NOTE: This page is where I'm gathering ideas and plans for a GM TBI swap onto a slant six engine. It is not a complete page/story yet, just the core of an idea that is growing as I research more, pick up parts, and play around with ideas. This idea may never come to fruition, but then again it might.
You should read up on my EFI Basics and GM TBI Swap pages for more background information - this page is only going to attempt to cover the details specific to the Slant Six TBI swap. This page will NOT cover generic details of EFI swaps in general, or even those common to all GM TBI swaps. This includes general wiring harness details, tuning the computer, running EFI fuel lines, general theory or ways of installing an EFI fuel pump, or other such stuff - they are generic to any GM TBI swap and I don't want to repeat the basics on every page about this.
The basic idea here is to take a GM TBI unit off a 4.3L V6 engine and bolt it onto a Super Six intake using an adaptor plate. This should allow a simple bolt-on installation using readily available parts. The TBI unit has a standard air cleaner mounting flange, so that will not be an issue. Other than the need to drill a hole in the firewall so you can mount the computer inside the passenger compartment, this should be a relatively easy installation. TBI units are nice that way - no need to fuss around with modified intake manifolds for the injectors, make up custom fuel rails, or other such things. It's very much a "bolt on and go" arrangement, which has obvious advantages to a first time EFI conversion project by your average DIY'er. The original GM TBI application was for a 4.3L (262 cid) V6 and that's close enough that the original GM TBI hardware should work just fine for overall airflow requirements and should easily be able to be tuned to match the slant six engine via burning a new PROM for the computer.
GM TBI Mounting
The first and most important thing you need to do is get the GM TBI unit mounted to the intake. I had done a lot of planning and thinking and research on this, to little avail (see below), but in December of 2008, I was contacted by a fellow who was making his own TBI adaptor plates for the Jeeps, which share the same carb mounting pattern as the super six intake. There's a posting at http://www.jeepz.com/forum/items-sale-trade-give-away/23962-fuel-injection-tbi-bbd-2bbl-adapter-plate-cj-yj-258-a.html that shows them, I've copied those pictures below in case that page goes away. The pictures belong to Chris Adam, the guy who makes these adaptors - you should visit his website at www.tbiadapterplates.com, or email him at email@example.com if you need one of these adaptors.
Here's the adaptor I bought from him installed on my super six intake. It mounted perfectly and without incident using the provided screws. From what I can see, it should work fine once I get everything mounted on the engine. That tells me that his adaptor plate will work for this conversion - score! I'm going to keep Chris apprised of the conversion so he can advertise his adaptors as working for this conversion.
Research and First Attempts
Before being contacted by Chris, I originally got a lot of ideas from reading up on the Howell TBI swap for 4.2L Jeeps at http://www.4x4xplor.com/TBI.html. I'm leaving the information here, because it has some useful background information, and may be useful to various folks.
The Jeep engine is a similar inline 6 cylinder design to the slant six, and it also uses a Carter BBD carb just like the Super Six versions of the slant six did. They're also not too far off in displacement - 4.2L (258 cid) for the Jeep and 3.7L (225 cid) for the slant six. The pictures before are from 4x4explor.com and show the installation of the Howell adaptor to the Carter BBD mounting base with the remanufactured 4.3L V6 TBI unit on top.
The key detail here is the the Carter BBD/Holley 2280 carbs used on the Super Six intakes have a smaller base plate and mounting pattern than a typical/common Holley 2-bbl carb. There are a ton of adaptors out there for the slightly larger Holley 2-bbl carbs to mount a GM TBI unit - check out the Trans-Dapt #2204 or #2205 as one example, a sample picture is below - but they will not work for this conversion.
If Howell would simply sell their GM TBI -> Carter BBD carb mounting adaptor, that would be awesome, but I called them and they do not sell it separately. They do sell some other GM TBI -> carb adaptors, but not this one. Why a business would refuse to sell a part they already make is beyond me, but some of them apparently feel this is a good way to do business. It's a $75-$100 part - fine, I get that it's not free to carve one out of a block of aluminum, and I'm willing to pay for it. You did the work, and you deserve to get a fair price for the part. You already make them up for your kits, so you obviously have a production line of some kind for them. Just sell the stuff you already have, will ya? Without a willingness to sell what you already make, I'm forced to make my own somehow, and that's the sort of thing which just ticks people off. The tech on the phone at Howell said it all when he said "we've made a decision not to sell them separately". I guess my money isn't good enough for them - and that sucks...
