1974 TVR 2500M

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  • The following will attempt to describe the fuel system I am assembling on my 74 TVR 2500M. I make no guarantees that any of the information provided here will work on any car, including my own. I am not responsible if you blow up your engine trying to follow this page. Legalities out of the way, let's begin.

    The original tank in my 2500M was a 15 gallon aluminized steel monstrosity. Since the entire tank sits behind the rear frame my biggest fear is pulling a pinto, since I do NOT trust the drivers in this college town. The factory tank was out, and it was time to start looking for alternatives.

    First up was a perusal of the usa-tvr mailing list. It seems Paul Robilotti has a 71 Vixen 2500 with a custom Fuel Safe fuel cell that was made to the same size and shape as the stock Vixen 2500 tank. Measurements of a Vixen tank found online appear to match the tank out of my M precisely, so Paul's cell (Fuel Safe part number [#]) should fit the M series as well. Unfortunately I couldn't get an answer from Fuel Safe with regards to the cost of this cell.

    The next option would be to follow Steve Barao and fit a Fuel Safe Sportsman Model 110 fuel cell (Fuel Safe part number SM110) which is a 10 gallon cell. Steve talked on the list about the 112 (12 gallon) but determined it was too tall to fit under the deck. Searching prices on the web this cell appears to run for around $600 to $700 depending on retailer. Steve's installer is preparing an article with photos by SJ Barao Photography of his install, so I will not go into the details of it in order to respect his copyright on the photos. You can find Steve on the usa-tvr mailing list for more info on his install. Unfortunately the price of the cell ruled me out of it, plus it's only 10 gallons.

    This brings up the final option, which is what I went with. I had a custom tank made. There is a short article on a replacement stainless steel tank at tvrna.com which enlarges the tank and fills the space. I didn't want to go this route because I want to add in steel bracing in the back to protect the cell in case of an accident and this tank fills the space. I asked around my friends and discovered a NHRA drag racer named Jeff Geisler who builds all sorts of custom pieces from aluminum in his spare time (he also happens to be the father of the guy doing the paint work on my car). I spoke with him about my needs for a fuel cell and we came up with a design for a tank to meet my needs. Since I'm running 3/8" fuel lines we fit the tank with a 3/8" NPT bung in a sump for a supply line and a 3/8" NPT bung for a return line. We also fit a 1/8" nipple for the vapor vent to the gas cap. The cell is pictured below. Jeff is willing to make these for other TVR owners as well. Price is around $325 depending on material costs, and he can make any design you want. E-mail me if you would like his contact information.

    The final stage for the tank is to fabricate the cage for the cell. As of this writing (November 8, 2004) I just picked the cell up from Jeff and am trying to locate a supplier for 1.5" box tubing. I will update this section as I begin fabrication of the cage.


    The pump I have chosen to use for now is the Master E2000. It is rated at 95psi max and 160gph with no head. This is the pump that people use when swapping a Jeep 4.0L MPFI engine into earlier vehicles (the Jeep engine produces 185HP stock, so this pump should be fine for what I need. Plus I already have an extra (I've used it on 2 different Jeep engines). It's available from Auto Zone for ~$70 with a lifetime warranty. If I end up changing the pump this section will be updated.



    On Lee Janssen's Turbo TR6 website he gives an equation to calculate the injector size required.
    Assuming we want a street car with 240 HP. Each injector will generate 40 HP with a 80% duty cycle and a BSFC (efficiency) of about 0.55. Doing the math: 40 * 0.55 / 0.8 = 27.5 lb/hr is the minimum size required.
    Using this equation and calculating that I want 200 HP we see that each injector needs to support 33.33HP, so the equation becomes 33.33 * 0.55 / 0.8 = 22.92 lb/hr. On the shelf I happen to have a set of 83 Datsun 280ZXT injectors. These injectors are rated at 160 cc/min, which converts to 24.76 lb/hr assuming 43.5psi (standard injector rating pressure) so they should work perfectly for this project.

