Putting a Honda VTEC Engine in a Standard Roundnose Mini
If you have decided that your Mini needs a more powerful, more reliable engine than the venerable A-series , and have decided that a Honda VTEC engine is the way to go, this swap guide will provide you with some guidance and suggestions to address some of the many challenges and decisions you will face. Any engine swap of this nature, which an engine from one manufacturer into a chassis built by another manufacturer, will require solutions to engine/chassis interfaces that were never designed to work together.
Some of the challenges you need to resolve include:
- Modifications to the body
- Mounting the engine in the chassis
- Aligning the drive axle centerlines
- Mating the driveline parts
- Mounting suspension and brake components
- Linking the engine and car clutch actuating mechanisms
- Fitting the intake and exhaust systems in the space available
- Ensuring clearance on all sides of the engine
- Modifying the shift mechanism to the new body
- Mating the engine and car wiring systems
- Mounting an alternator in limited space
- Finding a radiator that will fit
- A host of smaller challenges
Some of these are difficult issues to resolve, and can be made worse by making choices that increase the incompatibility between the engine and the car. The end result will need to be a balance between what you want and what is realistically possible. The ULTRIK subframe is built to enable compatibility between the Mini chassis and the Honda VTEC engine. It will allow the standard nose to be retained, and allows the use of standard suspension pieces and brake components.
Having decided on the subframe, there are a number of other choices to make. One is which engine you will use, and one aspect of that choice is the engine weight. The 1275 A-series drive train, complete with motor mounts, starter, alternator, manifolds and carburetor, weighs right at 350 pounds. Ideally your new engine should not weigh significantly more. It should also be able to fit in the Mini’s engine bay without major surgery, and it should be possible to align the axles fairly close to where the original axle center lines were. Fortunately, all this can be done with a Honda VTEC engine. But, which engine?
Selecting a VTEC engine
B-Series - The ULTRIK sub frame is designed around a B16A2, which came from a '99 Civic Si. All B-series engines are basically derived from the same block. The early B-series ('89 to '91) came with a cable transmission, so you have to figure out how or buy a kit to convert it to hydraulic operation to link to the Mini clutch master cylinder. The later B-series engines ('92 to 2000) came with a hydraulic clutch linkage, so will work well in a Mini. Two of the three transmission mounts vary between the two types, so I have designed transmission mounts for both, and either can be made to work. As you might expect, the earlier engines are cheaper than the later engines. The B-16A engine and tranny weigh right at 400 pounds, or 50 pounds heavier than the 1275 A-series Mini engine and tranny.
The B18 engines that typically came in the Acura Integra are basically the same block as the B16, but have a deck height that is 9 mm taller, due to the increased stroke, so give you that much less clearance at the bonnet in a Mini, and in this application, that clearance is already close. I have never installed one, but in my judgment, they can be made to fit. The B16B is basically a de-stroked and de-bored B18, so will fit the same. The B20 is taller still, and in addition to being even harder to make fit, in my opinion are simply overkill in a Mini. All are heavier still than the B16A. It is good to remember that quite a number of B18 engines were of the DOHC, non-VTEC variety, so had lower horsepower ratings. You may also run across the B17A1 VTEC that was available in the ’92-93 Integra GSR, but they are rather rare.
Price - Another thing to consider when shopping for engines is that while early VTECs ('89 to '91) are cheaper than the later ones, they come with cable operated clutches, and the newer ones ('92 and on) come with hydraulic operated clutches, making them easier to hook up to a Mini clutch master cylinder. Early engines often go for $800 to $1700, and the later engines often go for $1500 to $2500. It pays to shop.
If you must have the “R” version of either the B16 or the B18, you will pay dearly for the bragging rights. They are much sought after by the Civic/Integra hop-up crowd, so are priced accordingly.
Modifying the Mini shell to accept the VTEC engine
Converting the Mini body to accept the VTEC engine does entail some sheet metal cutting. The inner fenders have to be cut out to allow for the greater width of the Honda engine. A sawsall, a saber saw, or an air powered reciprocating saw will all get the job done. Use a fine tooth blade. Start on the rear side of the inner fenders by cutting vertically up, following a line that extends the rear edge up to the hood line. Make your cut just forward of the seam where the bulkhead and bulkhead gusset are spot welded to the inner fender. Cut up to the lower side of the little gutter that forms the edge of the fender. From there, cut forward just below that little gutter, leaving it in place as you cut. Follow the curve of the fender, cutting all the way down to the bottom of the inner fender, where it joins the front panel. Once finished, the whole inner fender should come out. Repeat for the other side.
On some Mini shells, there is a small sheet metal bracket that is spot welded in the center of the backside of the lower portion of the front panel. This must be removed to allow the front tube of the new sub frame to tuck inside the front panel, providing room for the exhaust pipes. Cut it out with a saw or die-grinder, and grind down the remaining sheet metal edges till smooth. There is also some minor surgery on the back side of the front panel for the exhaust to have clearance, depending on what exhaust header you use. If you want to stick with the stock Honda cast iron exhaust manifold, you will have to cut a shallow notch in the edge of the front panel, behind the lower edge of the grill opening. You will need to determine the placement and depth based on test fitting the engine.
The sub frame bolts to all the normal places if it is a Mark 3 or older. This includes using the stock 1/8” spacer plate that mounts between the top of the tower and the bottom of the firewall cross-member. This sub frame was also designed to use it. If it is a Mark 4 or newer, the towers bolt on per normal (I do recommend using a solid tower top mount kit), but lower rear mounts at the floor are solid rather than rubber mounted, and so you may need to drill some new holes in the floor to bolt it on. I recommend using some compressible gasket material on the floor mounts, to seal them against road spray.
Sometimes the alignment of the steering rack mount needs to be adjusted for minor clearance with a wood block and hammer (some shells varied from the factory on alignment of the floor panel the steering rack bracket is spot welded to). This entails placing a piece of 2by4 flat on the face of the rack mounting bracket, and driving the whole panel back a bit with a large hammer. A number of hits may be needed. I recommend you take some measurements before and after to verify progress.
Other than that there are no special things to do. I would recommend that in preparation for fitting the engine, you have all the body panels replaced that need it, have the shell primed, and hold off on final paint finish until you have fitted the sub frame and engine. It means you will have to take the engine out after fitting to paint the shell, and then re-install it, but that way you know everything fits like you want, and you will not have to be cutting on panels that are already painted.
On using a flip-front
I highly recommend a steel flip-front. Having said that, I don't believe a flip-front end is absolutely necessary, but it makes getting the sub frame and engine in a lot easier. In order to provide clearance for the exhaust header and the clutch slave cylinder, as well as a motor mount on the early trannys, the front member of the sub frame is offset forward, and must tuck into the recess of the front panel of the Mini, just below the grill. As the front panel curves rearward and down at its lower edge, getting the front member of the sub frame tucked in there as you install it will be a chore. A flip-front, made from stock steel body parts, as an ideal way to improve engine installation and make servicing easier. If done well, you cannot tell it has been modified.