After some amount of searching, I stumbled across something that may just work. This entire theory is based on the idea/notion that a Carter BBD/Holley 2280 and a Stromberg 2-bbl have the same mounting base - and my web searching indicates they do. By sheer luck, I stumbled across an interesting tidbit of information that makes this work - bear with me while I explain this because it really did come out of left field. Some of the Australian-built Ford inline 6 cylinder engines came with a cylinder head + intake manifold setup that had a Stromberg bolt pattern for the carb. These head + intake combos are a popular performance swap for the Ford inline 6-cylinder crowd, and there is a company - Classic Inlines - that makes an adaptor to go from the Stromberg (also Carter BBD/Holley 2280) bolt pattern to a more typical Holley 2-bbl carb bolt pattern. Score! But wait, we want to get from the Carter BBD bolt pattern to a GM TBI pattern, right? Well, various places already noted above make (and sell) an adaptor to go from the Holley 2-bbl bolt pattern to a GM TBI bolt pattern, so by stacking two adaptors we can get what we need here. The sequence goes like this: intake manifold -> Classic Inline adaptor -> Trans-Dapt adaptor #2204 -> GM TBI unit. Also, I found out a Trans-Dapt adaptor #2086 is basically the same as the Classic Inline adaptor, and more folks will carry the Trans-Dapt stuff. Some time after posting the original info here, courtesy of some of my readers posting links to my site in discussion forums, I found out that another fellow by the name of Frank Raso over at Raso Enterprises is making and selling the same basic "double adaptor" idea in a single kit, and it looks to be a bit shorter than the double adaptor route, which is good news. I love it when fellow car nuts make and sell problem solvers. The thing that bums me out on all of these two piece adaptors is that they end up with a large "step" in them that can cause airflow problems, fuel dispersion problems, and other such fun. It just feels kludgy and perhaps a bit taller than really needed, but that's what you get into when some people refuse to sell the parts they already make. The good news is that as kludgy as this may seem, it's still way better than a carb any day of the week.
Of related interest is another Classic Inlines adaptor to go from the stock 1-bbl carb on the Ford inline 6-cylinder engines to a typical Holley 2-bbl. This might just fit the stock slant size 1-bbl intake. I have not searched extensively to see if it does, but it's an idea worth exploring if you really can't find a super six intake manifold to use for this conversion. Mixture distribution and what not may end up being a bit dodgy when trying this, but it should still work a heckuva lot better than the factory 1-bbl slant six carbs did. As with the "double adaptor" assembly above, it's still going to be way better than a carb any day of the week.
Building Your Own TBI Adaptor Plate
When I could not get a single adaptor to do this, I was planning how to make my own adaptor. The details below are about how went about planning how to build one. Since I can buy one now (and I have) this is all not as useful, but I'm leaving it there in case any "home machinist" types want to use it. This is all gathered off the internet and via me messing around with used parts and some gaskets, and is strictly "use at your own risk" stuff.
First off, here's some pictures of the intake manifold.
Here are some pictures of a 4.3L V6 GM TBI unit that I scrounged out of a junkyard to use for mock-up purposes. The small block V8 and V6 TBI units are identical 2 bbl units and use 1 3/4" bores. The big block V8 units are also 2 bbl but use 2" bores. I believe the mounting pattern and the bore centers are the same, they just put slightly larger holes on the big block V8 units. These pictures also highlight the unusual mounting pattern of the GM TBI units - they use a triangular bolt pattern with 3 bolts, and the base plate on the TBI unit is a decidedly non-square pattern. The second picture also shows the maze of vacuum passages on the underside of the TBI unit that must be properly sealed to whatever the mounting surface is - in this case the adaptor plate we are figuring out how to build.
