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Over the years, GrimmSpeed has proven that our exhaust products are some of the highest-quality and best-performing in the industry because of the detail oriented approached that we put into their development. When it comes to improving on an OEM design, this attention to detail and overall exhaust knowledge allows us to identify aspects of the factory parts that can be greatly improved upon. One of the first things to note about the OE exhaust manifold are the several points where flow is decreased due to a neckdown in piping diameter. These disruptions in exhaust flow result in decreased turbine efficiency which ultimately limits boost and power production. Furthermore, the OE merge collectors are made specifically with ease of manufacturing in mind and the result is a compromise on performance. The collectors contain very odd shapes that are bad for smooth exhaust flow and have several diameter restrictions that make them one of the biggest weaknesses of the stock manifold. Finally, the angle of the exhaust flow merge is also not ideal, causing the exhaust pulses to “fight” each other, which can add to flow differences for the twin scroll turbine, sacrificing spool and performance.
After isolating the inadequacies of the OEM exhaust manifold, we were able to start identifying key areas of improvement: correctly sized and consistent exhaust runners that are more equal length, a consistent and non-bottlenecking merge collector inlet and outlet and a higher angle merge collector to direct flow into the turbine and prevent opposing flow disruptions. Beyond that, we decided on using thicker tubing and flanges for increased durability and longevity to more-effectively support the overhanging turbocharger.
All four of our exhaust runners are designed in conjunction with the merge collector to equal out the lengths as well as the overall bend angles. This is especially important in the FA WRX twin scroll turbine configuration because it makes the strength of each pulse, or “push” on the turbine wheel, at equal timing and consistency.
Since the exhaust runners are CNC bent and trimmed as a single piece there are no additional welds to introduce points of failure or junctions that would interrupt flow, resulting an in impressive difference of less than 1% in total length. In addition, maximum variance is only 5 degrees from the most bent to the least bent runner, this mean we were able to produce what is a truly equal length, and equal bend manifold. The collector being cast, allows for the runner spacing and angles necessary to obtain the equal bends and lengths of all the tubes. This part is a major player in the GrimmSpeed manifold’s ability to fit between the stock skid plate and the oil pan while still providing the ideal performance from the rest of the design. The cast collector also allows for more smooth and consistent flow in the interior compared to a welded variant. This greatly simplifies the overall design, removing five more welded junctions, which could be a point for flow interruption or the structural failure that we see with other headers.
The head flanges of our header are CNC cut and faced from a 1/2in thick piece of 304 stainless steel. This design is much thicker than OEM to increase reliability and longevity, as well as to provide additional material to be removed after welding to ensure flatness from flange to flange. This additional measure allows for greater gasket sealing which results in increased performance. The final touch is that the exhaust runners are welded inside the flange as well as outside, this is an extra step in manufacturing, but it provides a rounded lip to improve flow from the flange through the runner.
All of these things come together to make The GrimmSpeed 15-21 WRX Header not only the prettiest on the market, but also among the best performing and durable pieces you can purchase.
Full 304 Stainless Steel Construction – Flanges, tubing, collector and badge
True Equal Length Runners – CNC bent and trimmed, less than 1% variance from the longest to the shortest
Innovative Cast Merge Collector – Low restriction inlet and outlet, smooth flow and consistent performance
Smooth, Restriction-Free Flow Throughout – Single piece mandrel bent tubing welded to a single piece merge collector removes unwanted “steps”
Thick 1/2in CNC Cut Flanges and 14ga Tubing – Added durability and longevity
No Tune Required – Safe to run, just bolt on
No Ground Clearance Loss – Clears factory skid plate without using spacers
J-Pipe/Turbo Bracket Included – Retain the support that other aftermarket header lose
Gaskets and Hardware Included – Everything you need to get installed and on the road
Manufactured and Welded In The USA – For consistency and top quality control
15-21 Subaru WRX
With multiple distribution centers across the nation, we strive to provide the best and fastest shipping solution for your orders. Most in stock items will be shipped within 1-2 business days unless it is being shipped from manufactuer directly. Stock information on the website might be delayed/inaccurate, please click the help button at the bottom of the page for the most up-to-date information.
