Low compression STS 408 with 10lbs with a problem
09-16-2005, 12:22 AM
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Low compression STS 408 with 10lbs with a problem First let me tell you my setup I am running Forged 408 with 8.7compression, comp custom cam 234-230 .604-.598 116+2, Stage 2 patriot heads, comp 850 lifters, manley 7.400 pushrods, and Comp cams 1.75 rockers. We got 2 pulls done before we decided to pull back to find out whats up. The car is a built 4l60e with a 3500 stall. We hit 473 rwhp 4300rpms with 10lbs and 12 degrees timing. At 5700 rpms the car shoots down in power. I dont have the dyno sheet here. But usually with valve float it gets erratic it was smooth turn down tho. Other than valve float we think it might be a spark plug wire coming loose, due to the fact we have VC spacer on the car and they look to be stretching the wires so we are swapping out those tomorrow for some truck wires(longer). Am I if valve float was happening it would look like a siesma graph and not a big smooth turn down. I also am running a gt-76 turbo and no way am I oiut spinning it. I think Ill check for leaks too tomorrow. The car gets up on 10lbs boost well under 4k and my AFR is a smooth 11.6. I also have meth and a IC. Would a leak cause that? You guys input would be most appreciative there is anything else I am missing to check. I am trying to fix this so I can add the some real boost. I am also using a eboost controller if it makes a difference. The fuel system is a copy of mighty mouses with accelronics inj driver and 75lbs.Let me know if you need more info.
09-16-2005, 02:16 AM
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AR .70. I also have Long tubes, but I didnt think to check til I was typing. I very well couldnt check on the dyno. I was looking under there today and saw with my new K-member I have enough room to reroute the tubing to the inside of the driver side long tube and over the k-member. Has anyone else been able do that. That tubing underneath the k-member is a pain in the ***. Its been smacked twice. So that and leak hunting will be on the agenda tomorrow. That is what I thought. Thank you Jose.
PS Love the Eboost Great and quick service from you Jose
PS Love the Eboost Great and quick service from you Jose
Last edited by sagres; 09-16-2005 at 08:12 AM.
09-16-2005, 08:27 AM
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Well the A/R doesn't seem to bad, I would be curious to see what wheel though is being used. Also without addressing the leak first its hard to tell what the problem is. Just by the look of it the turbo itself doesn't seem to be the issue.
Jose
Jose
09-16-2005, 08:51 AM
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Check for leaks on both the HOT side and the COMPRESSOR side of things. A 408 even with that low of compression should still make at least 1hp:1ci. What were your piston rings gapped at? If I recall correctly, the bottom ring should be .25-.27 and the top ring .27-.30...or vice versa, I always forget ring gap.
Along with checking the compressor side, check your IC as many times people weld in provisions for brackets, probes, etc. It may be leaking out one of those ports.
Did you Dyno the motor N/A ? How much power ?
Along with checking the compressor side, check your IC as many times people weld in provisions for brackets, probes, etc. It may be leaking out one of those ports.
Did you Dyno the motor N/A ? How much power ?
09-16-2005, 09:47 AM
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I know I am not as much of a turbo guru as JZ, but the ar seems a bit small to me, I use a .80 on my 346 and its a stock engine to boot! You might want to check the backpressure in the exhaust as it could be choking it off...Just a thought. My A/R seems to work very well for stock displacement as it sees full boost by 3000 RPMwith the same turbo, so you quite possibly could have it too small for the larger built engine. I talked with STS about my setup and when I get the built 382 in the car I will be using the larger A/R which is a .96 so it seems a bit too small for your combo to me.
-Bryan
-Bryan
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09-16-2005, 09:25 PM
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No- that only works under pressure, at idle, the intake is under vaccuum.. Use brake cleaner or an aerosol that has flammable stuff in it on the cold side and use like a cigar or cigarette on the hotside and see if you can find any drafts that would cause the smoke to blow erratically..
09-16-2005, 10:40 PM
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I know this may seem very basic, but are you sure your pushrods arent too long? You have a large cam with aftermarket lifters and 1.75 rockers. Just a thought.