By comparing the pictures of the Howell BBD adaptor with the pictures of the Trans-Dapt Holley 2-bbl adaptors - scroll up a bit to find them - the size difference between the Carter BBD/Holley 2280 carbs vs. the typical Holley 2-bbl carbs is obvious. How can you tell this easily? Look closely - on the Howell BBD adaptor, the GM TBI mounting bolts are outside of the BBD mounting bolts, but on the Trans-Dapt adaptors the GM TBI mounting bolts are inside of the GM TPI mounting bolts. The Carter BBD/Holley 2280 mounting pattern is smaller than the GM TBI mounting pattern, while the typical Holley 2-bbl mounting pattern is larger than the GM TBI mounting pattern. The Howell BBD adaptor also clearly shows that the adaptor plate needs to be at least as large as the GM TBI mounting gasket - this is to ensure that all of the vacuum passages on the bottom of the TBI unit are sealed up. Even the Trans-Dapt mounting plates for the larger Holley 2-bbl have a flared out area on one side to accommodate the unusual shape of the GM TBI units.
A careful study of the Howell BBD adaptor also shows the tapered inner cavity that allows for a smooth airflow transition from the larger GM TBI bores to the smaller BBD openings in the manifold. This requires an adaptor with some amount of thickness to it - research indicates that the Howell adaptor is 3/4" thick, possible more.
These are scans of tracings I made of the carb mounting on the super six manifold and of the base plate on the GM TBI unit. The first one is the raw scan, with each successive picture having more and more things removed to leave just the outline of the bores and outer edges and the location of the bolt holes. Note that the TBI tracing was done with the TBI unit "upside down", which means the tracing is a reverse image of what's really needed - it should be flipped left-to-right to be correct.
Both original tracings were scanned at the same DPI level so that the scale would be consistent between the two pictures. This allowed me to transpose one over the other to give a very clear visual of the difference in sizes that is involved here.
After I did all that work, I found a great site that has details on how to build your own adaptor plate, complete with dimensioned pictures and drawings - http://www.bustedjeep.com/projects/junkyardtbi.asp. There are two great drawings linked to from that page - one details the adaptor plate with the fuel lines facing the firewall and one details the adaptor plate with the fuel lines facing the radiator. If the fuel lines are done facing the firewall, the throttle linkage will be on the driver's side, and that's what we want for the slant six as it will match the orientation of the original carb used on the super six intake.
My basic plan to make this adaptor is to get a chunk of 3/4" thick piece of aluminum approx 4" x 6" and start working on it with basic tools. I'll use a Carter BBD mounting gasket and a GM TBI mounting gasket as a guide to what holes go where - no need to measure if you use a template that is known to work.
Getting a TBI Adaptor Plate Custom Made
I sent out a request to a water jet shop to see if they could make this plate, but due to the angles involved, it would need to be cut on a true 5 axis water jet. Otherwise, you have to CNC machine it, and that's more expensive, especially for one piece. I never did get a price quote back from them. :-(
Computer Timing Control
The GM TBI computer can control the timing if you can run a GM style 7-pin HEI module. For non-computer use, converting to a GM 4-pin HEI module for the ignition on a slant six is relatively easy, so start there with understanding the process. All you need to add to that is a full conversion to computer control of the timing by locking out the advance mechanisms and some extra wires to the HEI module, or more specifically, the extra 3 wires that go to the HEI module in a 7-pin vs. a 4-pin unit. Locking out the advance mechanism is a pretty simply affair if you have a non-computer controlled distributor and you want to keep it. Just tack weld the advance weights in place and run a screw through the vacuum advance mechanism and through a hole you drill into the base of the distributor.
