A Stock a Manta has say 89hp give or take
With fuel injection 100-105
A stock '71-'74 Manta is rated at 75-78 hp. I've found this number to be closer to 62-65 hp at the flywheel, and as little as 45-50 hp as measured at the rear wheels. A 1975 FI Opel was rated at 80 hp, so you can figure a few more hp as compared those earlier engines...
The most recommended bolt on street set up on the Opel web sights the one with ported intakes, a proper exhaust and a 38 Weber has around 125hp. Car runs well enough and money is not a major factor yet
Yup, this is a realistic number, and about double the hp of a stock 1.9 engine.
The 1.9 to 2.4 with dual Webers as built to your article specs and advice gleaned (mostly from you) from various web sights gets say 150 to 170 real hp though it depends on the individual build of the engine. Your engine now costs about as much as your car does if you have a nice car.
That hp is definitely attainable, but of course it depends on the head mods, cam choice, etc. But simply increasing the displacement mostly adds torque
Still with this set up here stock trany and rear end can still be used but big brakes are now a must and the suspension should be upgraded at this point also. Sportwagon springs, a couple of 3 extra sway bars, koni’s etc. So far I have done that this is the point that my manta is now
I find since I live in a major metropolitan area that I don’t drive much over 100 for any reason so I guess I can rule need for top end out. The reason I say that is until now the different car builds are balanced.
Now that I have driven the car I begin to have some idea on what it can be used for.
Assuming that I have 165-170 hp right now (give or take ten hp) what is the easiest and or the most cost efficient way to reach say an additional 50 to 100HP?
The most cost effective way is via nitrous oxide. However, as we know nitrous oxide is not a 100% thing, it only works when you fill the bottle! You won't get a streetable 50-100 hp more with a naturally aspirated engine though (even twin cam), at this point some form of forced induction is required
At what point do you realistically HAVE to swap rear ends? 190hp, 200 hp 225? 250?
I can tell the 4 speed has sort of reached it limits right now.
It depends a lot on your driving style. Drag-race type starts and power shifts can destroy stock Opel stuff with 100 hp. But a stock rear end can take 190-200 hp assuming it's not used for hard launches and has a limited slip. Torque is really the killer, that and shockloading (shifts and launches). A turbo engine will make some serious torque...it will kill parts quick. My friend's roller-cam 2.5 has torque, and puts a hurting on the stock torque tube and even the Getrag 240 5-speed. I've found that for the kind of driving I do (weekend racing), a stock Opel differential will fail at 150-160 hp pretty readily.
I guess I would like the car to keep up with any stock car sold on the street for under $35,000 today. With a 2100 pound car I am guessing (and I mean guessing because I don’t know) 250 to 300 hp is need to do that. I guess I am looking for a way for a 4 banger to keep up with the modern 6 cylinders.
When we were considering running the Grassroots Motorsports challenge, we figured that we needed our 1800 lb (gutted) Manta to have 220-225 hp to run low 13's in the 1/4 mile.
I was going to use a Chrysler T3 turbo, since that was what we had to work with. But that would have been running that turbo on the 'ragged edge' of compressor efficiency....a bigger turbo would be better. But turbo technology is great, you can get a modern ball-bearing design turbo that has better response than that old T3 Chrysler, and makes 50-100 more horsepower too!
The throttle bodies that Tom Drake started using along with their aproximent $2500 cost will bring how much more power? I guess that would be the easiest since it would all be just bolt on and I don’t have to change my pistons. But is it enough?
No, it's not enough. They gained Tom 4-10 hp at various points in the power band. I know from your talking you want more.
The small turbo set up (after I changed the pistons) if I understand correctly, would be good for low end and middle grunt ,would bring how much more than the throttle bodies? Changing pistons is not the end of the world either as they are reasonably priced.
Depends on the turbo sizing again, but 250-300 hp is very attainable. BUT, you must use fuel injection, and you will need a stand-alone programmable ECU. You will need new, bigger fuel injectors than a 1975 Opel has, you will need the high pressure pump, high pressure fuel lines, a fuel pressure regulator, an intake manifold (1975 Opel works great), etc. This is where the real costs are. A good, ball-bearing Garrett GT25 or GT28 turbo is only about $800, quite reasonable for the power they can make. Most of the money is in the engine management. http://atpturbo.bigstep.com/item.jhtml?UCIDs=1253720|1254406&PRID=1387272
I guess that another rear end and a tranny will be needed. Up to what point is a 5spd Getrag good till? If that isn’t good over 200HP then I am leaning toward a used Quaife (and the noise) because I think it might be cheaper than a used zf.?
The typical 240 Getrags start to make noise before 200 hp. So you'd need either a 265 Getrag, a ZF (rare), or another tranny. The Quaife is a good choice.
What to do with the torque tube? No sooner than you add HP, change the tranny and rear end and it will go. At what point do my brakes become obsolete?
I am guessing it is about $1000 for every 10-20 horsepower (sadly) from here on out.
Assuming you have a limited slip, the next weak link is the torque tube itself. If you add a limited slip, then reinforce the torque tube, you can get away with 250 or so hp. A cheaper alternative would be a rear axle swap, similar to what Travis did with his GT....he added a Toyota truck rear axle. The rear drums from the Toyota could be retained (they're big), but you'd need to upgrade to bigger front brakes. Not a bad idea anyway.
However that is still cheap in comparison. If I can put another say $5000 in the Manta and get 250-275 HP I will have a car that will keep up on the street with the M3’s and little two-seater BMW, Nissan’s and Audi’s. The cheap part is that I have spent only about a 1/3 to 1/2 of the costs of a new car (which I could never afford) and have a classier car. It is a given that I am not interested in things like soundproofing, electric gadgets, heated seats and AC, just a car that performs.
What are the options for achieving more power?
PS
I still think those 16 valve heads look saturunish. Didn’t Saturn get their early motors from Opel's. Those sc1 and sc2 heads couldn’t be made to work cheaper than cutting down the 6clyender Opel heads?
While Opel and Saturn are indeed related, and the early Saturn single-cams were somewhat based on the CIH engine design, the bore spacing, deck heights, bore-stroke ratios of these engines are entirely different. The biggest factor is the bore spacing. The CIH Opel has a big bore engine...this means it's a long block. The Saturns are completely opposite, they have long strokes and tiny bores....so the combustion chambers in the head would not line up with the bore in the Opel block.
However, if you want to use the Saturn parts so badly, why not swap the complete Saturn twincam engine into your Manta? A nice lightweight aluminum block, 123 hp stock.....sure would be easier to install the entire engine than try to swap the head. It might not be a bad swap, the worst part is adapting a tranny.
Bob
