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Discussion Starter · #1 ·
Hello! Thrilled to find this group! I am looking for sage advice and guidance on how to get as much power as possible out of my 74/75 Opel Manta 1.9's I race them in St. Helens Washington under the number 44 (See pic's @ www.flattireracing.com).

I have just begun racing and found myself timing in terribly slow so I started the race in 14th position but finished in a modest 8th. :eek:

Sure hope you guys can steer me in the right direction... I just can't have these pinto's, toyota's and Datsuns crossing the finish line in front of my Opel like that! :D

Oh, I also own a 1972 Opel GT (daily driver type).

Best regards,
DirtTrackManta
 

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Old Opeler
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Welcome!

You certainly have found the right site to answer your questions! If you use the "Search" feature on the top blue line on the page and type in "performance" and then find your way to the "Opel Engine Performance Modifications" group of threads you will find heaps of information about Opel Performance. Any other questions you have will usually be quickly answered by the good people on this site. There are several who do (or have) raced Opels to - and beyond the limit!

I also have a 1972 Opel GT but do not race it - though used to race Vauxhall engines in Midget Racing cars.

Welcome to the Opel Community!
 

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What are your restrictions, rules-wise?
 

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Discussion Starter · #4 ·
Rules of the Track and Thank you(s)!

Thanks for the warm welcome GTJIM & RallyBob!

About the rules of our track. It is a 1/4 mile oval track and my class is called "mini-stock". As you are well aware there is nothing stock about a stock car. :D

I do have to run with the "stock" carbeuration which seems to be one of my greatest challenges at the moment. I am also looking at the fuel injection options. A few interesting points: at our track "stock" carbeuration means anything that does not say Webber. :) I am really curious about fuel injection and if that would be the way to go.

Also I can do some block and head work as long as I don't get too carried away. Anybody heard of boring .40 over and running Chevy 305 pistons? :eek:

I don't think I need a TON of horsepower. But enough to keep the 2300cc mustangs and the 2800cc pinto's from eating me in the stretch. They have lots of power they never get to use on our little track.

Thanks again!
DirtTrackManta
 

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The compression height of the 305 pistons is all wrong, you'd have the piston .223" down in the hole at TDC!

But there are still tons of things that can be done, from Euro engines to strokers to massive overbores, headwork, cams, etc.

As you've said, having to use the stock carb is a serious restriction. You can gain a bit more by using an early mechanical secondary Solex, and installing another large secondary venturi in the primary barrel for more airflow. Or you could search for one of the rarer 40 mm Solex downdrafts (non-Opel aftermarket fitment) which will bolt right to your manifold.

Basically, the best bang for the buck will be .090" over flat-tops (makes it a 2.0 litre), milling the heck out of the head, bigger valves, and concentrating on intake airflow through port development, intake development, and a special split profile camshaft favoring the intake port.

HTH
 

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Discussion Starter · #6 ·
Giddy...

RallyBob...

I need to know more about those carbs and the other engine work you referred to. I have some great milling/machine resources and would really love to engineer this beast and put her to the test. As mentioned I don't have to have a TON of hp but you have got me just giddy with the possibilities! :D

I have been working the geometry forward and backwards for the short dirt track... a little bit of weight here and there, some front end work and some of your mods and I'll be leading the pack in no time!

Where do you suggest I go from here?
Finest regards,
DirtTrackManta
 

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I really can't tell you much about the bigger Solex other than it exists. I've only seen one before, but my understanding is it was a popular performance bolt-on in the '70's and '80's.

What is the current state of your engine? What year head/block are you running? Still have hydraulic lifters? Stock exhaust manifold (or 1975 Sprint manifold?). Ignition system?

Just trying to get a feel for your starting point.

Bob
 

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Rally Bob,
I have a 1970 GT with a recently rebuilt 72 engine (I think). From the compression readings I'm getting and the PO's memory, I believe that it was rebuilt with low compression pistons and hydraulic lifters. I would like to achieve modest HP gains. Is it as simple as replacing the pistons with flat top pistons? Is there a significant gain in running solid lifters? I'm not interested in going the performance cam route.
 

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74/75? well that puts it real close to a factory fuel injected model. add a megasqirt programable and he could get much more power than a solex. and he may still be legal.
 

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opelwasp said:
74/75? well that puts it real close to a factory fuel injected model. add a megasqirt programable and he could get much more power than a solex. and he may still be legal.

