Opel GT Forum banner

Aug 2003 fastrack.

3496 Views 39 Replies 9 Participants Last post by  baz
It seems I have died and gone to heaven.

Am I reading this correctly?

It seems we have a competition adjustment in our favor. The 1900/Ascona and the Manta can now leagally use the 9.0:1 pistons and the GT intake valves.

On that note do the 40mm or 42mm intake valves create more flow in an unported head?

I know in the Volvo heads I have been working with the larger intake valves actually loose flow due to loss of velocity (no matter how the rest of the head is ported or the cumbustion chambers are modified).
1 - 20 of 40 Posts
Wow...awesome news. I had not read the new Fasttrack. It's about time we can use the flat-tops, the dished pistons are f*****g pathetic for a racecar.

The valves have been legal for the GT for a couple of years, a bunch of us had written to the BOD to get them legalized. For comparison, a stock 1.9 head flows about 88 cfm on the intake ports. With legal ITB prep work, I get them to about 92-94 cfm. With the 2.0 intake valves, it improves again to about 100-101 cfm.

All in all it adds substantial power to an otherwise restricted engine. The trick is to add the legal replacement valve seats (I use L-Joy intake and exhaust seats). The throat area is far larger, and with a 3-angle carbide seat cutter, the bowl area opens substantially and improves the airflow. Opels have fairly large ports compared to the valve area, so larger valves DO help the airflow here.

As you may know, Opel used gross hp ratings in the late '60's. So those 102 hp ratings on the early engines are overated. They are rated at 90 ps in Europe (about 88 hp). But I have found them to be closer to 82-85 hp in reality (at the flywheel).

With correct mods, 110-115 'real' hp is achievable. Mill head for 9.5:1 compression, use Total Seal rings, proper valve job with the bigger intake valves, 'Euro' camshaft, properly selected intake manifold, 32/26 Weber, and a good header....this will get the car competitive.

See less See more
Ok, I will take the head back to my machine shop for the larger intake valves. Are the L-joy seats common? Or will I need to supply them. Should I just get OE valves from Opel GT source?

I have a nice cam, and am using the 1.9 EFI. I was running a 32/36, but I feel the EFI provides better power across the board.

I have used a decent header and found them troublesome and too high RPM oriented. I am now using a sprint manifold with a custom made headerpipe merging into a 2.5" collector and 2.5" tubing all the way back to a magnaflow 4" round straight through muffler. The exhaust routs under the axle. Are you interested in pictures? The exhaust is off the car for my overhaul.
Yes, the FI will flow better than a stock carbureted intake and 32/36 Weber. Not to mention the longer runners are better for torque, which the Opel sorely needs.

In terms of a header, you simply need to get a proper header to reap the results the header can offer. There is no off-the-shelf header that works worth a damn, they're all far too short (usually under 28" primaries)v and only help high rpm power.

I agree the cast iron Sprint manifold offers a better torque curve than a shorty header. But a custom 4-into-1 header with 1.5 "primary tubes that are 36-38" long will run much better than a Sprint manifold. Not to mention, that's a lot of weight (the manifold) to be removed from the front of the car, and quite high up as well.

I'd try a 2.25" exhaust pipe too, 2.5" is too big for a 1.9 litre. It's 24.5% larger in area than a 2.25" pipe...which is a lot. You lose a lot of scavenging effect with that big a pipe. You might gain a touch on the very top end, but a smaller pipe will do much better in the mid range.

In fact, I use a 2.5" pipe on my friend's 185 hp 2.5 litre Opel engine! And that head flows almost 60% more than a 1.9's!

See less See more
Yes, I agree a proper header would be the best way to go, but It is not a priority for me right now. I know the sprint manifold will be reliable for me ( no leaks ) and provide good low end torque which is desirable in a relatively low RPM IT motor.

There are so many colliding theories in the exaust path to really make general assumptions (I am not saying that you were assuming anything). I will be dyno tuning the EFI and will then compare output as I try different setups. Right now I am subscribing to the theory that after the header collector you want as little backpressure as possible. I did run this setup through 3 drivers school sessions and felt the car was running real strong (and then it let go!) and this was with the Weber.

