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GT Resurrectionist
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I'm going to buld my motor soon and have some questions. I plan on shaveing the head and porting the exhaust. I was thinking shave the head .030. My question is how much can I shave the head and be safe? Im using standard bore rings,and standard main and rod berings. I guess the main question is what can you do ( CHEEP ) to a 1900 to get the most out of it? I know the big thing is change to weber. What kind of HP can I get?
 

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Considering cheapness....

Best HP bang for the buck (IMHO) is to port the intake. Doesn't cost much other than time. I wouldn't shave the head on a '70 GT - it's already high in compression, and real tough to run sans fuel with higher octane ratings than 93 RON. Head milling is best left to the 72 and up low-comp motors, and should not be done willy-nilly - there are rules to follow that Rally Bob prolly knows like the back of his hand.

Get it all to work TOGHETHER. A port-matched, fine-tuned motor will outrun the work of a poor slob who thinks HP is a matter of bolting on stuff.

While we're on the subject - has anyone done an analysis of the parasitic losses of the water pump? I did this once about ten yars ago, and the result was a 5HP (prox) reduction in parasitic loss with a trimmed pump impeller - but I don't remember how much had to be trimmed.

HP is a matter of airflow management. Get as much in/out as possible with minimal presure drop. You should always keep this in mind when it comes to engine mods. After that, you can pick up 'free' HP by reducing parasitic losses - make stuff lighter and lower in frictional losses. Mostly science - some art.
 

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70 GT

If you are not a member of the Classic Opels Group on Yahoo

http://groups.yahoo.com/group/classicopels/

Then you need to JOIN. The topic of head work has been covered in great detail. Search the archives under Head, Valves, Legere (RallyBob), etc. Lots of good info to digest, tooo much to retype here. For example you will find: "That the head can EASILY be milled .050 with std valves or even somewhat larger valves. (say 42mm intake). But then the cam will be retarded by 2 degrees for every .025" milled. This can then be corrected by one of several methods. The stated 9.0 compression ratio of the high comp engine, is really only about 8.38 : 1" So if done properly and mated with other reasonable mods, you should not have much problem with running 91.

Again, don't take just my answers, I may not have all your specifics or have taken something out of contest. Search the Archives in Classic Opels and STUDY ALL the info and develop your own plan.

Good Luck
Paul
 

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chuckspeed said:
While we're on the subject - has anyone done an analysis of the parasitic losses of the water pump? I did this once about ten yars ago, and the result was a 5HP (prox) reduction in parasitic loss with a trimmed pump impeller - but I don't remember how much had to be trimmed.
It doesn't really relate to street engines, but a former customer of mine (back in my Opel parts selling days) dynoed one of his road racing engines, and found that the underdrive pulleys I sold back then (crank and water pump) were worth 4 hp on a 170 hp engine. Personally, I didn't design them for the power gain, but rather for the cooling advantages. The stock water pump is overdriven, it spins faster than the crankshaft speed (about 10%faster). At higher rpms, our racecars used to get hot FAST, the temp gauge would move in a linear fashion relative to engine rpms. The pulleys reduced water pump speed 34% and the alternator by 12%. Water temps dropped from 230 to a more manageable 200-205 degrees at 9000 + rpms. Pump cavitation was the culprit here, it was simply turning too fast. We also had to remove the thermostat and ran a 7/8" restrictor washer to slow down the water flow through the radiator, allowing more time for the water to be cooled.

Years ago I wrote an article in the OMC's newsletter (the BLITZ), and I harped a bit about parasitic losses. Driveline friction, rotating mass, etc. Simple things like the underdrive pulleys, electric fan instead of 7-blade (noisy) fan, lightened flywheel, sticking with 13" wheels and choosing a lightweight design (less inertia), synthetic lubricants in engine/tranny/rear axle/wheel bearings.....it all adds up. Sure, it may not gain you 20 hp, and it may seem redundant on a 65 hp stock engine, but there comes a time when your cash investments into the driveline start delivering diminishing returns, and you find that while the first 20 hp only cost you XX dollars, the next 20 will cost you XXXX dollars and be harder to get. At this point, the detail stuff starts to make sense, and 'frees up' some of that hidden horsepower.

Bob
 

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Bob-

Funny you mention cavitation.

Maggie the Opel was out on the freeway the other day, zipping along with great joy de vivre. At speeds below 70 MPH, engine temps ran within a few degrees of the 165 degree stat. Above 80, tho...The motor began to build heat. The faster Maggie went, the hotter she got. when we got on the connector and motored at 65 MPH - temps dropped almost immediately

Cavitation is a function of impeller vane tip speed. A series of runs on the freeway should identify at what speed the impeller cavitiates. It appears this cavitation speed is rather low - aroind 3700-4000 RPM.

Please note I was asking about impeller trim - not underdriving the pump. A trimmed impeller will have lower vane tip speed with minimal reduction in performance at/near idle, whereas an underdriven pump can cause circulation loss at idle. The Opel pump impeller is desiged to be made cheaply, no pump water well. I's actually a very inefficient design; a few changes would improve circulation and allow it to be trimmed - win/win.

Pump parasitic losses vary as the cube of the speed of the impeller. Therefore, if you have a pump that draws 1 hp at 3000 RPM, it will require 12 HP at 6000 RPM - or it will cavitate and beat the bearings and seal to death inna race motor.
 
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