Very true. I suspect they would want the EFI to be 'stock appearing', but there's no reason a Megaquirt ECU couldn't be put inside a gutted stock Opel ECU box, and the air flow meter could be wired wide open to eliminate airflow restrictions. Add a Bosch TPS from a Saab or other newer car, and the whole thing would look stock. And the EFI manifold is good for about 1000 more useful rpms than a carbureted intake, plus the longer runners really fatten up the torque off the turns. Hmmmm.....

The biggest pain might be building a surge tank and/or baffled pickup since with EFI there can be no fuel pickup issues.

Bob
 

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Bill Daley

Might wanna try getting in touch with Bill Daley up in Massachusetts. Bill was a big Solex fan and a real guru at tuning them. He used to have a huge inventory and probably still does. (Bill Daley Opel Parts - North Brookfield, Mass.)
 

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Discussion Starter · #12 ·
WOW!~ You guys are great!

I spoke with our track tech and he very nearly qouted RallyBob: "It needs to look stock." This leads me to be very interested in the Fuel Injection.

I have already begun putting the car on a serious diet and getting weight placement and geometry where it needs to be for our notoriously dry-slick track.

So looking at 090" over flat-tops milling the heck out of the head, bigger valves, and concentrating on intake airflow through port development, intake development, and a special split profile camshaft favoring the intake port and getting the EFI manufactured we should be getting close to kind of torque and speed to put the Opel where she belongs; in front!. :D

Not to discount the Solex option... any dissenters on EFI being the better way to go?

Thank you!
DirtTrackManta
 

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boomerang opeler
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re bobs carbs

can you use the solex/zenith INAT's from a bmw pre 5 series (2800/3.0/3.3)
all available in the U.S. so they should be lurking in a junkyard at that age
they will fit an opel manifold ,just need the studs removed
this will give you a 24/30 mm choke group or 30/30 with a little work!!
 

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Intake Porting

Have you read Bob's article on Porting of the Intake manifold? The Opel side draft manifold is very restrictive. He wrote a great "How To" article on porting. There are pictures floating around as well.

Enjoyed the Pictures of your # 44 Manta. What are the class restrictions on wheels, tires and springs?

GL
 

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DirtTrackManta said:
I spoke with our track tech and he very nearly qouted RallyBob: "It needs to look stock." This leads me to be very interested in the Fuel Injection.
That opens up the windows of opportunity! We used to run a bunch of mini-stock Opels out here in CT years ago, and basically if it looked stock, the tech guys were gonna let it fly. Let me tell you, I got real good at 'camouflaging' stock modified parts and European parts! 2.2 cranks in 1.9 blocks, 1.6 heads, modified intakes, acid-ported exhaust manifolds, stock lift cams with 50 degrees more duration! Even built a double-layer firewall and stashed a Crane ignition box inside it, and ran the wiring through some vacuum lines....

Concentrate on the handling first though, if anything, there's not a car out there that can touch a Manta's suspension capabilities. Reverse the panhard bar, solid-mount the front crossmember, get a fast-ratio rack and pinion, alter your trailing arm attaching points, add some caster to it, etc. LOTS you can do!

Bob
 

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Discussion Starter · #19 ·
Scribble, scribble... OH I CAN PRINT!

RallyBob said:
That opens up the windows of opportunity! ....

Concentrate on the handling first though, if anything, there's not a car out there that can touch a Manta's suspension capabilities. Reverse the panhard bar, solid-mount the front crossmember, get a fast-ratio rack and pinion, alter your trailing arm attaching points, add some caster to it, etc. LOTS you can do!

Bob
Bob, I want to peer into that window! Any other ~must do's~ on the suspension is greatly appreciated too. I have purchased several books on weight placement and geometry but none of these would have given me information like reversing the panhard bar, etc.

Paul, Here are the rules for my wheels & Tires. Oh. I am not to use "racing shocks or springs" again. The appearance of stock is the name of the game.
(Enjoyed the thread on the manifold btw. :eek:

A. Steel wheels mandatory, maximum width 7”.
B. DOT passenger car radial tires, minimum 70 series. No recaps or racing type tires allowed. All tires subject to tech approval. Maximum “T” speed rating.
C. No wheel spacers or adapters allowed

Cheers,
DirtTrackManta
 

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I just moved this thread to a place better suited to where it is headed. The Racers Forum. Now carry on, so the rest of us non-racers can glean a few more performance ideas from the flow of creative juices...
 
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