This time around I have the ability to really gather empirical data to make sure I am going the right direction.
IT Manta said:
Right now I am subscribing to the theory that after the header collector you want as little backpressure as possible.
No problem, I'm not telling you you're wrong. I agree, you actually don't want ANY backpressure, but if it's done at the expense of velocity, power will suffer at lower rpms. And a strock engine simpy does not have enough exhaust gas volume to need such a large pipe.

I'm simply passing along my information gleaned from years of building Opel engines, porting/flowtesting heads, and dynoing them. It's VERY dangerous to run too open an exhaust on an Opel....they already have too high an exhaust/intake flow proportion, and too little backpressure will result in extreme EGT's (over 1700 degrees F are common on dyno runs)
This will definitely contribute to failed exhaust valves..... regardless of air/fuel ratio.

Just trying to save you the trouble of R & D on your own!

Definately appreciated Bob. I will proceed with caution. I have a spare EGT setup, but no real good location in the sprint manifold to test all cylinders at once. The EFI should be pretty even though.
First, you should double check the fast track. I petitioned the SCCA comp board and provided them with the information needed to get both the 42mm valves and 9.0:1 compression. (July Fastrack). However, I have not received confirmation of the change. (I also have not gotten an August issue of "Sports Car".

Now, I'm going to get into your wallet. I have been building race and championship winning IT heads for years. They have been protested and torn down and they are LEGAL. So, if you want to run up front you have two choices. First, convince Rally Bob to come out of retirement and send it to him... he's built a lot of winning heads too.... or second send it to me. You're local machine shop just wants to make money... and they probably didn't (or still don't) know how to spell OPAL until you showed up. Rally Bob and I want OPELs to win. Yea... we have to make money... and it will cost a lot more than your local machine shop... but running at the back of the pack sucks.

Or, you can pay them now and then pay me (or Rally Bob) after you get your doors blown off.
See less See more
I just re-read your post... about the cam... as long as your "nice cam" is a "stock" cam... you're OK. ITB only allows a "stock cam". Oh yea... and we do headers... not cheap either. Hummm.... as I re-read, we've got lots to talk about. email me: [email protected]

Also go to the performance forum on "High Performance Engine Build-up: http://www.opelgt.com/forums/showthread.php?s=&threadid=1574
IT'S TRUE!!!!!!!!!!!!

I just checked out the SCCA web site and the Aug Fastrack is posted!!!!


Break out the Manta's and Ascona's

Wanted - 1975 Manta... I don't care what condition the engine, or interior are in. I just care that it runs well enough to verify that the FI pieces are working properly. Body/chasis must be straight.
Bob couldn't you get a regular Manta/Ascona and put FI on it

Opel FI is easy 7 wires and a ground.

the fuel tank part is different but that would not be a big deal

the stock can the ECU is in is big also and you might be able to fit a VPC or F-CON inside

basically lock the AFM wide open and run it that way

IT Manta said:
Definately appreciated Bob. I will proceed with caution. I have a spare EGT setup, but no real good location in the sprint manifold to test all cylinders at once. The EFI should be pretty even though.
If you have to make a choice as to where to check EGT, cylinder #2 always runs hottest on a 1.9 head. Cylinder #3 is next, then #4, then #1. This is why I ALWAYS read spark plug #2 when looking at air/fuel.

How much difference? About 200-225 degrees variation from cylinder 1 to cylinder 2.

Why? Higher exhaust flow on cylinder 2 exhaust port, which tends to overscavenge. It is also right next to to exhaust port #3, so they share a lot of heat (no water between the ports).

Edit: I almost forgot, if you are going to run the 1975 exhaust manifold, there's a little racing trick that helps. Weld a divider between ports #2 and #3, it reduces the turbulence at the exit of the ports, and helps with engine tuning. You can see it in the spark plugs. We used to do this in our 'stock' class circle-track racers.
davegt27 said:
Bob couldn't you get a regular Manta/Ascona and put FI on it
Come on Dave, you should know the SCCA better than that! You can't 'create' a model of Opel that doesn not exist. So technically, you could not put FI on a 1971 Manta, they never came that way, only the 1975 model. UNLESS you switched over all the nuances of the 1975 Opel such as the big bumpers, the side impact beams, the frame reinforcements, the bigger brake booster, removed the B pillars and inner rocker panel reinforcements from the early Manta, etc. I suppose you could swap everything into a 1974 Manta and no one would say anything, they are esssentially the same car ('74 and '75).

