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Discussion Starter · #1 ·
Years ago I got a 4into2into one tuned exhaust from sweeden for the manta. I remember in 79 it was expensive then and I am sure that is is worse now. The germans swore it was far better than the little header like what I have now. Does anybody know who still sells one?
 

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The Swedish company that makes them is called Simons, the 4-2-1 header kit is called Rohret, while the really big header kit is called Rohret II. I have two of the Rohret's (used) kicking around, but one of them required the floor of the car to be hammered a bit to fit it in place. I have a brand new Rohret II kit which has never been welded/assembled. That kit was designed for rallycross cars, with a powerband from 5000-9000 rpms, and something like 1 7/8" primary tubes.

In truth, I tested the 'smaller' Rohret and a home-built 4-1 header, and the home-built header made better power, even though both have 1 3/4" primary tubes. But that was a racing engine, and the 4-2-1 might work better for you, especially with your larger engine displacement. I'll try to take a picture of one of them tonight.

Bob
 

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Standard Set-Up

Of course, the standard exhaust system is a rudimentary 4-into-2 system with short primary pipes - so Opel must have found that most suitable for street use. The "Sprint" manifold goes further in that direction and some of the later, 2.0/2.2/2.4 manifolds have larger tubes and the secondary pipes can be easily varried in diameter and length - they are just exhaust tube.
 

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Discussion Starter · #4 ·
I would be very interested in a used Ronret. I can just bolt that in and not try to find someplace to make the rest of the header if I had the flange. I was pretty happy with the one I had in Germany.

I am sure your home built header was made properly with flow in mind and is better than the header that I have, (the little one that comes up on ebay all the time) so the ronret would be an improvement.



a few quick questions if I may

I have a 2 1/4 exhaust from the back of the header back. Samdog said I should go bigger to above 2 1/2. what do you suggest?


I do intend to rallycross in oct with the manta at a sanctioned event. The car is very very low though, the top of the Manta is actually lower than that of a gt on stock wheels and tires.. the lowest part is the exhaust of course, which scrapes a lot going in and out of parking lots. Being stans old backup car it has a beefed up suspension and I do know the rear sway bar s (3) will have to come off.

To avoid dragging I was going to find some 14 or 15 inch wheels and put rally tires on. Which do you think would be better 14 or 15 wheels? With the wheel size in mind what size tires would you suggest?

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I can feel the car flex a little bit like an H when I shift unless I am really babying it. I feel the drivers side shoot forward when the tire grabs then the passenger side catches up. Should I be worried and thinking about beefing the frame up?


thank you,
C
 

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Calvin, I'll dig out the Rohret headers tonight if possible, and see which one is the best choice.

Samdog is correct, for that sized engine and the specifications it has (especially carbs and camshaft), you can easily go with a 2.5" exhaust. Expect both a power and torque increase.

Warning! Rallycrossing is very rough on the car. You WILL remove a lot of paint from the rear quarter panels unless you have substantial mudflaps. You've been warned!

I wonder if you can actually run tall rally tires with your lowered suspension, seems to me you will tear up the front fenders at full lock. Been there, done that....

We run 13" rally tires on Gregg's (Samdog's) Ascona beater car, and they're Kumho 195/70-13's (23.74" tall), and they would rub if we hadn't cut the front valance and weren't running our taller ride height with 380 lb springs. That car has no rear swaybar at all, and the stock front swaybar has been milled down 1/4" in the center to soften it up. Realistically, 13" rally tires are hard to come by, so I'd go with 14" if you can find them. A lot of VW and Sentra rally drivers use this size, and the bolt pattern fits the Opel. Most of the 14" tires are 24" tall....15" rally tires are usually 24.5" to 25" tall.

HTH,
Bob
 

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Calvin, here are the various Swedish headers I have laying around.

First is a Rohret I that was run in a circle track Manta. It is configured in such a way that it requires floor modifications to fit around the sway bar.

