LLY: Which Big single for 7.1

[Ben46a]

Getting set to build a 7.1 for my LLY. going with stage 2 heads as well. Its going to be a puller and daily driver. But drivability is not much of a concern. No towing etc. I was thinking S480 but was wondering if i should go with the big wheel with the 1.32 or the 83/87 with a 1.10 AR. No twins as class wont allow.

 

[bullfrogjohnson]

I would go with a S480 with a 87 exducer. stay away from the 83 wheel it will choke you off above 4k. You can can also go with a 96 wheel and get a .90 housing from ED.

 

[super diesel]

The 83 will surge to much when not being pushed hard. The 87 can do it as well but not nearly as easy. If using it, get a .90 A/R exhaust and waste gate it (you would need this even with the 1.10 as well). A 38mm waste gate should be fine on the housing. This will have decent spool up and help in the upper rpm (this will also keep you in the meat of the map when rpms drop from the load). Also, be sure to go with no less than a 5" intake for it. If it comes with the 5.5 opening on the compressor go this size. This will help greatly with the spool up and staying on boost when you get loaded by the sled.

 

[bullfrogjohnson]

How are you gating the charger Micheal? I would love to gate mine but nobody makes a kit except for ED and there setup looks hard to run on a dmax.

 

[bullfrogjohnson]

The converter should play a big part in your choice. Things have changed.

You making converters for the ZF6 now Mike

 

[super diesel]

Travis. You can either run a welded tube or bolted on tube off the ped or machine a spot on the turbo housing itself like what Newly has. I originally welded the bung of the waste gate to the housing in that location about a year ago. It can crack from heat cycling if not recessed and sealed with a gasket. It's easy to machine it for a 38mm Tial and bolt it on. A stock cast exhaust housing has the meat for it.

Mike has a very good point on this for the Allison crowd that travels this route. I would find out the details on this from him.

Also keep in mind, the bigger the single is, the more rpm your going to need to spool it and where it likes to live. However the turbo side plays a huge part in this as well. The closer the turbine wheel is in exducer size to the inducer size of the compressor, the more easily it will surge (slight bark or reversing) with lighter drive pressures (partial throttle settings when climbing a grade or hill). A larger A/R incorporated to this equation makes it worse. However tighter ungated housings can make drive pressures spike when the Rs really climb. These are all general workings when you get into this field. Optimum set up really does require a drive pressure gauge and a turbo speed sensor to keep these in there best map. There are + & - to all this as well, but it's not rocket science either.

 

[Ben46a]

As far as a wastegate i was planning on milling my PPE spacer for one.

 

[super diesel]

As far as a wastegate i was planning on milling my PPE spacer for one.

Good deal. It will have to be on an angle up out of the valley a little to get something on it. An up pipe with a flange to bolt to works wonderful.

Tip here; Slightly recessed hole to locate to pipe and keep heat cycling stress to a min on the weld (IF welded, but there are other options as well). I used a 1 1/2" 304SS (part of a 90 deg.) that is pretty thick walled.

 

[McRat]

1.32 is going to be too big IMO. My personal opinion is that a 1.1-1.2 is best for max power.

For a 7.1 you are going want one step up on the charger IMO. But with sledpulling that is dictated by the rules. #1 question is whether your intended class allows sleeving. If it does, go big and sleeve. If not, then get a charger that has a range of available covers/wheels, so you can buy extra wheels.

 

[Ben46a]

Its unlimited single. so a 480 with a 1.10 sounds pretty good?

 

[McRat]

Its unlimited single. so a 480 with a 1.10 sounds pretty good?

If it were my truck, that's what I would do.

There are folk who don't think a 3.2" inducer is a good choice, since they did not make more peak HP on the dyno.

But what they don't look at is area under the curve. A GT45 sized charger will have about 30% more RPM range than a 42 will at the same peak HP. Curves are very similiar up to 3800, but after that the 45 walks away.

 

[Ben46a]

Thanks pat, Ill probably consult you for tuning once i get it together. Thats pretty much the turbo i figured i would be the best to run, but the confirmation is nice.