dds92780 Posted February 23, 2015 Share Posted February 23, 2015 So right now i have 20 percent oversize injectors, pump turned up enough to get a puff of black then grey then disappear.My truck is a 95 mack e7 350 MECHANICAL 442 rears stock trans (RTXF1409B)Problem is that im on a stock s3b turbo and i get 32-35 pounds of boost by 1300 rpm. Truck runs great and pyro temps are low and i can get by using half throttle all day long.I was told getting a bigger turbo is going to really help with breathing better and saving fuel. How can it breathe better though if ive got more power and my pyro temps are only 700-800 all day long currently?i was all set to get a s400 turbo that is designed for 400 hp and has a size of 1.25 exhaust size. Only problem is that i was told that i need a 5 inch exhaust to make it fit. In understand that 5 inch will make it breathe better and all that but arent i just making a recipe for the engine to blow up or blow a headgasket? This is my work truck and it has 450k on truck now.If i get 5 inch exhaust, what does it consist of? I need a pipe that goes from turbo to flexpipe, then a pipe that goes to muffler? i'm new to all this and my dad who is older is recommeding against all this because he thinks im just going to blow it up and im wasting my money. I need some positive advice and also some info on how to get a 5 inch exhaust. Only thing i can think of is to use the vin number off a mack rd legend that had the 460 hp in it and i can use the info to at least get the pipes needed for the exhuast. Any other advice? Quote Slow and Steady Wins the Race! Link to comment Share on other sites More sharing options...
RedBullDog Posted February 23, 2015 Share Posted February 23, 2015 If your exhaust temps are in the 7-800 range and it isn't heating up at half throttle, then my opinion would be 5 inch is a waste of time and money. The question is, are you happy with the current power? A larger turbo is going to flow better, but that is a lot of expense for the horsepower. If you upgrade the turbo, a wastegated one might be a good idea. Quote Link to comment Share on other sites More sharing options...
dds92780 Posted February 23, 2015 Author Share Posted February 23, 2015 I am happy with the power but i want to increase fuel economy. since turning up the pump and getting bigger injectors the truck builds boost FAST but its a tiny turbo and therefore with the amount of fuel im using to spin a tiny turbo, i feel that i would be better off with a larger turbo with the same amount of fuel. I also understand the kiss method too. only reason i would be getting a larger exhaust is because that is whats required to make the turbo work. The more time that goes by though, i just lose interest. Quote Slow and Steady Wins the Race! Link to comment Share on other sites More sharing options...
dds92780 Posted February 23, 2015 Author Share Posted February 23, 2015 Here is how it runs. I get 35 pounds of boost by1300 rpm, then by 1600 rpm or more i can barely squeeze out 37 pounds. This tells me that the turbo is too small. But should i leave it alone? My goals are to get better mpg. I can drive it with half throttle all day but it still doesnt get better mpg. Not looking for a tractor pull truck either this is a work truck. Quote Slow and Steady Wins the Race! Link to comment Share on other sites More sharing options...
RedBullDog Posted February 23, 2015 Share Posted February 23, 2015 The turbo upgrade should improve the engine's efficiency, but how long is it going to take to recoup the cost of a turbo and exhaust upgrade, if the only reason is to save money(increase mpg). If the new turbo is much larger it could have some turbo lag and cause the truck to not feel as peppy. I've seen this before, putting larger turbos on smaller displacement engines. I maybe thinking a little wrong, but if your current turbo is/was too inefficient, you wouldn't make good power without the restrictive turbo creating heat. Quote Link to comment Share on other sites More sharing options...
RedBullDog Posted February 23, 2015 Share Posted February 23, 2015 (edited) If its making that boost at 1300 and holding it all the way up, then you sure wouldn't have any lag problems with a slightly larger turbo. The downpipe and muffler wouldn't be a major cost. The turbo itself is where the cost is. Have you ever put a larger guage in place of the one in the dash for test purposes, it looks like that one pegs out. Edited February 23, 2015 by RedBullDog Quote Link to comment Share on other sites More sharing options...
dds92780 Posted February 23, 2015 Author Share Posted February 23, 2015 I'm wondering that even if i stuck with my 4 inch exhaust if they even make a bigger turbo than what i got that would work. Quote Slow and Steady Wins the Race! Link to comment Share on other sites More sharing options...