TGSI, don't tell me you are considering coming over to the 'dark side' and running a model 57! You'll love the suspension of a Manta compared to the GT!

Well, this certainly opens up things for my own ITB Ascona, so now I have something to look forward to....at least a little more power.
I suppose you could swap everything into a 1974 Manta and no one would say anything, they are esssentially the same car ('74 and '75).
74 Manta on ebay.
Wow, they are all of 2hrs away from me. Are those dual sidedrafts I see? Must resist urge to build another Opel.
The GCR clearly states that updated or backdating between a specific model is allowed as long as the update or backdate is done as a complete assembly.

We won the SF regional ITB championship in the eary 90's with a 74 manta that was converted to EFI.
Yes, that's what I was getting at. You can't create a 'super Manta' by using the best of the early stuff (every thing was lighter) plus the best of the late stuff, e.g., no mixing parts. So to make an FI Manta, legally ALL the stuff that made that car a '75 FI model must go into the earlier car. Including the block with the relocated heater hose, and the later crack-prone heads. Gray area, I know, and most tech guys don't know the difference, but by the book it's not legal. Otherwise, I'd have a flat-top 1971 block, 1.9H head, GTE camshaft, fuel injection, and a late 1970 Manta out on the track! All stock parts, but they never came together on the same car......

I have an Ascona I'm prepping for ITB right now. It's a 4-door though. So even though there was a 1975 Ascona with FI, they only imported the 4-door from 1971-1973. So I can't legally use the FI in that car, I would be creating a model that never existed.
Bob (Rally)- Could you expound a little on the sprint manifold weld up? My engine is still out of the car and I don't have the sprint manifold bolted on quite yet. Wouldn't happen to have a picture would you? When I get home I'll pull it off to see if I can figure out what you mean.


You may "update" a car. Thus, you may take the FI and Big brakes from a '75 and put it on anything earlier. I'll get the 2003 GCR page & paragraph later this evening... I've got to get some work done.
A bunch of stuff to address, so this will be kind of long.

As promised, here is the GCR rule from the SCCA 2003 rule book.

Paragraph 17.1.4.C (pg ITCS-6) says in part:

To maintain the stock basis of Improved Touring, updating and/or backdating of components is only permitted within cars of the same make, model, body type (eg., sedan, station wagon, convertible, etc.) and engine size as listed on a single Improved Touring Specification Line. Any updated/backdated components shall be substituted as a complete assembly 0engine long block, transmission/transaxle, , differential/axle housing.) No interchange of parts between assemblies is permitted.

...(TGSI NOTE: that takes care of the FI system. It goes on.) ...

No interchange of parts between assemblies is permitted, and all parts of an assembly shall be as originally produced for that assembly (such parts may, however, be painted or plated). Additionally, it is not permitted to "create" a model or type of car by updating or backdating assemblies.

... (TGSI NOTE: it goes on to say a bunch more about the manufacturer "superseeding" parts are OK...

So, we are not creating a new model. The Manta 1.9L was/is the model. We are not creating a new type of car... we are not creating a Yugo nor an electric/steam/flux-capacitor powered car.

Would any year Manta work just as well? Yea... considering all the stuff it takes to turn it into a front running ITB it really doesn't make a lot of difference. It's just easier to get everything all at once and know it's working to start with... then replace it all. The FI rules require a stock harness too so that would be a lot easier than creating a new "stock" harness. In reality, very little of the stock stuff will get used without being replaced or having significant changes... I don't even care about the computer except for the housing. The rules allow anything inside the stock housing.

The '75 does also have the "big brakes"... but I would go with only new rotors and calipers. I could just as easily "update" an earlier model, so earlier brakes don't really matter. I did just think of one thing. The early Mantas didn't have the big 5 MPH bumpers and they're ugly. So, I guess any Manta would be fine.

Rally Bob... Come over to the dark side? I guess that I've always been on that side since I've always liked the Mantas a lot. It's just that they could never legally be made to run anywhere near the front. As far as handling goes, I think a properly done GT and Manta will be about equal. So the real difference will come down to the FI. With a real engine management system (electromotive) stuffed into the stock housing, the FI will probably make enough more HP to bring me completely over to "the dark side".
See less See more
1 - 20 of 40 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.