Opel GT Forum banner

1 - 20 of 35 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter #1
Hi guys!

I have a 400hp engine that I will be swapping in my 71 GT. I read a lot and I know I will have to strengthen the frame so it can take the added power.

I would like to know what kind of work people who drive big horspower GTs have done to strengthen their car. Car will be a weekend/summer car, not a daily driver, but not a full race car either so it needs to stay reasonable for a street car.

Pictures of actual work would be great!

Thanks for the help!
 

·
Can Opeler
Joined
·
3,282 Posts
You won’t be happy with 400HP in a GT. I can guarantee.

What engine is it though?

None of the unibody can take 400HP you’ll need to do a lot of strengthening. I’d recommend a jester 942105K roll cage for a basic starting point and also really strengthen the rear suspension mounting points and a hoop above the gas tank area.

The rear end can barely handle 150Lb/ft of torque. You’ll need to swap in one from another car.

The biggest problem will be cooling the engine. Pretty much all of the guys who have above 200HP suffer from major cooling issues. There isn’t enough airflow to cool the stock engine adequately.

I’d reccomend looking into getting a cheap Miata to put your 400hp motor in. V8 roadsters makes kits to install pretty much anything into a Miata for loads cheaper than this project will cost in fabrication alone.
 

·
Your Noble Friend ;-)
Joined
·
4,051 Posts
You will have to weld a full frame underneath / partially inside the existing unibody. All the cutting and welding alone will twist the body already. When you then discover that there is additional rust issues to be dealt with, you will throw the towel and give up, having another wasted GT body to throw away.
If you do succeed, surprise us by driving it 300+ miles to one of the upcoming Carlisle, PA car shows.

BTW, you haven't mentioned yet what engine you have. 400HP could come out of a fuzzy turbocharged 4-cylinder, or a almost stock BBC.

Good luck, and we need pics!

Dieter
 

·
Registered
Joined
·
2,894 Posts
You won’t be happy with 400HP in a GT. I can guarantee.

What engine is it though?

None of the unibody can take 400HP you’ll need to do a lot of strengthening. I’d recommend a jester 942105K roll cage for a basic starting point and also really strengthen the rear suspension mounting points and a hoop above the gas tank area.

The rear end can barely handle 150Lb/ft of torque. You’ll need to swap in one from another car.

The biggest problem will be cooling the engine. Pretty much all of the guys who have above 200HP suffer from major cooling issues. There isn’t enough airflow to cool the stock engine adequately.

I’d reccomend looking into getting a cheap Miata to put your 400hp motor in. V8 roadsters makes kits to install pretty much anything into a Miata for loads cheaper than this project will cost in fabrication alone.
Truer words never said better. Why RUIN a good car and do that? Jarrell:no::no:
 

·
Registered
Joined
·
2,894 Posts
You won’t be happy with 400HP in a GT. I can guarantee.

What engine is it though?

None of the unibody can take 400HP you’ll need to do a lot of strengthening. I’d recommend a jester 942105K roll cage for a basic starting point and also really strengthen the rear suspension mounting points and a hoop above the gas tank area.

The rear end can barely handle 150Lb/ft of torque. You’ll need to swap in one from another car.

The biggest problem will be cooling the engine. Pretty much all of the guys who have above 200HP suffer from major cooling issues. There isn’t enough airflow to cool the stock engine adequately.

I’d reccomend looking into getting a cheap Miata to put your 400hp motor in. V8 roadsters makes kits to install pretty much anything into a Miata for loads cheaper than this project will cost in fabrication alone.
I and a lot of others saw a small block chevy dropped into a Gt at Charlotte at the Nationals. I won't post pictures on here, you can email me, I'll send them to you, but lets say without hurting any feelings. It wasn't pretty, nor unique, ugly in fact. I won't say anymore.But hey as was posted, do it, drive it to Carlisle Pa, we'll look at it. Jarrell
 

·
Registered
Joined
·
1,698 Posts
Do what I did with mine and go mid-engine to better distribute that weight. I used the Lamborghini Miura rear subframe assembly and it fit right in like peas in a pod. As I have found, most any local scrapyard will have these Miura subframes for cheap. Recommend you DO NOT use a Diablo or later Hurracan subframes as they are a touch too wide to fit behind the rear seats of our GT's.
 

·
Vendor
Joined
·
2,558 Posts
Do what I did with mine and go mid-engine to better distribute that weight. I used the Lamborghini Miura rear subframe assembly and it fit right in like peas in a pod. As I have found, most any local scrapyard will have these Miura subframes for cheap. Recommend you DO NOT use a Diablo or later Hurracan subframes as they are a touch too wide to fit behind the rear seats of our GT's.
:p:):eek::veryhappy:yup:
 

·
Registered
Joined
·
14 Posts
Discussion Starter #12
You will have to weld a full frame underneath / partially inside the existing unibody. All the cutting and welding alone will twist the body already. When you then discover that there is additional rust issues to be dealt with, you will throw the towel and give up, having another wasted GT body to throw away.
If you do succeed, surprise us by driving it 300+ miles to one of the upcoming Carlisle, PA car shows.

