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?
This is the Wrenchrat kit installed on Ted Toki's '55 Chevy gasser. Everything that is not a standard-running small-block is included. The pulleys are from Millerspeed. After the first few runs, the hot side turns to this gunmetal hue. We like it, but if you don't, get them ceramic coated in black or blue. The kit fits D-ports or rectangle ports and iron or aluminum aftermarket heads. Let Wrenchrat know what heads you plan to use.
The Mill
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.
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.
We wanted to make this a test of an average small-block, so there is nothing monumental about the four-bolt block. The crank is factory GM, and rods are from RPM sold through Westside Performance.
The Kit
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.
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 Ross pistons have a 4cc total dish with a 1.585-inch compression height and are 0.005 inch in the hole for a 9.46:1 compression ratio. They were ordered with 0.300 inch of meat above the top ring land to cope with the boost. The 1/16-inch rings are from Akerly & Childs; Toki gapped them at 0.022 top and 0.025 second so they don't butt under pressure.
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 Turbos
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 cam is a Comp hydraulic roller with 242/248 duration at 0.050 and 0.584/0.579 lift using a 1.6:1 rocker. The LSA is 113 degrees. The theory is that a cam with a lot of duration and overlap will create a lot of reversion, and the cam selected should be based on the rpm range of the engine. A huge cam that doesn't peak until 7,000 rpm, is going to be a pig everywhere else in the powerband.
The Test
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.
Next Stop
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.
DYNO DAY RPM HP TQ 3,078 246 419 3,134 258 432 3,250 287 464 3,314 308 488 3,458 359 546 3,540 400 594 3,631 453 656 3,731 518 729 3,840 591 808 3,954 662 880 4,074 733 945 4,194 775 971 4,314 803 978 4,435 820 971 4,556 826 953 4,674 829 931 4,792 834 914 4,908 838 897 5,023 845 883 5,136 851 870 5,248 851 852 5,357 858 842 5,464 868 835 5,568 875 825 5,673 877 812 5,776 884 803 5,879 891 796 5,980 901 791 6,081 912 788 6,182 921 782 6,281 929 777 6,378 936 771 6,461 918 746
DESCRIPTION
PN
PRICE
Wrenchrat twin-turbo kit
Stage 1
$4,999.00*
Remflex exhaust gaskets
RF2005
29.95
Ross pistons
2618
Call
RPM H-beam rod
5700H
$420.00
GM steel crank
NA
NA
MSD distributor
85551
221.95
MSD 6AL ignition
6420
197.95
Snow Performance boost cooler
20001
300.00
AFR heads
1120
2,016.95
T&D shaft rocker arms
2300
1,700.00
Comp cam and lifters
12-468-8
738.01
Fel-Pro MLS head gaskets
1144-053
81.99
Akerly & Childs
19100-35
171.21
BHJ balancer
CH-IBS-7
330.14
Milodon oil pan
31505
438.00
M/T ET Street Radials
376ZR
207.32
Manley pushrods
25735
53.49
25736
53.49
*Base Kit
