[RallyBob]

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.

Bob

 

[RallyBob]

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!

Bob

 

[RallyBob]

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!

Bob

 

[RallyBob]

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.

 

[RallyBob]

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.

 

[RallyBob]

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.

 

[RallyBob]

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".

*****I think you will like the Manta's greater suspension tunability. It has a better camber curve, more caster available, less bump steer, a wider track, a solid-mounted rack and pinion, more suspension travel front and rear, better shock absorber geometry, etc.

I recall in the days when I crewed on my friend's 'Mini-Stock' Opel Manta...the guys running the Nascar Modified Tour cars would stare at the car's suspension, and remarked that it looks like it was built as a racecar from the factory...they liked the suspension that much. The only criticism was usually the lower a-arm/sway bar attachment on the front suspension...but rightly so, it's the worst part about the car.

Bob

 

[RallyBob]

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.

I'd still consider running a '71 or '72 Manta. The heavy bumpers/frame reinforcements add a bunch of weight. There were no side impact beams in the doors (another 22 lbs off the car). As I mentioned, the earlier Mantas had no b-pillar (I think I inverted this statement in a previous post), but had a double-layer inner rocker panel. This adds a lot of chassis stiffness, similar to welding a rollcage tube along the inside of the rocker panel. Just my 2 cents worth.....this would be my first choice for a Manta.

 

[RallyBob]

TGSI, although the Manta has 54% front weight, a lot of it can be altered legally. An aluminum radiator helps a bit, a header is lighter than a cast-iron manifold, the main hoop of the rollcage can be shifted rearward, as can the driver's seat (assuming the driver has long legs!). The fuel cell can be shifted aft a touch too.
All these things ad up and can make about a 2% change in front/rear balance.

 

[RallyBob]

Well, regardless of the FI issue, I'm just happy I can now legally run the larger intake valves and the flat-top pistons. It would suck running my Ascona with *75 hp* against the local Volvos with 148 hp (dynoed numbers!). Now at least I know I can get 110-115 hp with legal mods and a Weber.

Bob