What's a good upgraded throttle body for an 03' ecotec and is a spacer plate a good idea?
WHAT DO YOU MEAN I NEED TO TUNE MY CAR?
Spacers don't do anything for fuel injected motors unless you're using that to tap for chemical injection or nitrous. Unfortunately you're limited for throttle body options with the stock intake manifold. Best option besides a custom adapter is a ported stock throttle body. That will take you from 58mm to about 61-62mm. Up to you whether that's worth the cost or not.
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Depends on year you can get a throttle body off of a v6 blazer which is same as most cavys but bigger but won't do you much good if not boosting. Heads can only flow so much air if doing a port and polish then it will.
I have a 62mm TB and I paid $200 for it back in 2004!. I only had a crank pulley, 4-2-1 header, 2.25 exhaust with hi flow cat, WAI at the time. Noticed a nice difference in the TOP END (after about 4,500 RPM). I got a few ponies and I was happy with it.
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