I have a REW in the back of my kit car, and due to an oil line failure I’m rebuilding my engine. Car weighs around 2000lbs and while it’s street legal, it’s being built for lapping/time attack.

I already have a 8374 IWG, and I don’t want to change that. I should also note that my fuel system is all E85 compatible and peak power will always be pursued on E85. However E85 isn’t available at the pump here (2hr drive away to fill a slip tank in my truck, or order a drum) so I want to be able to run on 93/94 pump gas. As the car has yet to see the track, I’d also like to start at as low power as possible and doing so on pump gas would be ideal. My fear is that with the IWG and such large ports my boost creep might push me out of a safe pump gas range.

The shop I’m using for my machine work convinced me to go full bridge (cnc porting). I was considering a DIY semi-p but he’s seen many failed attempts and discouraged me from trying that. I realize these turbos make great power with a stock port, or a street port, but I have lofty goals with this car that may even exceed this turbo at some point down the road but I want to max out it’s potential first.

In searching I didn’t find many Bridgeports on the 8374, so I’m in need of some advice.

 

First of all, that kit car is super cool! Secondly, with the 8374, I don't think that with e85 you'll even have a need for a big ported engine. You lose engine durability with bridgeports allegedly and with stock ports and only 2000lbs, I think you'll be more than happy with what that turbo can put out. Shops will always try to sell you stuff even if you don't need it and I would be cautious. If you're dead set on porting, just go with a street port and call it a day to really get the range out of that turbo. You should be able to run it around 12-14psi on pump gas with no issues and I think that will be plenty of power on the track in such a light car. Those are just my two cents though and I'm sure someone with farther experience will chime in.

 

Personally I wouldn't consider messing with a bridge or peri port, they're just going to push your powerband to the right and make your low/mid range more limp. That turbo can easily hit 500whp on a streetported rew.

 

My understanding is that’s something of a myth, large ports make more power throughout the Rev range, but are able to flow so much more up top that their dyno graphs always appear as though they’re all top end only. Which considering on track it’ll probably stay above 5000rpm anyway.

Maybe a half bridge on the secondaries only would be a better balance.

 

Large ports are annoying. Driveability bad. Sure, they make more power at WOT. Everywhere else they suck.

 

I have an 8374IWG on a large street port in my FD. I originally built the car for 500whp which it could do. I am at 408 to the wheels right now and it is plenty. My car is 28-2900 ish like most FD's and I really cant see needing 100 more hp. I do track my car and am considering turning the power down actually so I can be more consistent. If I raise the power anymore I will need to add aero.

 

I'm guessing the IWG will be a bit restrictive on a bridge. I'd imagine a 1.05 EWG housing swap or a bigger turbo would be in order.

Here's what my large streetport with 1.05 EWG 8374 looked like on a safe and dirty tune and pump gas (98RON) and an ecu from the flintstones era
edit; on basically a t2 engine with t2 intake manifolds and throttle bodies. Plumb back wastegates.

Your car is looking sick btw. I cant believe iv missed all the updates for so long. Was following that.

 

I don’t really have a HP goal, but I do have some lap time goals and I’m not sure what it’ll take to get there. My big spoiler isn’t on in this pic, and I’ll probably add more aggressive aero as I turn up the boost. Also have 305 NT01’s tucked under there in the back.

 

Thats a pretty sweet dyno graph! I’m actually waaay behind on my updates, but should catch up here real soon. My Instagram is usually up to date @popes_projects

 

We later upped the boost to hold 24 psi the entire rev range( not shown here), and this same car made 557rwhp on a lower reading dyno FYI.
This is the .92 T4 IWG

You will need to machine the turbine housing for lower boost pressures on your combo, especially if you are running bigger than 3" exhaust.

This car was a MONSTER at 2800#s.

 

Looks sweet! Did you try running lower boost at all?

Have any pics of the machining you’re referring to? While I wait for my machining I was going to get my turbine housing and manifold ceramic coated and was going to check and see if there was any room to port the wastegate area. Car has a short exhaust, but it’s 3”, two 180* bends (aids in noise suppression) a high flow cat and strait through muffler.

The bridge ports are shorter than what is typically used for a BP. Shouldn’t be anymore overlap than a large street port.

 

Rad car, will be a beast and if done properly a bridge (or even a PP) isn't all that difficult to drive. I believe that most of the comments I see saying otherwise are just people parroting information that's outdated due to modern tuning techniques/components/EFI/etc.

