Jim G’s SLURP Project – Posting 19: Red’s special Phoenix transmission
This posting is one in a series. If you have not yet read the earlier postings in the series, you’ll need to, as this posting won’t make much sense without having done so! Just do a search using the word “SLURP”.
Inexperienced street rodders spend a lot of time talking about their engines. The experienced ones know that in actual use, the transmission is equally – or more – important. A well chosen transmission will be reliable and will bring out the best in the engine, while a poorly chosen one will be fragile, inconsistent, and can easily make even a great engine feel bad.
I spent a lot of time and energy planning for Red’s transmission, and he’s getting a very special one.
My friend Greg Ducato, who owns and runs (I mean RUNS – not just visits) Phoenix Transmission has designed and built it, and its shipping to me from there right about now.
Because Greg is a car collector and street rodder himself, and a very experienced one at that, he knows way better than most just how important each transmission decision made really is.
Let’s review very briefly the planning and design thoughts that went into the tranny that Red is getting.
First, I ran some numbers early on, and realized that despite my strong preference for higher highway rpm (I don’t like lugging a high performance engine at low rpm just to get slightly better fuel mileage), a non-overdrive tranny, like the GM TH350, was not an option unless I changed the rear axle gearing, which I do not want to do. With Red’s 3.90 axle, and tire size the same or anywhere near his current ones, a non-overdrive tranny would have the LQ9 spinning at 2825 rpm at 60 mph. Fine for Red’s vintage inline six, but very excessive for the modern 6 liter LQ9.
Second, I needed a non-computerized transmission, as Red will have only one computer on his chassis – the MSD one that fires the sparkplugs.
Third, we wanted an easy adaptation for the LQ9 engine. No exotic special and rare parts, thank-you!
Combining all the above led Greg to suggest a custom built version of the General Motors 700R4 transmission. Notice that I said “custom built version”.
This is because the torque capacity of a factory stock 700R4 is not adequate for a modern performance vehicle, and the shifts are, well, “consumer-oriented” (not snappy).
The 700R4 is in fact the “mechanical” versus “electronic” version of the 4L60E and 4L65E computer controlled automatics used in GM vehicles until the current phaseover to 6-speed automatics. However, the 700R4 was last installed in any vehicle at a GM factory a LONG time ago, since powertrain control modules (computers) have been a staple of consumer cars and trucks for many years now.
The 700R4, and the 4L60E / 4L65E that replaced it, had a HUGE performance range to cover in the broad array of vehicles to which they were applied by GM. They were used in passenger cars, vans, pickup trucks, SUVs, and performance vehicles like the Corvette, Camaro, and SSR. GM wanted a transmission that could be readily adapted to this very diverse set of applications, with no internal gear ratio changes required. While that was good for “cost effectiveness”, it was bad for both performance and durability.
The reason it was bad for performance is that EVERY vehicle in the above list, regardless of weight, size, and payload capacity, got the same internal ratios. The only way that the drivetrain designer could compensate for lighter or heavier vehicles, or vehicles with wildly different power curve shapes, was via rear axle ratio changes. Any competent automotive transmission designer will tell you that the correct way to select ratios for a vehicle is to select the appropriate number of ratios (few for engines with broad power curves, more for engines with narrower, peakier power curves) and then set the ratios to maximize “the area under the curve” on a tractive force versus road speed graph, ensuring also that there are no large “gaps” where a shift to the next gear drops the engine low in its power curve, which would cripple its ability to accelerate the vehicle under open or near open throttle or into a headwind or up a hill. THEN, the rear axle ratio is selected bearing in mind the desired operating road speed range, the desired cruising engine rpm, and the weight of the vehicle under its most typical, or critical, operating conditions.
When you use just ONE set of internal ratios to cover vehicles whose weight, operating speed range, and engine power curves vary wildly, you really UNoptimize performance.
