Choosing between IWG or EWG Rx7 Turbo Systems

This article will help guide you through choosing which turbo system design better fits your needs; IWG( internal wastegate) or EWG( external wastegate). The IWG concept is generally misunderstood for most rotary owners, as most single turbo upgrades up until a few years ago were all EWG. The only IWG turbos were the OEM Units. 

Lets discuss the Turblown EFR IWG turbo systemsfirst. If one wants to recirculate their waste-gate discharge for either noise, stealth or emissions this is definitely the way to go. The IWG turbo as seen below discharges the 42MM waste-gate right into the down-pipe connection. 

Here is what is required to reroute the wastegates on an EWG turbo system. As you can see it adds a lot of complexity, and heat into the engine bay. Not to mention its not easy to build, and generally costly. 

Speaking of complexity, again the IWG outshines the EWG. Its much easier to install, and has less failure points. Wastegate diaphragms are a wear item when using an EWG turbo system. The diaphgram on a external wastegate is within inches of the exhaust heat. This puts considerable wear on them, and its very common for them to fail on a roadcourse driven Rx7s over time. Especially those that are not water cooled. The IWG option removes a lot of this issue. The diaphgram is 7+ inches away from the exhaust system, connected to the compressor cover.  Not to mention the wastegate lines are also far away from heat too. If a wastegate line melts, the wastegate will not open and the boost pressure will usually result in an engine failure.

Turblown's IWG turbo system is by far the fastest responding turbo system on the market. There isn't anything that comes close. With the right combinations once can see 30PSI by 3400rpms with both the 7670, and 8374 versions of the kit. This is due in part to how short the exhaust manifold is & its construction. Heat and the expansion of the exhaust gas is what drives the turbine wheel. The closer you are to the engine, the more you have of both. The Turblown Cast IWG manifold is an investment cast that leaves the runners and transitions extremely smooth; coupled with the proper tapering runner size produces massive response. We typically see a 600rpm difference between the cast IWG VS cast EWG turbo manifolds which is mostly due to the difference in runner length( see below ).

Now lets talk about the EWG turbo system, and its strong points over the IWG system. We know its more complicated, and doesn't have as fast as boost response... So why would would we advise it to anyone? There are 3 reasons;

The EWG ultimately makes more power. The biggest IWG EFR is the 9180, a 68mm compressor. If you want to make more than 650rwhp, its best to move to an EWG SXEsetup. Max power on an IWG turbo system requires a 4" exhaust. This is the same as having a 3.5" exhaust on a EWG turbo system, since the EWG turbo system is releasing a fair amount of the exhaust flow outside of the main exhaust system( Downpipe, midpipe, catback). The IWG system is sharing all of the exhaust flow in the main exhaust system. The higher your exhaust back pressure( EMAP) is, the less power you will make. Furthermore one can choose bigger turbine a/rs, and bigger turbine wheels with an EWG system to further lower EMAP. 

Secondly one can run much lower boost pressures with a proper EWG turbo system. The heart of the Turblown EWG turbo system is the Cast twinscroll turbo manifold. The wastegate runners are placed in a spot for maximum flow. Exhaust runners should never be placed at right angles to flow, or on the inside radius. The exhaust system, even when under pressure, wants to take the path of least resistance. Improper wastegate placement leads to boost creep, especially on a car with a big exhaust system that can breath properly. The picture below shows the entrance to the wastegate runners is almost a direct shot out of the engine. The only IWG EFR that holds low boost pressures is the EFR 7670. Typically one can see 8 psi with a free flowing exhaust. The EFR 8374 or bigger 98% of the time never seen below 12-13psi. Some won't hold less than 15 psi. This also gets worse with bigger exhaust systems. Now one can port the turbine on the IWG EFRs, but it requires a machine shop with a mill and usually runs $200-300. It also costs one about 200-250rpms.  

Lastly some people are going to simple choose EWG because the turbo systems cost less. An SXE turbo system is the least expensive option we offer. Keep in mind that the SXE turbos don't have a build in BOV, like the EFR units. So if you don't have a BOV, you will have to add one on the SXE turbo systems. 

Lastly lets cover how porting affects your choice of turbo systems. Generally the bigger the ports are on a rotary engine, the more you shift your powerband further up in the RPM range. This is because you are hurting low speed air velocity, and sometimes increasing overlap. A stock port engine responds better, and makes more power down low, compared to a ported engine that makes more power on the top end. Heavily ported engines should use bigger turbochargers, as they require a lot more CFM in the higher rpms. Furthermore what goes in should be allow to come out, so you don't want to choke the exhaust side of the turbo. Do not pick a Bridgeport if you want 400rwhp. Do not pick a stock port engine if you want to try and make 800rwhp. The IWG kits favor stock to street-ported engines, and the EWG kits favor BP/semi-pport engines.