dds92780 Posted February 23, 2015 Author Share Posted February 23, 2015 Just answered my own question. the turbo im looking at is the 631gc5173. its the same turbo the rd legend used for 460hp. guy at mack was dumb and told me they all had 4 inch exhaust. I called my turbo guy and he said i need 5 inch exhaust. My thoughts right now are to get a 5 inch downpipe made. I guess i would just need to figure out the measurements of it and have a shop make me one. Then i can use 5 inch flexpipe all the way to the muffler and be done? Quote Slow and Steady Wins the Race! Link to comment Share on other sites More sharing options...
RedBullDog Posted February 23, 2015 Share Posted February 23, 2015 That would work. If your muffler is straight through 4 it wouldn't be a bad neckdown. How much is the new turbo? Quote Link to comment Share on other sites More sharing options...
dds92780 Posted February 24, 2015 Author Share Posted February 24, 2015 The turbo is going to cost me 830 dollars and im picking it up tomorrow. I am confident that it will work with my stock exhaust which is 5 inch inlet from turbo to DP, then goes to the frame of the truck where it goes to 4 inches all the way back. It seems that its a really tight fit to get a full 5 inch in there. I am not sure what is needed but i think 4 inch is enough. Also, would it look cool since i have 5 inch exhaust to just get 5 all the way through and then put an adaptor on just after the flexpipe that lets me get 6,7,8 inch that goes to a muffler / straight pipe or just leave it alone??? Quote Slow and Steady Wins the Race! Link to comment Share on other sites More sharing options...
Yoos Brothers Construction Posted February 24, 2015 Share Posted February 24, 2015 Mine has a stock 5in. reduced to 4in. down pipe and I have no issues with. Thanks, Josh Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted February 24, 2015 Share Posted February 24, 2015 I was going to say the same thing. Get a reduced elbow. It is 5" at the turbo and 4" at the end of the pipe. Simple solution . That being said the reducer will be the most restrictive part of the system. Think garden hose...water only flows as fast as the smallest hole allows being pushed by said pressure behind it.Regarding 4" vs 5" And turbo size. It really does not matter how big or how small ( physically) a turbo is. The important part is what's inside. A larger turbo can flow the same amount of air as a smaller turbo but with less restriction or boost. However of you go to big you get turbo lag. If your making 37 psi your doing very good. If anything I would do some tests with your current 4" exhaust. Remove the muffler and see if it runs better. If it does your muffler is restrictive or you have too many bends in the system.If you do get the larger turbo Try a 5" pipe with an open exhaust routed under the truck.do a few tests runs like that. Then hook up your exhaust with the 5" into 4". If the boost is the same with both tests than you don't have a restriction issue with the 5 into 4 Quote Link to comment Share on other sites More sharing options...
Dirtymilkman Posted February 24, 2015 Share Posted February 24, 2015 I use a 4" hole saw with about 3 feet of extension on it and I drill out my mufflers. Its not overly loud and it flows excellent. Quote Link to comment Share on other sites More sharing options...
RedBullDog Posted February 25, 2015 Share Posted February 25, 2015 $830!!! Man, thats reasonable. Mines 5 inch all the way (01 etech 460) and its single muffler. Finally got it home from Mack this morning and looked,(couldn't remember )I've gotten so used to pricing stupid wastegated variable geometry turbos for Cats that a simple one seems like a steal now.. Keep us updated. Quote Link to comment Share on other sites More sharing options...
MHfred Posted February 25, 2015 Share Posted February 25, 2015 I use a 4" hole saw with about 3 feet of extension on it and I drill out my mufflers. Its not overly loud and it flows excellent.I had to buy a new muffler for my MH and you can see straight through it. No sawing was nescessary. Quote Link to comment Share on other sites More sharing options...
felicello122 Posted March 1, 2015 Share Posted March 1, 2015 The rd i got is a 2000 with a e7 tech 400, has 5 inch off turbo, goes down to 4 inch soon after all the way to inlet on muffler and comes back out 5 inch, i run a 6 inch top, all factory v except my stack top Quote Link to comment Share on other sites More sharing options...
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