Quarkdog.com
Copyright 2013, Leo Stearns
Project Goals
Project Outline
For V8s, I did not consider anything older than the LS2 because those drivetrains are not typically available with low mileage, offer lower output power and are not as clean as the LS2 and later engines. With the exception of the L92, I also did not consider the Vortec family of LS engines used in light duty trucks because of their lower power output and greater weight (iron block).
For V6s, I did not consider anything older than the LFX because the power output was not sufficient for my interests.
LS2/4L65-E: 6.0L, 400hp, 4-speed auto. - Sourced from an '05+ GTO
L92/6L80-E: 6.2L, 403hp, 6-speed auto. - Sourced from a '07+ Escalade/Denali.
L99/6L80-E: 6.2L, 400hp, 6-speed auto. - Sourced from a '10+ Camaro, '08+ G8 GXP
LFX/6L50-E: 3.6L, 326hp, 6-speed auto. - Sourced from a '12+ Camaro
LS3/4L70-E: 6.2L, 430hp, 4-speed auto. - Sourced from GM Performance, part of the E-Rod series
Drivetrain
From a long potential list, I considered 5 drivetrains for this project:
All of these powertrains offer:
Aluminum block to reduce front-end weight – The El Camino is already nose heavy.
CARB ULEV or better emissions performance – This engine swap will receive a CARB approval.
For more on California emissions and engine swaps, click HERE.
Automatic Transmission – Though I do like to drive a manual, I spend time in stop and go traffic. I don’t have enough cartilage left in my knee for a manual.
Good Condition – All of these drivetrains are available with under 50K miles. Given the longevity of modern equipment, these would outlast my needs.
Not Considered:
Powertrain Selected:
Though I was interested in the 6-speed automatic and was quite intrigued by the balance offered by the LFX, because some other important pieces from the 2004-2006 GTO can be made to fit into a 5th generation El Camino, a GTO donor car was the most cost effective way to go, hence the LS2/4L65-E is the power train we will use. Further, because of the other parts I will utilize for emissions and the other subsystems I will be transferring over, I will need to purchase the entire vehicle.
Port Injection / Distributer-less Ignition, Computer controlled automatic transmission, ULEV. Fast.
Large discs all around with 4-chanel ABS.
Improve suspension geometry and provide much improved feedback through the steering wheel. Lower car.
Investigate IRS. Modifications for increased wheel/tire width. Lower car. Improved suspension geometry.
Install a more modern interior. Supportive seats. Modern conveniences such as remote entry, power mirrors, express down windows, integrated satellite radio/iPod integration. Modern safety such as air bags, comfortable seatbelts.
Perfectly straight body with high quality paint. Simplify chrome. Integrate bumpers into body. Extensive, professional use of LED lights.
Brakes
The OE brakes on the El Camino were probably acceptable for their day and the drivetrains available. For a daily car today, they are not acceptable. There are several big-brake upgrade choices available. From a Corvette C5/C6 through to Wilwood. Clearly, my best choice for upgrading the brakes is to install Corvette C5 rotors and calipers. This will be explained in a bit.
4 channel ABS systems are a requirement for a daily driver in my opinion. I have not seen much work done porting ABS systems over to custom cars and hot rods. There's good reason for that. The programming for ABS systems is pretty complex. Tuning software vendors such as HPTuners won't touch ABS. Consider the liabilities of one of their customers "tuning" their ABS so their car runs into a bus load of lawyers wives.
A good overview of how and ABS system works can be found HERE. I have never designed an ABS system, but I have professionally designed several other types of control systems, and I believe Stoptech is correct about the importance of the PT (Pressure vs. braking torque) and PV (pressure vs fluid volume) curves of each brake. The article's conclusion is that if the PT and/or PV curves of the brakes you install on a vehicle are MORE aggressive than stock, the ABS system is going to be confused and braking performance will suffer. What they are really saying is that, if your brakes "exceed" the capacity programmed into the ABS system, your dry weather braking performance may get worse. If you've ever stomped on the brakes of an ABS equipped car in the wet or snow you know that means pulsing and shuttering stops that are halfway to forever long, but shorter that without ABS. However, halfway to forever on dry pavement is longer than no ABS.
Though not covered in Stoptech's article, the maximum about of braking torque which can be applied is impacted by the tire contact patch and vehicle weight on the tire. If the maximum amount of possible braking torque is much less than what was programmed into the ABS, the braking performance will again approach wet weather.
I conclude form all of this that in order to successfully install an optimal ABS system on a custom car, it is necessary that the ABS system be designed for very similar brakes, vehicle weight, suspension dynamics and tire contract area as the custom car. A brief article in Hotrod magazine (linked HERE) confirms my conclusions.