BTW, you haven't mentioned yet what engine you have. 400HP could come out of a fuzzy turbocharged 4-cylinder, or a almost stock BBC.

Good luck, and we need pics!

Dieter
The engine is a Nissan SR20DET (4 cylinder 2.0 liter turbo). This swap has already been done in a GT by Big Ben who uses the car on the street and also for autocross. He has a pretty much stock version of it. Mine is out of my race car. It is a fully built engine. I changed the race car engine for one that makes 600hp now (car is not a Opel).

I have access to a great fabricator who actually built my racecar and many other cars so the project doesn't scare me. I would just like to see if someone has done some work on a GT that has some pretty big power just to give us some ideas to start from.

I will surely come by a car show in your area, but you'll have to give me some time. It's a pretty big project so it will not be ready in a few months ;)
 

·
Registered
Joined
·
14 Posts
Discussion Starter #13
You won’t be happy with 400HP in a GT. I can guarantee.

What engine is it though?

None of the unibody can take 400HP you’ll need to do a lot of strengthening. I’d recommend a jester 942105K roll cage for a basic starting point and also really strengthen the rear suspension mounting points and a hoop above the gas tank area.

The rear end can barely handle 150Lb/ft of torque. You’ll need to swap in one from another car.

The biggest problem will be cooling the engine. Pretty much all of the guys who have above 200HP suffer from major cooling issues. There isn’t enough airflow to cool the stock engine adequately.

I’d reccomend looking into getting a cheap Miata to put your 400hp motor in. V8 roadsters makes kits to install pretty much anything into a Miata for loads cheaper than this project will cost in fabrication alone.
I know the rear ends are weak. I already have a chevy 10 bolt rear end that I will also install at the same time.

For cooling I will fit a 3 row racing radiator. Big Ben has done it on his car. I'll just need to find a way to dissipate the heat that gets stuck under the hood, without changing the hood too much so it doesn't look ugly.

I want to keep the body of the car as original as possible. Will get a new paint job, different wheels and lower the car, that's it.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #14
You'll need to replace just about everything for 400hp for road and track. It'll turn into crapp pretty quick if you don't.

I/we suggest installing a 250hp or so V6. There's threads on the subject.
I know and I will replace just about everything. It will not be a cheap project, but it will sure be interesting. Who has the street GT with the most power that you guys know of? I would really like to talk to people who have gone through a similar process.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #15
I and a lot of others saw a small block chevy dropped into a Gt at Charlotte at the Nationals. I won't post pictures on here, you can email me, I'll send them to you, but lets say without hurting any feelings. It wasn't pretty, nor unique, ugly in fact. I won't say anymore.But hey as was posted, do it, drive it to Carlisle Pa, we'll look at it. Jarrell
Sure will! I would not drop a V8 in a GT, I am sticking to a 4 cylinder. Just not exactly the kind of 4 cylinder we are used to. I'm curious to see those pictures though! I will send you a PM so you can send them to me.
 

·
Can Opeler
Joined
·
3,282 Posts
400hp Opel GT

Big Ben has the most HP GT I know of that is drivable for more than a few miles. Keep in mind his SR20 makes 200HP NOT 400hp. The most difficult strengthening work was not really important for him.

There are a handful of v8 and v6 GTs but I don’t know of any that are driven except for to car shows.

There are a lot of tube chassis cars pushing that much power though.
 
  • Like
Reactions: soybean

·
Registered
Joined
·
2,102 Posts
The better approach might be to build a tube frame, build it out like a vette, then drop the GT body on it.

There was a guy here a few years ago who built his own fiberglass body over a tube frame that was built from scratch. His fab skills were amazing but, unfortunately, he seems to have disappeared.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #18
Big Ben has the most HP GT I know of that is drivable for more than a few miles. Keep in mind his SR20 makes 200HP NOT 400hp. The most difficult strengthening work was not really important for him.

There are a handful of v8 and v6 GTs but I don’t know of any that are driven except for to car shows.

There are a lot of tube chassis cars pushing that much power though.
Ya I know there's a difference... I could always lower the boost, but will still make tons of power. I want to build it right once so I don't ruin the car because of the power.

The better approach might be to build a tube frame, build it out like a vette, then drop the GT body on it.

There was a guy here a few years ago who built his own fiberglass body over a tube frame that was built from scratch. His fab skills were amazing but, unfortunately, he seems to have disappeared.
Interesting! I wish I could find some pictures of that built. Do you know if his project ever made it to the street or you never saw the final result?
 
1 - 20 of 35 Posts
Top