Another idea I had here is to get a later model distributor intended for a computer controlled carb on a slant six. The computer controlled the ignition timing on these setups, which is exactly what we want/need here. The application I looked up is a 1986 Dodge B150 Van with a 3.7L (225cid) slant six and an automatic transmission. The auto trans part is critical because you want the one with dual pickups and no vacuum advance mechanism, and the manual transmission versions were a typical electronic ignition distributor with advance weights and a vacuum advance system. Here's a link to the distributor listings page for a 1986 B150 Van with a 3.7L (225 cid) slant six in the RockAuto.com catalog. They have links to pictures of each unit - compare the top-down pictures of the automatic and manual transmission units to see the difference. The auto trans distributor has dual pickups - and thus two wiring plugs coming off of it. In the original setup, one was used for starting only and the other was used once the engine was running. You'd only use one of them - the one normally used while the engine was running. I stumbled across this idea because I have a friend with a 1986 B150 van with a slant six and we had to replace the distributor, and seeing all of the details in the factory shop manual for the timing control computer system got my idea hamster going for this conversion. :-) I still need to spend some quality time with the shop manual and an example distributor, but the basic idea seems simple enough and as I understand it, the distributor will drop right into any slant six engine.
Pretty much any EFI swap needs a vehicle speed sensor (VSS) so the computer can tell if the vehicle is moving, and if so how fast. Various things are tied into this knowledge inside the computer. You can get an EFI system to work without it, but it's not going to work as well as a system without it. So, my plans include using one for the EFI conversion. The important details are to match the physical mounting of your existing speedometer cable (so you can actually make all the mechanical connections) and to make sure the VSS you use puts out the proper electrical signal to the computer (so that they speak the same language).
For the mechanical side of things, it seems that most Mopar transmissions use a speedometer cable that has a fairly standard 7/8"-18 threaded connector at the transmission end - the same as typical a GM transmission does. This means that if it will screw onto the speedo cable mounting of a Chevy TH350 transmission, it should also work on your favorite Mopar transmission. I don't know if all Mopar transmissions are like this, so if you know of some that are not, please email and tell me all about it.
For the electrical side of things, the GM TBI systems use a VSS that puts out a 2000 pulse per mile (PPM) signal, and the computer only needs to have one wire connected - the other one from the sensor (if present) is grounded. Some sensors may be grounded via their case, but not all are.
So, this means you should be able to use a typical EFI swap VSS for a Chevy - and there are plenty of great options for "retrofit style sensors" out there from various places. I would recommend that you hit up eBay and search for "VSS 2000" and see what you get. Try Google as well. JTR sells them too. Find one you like and get it - they all seem to run about $90 or so, and as of yet I have not found anything cheaper. Because these are retrofit-only items, the odds of finding one used are about nil, so new seems to be the only choice.
Alternate TBI Idea - Dual TBI
Dual carb manifolds are readily available for the slant six engines, and a friend of mine has a dual Weber carb setup on his 1964 Valiant. I was thinking about how to adapt a TBI setup to this when I came across the fact that some V8 engines (specifically, the "cross fire" setup in the Corvette used for a few years) used dual 1-bbl TBI units set up much like a dual carb setup on a cross-ram intake manifold. I then found out that some 4 cylinder engines used a single-barrel TBI unit on them - the list I found is below. If I could get two of these 4-cylinder 1-bbl TBI units cheaply from a couple of junked cars that no one cared about and wire them up to the same computer setup as the regular two barrel TBI units (basically treating the two single barrel/single injector 4-cylinder TBI units as a "split two barrel/two injector" TBI unit), the computer shouldn't know the difference and it ought to Just Work. My research into how the "cross fire" setup was done on the Corvette seems to confirm this theory.
Each TBI unit would be handling 3 cylinders so it should be able to do it quite easily. As far as I can tell, the TBI injectors on the 4 cylinder units are pretty easily available, but I haven't been able to dig up flow ratings on them. The first set of GM part numbers I could find on the 4 cylinder TBI injectors were 17068993 and 17111544. Then I came across another site that showed the possible numbers as 17068989, 17079596, 608, 17082060, 17083060, 17084060, 082, 083, 17085062, and 17086109. These also showed on that page at the bottom in the interchange section that they interchange back to the same aftermarket number as the previous units. Lastly, the chart also shows that these interchange down to one aftermarket number - 15001. Tracking that back to something using the more popular V8 applications, I found that the 305 V8 uses OEM number 17112400 (which crosses to the 15001 aftermarket injector), which was used in a few popular applications so I could find data on it. It is rated at 40 lb/hr and has a color code of green/white. These search out (aka, just Google for those part #'s and see what turns up) to be correct for this application and a number of others. It seems that the TBI units came in different styles, and the injectors varied as well. The trick here would be that each TBI unit would have it's own IAC motor and would be controlling the idle air for it's 3 cylinders. The computer should be able to handle this (they did it on the crossfire V8 units, after all) but it could be tricky to set up.