Likewise, durability suffers in the “one tranny for almost all needs” scenario. This is because the designer and supplier cannot specify a level of parts quality and durability sufficient to meet the most demanding application, as that would make the transmission WAY too costly for use in price sensitive vehicle models. Instead, they select rather lower-end components, and try to only selectively upgrade key components for the tougher applications, and only where warranty experience indicates this is required. Sometimes, they “cheat” too: when they KNOW the tranny might not be strong enough, they built sufficient “torque management” into the drivetrain to ensure that full engine power is never delivered to the transmission in the lower gears.
For Red, this corporate standardization philosophy creates two obvious problems. One is that Red will get internal gear ratios of 3.06, 1.625, 1.00, and 0.70 overdrive – whether these are a good fit for him or not. They are in fact NOT a good fit, since Red’s light weight would normally allow us to specify an engine with an aggressively high rpm oriented power curve. But, with these gear ratios, that would create serious “gaps” at multiple places. In fact, if you have the tranny shift at 6500 rpm, you STILL drop down to 3500 after the 1st to 2nd shift, and down to 4000 rpm after the 2nd to 3rd shift. A peaky engine would bog after each shift. Red would really like a “closer ratio” gearbox, but that is not available. So, we were forced to go for a broader power curve – whether we would have wanted to or not.
The second problem created was that Red’s projected power would likely destroy a stock 700R4 rather quickly, since Red’s engine is projected to produce more power than a stock Corvette but less than a Z06 Corvette. Like the 4L60E and 4L65E transmissions, the 700R4 needs a lot of re-engineering to handle that kind of estimated power. This is why shops like Phoenix Transmission exist and have market programs designed specifically for street rodders and customizers.
There is yet another constraint created by the transmission. The 0.7 overdrive ratio, coupled with Red’s rear tire size, results in a cruising engine rpm of about 2000 rpm at 60 mph. I live in hilly terrain, and I don’t want Red downshifting frequently just to be able to climb hills. So, this effectively created a situation where I needed to select my camshaft with a requirement beyond the norm: the cam has to create at least 130 crank horsepower at 2000 rpm, so that after drivetrain losses, I still have at least 100 rear wheel horsepower.
See how we are getting boxed in here by the transmission realities?
Why not go with a 5-speed or 6-speed manual transmission? I did not want to do that for the following reasons:
- I really like the column shifter and the way it makes the truck into a true “3-seater”
- column shifter MANUALS are not that much fun
- I did not want to have to engineer a clutch pedal mechanism along with the other space issues
- I did not want to subject the rear axle to the types of shock loads that a manual can generate
I told Greg that, depending upon exactly what exhaust WOULD indeed fit, and how good that dual carb Edelbrock RPM Air Gap manifold actually is, the expected peak power for Red’s engine, per the engine simulation program, ranges from around 425 to 505 crank horsepower. I told him peak power would be between 6000 and 6500 rpm, and we wanted to shift at 6500 under WOT. That told Greg effectively what range of parts in the tranny need to be addressed in order to provide sufficient durability.
Greg selected the Phoenix “PT700R4ST” model as the basis for Red’s customized transmission, as it will meet or exceed the horsepower objectives and still be good for occasional towing or other truck usage.
This transmission has over 40 performance and durability upgrades and modifications over a stock tranny. These include: high load capacity sprags, high energy friction and band, increased pump volume and pressure, stronger input drum and reaction shell, modified reverse input drum, special performance band, and more, to provide the highest level of performance and economy possible. Phoenix describes this as a great tranny “for Streetrods, Muscle Cars, and Sport Trucks whose owners crave the awesome acceleration and tire-spinning, wide open throttle shifts this trans is built for” and rates it for use with engines up to 500 hp. The tranny comes with Phoenix’s own High Performance "Torque Max" torque converter with a choice of stall speed.
