This is the Wrenchrat kit installed on Ted Toki's '55 Chevy gasser. Everything that is not
In hindsight, this experiment could have been a lot more scientific. For instance, we could have run this cool new turbo kit against the eBay turbos we ran in the Sept. '10 issue. Or, we could have run this cool new turbo kit against itself by swapping a set of cylinder heads and making more power for less boost. But all of that is going to come later. For now, we wanted to get a taste of the kind of WOT power a well-designed twin-turbo system has to offer. Our reward was 936 rwhp from a 355-inch small-block or about 2.64 hp per cubic inch. That's close to 1,100 hp at the flywheel. What else do we need to say?
We've seen stock 350-inch engines take plenty of boost without tossing chunks, but we knew this setup was going to be too much for a set of cast slugs swinging on some stock rods. The solution was simple: Garrick at Kelly's Block Welding in West Los Angeles prepped a four-bolt block for a little forced air. Ted Toki at Westside Performance added a set of custom Ross forged pistons, RPM H-beam rods, and a 3.48-inch nitrided and polished steel GM crank. The cylinder heads are the 227cc Competition Package from AFR, and according to the company's specs, they flow a staggering 329 cfm at 0.750 lift and more than 300 cfm from 0.500 lift on.
We wanted to make this a test of an average small-block, so there is nothing monumental ab
Even though the parts seem exotic, they all had shelf part numbers. The only hands-on tweaking was performed by Eric Solomon at Westside Performance to port-match the Edelbrock Super Victor intake to the cavernous intake port in the AFR head. The cam was suited to both the heads and the turbo, with a good lift number to put the valve right in the fat part of the flow curve, and additional LSA to reduce overlap and build boost in the cylinder. The ignition was an MSD billet distributor with a 6AL box. The carb was the 850 Holley from the Sept. '10 issue.
The turbo kit from Wrenchrat makes monster power. For the price of a good centrifugal supercharger you get twin stainless steel turbo headers, two turbochargers, stainless downpipes, wastegates, the cold-side charge pipes and merge, a blow-off valve, and all the little parts to put it together. If you have a well-running engine with less than 9.0:1 compression, you can install it in a weekend, and with a few simple carb modifications, run it on pump gas.
The Ross pistons have a 4cc total dish with a 1.585-inch compression height and are 0.005
What makes the system different from anything else we've seen is the 4-into-2 turbo header design. The system reduces turbo lag by maintaining the energy of each exhaust pulse to keep velocity high and scavenge the neighboring cylinder. The management of pulse energy allows the use of larger turbos that respond like smaller ones.
The exhaust manifolds have T4 flanges that allow you to run any turbo from 60 to 76 mm on the compressor side and up to 0.81 A/R ratio on the turbine side. The base kit comes with a pair of turbos that can make 650 to 700 hp on a pump gas tune or 1,000 hp with race gas, but you can order whatever turbos you want, or get a recommendation from the guys at Wrenchrat.
The cam is a Comp hydraulic roller with 242/248 duration at 0.050 and 0.584/0.579 lift usi
For this engine, Joe Delgado from Comp Turbo selected a set of 67mm CT4 turbos with X-HF billet compressor wheels and 65mm P-trim turbines in 0.81 A/R housings. The selection was based on the size of the engine, compression ratio, cam timing, and cylinder head design. Even though each of these turbos is designed to deliver a maximum of 95 pounds of air per minute and support 950 hp, we were looking for instant boost delivery in a usable rpm range. The CT4 triple-ceramic ball bearings are perfectly smooth, lowering friction losses and temperature for more speed. The turbo's design, combined with the X-HF high-speed billet compressor wheel, allowed Toki's '55 to make usable boost (6 to 8 pounds) as low as 3,100 rpm and make more than 400 lb-ft of torque. In addition, we saw torque gains of 527 lb-ft from 3,100 rpm to the torque peak of 978 lb-ft at 4,314 rpm. That is a lot of usable power.
The cylinder heads are 23-degree Competition Package 227s from Air Flow Research. The Comp
The 80cc exhaust port is treated to the same level of CNC machine work. Note the bronze va
The intake valve is 2.100, so we needed a big valve relief in the piston, and the exhaust
The intake port is 227 cc. Note the offset of the valves.
Toki used a set of TD Machine Products shaft rockers, but you can use a standard stud syst
The Comp turbos are designed to fit on a T4 flange. The T3 flange is also available.
If you look at the numbers in the dyno-day sidebar, you are going to see that the turbos doubled the boost from 10.4 pounds to 21 pounds and picked up an additional 377 lb-ft of torque between 3,500 and 4,500 rpm, right in the sweet spot. We are always saying that torque equals a good e.t. and horsepower makes for a good trap speed. This system does both with a torque peak of 978 lb-ft at 4,300-rpm and a horsepower peak of 936 at 6,400.
After some tuning runs, we made this number using 25 degrees of timing total and 86 primary and 94 secondary jets in the 850 Holley. To control detonation, we used Rockett Brand 114 race fuel and a methanol injection kit from Snow Performance.
To run this combo on pump gas and cruise, we'd need to dial out a lot of exhaust pressure with the wastegates and use an MSD BTM to control timing on the street.
We made whopping power on the first installation of the Wrenchrat kit and opened the door to a lot of questions. Cam, carb, and cylinder head size will be a factor in where and how much power the system makes. In the usual Car Craft fashion, we went for the big number first to have a little fun. In fact, we have an even bigger set of Brodix 233 heads and a 420-inch small-block being assembled right now at Westside Performance as a dyno mule. Using that combo, we are going to get scientific and figure out what the best twin-turbo combination is for street and strip.
The AR ratio in the turbine side is 0.81. This is as large as you can go on the Wrenchrat
These are the 67mm twins from Comp Turbo. They have billet compressor wheels, ceramic ball
If you look closely, you can see the recirculation slot right at the tip of the inducer (s
When Wrenchrat advertises the 4-into-2 system, this is what the company is talking about.
The kit also comes complete with a 2-into-1 merge carb hat and a 50mm blow-off valve. The
The Wrenchrat kit comes with a pair of 41mm wastegates and a downpipe merge to properly ve
From left: George Diagne, Marty Stromberger, Eric Solomon, and Steve Berg working on the '
Even though this kit can be tuned to run on pump gas, we used Rockett Brand 114 for the bi
The Stage 1 Boost Cooler from Snow Performance injects Boost Juice into the carb hat when
Throughout all the tests, we used this simple 2-inch cog drive system from Millerspeed to
Toki's blem tires were throwing chunks on the last dyno day, and Ernie Mena from Westech t
Looking at the dyno chart, you can see the copious amounts of torque these turbos are capa
|Wrenchrat twin-turbo kit
|Remflex exhaust gaskets
|RPM H-beam rod
|GM steel crank
|MSD 6AL ignition
|Snow Performance boost cooler
|T&D shaft rocker arms
|Comp cam and lifters
|Fel-Pro MLS head gaskets
|Akerly & Childs
|Milodon oil pan
|M/T ET Street Radials
Summit Racing Equipment
PO Box 909
MSD Ignition (Autotronic Controls)
1490 Henry Brennan Drive
1017-A East Highway 24
221 West Allen Avenue
Remflex Exhaust Gaskets
Ross Racing Pistons
625 S. Douglas Street
Mickey Thompson Tires & Wheels
4600 Prosper Drive
Holley Performance Products
1801 Russellville Rd
P.O. Box 10360
T&D Machine Products
Air Flow Research (AFR)
28611 W. Industry Drive
Kelly's Block Welding
W. Los Angeles