sbc 383 with gt4788 help with exh housing
07-07-2010, 09:38 PM
#23
Ok cool. Vee8 has been working on another members car(they call it the cookie monster) and it has the Precision GT4788 on it and made 1000+rwhp and no mention of backpressure issues. The Precision unit is more efficient than the garrett although I think the exhaust housings are the same. Keep in mind that this car has a 370ci motor but I dont see you having issues even with a 383 at 13psi. That isnt ****. I just think you have alot more going on than the turbo. It should make good power past 13psi. Granted it will hit a point where it will be expected on your setup to fall off due to backpressure. Let us know if you get any improvement out of the straight 5 inch DP.
On the dyno we have yet to see more efficient
..... GT47 will have backpressure problems period. They use the same turbine wheel....can't cheat physics.
07-07-2010, 09:39 PM
#24
07-08-2010, 12:39 AM
#25
I should have used the word "powerful". The precision version does make more power. Precision confirmed this when I ordered my 4788. And mine has the billet wheel. I hear it makes a **** ton more power in the middle of the curve. Cuts spool a little. Only one way to find out....
07-08-2010, 06:18 PM
#30
Yeah, I think you're chassing the wrong problem. At 15 psi, you have lots of exh pressure going out the WG. You got a pretty big exhaust housing on there also. You sure that your timing isn't coming out due to some modifier table in the tune? Maybe IAT.
07-08-2010, 08:08 PM
#31
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i have bigstuff3 it shouldit be pulling timing out and i have a air to water temps dont get over 75deg. and i meet be chassing the wrong promlem i just cant find anything eles acting up but am not sure where eles should i be looking thx every one
07-08-2010, 10:42 PM
#33
You have another issue. Maybe several actually. No doubt headers would prove to be much more efficient although that alone shouldnt cause the problems you are having. Stick with a single 5 inch dp and see what you get. I wouldnt even swap the housing just yet. These things see 1000rwhp fairly easily.
07-09-2010, 06:57 AM
#34
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yea for sure wut am going to do is get my back psi reading with the 4" and muffler than get a reading with out the muffler than put the 5" down pipe reading and ill post it up here am building the 5" down pipe right now should be done in a few days
07-09-2010, 09:30 AM
#35
Both myself and MightyMouse are running PT88's with T4 .96 backhousings and making over 1000 rwhp. Granted that we have almost 20 less cubes than you but that shouldn't be that big of a difference as your exhaust housing is huge compared to ours.
Try putting in a heavier spring in the BOV. On LS2Formula's car, we were having a problem with the BOV cracking open going down the track. That took us a while to figure out as it didn't start to happen until we turned it up over 20 psi.
Try putting in a heavier spring in the BOV. On LS2Formula's car, we were having a problem with the BOV cracking open going down the track. That took us a while to figure out as it didn't start to happen until we turned it up over 20 psi.
07-09-2010, 10:13 AM
#36
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ok I can try that see if that helps but my boost don't fall of at all and even with the big housing T6 1.39 I can make 14psi on the Trans brake no prob use a MBC
07-10-2010, 03:58 PM
#39
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ok with the 4" down pipe dumping by the pass side front seat at 18 pounds of boost it had 42 pounds of back psi with the 5" dump right down at 18 pounds of boost it had 21 pounds of back psi and it pulls all the way thru the rpm and don't flat line so thx for all the help does anyone know of a good 5" muffler I can use