the tooling from GM) and it's variants. It has all the same problems as the 307, you still have to do cutting and welding, but it weighs a lot less because it is aluminum. In fact, I hear it is actually lighter than the Opel 4cyl. HP is anywhere from 140 to 200 for stock and MUCH higher for modified.

 

[chuckspeed]

I had one of those motors for a while...

If you want an indication of their performance, check out road tests on the Triumph TR-8. This was BL's attempt to stuff a big motor inna bitty car.

The results were mixed. I don't have the 0-60's and ET's in front of me, but they weren't any better than an average hot small displacement econobox.

Keep in mind the Buick Special (with the alloy V8 made in 1962 &1963) weighed only about 500 lbs more than a GT out of the box. These were not stellar performers back then...

It comes down to SAE gross vs. net vs. advertised HP. The 2 bbl. variant made 155 SAE gross HP, the 4 bbl 200 SAE net. The 'real' HP of this beastie (4bbl form) was probably closer to 120 HP. This is an easily attainable figure with an Opel-based motor, so the added expense and frustration of adapting the car to fit the motor is kind of a wash, IMHO.

If you want 'wow' factor, go with dual sidedraft Webers. A properly set up motor with these beasties will turn 150 HP (prox - after other mods) and there is no cutting required.