    Fuel Rail

    I haven't decided what to do here yet. I'm looking at the Dash 6 fuel rail extrusion from Ross Machine Racing. If finances get tight though I'll just modify the stock Datsun 280ZXT 3-piece fuel rail to fit my manifolds.

    Electronic Fuel Injection

    For the fuel injection system I have decided to use the MegaSquirt DIY fuel injection system. This system is a really neat home build system designed by Bruce Bowling and Al Grippo. I have now assembled two of these, one for myself and one for my roommate.

    The first one I built was the standard MegaSquirt as sold by B&G through their vendor, Glen Hoag. At Glen's Garage, Glen sells the complete kits with all parts ready to install. Each component is bagged and labled with its position on the board so finding the pieces for assembly is a snap. This kit was a joy to build and I would highly recommend it. Note, however, that Glen is swamped with orders so it may take 6-8 weeks after placing the order to receive it, and you may not get a prompt response to emails as time spent answering emails is time not spent assembling kits. My roommate is updating the firmware on this one to the MegaSquirt 'n Spark firmware which provides spark control as well. I'll try and post more info as this goes into his Datsun.

    Here I am starting to solder the Stimulator board, which simulates engine signals (Throttle, O2, Temp sensor) to test the board. The iron I am using is a Weller Portasol P2KC which is an awesome Butane powered portable soldering iron that has temperature control and a wide variety of tips, including hot air (shrink wrap) and flame. From ignition the tip is ready in 30-40 seconds and cools quickly, unlike my previous electric one.

    And here I am soldering the relay board, which triggers high-draw devices like the fuel pump and provides a clean interface in the engine bay while protecting the ECU inside the car.

    Here is the completed ECU with the Stimulator board plugged in for testing. Look at how small these are.

    Here's the front of the ECU. The DB9 is a serial connection to a laptop computer or Palm pilot for datalogging anf tuning, while the LEDs tell you the status of the system (ie whether the engine is warmed up).

    Here's the back side which shows the DB25 connector for the cable to the relay board, as well as the relay board. This is the part that concerns me about the MS kit, I don't like the use of DB25's and an open relay board (no lid). That's why I'm using a slightly different kit for the TVR.

    In the TVR I am using a Mini-MS kit from Mark Amundsen. This kit combines the B&G V2.2 MegaSquirt ECU board with the relay board to provide one sealed enclosure suitable for mounting in the engine bay (the original MegaSquirt ECU is intended to be mounted inside the car with the open relay board in the engine compartment). The new kit uses Ampseal sealed connectors instead of computer DB9 and DB25 connectors which I feel will provide a more weatherproof solution. Plus I think I came out just under my roommate's costs for all the pieces, and Mark shipped my parts the same day I ordered them. The downside is that the resistors, capacitors, etc have to be ordered from Digikey or another parts company and do not come nicely bagged as the Glen's Garage kits do. If you have not soldered before, however, I would recommend going with the original Megasquirt as the Mini-MS has parts much closer together and is a much trickier soldering job.

    Here is a photo of the parts that came from Mark Amundsen. Note the beautifully machined case which has a silicone seal on the lid to make it watertight.

    Here's a photo of the parts from Digikey. Man, that's a lot of bags and no labels on them as to which part of the board they go to, unlike the nice Glen's Garage kit. After building this I spoke to Glen through email and he said that he may offer a Mini-MS kit in the future, so if you're going to order this board, you might want to check with him first.

    Here's a photo of the completed kit, just waiting on the CPU. Man that's tight in there.

    And finally here's the box sealed up and ready to go. I will add more on wiring it for the car once the body is back from paint and I can start wiring.


    I am currently planning on using a MSD 6BTM, possibly with an Ignitor or the optical trigger out of an old Lumenition I have for more accurate triggering without worrying about points. However, my roommate has ordered a Megasquirt that he is changing the firmware on to be a MegaSquirt'nSpark which adds spark tables. If it works well for him I may go this same route.