JDMuscle ships via multiple carriers such as FedEx, UPS, USPS, and DHL. We cannot guarantee the shipping company used to deliver your products. Your order may be shipped in multiple boxes from different carriers.
Process Time and Cut-off Time
Orders take 24hrs to process and transit times vary. Shipping cut-off for JDMuscle is 3:00pm EST. Freight shipping will require an appointment for pick-up which might take a few days extra.
International orders are subject to higher shipping fees then notified on the site and we reserve the right to add to it. Any modifications to an address after the order is placed may subject to a fee. The flat rate fee for a single smaller package is $20, and for larger or multiple packages the fee is not limited to $60. For International shipping please send us an email(email@example.com) with your full address and items to purchase.
Freight Shipping(Please read carefully)
Any orders shipped Via Truck Freight which requires you to be available at the time of receipt. There is a possibility the trucking company will try to schedule a delivery time with you. At the time of delivery, the driver will hand you the delivery receipt also referred to as the bill of lading, you will use this to notate any damages to the shipment. It is important that you fully inspect the shipment from all sides and notate any dents, punctures or rips in the outside packaging on the delivery receipt. Once you've inspected your shipment from the outside, you will need to open it and check the product in its entirety for damages and notate them if any. If there is no damage sign for the package and enjoy! In the rare case, you do find that your order arrived with damages, it is important you follow these steps.
- Do not refuse the product
- Document the damages in as much detail as possible on the Bill of Lading
- Take numerous photos from all angles (including packaging)
- Keep the product and contact the shipping company to start the damage claim
- Contact us either by phone or email for the next steps In the situation where the delivery driver is unable to wait for you to open and inspect your product, simply document "driver was unable to wait for inspection."
All damage must be noted on the Bill of Lading before signing and initiating a damage claim. If the damage is not notated before signing for the item it is assumed to be in good condition. This will forfeit the ability for a shipping claim and you will not be eligible for refund or replacement.
Our policy lasts 30 days. If 30 days have gone by since your purchase, unfortunately we can’t offer you a refund or exchange. Please send an email to firstname.lastname@example.org to set up a return.Please do not send your purchase back to the manufacturer.
To be eligible for a return, your item must be unused and in the same condition that you received it. It must also be in the original packaging.
Additional non-returnable items:
There are certain situations where only partial refunds are granted (if applicable)
You have 7 days to cancel an order, once the order has been packaged/ tracking number has been created, a cancellation is not allowed.
Full refund will be issued if the order has not been shipped, otherwise buyer will be responsible for a 10% restock fee and return shipping.
Special-ordered item cannot be canceled.
Refunds (if applicable)
Once your return is received and inspected, we will send you an email to notify you that we have received your returned item. We will also notify you of the approval or rejection of your refund.
If you are approved, then your refund will be processed, and a credit will automatically be applied to your credit card or original method of payment, within 7 days. Some brands/products might be subject to a restocking fee up to 25%, please check with us prior before purchase.
Late or missing refunds (if applicable)
If you haven’t received a refund yet, first check your bank account again. Then contact your credit card company, it may take some time before your refund is officially posted.Next contact your bank. There is often some processing time before a refund is posted and can take up to 10 business days in rare cases
If you’ve done all of this and you still have not received your refund yet, please contact us at sales@JDMuscleUSA.com.
Sale items (if applicable)
Only regular priced items may be refunded, unfortunately sale items cannot be refunded.
Exchanges (if applicable)
We only replace items if they are defective or damaged. If you need to exchange it for the same item, send us an email at sales@JDMuscleUSA.com
If the item was marked as a gift when purchased and shipped directly to you, you’ll receive a gift credit for the value of your return. Once the returned item is received, a gift certificate will be mailed to you.If the item wasn’t marked as a gift when purchased, or the gift giver had the order shipped to themselves to give to you later, we will send a refund to the gift giver and he will find out about your return.
You will be responsible for paying for your own shipping costs for returning your item. Shipping costs are non-refundable. If you receive a refund, the cost of return shipping will be deducted from your refund. Depending on where you live, the time it may take for your exchanged product to reach you, may vary. If you are shipping an item over $75, you should consider using a trackable shipping service or purchasing shipping insurance. We don’t guarantee that we will receive your returned item.
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