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I am currently working on a 1974 Opel Manta Luxus, and I've gotten the cleaning and rebuild stage, but I'm left with a dilemma, the engine is in a questionable state but I believe it is salvageable, however I have been told by friends and family that I should swap the engine for a v8, but I want to keep it almost original, so I'm stuck with a question, should I keep it original or swap it for a v8?
 

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Pedal Smasher
1973 Opel GT
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2,805 Posts
You need to decide what you want out of the car. Do you want tire melting acceleration and a muscle car rumble? Which also means chassis reinforcement will be needed and take a ton of work. Or do you want a mostly original Manta that will take far less time to enjoy? And you won't really have to worry about traction problems.

A V8 swap could be a lot of fun, if that is something you're confident you could do properly. The chassis is not designed for 400 hp though, so you would need to reinforce it a little. Put some extra bracing in the engine bay and probably a stronger rear axle.

Once you start letting others tell you what you want, the car is no longer your project. It has become a group project. A bunch of people saying what needs to happen and one person doing all the work.

What I want my Opel GT to become is only my vision, no one else had any say in that. So, my vision for my GT is to make it as close to how it should have been, like if Nissan or Porsche could have developed the car instead of the bean counters at Opel. I can't change the solid axle to an IRS without a serious amount of work but I can improve the suspension. I can swap the 1.9L out for a 2.4L CIH, likewise with the 4 speed for a Getrag 240 5 speed. In the end, my GT will only look similar to what rolled off the line but everything else about it will be improved. I won't use EFI or an electric fan however. I want to keep it as mechanical as possible, save for replacing the points with an Ignitor II and the AM radio with a newer radio.

Come up with your own vision and follow it.
 

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Can Opeler
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There are a lot of ways to tackle a project. All of my friends always have tried to get me to V8 or turbo my cars. Most of them have been working on similar swaps to other engines and such for the several years I’ve spent fInishing and driving 3 cars that I bought non-roadworthy.

I have never regretted taking on too small of a project. I have almost always regretted taking on custom work.

Stick with the things that fit like they are supposed too. You can make a 1900 engine sing mighty pretty with very little cash. And you can make your manta out handle nearly every car on the road with some bolt on suspension upgrades, bushings, and nice 200 treadwear tires.

I will never do a non-Opel engine swap. It’s too much time and money to come up with something that will inevitably be worse than stock in every way except for speed.
 

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Pedal Smasher
1973 Opel GT
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Thinking of a V8 swap reminds me of the 1990 era Jag XJS coupe I saw the other day. I pulled up along side it, thinking it's just a XJS. I look over and to my pleasant surprise, there was a blower! Someone had put an old school blown V8 in it, probably a SBC. It had the butterfly air scoop and everything.

So, a blown V8 Manta would be pretty cool to see. But if you go that route, you better put a wheelie bar on it because it will want to stand straight up on the rear bumper. And get your life insurance sorted out too while you're at it.

Again, do what you want however. Talk is easy, actually making a V8 swap work well in a Manta will be a large project. It's way easier to rebuild a 1.9 and get it performing really well. You could put a couple side draft Webers on it... and I doubt anyone will say a damn thing if your engine winds up looking like this.
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Opeler
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if you have never done an engine swap, then stick to the Opel engine. the stock engine doesn't have a lot of room by itself. what makes you think there is room for a V-8? start cutting, and then your structural integrity is gone and you will possibly have to scrap it.
 

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Solo II is fun in a GT!
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... I have been told by friends and family that I should swap the engine for a v8, but I want to keep it almost original, so I'm stuck with a question, should I keep it original or swap it for a v8?
I stole this quote from NASCAR Hall of Famer Junior Johnson:
“The best way to make a small fortune in racing is to start with a big one.”
 

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Über Genius
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Compromise and put in a V6. Far easier, I'm sure.
90% or more V8 swaps have been abandoned.
 

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Pedal Smasher
1973 Opel GT
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A Buick Dauntless V6 could be pretty cool. You don't see that engine everyday and Opel was sold in Buick dealerships. These days, the Jeep crowd is where you'll find the most support for it. A V6 might just be perfect for a Manta. Not crazy enough to really have to worry about the power it will put out, but more power than a 4 cylinder CIH and unlike the TE2800, you don't have to worry about how long the engine is.
 

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Keep the Opel Engine. We've seen too many people who start to "swap" engines, get frustrated, quit and walk away, and a good car is destroyed. However, the engine bay in the Manta is a lot larger than the Gts. There is room for a larger engine.
But, keep the engine, rebuild the engine, upgrades to a 2.4 are possible. Add a cam, rebuild the head, intake, carb and the proper exhaust. You'll have a heck of a "sleeper''.
Pop the hood, it looks almost stock . Almost.
Look up Rallye Bob. Read what he has to say. He is the Foremost engine builder on this site. And I hear he has a soft spot for Mantas.;)
 

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Sounds like your friends BELIEVE that it will be cheaper to put transplant a more modern V8 than to rebuild the Opel engine. It won't.

Keep the Opel engine.

If you must go with something bigger on a budget, consider a 3.1. They were plentiful 20 years ago, but shouldn't be too hard to find today.
It will likely need rebuilding as well. Here is a short story about one such vehicle. Most of the stories don't end this well: Curbside Classic: 1975 Opel Manta 3100 (That’s Not A Typo) – The German Camaro
 

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My opinion is that it is your car and you should do what you want. I bought my present 74 Manta because of the warm memories of my 75 Manta which was my first new car. I always enjoyed driving that car just the way it was. More power is always nice to have, but a what cost and to what end. If you want a track machine, then go all out in that direction. If you want a nice road machine, then consider taking the engine that you have already removed and get it rebuilt with what ever mods you like. It should fit back in with the least trouble on your part. I would recommend putting a 5 speed transmission in for more shifting fun and lower rpm at cruise speeds. There are a lot of other parts that can probably stand to be replaced to keep you busy for a long time. As others have said, the Manta was a decent performer as is and moved well at less than 100 hp. You probably don't need to add a lot more hp for more zip. And you would still have a well balanced Opel for better or for worse. Probably both.

Good luck and thanks for sharing. Besides more pictures, total miles and more details would be interesting.
 

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Detritus Maximus
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Keeping the Manta all Opel will be less headache and easier to work on. The Mantas in the US always had the low compression motor. Flat top pistons are too easy to get you near to 100hp. 120 is not far off from that and will make a very fun car.
 

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Opeler
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116 Posts
I can speak from experience back in the mid 1980s going from a low compression engine to a high compression pre-1971 engine makes a measurable difference in a Manta. That combined with a better Weber carb and a 5 spd transmission and the manta will be a lot of fun to drive and the project will be significantly cheaper than a V8 install. even for a very mild V8 you will have to not only make room for the engine but you will also have to strengthen the chassis and rear suspension mount points and likely swap in different axle due to torque. I think your car would be more fun to drive being all Opel but with an engine that is 30-50 hp stronger than stock.
 
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