One thing I've learned in researching this is that the GM TBI units have different series designations. TBI 100, 200, 200, 300, 400, and 500 seem to be the ones that most folks are familiar with. There is also a TBI series 700 that uses side-feed injectors that are different, and it seems that the TBI 700 units came into use in the later models - 1987/88 and up mostly. This chart is most helpful for ID'ing injector #'s, what used them, and the TBI series/model that was on that car. Searching around, the TBI 220 seems to be the one that shows up on most V8 applications and has a number of Google hits when searching for "TBI 220". The others have less information out there. I found an assortment of pictures of TBI units that might be helpful, but it's all about the common 2 barrel TBI units, mostly the 220 series. The injector part #'s I listed above seem to be correct for the earlier non-side-feed setups, which would seem to confirm that they are a single barrel version of the V8 TBI units. However, I've yet to get my hands on an actual single barrel TBI unit that uses the same basic injectors as the V8 units so I can actually confirm my ideas here.
The good news is that after a lot of searching, I stumbled across a great page (actually, website) by a fellow over in Australia who has done a bunch of TBI work - the initial page I found was a TBI conversion on a Land Rover. The very first picture on the page shows a single barrel TBI unit sitting on the intake manifold for the Land Rover - bingo! Another page he has on this project shows the manifold and how he installed the TBI unit using a custom adaptor plate. Since GM electronics are reasonably standardized world-wide, this information was very useful for me. In this case, he sourced the TBI unit off of mid-80's car made by Holden (GM of Australia, basically) called a Camira. This shows me the parts do exist, which is very good news.
Since I knew the Australian stuff was similar, I started searching on that and found a site that lists injector flow ratings for the various Holden (Australian GM) engines of that era. It's all in metric and shows the TBI injector on a JD Camira at 70-80 ltr/h, or 7.2-8 cc/min. Converting to our typical English measurements (cc per min / 10.2 = lb per hr, or lb per hour * 10.2 = cc per min) those figures make no sense. A typical 61 lb/hr 350 V8 TBI injector converts to 622 cc/min, which makes sense looking at this chart - the chart only goes up to 49 lb/hr injectors, but you get the idea. It also contains a few of the conversion formulas that you might want to use. The online calculator at WitchHunter Performance is handy, though is uses a 10.5 multiplier/divider vs. the 10.2 I found on other pages, so the final numbers are a bit different. Anyways, the 8 cc/min rate quoted for the Camira injectors converts to a ridiculous .76 lb/hr rating, which is just flat out bogus. Something isn't adding up here.
Here's some injector flow rate information I found on another site:
I found this quote on a site about the Megasquirt EFI system: "1982-86 2.5L GM engines used a 1bbl version of the 4.3L GM TBI." That means they would have had a 1-13/16" bore size and used a "standard" TBI injector. It would also seem to indicate that they used a single 40 or 45 lb/hr injector - which makes some sense since the 2.5L engine is essentially half the size of a 5.0L engine and the 4.3L and 5.0L engines used injectors in the range of 40 and 45 lb/hr. Based on the comparisons of the chart up above, the 40 lb/hr injector seems right.
Here's the 4 cylinder applications I found that are good possibilities for the single barrel TBI unit, grouped by the VIN code.
For 1981 and up VIN codes, the engine code is in the eighth spot and the year is in the tenth spot. The 1980 and earlier VIN codes are noticeably shorter and do not use the same coding scheme. The year codes are below. Note that they extend beyond the range we care about for this (just the bold stuff) - if you see something else, ignore it.
In the example VIN of "1G1AP87H4CN100000" it decodes to engine code H (not something on the list above) and a year of 1982.
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Page last updated 12/27/2011 10:23:21 AM