I have a 351w with a f cam and some cantfeild heads in my ltd and im getting ready to convert it to efi and do a turbo setup on it. the turbo I plan to use is a gt4202 with a 1.15 t6, or a s475 1.32 t6... I already have the gt4202 that's why im thinking of using it. My question is should I do a divided 2.25 hotside and run two 38mm wastegates or just a open 2.5 with one wastegate?

 

I would lean towards the divided with twin gates, even though a large single gate should be sufficient.

 

Personally, I'd go divided.

 

That's what I was thinking, It should help it spool a lil better.

 

I did a dived setup on my gt45 with 2.25. Haven't added the wastgate yet though.

 

The whole purpose of a divided hotside/housing is to separate the exhaust pulses that would normally interfere with each other. Unless you have the cylinders properly split to each port on the divided housing it won't work properly. You can't just run all of the cylinders from the left bank to one side of the housing and the right bank to the other and expect it to work correctly. So if the LS firing order is 1-8-7-2-6-5-4-3 Then you would need to have 1-7-6-4 going to one side of the scroll and 8-2-5-3 to the other. Then it would work properly and spool much faster. If you can't do this then it isn't worth your time IMHO.

Most of the builds you see where guys think they have a twin scroll setup aren't doing themselves any favors. Run both banks into a merge then into the housing. Don't mess with trying to make it a true "twin scroll" system unless you are a badass with a welder and are prepared to spend ALOT of time on the manifolds. I've yet to see a true V8 twin scroll DIY setup on this forum.

Here is a good article explaining it.
http://www.modified.com/tech/modp-0906-twin-scroll-turbo-system-design/viewall.html

Good luck!

 

fully divided on mine and works great, spool up is just as fast with my 1.32 t6 s480 as was with the t4 1.25 s475 that was merged through a Y before the turbo. plus my s475 had the smaller 83mm turbine wheel vs my s480 with 96mm turbine. jmo

 

Did you drop your hotside piping size when you did this? If not i see no advantage in splitting the exhaust banks If your not eliminating interfering exh pulses.

 

I see what you're saying Forcefed, but I can tell you it works. I don't know if you're into diesels at all, but if you know the name Hypermax, that company basically got it's start selling a divided turbine hot pipe system for the old IDI 7.3 Fords. I knew a guy in college that put the kit on his truck, and even with a larger turbo spooled way better than stock.

Keep in mind, turbines can draw energy more efficiently from a pulse than from a steady flow. If the OP ran a divided setup on his car, cylinders 1&3, and 5&6 would be paired together, creating a pressure spike on each side.

Another way to look at it is this: Do you want two pairs of cylinders that "cross-talk" with each other, or do you want all 8 cylinders that cross-talk with two others?

 

I guess a h pipe or x pipe is crap too....

 

I’m not saying it didn't, but IMO you changed to many things at once to document the exact gains you netted from your new merged setup.

Did or didn't you change your hotside diameter when you switched to your new divided setup? Do you have data logs of before and after? You’d need datalogged engine data both with and without your divided setup with the same turbo and same size and length piping in the hot side to provide any accurate comparison.

In your version of a “twin scroll” setup, the exhaust gas pressure pulse from improperly paired cylinders is going to interfere with other cylinders ability to expel exhaust gases. It is defeating the purpose of the twin scroll housing. As you say there may be a marginal gain by separating the 2 banks. But is it really worth the gain when you factor in the added cost and labor? A properly sized hotside (not divided) with any LS series engine will spool a s480 with 96mm wheel in a 1.32 T6 great. Bunch of guys on yellow bullet have proved that.

They have their place on an NA engine. In a turbo system, pre-turbo X or H pipes will do nothing but slow velocity and drop power. There are no gains to be had with them on a turbo car, pre or post turbo.

 

You missed my point.

You missed ky

 

Very interesting subject, anywhere I could find some examples of this?

 

Yes I did drop my pipe sizing because I was putting the t6 flange turbo on and wanted the turbo to sit side to side rather than front to back, and in the end it was much easier keeping it divided the whole way. I am not arguing anything just stating my experience and I built both my setups and I think the divided was easier.

 

Don't' mean to discredit your findings either, I'm sure it did pick up. Just trying to help all those out there that haven't built a system yet. Don't want them thinking that dividing the L&R cyl banks will give them the advantages of a true 'twin scroll' setup.

To the OP'¦ with a GT45 a 2' hotside (good to roughly 1000fwhp before it becomes a restriction) bumped up right at the turbo flange inlet would be the cheapest and easiest route to speedy 'spool-u' IMO.

 

So one GT45 would spool up faster then a pair of GT45's? So there isn't excessive backpressure on the system causing other parts of the system to break down faster due to thermal fatigue running a single?

 

Yes a single wills pool faster. No, it won't be excessive.

 

Thanks guys Itll be awhile before I start the turbo build, I still have to convert it to efi and find a core trans to build. Not looking for a bunch of power just a nice cruiser that can suprise a few ppl on the street. Lol

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A proper pulse divided header does provided some significant benefit. How much really depends on the application. Some years ago on my 2.3L Ford 4 cyl I built a properly divided (i.e. 1-4 and 2-3) header to run with a divided housing on an HX35 turbo. With that setup it spooled up at 3000RPM. Unfortunately due to only one side being wastegated it spooled up right off the top of the boost gauge. The temporary fix was to mill out the divider wall in the turbine housing so that both side would vent. I was now able to control boost but it came in closer to 4000RPM now. The division was worth ~1000RPM earlier spool.

Now this was an ideal setup having even pulse splitting and a low number of pulses. This doesn't mean that it doesn't work on a V8 though (even if it isn't truly split by firing order). The results won't be as dramatic as it would be on something with fewer cylinders but it will see some benefit. Now to be fair you could probably see nearly the same effect on a V8 simply by keeping the header and crossover volumes small. Basically it's all about maintaining high gas velocity hitting the turbine wheel. Larger tubing and/or open turbine housings dampen the magnitude of the pulse hitting the turbine wheel.

Steve

 

Huh... All this time sketching out a 'twin scroll' system for the Fjord I didn't even consider the proper pulse pairing... I'm having trouble even picturing that piping but it sounds awful.

I realize you are not going to get the type of effect you do on an inline engine, but does that make it worthless? Assuming the 4-1 section on each head is ok, now you have two pipes with orderly flow and 4 banger spaced pulses. If you merge the two, won't the pulses be dilluted by wedding the two pipes pre-turbo? Besides which, is making a clean merge for the two banks just as much of a PITA in terms of space and work as the divided flange pipe?

I don't have a horse in this race yet, as I haven't welded together anything. Lord knows wastegates ain't free, so buying just one sounds ok. Would it be better to merge the pipes and invest in a good quick spool valve instead?