Help on modifying Old School Magnuson MC220 Twin Screw Supercharger

[alnukem]

Hi, I bought a 81 vette with a Magnuson MC-220 Supercharger, headers & a Doug Nash 5 Speed. Very nice old car! It runs well, but I think I want to make it a little healthier. I was considering the following, let me know your thoughts.....

1) Change the rearend from 2.72 to 3.36, the Doug Nash 1st gear is 3.27.

2) Swap the stock heads to something like the Profiler 195cc heads with the smaller 65cc chambers. The stock compression is 8.2, this will probably bump it to about 9.2.

3) The stock cam is the L-82 Grind, 222/222 450/460 114. Magnuson said a cam change greatly improved power.....I don't know where to go with this? I love a really drivable cam.

Thanks & please let me know if you have some insight on this.

[RICHARD TILL]

Change the rearend first. Why not go just a wee bit lower on the gears? That`ll wake it up real quick. Next change the cam lifters and by all means the springs. I`ve always found Bullit Cam Co. to make good recommendations. Ever heard of a forum called Speed Talk? Very informative.

[alnukem]

Originally Posted by RICHARD TILL

Change the rearend first. Why not go just a wee bit lower on the gears? That`ll wake it up real quick. Next change the cam lifters and by all means the springs. I`ve always found Bullit Cam Co. to make good recommendations. Ever heard of a forum called Speed Talk? Very informative.

Thanks Rich.....I think I'm going to do the gears first & install a boost gauge before anything else. From doing some research I have found 3.31 & 3.54 gears, the Doug Nash is only 1 to 1 in top gear. I am only going 3.31 because of the ultra-low 1st gear ratio. Here's how the math works out

81 vette 3.28 1st gear x 3.31 rear end = 10.85

90 ZR-1 2.68 1st gear x 4.09 rear end = 10.96

Actually, pretty close! I am sure I will do a Head/Cam, I think I should see where I'm at first. I always get ahead of myself!!!!! Thanks!

[Hog]

My 57 runs a 3.36:1 rear gear with a 1:1 high gear and its a decent all around gear for a driver. With the blower you dont require the same gearing as if you were naturally aspirated. I personally wouldnt go any higher than 3.42-3.73 if not running an OD, of course depending on tire height.

Of course heads would help, you will probably lose some boost, but boost is merely a measure of restriction, not a measure of power. Only a dyno or the mph reading at a drag strip will measure power.
Boost can drop while power goes up markedly. Kinda like blowing through a straw vs. a garden hose. Sure it requires less pressure to blow through a garden hose, but the amount of air moving is much more.

So far as a cam, you can get decent gains and still remain driveable. Cam and heads will really wake up you combo.

[alnukem]

Thanks for the reply Hog. It's a very cool old car, I kinda like it. This is not a max-effort. I am going to stick to the 3.31's. I haven't plated it yet, so my driving has been limited to the one 25 mile freeway drive home & some "couple mile rural drives". It seems to have a lot of bottom end now, so I think this might be the ticket. I'll get the gears & boost gauge in this winter, then evaluate & maybe try to build a badass exhaust from the stuff I learned here. Early spring I'll dyno it & go from there. Do you know how many people don't realize.....dropping restriction ends up lowering boost, which increases HP/TQ??????? Here's a couple more pics

Peace out!

[USAZR1]

That is a very cool ride! Love those twin blower set-ups.