Second is a Rohret I that was run in a GT-4 road racing Manta. I never saw this one in place, I do not know if the floor needs to be modified to fit, but I am assuming it does. Note the longer secondary pipes.

Third is a Rohret II that was never welded together, it is brand-new. But again, it is made for European Rallycross competition (not like US rallycross, more like stadium truck racing). For comparison, a standard Sprint manifold is layed next to it, but with a custom 1.75" secondary pipe diameter.

Let me know if any of them interest you (except the Sprint).

Bob
 

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Discussion Starter · #7 ·
Since I don't have a roller cam (yet) I guess it would be between number one and 2. For some reason I am leaning towards number two in the middle picture. Since mine is basically a street car/weekend wannabe do you do you think that the ronret I would be the best application for the car?

My email address is [email protected] if you would be so kind as to let me know how much and where to send it.

If the tall 14 rally tires are to tall do you think the
195x70x13 that would bring it up a enough?. The upside is I have extra 13 wheel and tire rack has the Kumo rally tires in that size.

Otherwise I should be able to find Sentra wheels and hope the fenders hold. My springs are very low but the fenders have been rolled.

Thank you for the tip on the mud flaps the car has a $250 macko paint job with that in mind but that was for the gravel roads in the ozarks.. The scca course looks like it is just in a field, I guess they have moved the major rocks.

Thank you
calvin
 

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calvin said:
If the tall 14 rally tires are to tall do you think the
195x70x13 that would bring it up a enough?. The upside is I have extra 13 wheel and tire rack has the Kumo rally tires in that size.

Otherwise I should be able to find Sentra wheels and hope the fenders hold. My springs are very low but the fenders have been rolled.

Thank you for the tip on the mud flaps the car has a $250 macko paint job with that in mind but that was for the gravel roads in the ozarks.. The scca course looks like it is just in a field, I guess they have moved the major rocks.
Calvin, you still have to be careful up front at the lower valance, the tires can rub while turning and hitting a bump, and they will bend the heck out of the valance if they catch.

Regarding the rocks, it's amazing how much stuff will get turned up...I've seen ruts develop that are 8 " deep that will practically swallow a lowered car! Rocks will get pulled out of the ground and can wreak havoc on bodywork, but don't underestimate what good old sand and dirt can do. On my Nissan, it completely stripped the undercoating from the floorboards after one event. In your case, with rear wheel drive and lots of torque, it's the spectators that will have to keep ducking from the debris being thrown off the rear tires!

I'll e-mail you about the header.

Bob
 

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Not an Opel, but here's my Nissan at a rallycross a few years ago. This started as a grassy field! But after two days of cars tearing things up, you can see the size of the stones unearthed. They will remove paint! I used huge mudflaps on all 4 wheels, yet I still had rock chips as high up as the door handles.

Bob
 

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rohret exhaust system

RallyBob said:
The Swedish company that makes them is called Simons, the 4-2-1 header kit is called Rohret, while the really big header kit is called Rohret II. I have two of the Rohret's (used) kicking around, but one of them required the floor of the car to be hammered a bit to fit it in place. I have a brand new Rohret II kit which has never been welded/assembled. That kit was designed for rallycross cars, with a powerband from 5000-9000 rpms, and something like 1 7/8" primary tubes.

In truth, I tested the 'smaller' Rohret and a home-built 4-1 header, and the home-built header made better power, even though both have 1 3/4" primary tubes. But that was a racing engine, and the 4-2-1 might work better for you, especially with your larger engine displacement. I'll try to take a picture of one of them tonight.

Bob

hi bob i am just wondering if you still have a rohret 1 that you may want to sell as i would be interested in purchasing ? i have a project gt nearly finished 2.00litre tuned, sports koni shocks, sat on 225-45-17 rims which came off an early bmw, thanks [email protected]
 

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Sadly it won't fit a GT, not even close really. And if I read correctly, you're from the UK, in which case it would be quite expensive to ship from the US. Jetex is the UK distributor, I'm sure you could find a local supplier.

Bob
 
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