As it turns out, the '05+ GTO is a really good match to a modified 5th generation El Camino with C5 brakes:
GTO
12.6"
2
1.56"
11.25"
1
1.75"
3,750 lb
110"
El Camino/C5
12.8"
2
1.56"
12.0"
1
1.75"
3,550 lb*
117"
Front Rotor Diameter
Front Caliper Piston Quantity
Front Caliper Piston Diameter
Rear Rotor Diameter
Rear Caliper Piston Quantity
Rear Caliper Piston Diameter
Vehicle Weight
Wheelbase
I believe the biggest risk factors here are:
- The PT curve for the rear brakes on the El Camino may be more aggressive than the GTO.
- The static load on the rear brakes of the El Camino will be less than the GTO.
- Work will need to be done on the suspension to ensure forward weight transfer under braking is not excessive.
The PV curves should be identical between the two vehicles (assuming matched the lengths of flexible brake hose). So, the question is the PT curves.
There remains the issue of wheel speed sensors. I will attempt to address them in the suspension sections.
Two further notes. The GTO was equipped with switchable traction control and I intend to carry that in to the El Camino. The Hot Rod magazine article states that maintaining tire diameter within 5% of stock is necessary to preserve this feature. I do not yet understand why this is critical, but will monitor it as the project continues. Second, the GTO was not equipped with stability control, so I can ignore those constraints.
Front Suspension
The 5th generation El Camino's steering performance was adequate for the day. However, the geometry forces a subterranian roll center, significant understeer, on-center numbness and has a slow steering ratio. The design of the SLA suspension and recirculating ball steering was antiquated when the cars came off the production line. Please understand, I'm not saying the cars are bad, just antiquated. My '07 Acura RDX (which is a sport utility with a CG (and roll center) probably a foot higher than the El Camino's) can drive circles around it. There are a few options for changing the front suspension and steering dynamics. There is also a wide variety of opinions about those changes. I spent some time investigating the B-body tall spindle swap, but decided against it. There were two killer issues:
Rear Suspension
It's pretty obvious that the stock 10 bolt rear would not hold up to the upgraded drivetrain. A popular and simple swap is to install a 12 bolt rear out of a Buick GN. However, these axles have become quite expensive, will require a complete overhaul because of age and mounting ABS wheel speed sensors on them will be painful.
Another possibility is a custom 12 bolt axle. There are several shops which will modify a standard GM 12 bolt to fit into a G body. Most of these shops also offer 12 bolt rears modified for '98-02 F body cars. These F bodies were equipped with 4 channel ABS systems and custom 12 bolt rears can be ordered with the appropriate reluctor rings and sensor mounts. by mixing and matching, a G body drop in 12 bolt rear with ABS sensors is possible. The number of teeth on the reluctor rings is a mystery to me at this time. The primary issue with this is cost. I have not completely priced this out, but I can see $3,000 before it's complete.
Because I do want the car to handle well on real roads, an IRS is very appealing. I read several arguments that solid axles are just as good around corners and better in a straight line. I understand and believe a solid axle is better in a straight line. It's wishful thinking to believe a solid axle is as good as an IRS around corners on real roads.
I reviewed several possible IRS systems and discounted the:
I considered using the IRS out of the GTO. It would certainly simplify the ABS issue and it's included with the donor car.
- C5's IRS because it's too wide and too hard to modify.
- Jaguar IRS would have a hard time with ABS.
- Aftermarket IRS systems I've seen are amazingly expensive and have the same issue with ABS compatibility.
- 90's Thunderbird SC IRS is too wide, but can be modified and is available cheap. Mounting into the chassis will be more of an issue because it requires 10 mounting points (6 for the suspension, 2 for the springs, 2 for the shocks).
Interior
I will be swapping out the interior of the El Camino for much of the GTO's interior. All of the electronics and HVAC from the GTO will be moved over to the El Camino. This includes the instrument cluster and the electronic gas pedal. In order to make all of this happen, I will need to bring the BCM and body wiring harness over from the GTO. This pretty much necessitates that the firewall and part of the floorpan from the GTO be integrated into the El Camino. The dash from the GTO is much deeper than the El Camino's but it is designed to sit closer to the occupants, however I will need to be careful with seat location. The door panels will be fully custom, but will incorporate several parts from the GTO. The GTO interior has a total of 5 badges, one in the instrument cluster, one on the dash, one on the steering wheel airbag cover, one on each front seat. The instrument cluster appliqué, it's just a matter of the 8-10 hours to design it and the $300-$400 cost to have it printed. The dash emblem will require measuring the existing one, machining a new one and then finishing it. The air bag cover will be about impossible to put an El Camino or Chevy logo on, but I could swap it out for a cover from a Holden and live with a lion logo. If I want to remove the GTO logo from the seats, I will need to have them custom refinished, that will be expensive.
The stock radio in the GTO is a double high DIN. There are several good options to incorporate a ~7" touchscreen into that area. iPod integration, satellite radio and a backup camera could be easily addressed. The existing steering wheel radio controls can be integrated into this system.
The GTO offers remote entry and express down power windows which both can be interfaced to the existing El Camino solenoids and motors. Same is true for the automatic headlights.