Greg knew I favored a low-stall speed converter in this situation, since Red is so light and traction-limited that we don’t NEED to “wind up the engine” much at lower rpm to get him moving pretty quickly, and he’ll probably never visit a dragstrip. Greg told me that if this was a fuel injected engine he might be tempted to use a 1500 stall converter but the fact that the truck weighs 3000lbs and the cam has as much duration as it does, and the carbs need a good vacuum signal for idle quality, makes him think we need to build about 1800-2000 into this converter to keep the engine idling smooth enough in gear to be comfy. I really appreciated this converter expertise and advice, as Red’s current inline six and Hydra-Matic combination is in fact less than ideal at idle for that very reason: the engine is trying to idle at too high an rpm for the fluid coupling to be comfortable at, and so Red is always “straining at the starting line” like a race horse, to an extent. You see, that cast-iron Hydra-Matic fluid coupling was designed originally to couple to an engine idling at just 400 rpm. Red’s “wild” (
) inline six cam made that slow an idle impossible.
Greg made an early point of asking me what lobe center the cam is ground on (113). He did this because he was trying to get an idea of what the engine will idle at rpm wise with this cam and carb combo, and the above torque converter stall speed was what was on his mind when he asked.
This is the kind of experienced value that a shop like Phoenix provides, and you can see that an ill-advised purchase without consultation from “this week’s best Internet deal” could lead to a pretty incorrect transmission solution.
With the 700R4 being a mechanical versus computerized transmission, I asked Greg how he would activate the converter lockup. Phoenix will wire it internally off a pressure switch in the 4th gear circuit so that when the trans shifts into overdrive it applies the converter clutch at the same time. Greg will also supply a pigtail that I can run 12 volts to on the outside of the trans, if I wish, and I can use a toggle switch to interrupt the 12 volts if I don’t want the tranny to always lock up the converter after going into overdrive.
The trans will be shipped empty except for a little bit left over from dyno testing (shipping regulations). The converter will have about a quart and a half in it. Greg says I will need about 10 or more quarts of fluid to complete the system. Greg likes any synthetic Dexron III fluid. Phoenix stocks Amsoil and BG products in house, but Greg says that Mobile 1 synthetic is good stuff, he recommends it.
Phoenix does not do the yokes. Greg suggests getting the driveshaft builder I plan to use to supply one, as he will need to match it to the weld yoke and tube diameter on the shaft he builds. There is more than one choice on sizes which is why it is best to let the driveshaft builder help with this.
I asked Greg what starters would fit and work well. The flywheel Phoenix will be providing is the same dimension as stock and Greg suggested a late model block mounted starter off of a 99-up 6.0 ¾ ton truck with 4L80E automatic. This is compact and light but strong and dependable in his experience.
The trans and converter package includes converter to Flexplate bolts, and speedometer gears set up for my application (I had to tell Greg the rear axle gear ratio and tire size). Phoenix is also providing the TV cable set up including special linkage, bracket and cable. There is a special LS flywheel with adapter and bolts, and also a tranny dipstick and tube.
Phoenix sets up each one of these per order, and also uses a special case finish. The transmission comes with a 2 year / 24,000 mile warranty that starts when the trans is “in service” not just when purchased. Try getting THAT kind of warranty from some of the places that sell transmissions!
I also know that the warranty is a REAL and meaningful one. On my previous Phoenix purchase, the built 4L60E for my supercharged SSR project, the transmission experienced a problem after about a year, due to what was traced to be a faulty component supplier part. Even though the fault was not with Greg’s team’s work, but rather simply a bad part from a component supplier, Greg not only did a full disassembly and replacement, all labor included, but he also made it the very best warranty experience I have ever had. So, when it was time to buy another tranny for another project, there was no question where I would go to get it.
So, this is how I selected and purchased Red’s transmission. You can see that I hold Phoenix transmission in pretty high regard, and Greg’s personal advice particularly so. If you need a performance transmission PROPERLY done, Phoenix is a great place to go.
Jim G
