Fine Tuning GMPP Motor...........Please offer up some advice
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Joined: Dec 2005
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From: NW OH
Car: '79 Cutlass
Engine: 357cid
Transmission: 200-4R
Fine Tuning GMPP Motor...........Please offer up some advice
Ok first of all here's the combo: GMPP 350H.O. 330hp out of the box.. mods include Comp Cams XE274 (230/236* at 0.050, and 0.487/0.490-inch lift, 110-degree lobe separation), Vortec heads milled down about .025 + thin fel-pro head gaskets(compression is close to 10:1), studs and corresponding Comp springs installed, stock HEI distributor/MSD High-Voltage Module with built in rev limiter set at 6000rpm, has 1-5/8" Long tubes into x-pipe and 2.5" dynomax bullet duals. '97 T56 6 speed and 4.10s. Currently has a 1405 600cfm Edelbrock but I have a 1407 750cfm Edelbrock waiting to go on. I am trying to get it dialed in and I have a few questions...
1.) What should I set the timing at? It's only adjusted by sound right now..It's pretty close but I am going to put a light on it to get it perfect.
2.) I have a distributor advance curve kit with three different sets of springs. Which set should I run?
3.) The 750 carb came with an assortment of primary jets, secondary jets, metering rods, and step-up springs. A performance tune for a 750cfm out-of-the-box is as follows Primary Jets - .113, Secondary Jets - .107, Meterings Rods - .071x.047, with an Orange step-up spring. Should I set it up like that to start out or change something?
4.) Any other suggestions are greatly appreciated! I am shooting for high 12s with slicks when I go to LaRue on May 30th. Thank You
1.) What should I set the timing at? It's only adjusted by sound right now..It's pretty close but I am going to put a light on it to get it perfect.
2.) I have a distributor advance curve kit with three different sets of springs. Which set should I run?
3.) The 750 carb came with an assortment of primary jets, secondary jets, metering rods, and step-up springs. A performance tune for a 750cfm out-of-the-box is as follows Primary Jets - .113, Secondary Jets - .107, Meterings Rods - .071x.047, with an Orange step-up spring. Should I set it up like that to start out or change something?
4.) Any other suggestions are greatly appreciated! I am shooting for high 12s with slicks when I go to LaRue on May 30th. Thank You
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Joined: Jan 2008
Posts: 274
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From: Kitchener, ONT
Car: 2000 SS, M6
Engine: Modified LS1
Transmission: T-56
Axle/Gears: 3.42
Re: Fine Tuning GMPP Motor...........Please offer up some advice
1.) What should I set the timing at? It's only adjusted by sound right now..It's pretty close but I am going to put a light on it to get it perfect.
~ 20 initial
36-38 total
Measure the total as it's most important. You will need a dyno, or track
to get the best power/MPH for the timing.
2.) I have a distributor advance curve kit with three different sets of springs. Which set should I run?
Swap in lighter pairs, or mixed springs progressively lighter and do
acceleration tests.
0-60 , or 60 foot times at the track will indicate the best advance curve.
You should be able to feel the difference when changing these springs.
3.) The 750 carb came with an assortment of primary jets, secondary jets, metering rods, and step-up springs. A performance tune for a 750cfm out-of-the-box is as follows Primary Jets - .113, Secondary Jets - .107, Meterings Rods - .071x.047, with an Orange step-up spring. Should I set it up like that to start out or change something?
deposits.
Alternatively, tune the carb under load on the dyno/track for best results.
Are you able to post pictures of the plugs? You will need a shot of the
ground strap, close-up of the center electrode, and a shot of the core
and base ring. You will need good lighting and focus to get a shot of
the core.
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