ok something is wrong here..

with my base timing set to 0* and running the engine too cold and using my stock 235/75/15 I was running 15.45's at 96mph (GTECH TIME)


now I have base timing to 5* and the new thermostat allows the engine to get up to temp (about 175F) and I'm running my 255-50-16's.. best I could get was 15.85 at 88mph or something like that.. other times where 16 flat and 16.3

I dunno if not launching well makes a big diff in the time but I can't seem to hook up .. so I'll get on it and it starts to spin and then I let off and get back on it..

if I take off nice and slow and then lay into it I get a 16..

pavement is still cold here and maybe I should run like 30psi in the rear instead of 38 for the runs?????????

my buddy seems to think I should be able to get 14's out of it?

 

i would drop rear tire pressure to 25 psi at least. i wouldnt think you would be able to hook with 38 psi on a cold street

 

ya that seems a little firm at 38.. but for some reason kumho themselves told me to run 40 all around because of the weight of the vehicle.. I ended up going 40 in front and 38 in the rear..
maybe I'll try it at 25 just for a run. I don't want to ruin the tires..
or maybe I'll put my stock on the rear to do a run and put 25 in them..

anyone else have opinions? do you think I'm loosing more than a second from spining and stuff?

 

I hate to burst your bubble, but its highly unlikely that a bump in timing and bigger rims will take a mid 15's truck (or car for that matter) into the 14's. You *MAY* gain a tenth or two.

 

Agreed. Sorry

 

15.45 @ 96 is too quick and waaaay too fast for a CK pickup, even with your mods.

The GTech is typically 0.2 sec too soon and 2-3 mph too fast, as compared to track data, due to the differences in how the GTech vs track measures time and speed.

So 15.45 @ 96 should be more like 15.7 @ 92+ mph at the track.... which your truck MIGHT do given the mods, but ONLY if you have a custom ECM, and more specifically more fuel to feeds the mods. You won't get more power unless you have more fuel.

I suspect however that you didn;t have the GTech zero'd properly when you did the 15.45 run.... so the later runs were probably more representative: 15.85 @ 88 mph.... which at a track would be 16.0 to 16.1 at 85 mph.

Remember that your truck weighs as much, or more, as a fullsize Caprice, and you have the same engine (LO5). A neighbor of mine has a 93 Caprice with similar mods to your truck, and his car is a lot more aerodynamic. He's run 15.50 @ 87 mph at a track, and he too lacks fuel/ECM mods. So with a good launch (slightly warmer weather, lower REAR tire pressure), you might actually run 15.7 to 15.8 @ 85 mph at a track.

You will need to get more fuel to really see the benefit of the mods to your engine. It gets said over and over on this forum that speed density cars (and trucks) don't see significant performance gains from bolts ons because the ECM can't respond to the mods like a MAF-car can.

In summary - your 15.45 @ 96 GTech run was a fluke. Don't believe it. The 15.8 @ 88 mph GTech run is probably very representative. Lastly, IF you mods the fuel system // ECM, then you might see high 14s on a good day. IMO. HTH. - Ken

 

ok well I did a couple more runs tonight with 25 lbs in the rears.. (btw the 16 " wheels are actually a bit smaller diameter than the 15" 235/75's) I still can't get it to hook up as well as I would like.. I lay into the throttle about half way and it still spins both wheels and then I always for some reason end up laying into it more and spins even more..

anyway best run tonight was 15.22 @91mph

dunno If I should put my stock wheels on the back this week-end and run 20lbs or sometin..

 

Just for the heck of it, try setting the timing back 1° to 4° BTDC, and put a little weight in the bed.

The reason I say this is my TBI car runs faster at 4° than at 5°, and you might get a little better traction with something over the rear wheels (but not so much it slows you down obviously) .

 

do you have the same mods as me???

I have a custom chip the edelbrock sent me to match their heads,cam,intake combo.. they told me it had a very agresive spark curve.. apparantly it was made to use on regular fuel with base timing of 8 degrees.. I was getting a little pre-ignition with it at 8 and I was use 93 octain fuel.. at 5 it seems ok.

btw so everyone knows my truck weighs in at approx 4160lbs..

 

ttt