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For the T4 1000+whp guys, is everyone running twinscroll manifolds these days, or open collectors?
I feel like years ago, everyone gravitated towards twin scroll setups. Then there was an open discussion about EBP and equalizing the banks, and from then on, I felt like people started gravitating towards TS housings on an open collector.
Currently on a TS manifold setup, and getting another made for my back up/replacement motor that will be a longer runner design, as well as designed for better WG priority. I'm contemplating going open collector due for simplicity/space constraints, but thought I'd get other's views.
If open collector, would having the collector earlier in the manifold, so that it feeds into a single 3" pipe for the rest of the way to the flange be a restriction at all versus having all the runners going directly to the flange?
How vital is runner length, and whereabout's is a good target? I've seen 3x" range thrown around on more than one occasion?
Twin scroll still important at all in today's landscape, where shift cut antilag's and clutchless shifting exists?
Thinking of keeping it TS. I'm thinking of doing a 4-2 manifold so I can get better WG priority location versus the standard WG location on the collector.
Does a 1.75" > 2.25" merge for the 2 secondaries seem about right, which the (2) 2.25" pipes would run up to the flange collector?
Thinking of keeping it TS. I'm thinking of doing a 4-2 manifold so I can get better WG priority location versus the standard WG location on the collector.
Does a 1.75" > 2.25" merge for the 2 secondaries seem about right, which the (2) 2.25" pipes would run up to the flange collector?
Expanding on this further, are the 1000+ guys using 1.6x" ID tubing still, or opting up for 1.75" ID?
I've found that using a collector any more than a few inches from the flange causes excessive backpressure and a hefty reduction in exhaust velocity as well as a lot of turbulence, which has a negative impact on spool time and a drop in overall power.
as for runner length, it largely depends on engine specs. thing is though, the gains from a proper pulse tuned turbo manifold are very minimal, because it requires stupid long runners to take advantage of it, and runners that long (around 32", or longer depending on backpressure) usually cause a loss of heat and velocity which slows down the spool time, and has a mild restrictive impact causing a bit higher backpressure at the valve. typically, anything from 14"-20" seems to work quite well, with little difference in performance throughout that range. the only key is to get all 4 runners as closely matched in length as possible.
runner diameter is tricky too, because it affects velocity. smaller diameter runners increase velocity which spools the turbo faster, but becomes a restriction at higher rpm and higher power levels. larger diameter runners give more top end power and more overall power, but have a noticeable impact on spool time which can actually slow the car beyond what less power and faster spool could accomplish down the track. Ideally, you could use a larger diameter and spray a little to spool faster, but that's definitely not allowed in a lot of classes.
I've found that using a collector any more than a few inches from the flange causes excessive backpressure and a hefty reduction in exhaust velocity as well as a lot of turbulence, which has a negative impact on spool time and a drop in overall power.
as for runner length, it largely depends on engine specs. thing is though, the gains from a proper pulse tuned turbo manifold are very minimal, because it requires stupid long runners to take advantage of it, and runners that long (around 32", or longer depending on backpressure) usually cause a loss of heat and velocity which slows down the spool time, and has a mild restrictive impact causing a bit higher backpressure at the valve. typically, anything from 14"-20" seems to work quite well, with little difference in performance throughout that range. the only key is to get all 4 runners as closely matched in length as possible.
runner diameter is tricky too, because it affects velocity. smaller diameter runners increase velocity which spools the turbo faster, but becomes a restriction at higher rpm and higher power levels. larger diameter runners give more top end power and more overall power, but have a noticeable impact on spool time which can actually slow the car beyond what less power and faster spool could accomplish down the track. Ideally, you could use a larger diameter and spray a little to spool faster, but that's definitely not allowed in a lot of classes.
Thanks for the input and giving your experience. And thank you for noting that you've seen an increase in back pressure due to a merged collected before the flange.
My reasoning for wanting to do a 4-2 manifold, with 2 tubes running up to the flange was to get much better WG priority location on the secondaries, versus typical locations for the WG's right off the collector.
(2) 2.25" pipes ran to a divided flange... (2) 2.25" pipes has close to total area of that of (1) 3.25" pipe (7.9522 vs 8.295... r^2 * Pi), so I'd like to hope it isn't a restriction, but I can see your thoughts on causing turbulence, as being a legit claim. Would it being divided help it's case here, versus instead of open scroll?
Wondering if I would theoretically pick up velocity doing a 1 7/8" primary off the flange, and have it step down to 1.75" a few inches down, before eventually going to the dual 2.25" merges, versus if I did a 1.75" straight off the flange
Lots to think about here. I want to make sure whatever I do, it's correct, and as best as it could be given the setup and constraints.
Thank you for your input, especially with the runner lengths, too.
if you do a 4-2 setup with a twin scroll, that would be a different story regarding backpressure. that type of setup actually works really well, but only if you make it so cyls 1 and 4 are on one side and cyls 2 and 3 are on the other side, for pulse timing reasons. assuming I know the style you're attempting, best I can say is don't make it so it's like a collector going to a tube. just take the primaries and angle cut them to merge them together, where the end of those primaries is the correct size for the port in the flange. and merge them at a super crazy angle to each other, meaning damn near parallel. doing this will give you an ideal taper, lowest backpressure imaginable, and great wg placement because the inner edge of each runner merging to the other will be a good distance away from the flange allowing for tons of room to flow to the wg without causing spikes or creep or anything.
Ok thanks for confirming the idea of the 4-2. And you're correct, the merges would be paired 1-4 & 2-3.
I know it's not ideal, but I planned to use 304 16ga (i use the car maybe 5x a year). 321 is very expensive and my wallet can't hang, lol. I planned to weld a support bar from the head flange to the turbo flange...then also add a heim bar from the back of the turbo flange, to my block to support the weight of the turbo to prohibit cracks.
Additionally, the plan is to use two double-slip merges to allow for pipe expansion to further keep cracks down. It also has a very mellow merge entry, so turbulence will be at a minimum at the merge. And those secondaries will lead up to this flange I had made that matches their ID
I guess my last hang up is if I keep the primaries all 1.75 (1.62" ID) or to run 1.88" (1.75" ID) and step down to 1.75" piping after 6" or so. The head flange is countersunk with 1.900" ports so that a 1.5" sch10/40 piping can fit in it perfectly. Nervous to use 1.75" off the head and possibly shroud the port with the tubing. Was also thinking going 1.88 off the headflange and stepping down to 1.75 will increase flow without any adverse effects since the step down should theoretically keep velocity up?
Tried searching step down primary runners online, and any/everything I could find in the NA and turbo applications, people were doing step-up runners (small to large). I would think it'd be the opposite, but my experience is limited.
07-09-2017, 06:04 PM
1000+ guys, TS or open?