I'm a little confused as to what you're actually asking for information on? It seems as if you're locked in to a config at this point for version 1.0 sine you're set on the IWG you're using and (unless I'm mistaken) the port the machine shop already put on your irons. While most of my experience on the 8374 is with larger than normal street ports I've run in to the same things mentioned RE: out of control boost so I'd definitely heed Elliot's advice: hog out the turbine housing, smooth and port the wastegate, and have exhaust restriction options on deck to mitigate boost if needed.

 

My question is simply will I be able to maintain a low enough boost to safely run this combo on pump gas?

The irons are not ported just yet, but they could very well be past the point of no return. Either way I don’t think I’ll be changing my mind, and hopefully I don’t suffer too bad boost creep. The ports will be perfect, and I’m using a modern ecu, fuel, all the bells and whistles.

I’ll get the turbo and manifold apart today and see what the turbine housing looks like and how much porting will be possible. Exhaust restrictions are mentioned above and I’m able to add more if needed.

 

Defiantly some room for porting in there. I’ll keep the two sides divided, but there’s no need for so much meat between them. Wish I could remove the wastegate flap. I guess I could but I’d have to grind off the weld on the outside arm and then re-weld it on after I get it ceramic coated.

 

Word. Tune it well and don't fall into the trap of trying to avoid putting exhaust restrictions in post turbo, sure it doesn't flow as well but you've got to make a compromise somewhere.

 

I finished porting my turbine housing, not I’ll get it ceramic coated. I’ll try to remember to update this post once the engine is done, but if anyone searches this and doesn’t get an answer then check my build thread. There’s also more pics of the porting there.

cheers

 

You will have to remove the divider on the WG runners completely , and the T4 divider in the turbine housing if you want to run pump gas. I have already experimented with every variation, and this way is the most effective( at the cost of 250RPMS of boost response- dyno measured).

 

I thought about removing the divider back to where it’s a sharp bend thinking it might flow better and whichever side flows better would have a Venturi effect on the other(although I’m not sure how much if both sides are under pressure). Can’t really see removing the T4 divider helping that much, I would think it’d cause a lot of turbulence and negates the purpose of running a twin scroll.

 

Removing the T4 divider helps so much because it reduces the exhaust gas velocity and introduces turbulence.

This allows more of the exhaust gas to turn away from the more direct turbine flow path and into the wastegate runners.

i had the same experience a couple decades ago slowly modifying a stock S5 exhaust manifiold/turbo housing with a 60mm external WG so it wouldnt boost creep on a hybrid T4 turbo and 3.5" exhaust.

 

Yes, on negating effects of twin scroll hence the impact mainly on turbo response and a bit on boost threshold as well.

You are building a very compromised set-up and will have to choose where your innefficiencies are to keep it operating within your parameters (pump gas boost level).

Putting a 1.75" -2" outlet on the exhaust tip might be enough from my experience (though that was a ~7ft long exhaust so results will vary for your shorty exhaust.)

 

I think I’ll leave it as is for now, and if I do suffer from any creep I won’t hesitate to take it off and port more.

To be clear I’m certainly not building it for pump gas, if I was then stock ports would’ve been fine. I just want the ability to still use pump gas since it’s street legal and I don’t have E85 available at the pump.

The before video shows my exhaust, I feel it’s already fairly restrictive as my goal was some noise suppression. I’ve been wanting to remake it as now that the car is mostly finished I have much more room to work with.

 

Gotcha.

So, before rebuilt my motor with a lower overlap street port and hogged out the turbo manifold, exhaust manifold and wastegate runners and finally fixed boost creep-

I could control boost and tune on pump gas by running the muffler tip silencer with its ~1" opening.

Then I would fill with race gas and try to tune/ see how low of boost I could run without the tip silencer.

OFC the maps were off from improved VE - so you gotta leave the load parts of map at the unrestricted exhaust mapping.

Drill the muffler tip silencer bolt end for a hitchpin spring clip after the nut and insert the bolt head up- I had to chase down my tip silencer more than once in the dark after it ejected itself.

 

My triple tip will require a custom silencer if I go that route, but I’d be more inclined to pull off the turbine housing and port more first. Either way, my plan (after break-in) is to use race gas initially when tuning under any real load and watch for boost creep. Unfortunately my bearings failed just as I was tuning under load so I don’t have any idea if my manifold/exhaust setup is prone to any creep prior to the engine porting.

Thanks guys for talking it out with me. I’m no longer worried about the creep as if it happens I have options to control it.

 

https://www.rx7club.com/3rd-generati...-hate-1148058/

 

Very different cars and goals. Guy wants a nice street car to go get coffee, I’m building a track car with a licence plate but no radio or cup holders. My daily is a truck, and I have an Rx8 for getting coffee on the weekends. I’ve made the mistake of trying to build a multipurpose project vehicle, too many compromises, always sucks.