Exterior
I really don't want to radically change the exterior appearance of the El Camino, just a bit of modernization. The list includes:
- Remove some chrome.
- Narrow and tuck the bumpers into the chassis. This will probably necessitate painting the bumpers.
- Incorporate the rear license plate into the bumper. Smooth the tailgate.
- Remove the antenna and relocate into the windshield.
- Replace the existing door handles with flush mount units. These could be out of the GTO. I need to find a donor car with an identically curved door panel to execute this conversion properly.
- Incorporate power sideview mirrors.
- Incorporate a 3rd brake light.
- Incorporate the satellite radio and possibly GPS receivers. Probably under a small shark fin.
- Upgrade the rear lights to LED with better integration into the bumper.
- Incorporate narrow and wide beam LED driving lights into the area currently used for the front turn signals. I will also need to replicate the turn signal/parking light function.
- The Cobra IRS requires Eight mounting points.
- The rear brakes are 11.6" rotors using 1.5" diameter single piston calipers. I'm concerned that the smaller piston size could be an issue because it will skew the PT and PV curves. If it is an issue, I could fabricate a simple adapter and mount Mark VIII calipers (1.78" diameter piston).
- The Cobra lug pattern is on a 4.5" bolt circle, versus the 4.75" diameter one might expect on a G body. You could not accidentally mount 4.75" wheels on a 4.5" hub, but it would be nice of all 4 wheels had the same bolt circle. However, I can probably modify a standard hub and rotor to a 4.75" bolt circle. Because the parking brake is integrated into the calipers, the hub and hat area are clear, the modification will be much simpler
- A really nice security blanket, if the IRS does not work out, I can easily swap in a solid axle form a 99-04 Mustang GT for under $1,000.
- ABS wheel speed sensors are incorporated. The Mustang uses 50 tooth reluctor rings compared to the GTO's 48. I do not yet understand if this is an issue. If it is, I can fabricate custom reluctor rings. This is still much simpler than starting from scratch.
- The Cobra IRS is 62-1/4" wide from hub to hub. This is 4-1/4" wider than the OE axle in the El Camino. Stock, the El Caminos ran Zero wheel offset but wheels are readily available for the Cobra IRS with +1.77" offset, reducing the effective difference to 0.7" (0.35" per side). With more searching I can find wheels with a bit more offset.
- On G body cars, the tires typically hit the frame before the fender. Once completed, I believe the new subframe will be inboard of the existing frame, so the outer fender will ultimately limit the rear tire width.
- The limited slip differential is set up with 3.55:1 gears versus the stock GTO's 3.46:1. That's a 2.6% difference which should not impact ABS or TC. The speedometer can be easily tweaked during the tuning process.
Next thought was the IRS out of a '99-04 Cobra. This IRS has gotten a bit of a bad reputation due to some wheel hop and half shaft breaking issues at the drag strip. At this date, there has been seemingly a bunch or work done to improve the performance of the rear and apparently a stock '03-'04 rear, with bushing changes, can handle 600 RWHP without issue.
- The GTO IRS requires Seven mounting points.
- It is about 1.5" wider than the stock 10 bolt. This could easily be corrected by adjusting wheel backspace.
- The GTO IRS has only a 7.75" ring gear, so it's marginal in the stock application and may well have issues should I decide to modify the motor.
- The design of the IRS is ancient. GTO's do suffer from wheel hop, the suspension changes geometry as it moves and there is no camber adjustment.
- The GTO has a 120mm bolt circle. 120mm is NOT 4-3/4". One of the issues with a 120mm (4.72") circle is that you can fit 4.75" pattern wheels on the hubs, I can't believe that's a good idea. So modification of the hubs and rotors to 4-3/4" would be required.
- But my biggest concern is the lack of a backup plan. Installing this rear will require a good bit of customization to the El Camino's structure. I have confidence in my ability to design and fabricate the mounting points. However if this IRS turns out to not work well, I will need to replace the entire frame to fix the problem and start all over again with a suspension.
At this point, I've settled on the Cobra IRS. As I design the rear subframe, I will lower the rear of the car by about 2".
It seems my choices are limted to AFX spindles with C5 hubs or a custom subframe with a C5/C6 based suspension.
- The steering arm on the B-body spindle is about 5/8" lower than the original spindles, this will make bumpsteer even worse. I've read that these spindles also reduce the effective steering ratio and negatively impact the ackerman angle, but as I measure the two spindle types, I just don't see these.
- Mid 90's B-body cars were equipped with ABS system. The spindle has a design feature for the ABS sensor and the reluctor ring mounts to the hub/rotor. The issue is that the system used a 34 tooth reluctor ring. The GTO system is based on 48 tooth rings. I could fabricate a 48 tooth ring easily enough, but tI'm concerned he magnetic pole on the ABS sensor is too large to work with the smaller teeth necessary.
