Looking for more MPG

[rscurtis]

I am looking to improve highway fuel economy by reducing turbo drive pressure in the exhaust. Which after market manifold have some of you used? Which aftermarket turbo is a direct bolt-on, using the stock exhaust and intake system? What size exhaust housing is a good choice from the 9 cm/2 stock housing? And who would be the vendor of choice for these items?

 

[AH64ID]

Do you monitor drive pressure?

I do and cruising at highway speeds its only ever 2-4 psi higher than boost. I don't think you'll see a huge drop in that even with an aftermarket turbo.

 

[rscurtis]

I do not. The reason this is intruguing is that I know someone who works in a scrapyard and grabbed a 16cm turbo from a school bus that was being scrapped and put it on his 12 valve. He claims he picked up 3-4 MPG on highway driving. I am assuming (which is why I'm asking questions) that going to even a 12-14 cm housing would be an improvement over the 9cm that is on the truck now. And while you're at it, you may as well change the manifold.

 

[AH64ID]

It would take more fuel/air to spool a 12-14 than stock has. The cam is retarded and doesn't flow as much air as it could, making more fuel needed to spool a larger turbo, especially with your automatic.

You may simply try bolting a HE351 up to it. Still has a 9cm housing, but has a slightly larger comp and exh wheel.

The 9cm wheel also is a newer design, Holset claims it flows as much or more than an older 12cm housing.

 

[cerberusiam]

I do not. The reason this is intruguing is that I know someone who works in a scrapyard and grabbed a 16cm turbo from a school bus that was being scrapped and put it on his 12 valve. He claims he picked up 3-4 MPG on highway driving. I am assuming (which is why I'm asking questions) that going to even a 12-14 cm housing would be an improvement over the 9cm that is on the truck now. And while you're at it, you may as well change the manifold.

I think he had a bad turbo to begin with.



Fueling is going to be determined by boost not drive pressure on all these engines. A larger housing is going to drop the boost at cruise and drop the amount of fuel supplied. It will take more fuel to spool it so there is a tradeoff.



Going to a 12 or even 14 cm S300 housing is going to lower the drive pressure and the boost for a given amount of fuel. Given the compressor design is better the odds are you will gain mpg at some point. It won't be across the board so driving style and use will play a larger factor. They tend not to spool as fast so the tradeoff is there.



The costs are going to be pretty close to $2000 for a good turbo and manifold. If that can be translated to ROI then go for it. II and HTT both have good turbos, ATS has a 2 piece manifold that is probably the best there is overall.

 

[CKelley1]

i agree the he351 would be a good choice. you can find good ones for between $350 and 500. take the roktek off and get the smarty jr will help. most of the 03's and all of the later have the bad cam. i use the pdr cam but don m,fi, or colt will custom grind. and give about 1. 5 mpg. on the 04. 5 up the 50hp nozzles give an additional 1. 5 mpg but i have not tried it on any of our 03 or 04. 4s. but i would think it will also work the same with them. the he351 has two variations. the ve is used on the 6. 7 do not get one of them. leave that mod to the pro. if you do change the exhaust out go to a 5" the mufflers are a lot cheaper because that is the size used on on most big trucks. the fbd straight pipe kit is cheap and very easy to install the muffler from ryder truck is about $100 depending on model. if you change to the 5" pm me with how quiet you want it and i will give you the part #.

 

[rscurtis]

I appreciate all your comments, but I still have this nagging question. If a 12 or 14 cm housing would be too big for the 305 engine to produce boost, how did the 160 HP 12 valve engine do it with a 12, 18, or even 21 cm housing on a little more than half the fuel delivery?

 

[AH64ID]

I appreciate all your comments, but I still have this nagging question. If a 12 or 14 cm housing would be too big for the 305 engine to produce boost, how did the 160 HP 12 valve engine do it with a 12, 18, or even 21 cm housing on a little more than half the fuel delivery?

Much lower boost number, much slower spool time, a non emissions based cam, and the way the truck fueled was different. It why swapping it out for a smaller housing is so popular.

 

[cerberusiam]

I appreciate all your comments, but I still have this nagging question. If a 12 or 14 cm housing would be too big for the 305 engine to produce boost, how did the 160 HP 12 valve engine do it with a 12, 18, or even 21 cm housing on a little more than half the fuel delivery?

Half the HP, half the boost, and much slower spooling. The cam profiles are drastically different from the CR's to a 12V, much better exhaust flow in the low rpm's to support the larger housings but they tended to fall on their faces as soon as you topped 2500 rpm's.



The CR's will pull all the way to redline with a flat TQ curve and a lot more HP. The 12V's also did not have to meet emissions and could smoke a bit on the spool up where the CR's are really clean all across the rpm band.



The peak HP is really a bragging point for the most part unless you are loaded as you normally are not using more than 100-150 HP anyway. You will find pound for pound the CR's are not using much more fuel than a 12V to move the weight and fight the wind resistance.

 

[CToney]

Take CKelly's word on the turbo. He has tried aftermarker turbo's and did not see a MPG benefit. He gave me the head's up on my 351. I put on the 351, ATS, and 4" exhaust. all at once and dropped 2psi when cruising. I fabbed up my own exhaust since I got the 4" elbow with the 351 and the 4" downpipe from dodge and bought 4" heavy truck parts for the rest and used the stock 4" tailpipe. No drone and not loud but free flowing. I have seen cfm #'s for the 341, 351 and hx 35. The 351 is ~100 higher (correct me if I'm wrong) than the 341 and a couple hundred higher than the 35.