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MG MGB GT V8 Factory Originals Technical - Which engine to choose?

I have a RB MGB I am thinking of converting to V8. What would be a good engine to use, coupled with what transmission? Should be something fairly easy to obtain and not require a lot of modifications to the car. Thanks.

The general consensus seems to be that a 3.9 or 4.2 Rover is your best bet, and in an RB that's as close to a drop-in as you are going to get. As far as a gearbox, it's a bit difficult to get hold of a TR8 unit in the U.S.; so a better bet may be to use a T-5 or T-56 tranny. I know you can get the bellhousings, but I forget where; someone here will know. Perhaps from D&D. Then you have a host of choices such as headers, etc. ... block-huggers don't require any alterations to the car, and that's what I have and they are fine, but a lot of folks feel that the RV8-style headers, which entail cutting a hole in the inner fender, are a better bet.

A V8 with a minimum of modifications? I have to agree with Harry, VA. A Rover 3.9L V8 with blockhugger headers is the best and easiest way to go. The Range Rover has been around on the US Market long enough for you to be able to obtain this engine at a very reasonable price, plus there's a considerable body of knowledge available in how-to book form to enable you to do it right without the end result looking like it was cobbled together by a pimply kid in his dad's garage. A GM T-56 (Camaro) transmission complements the engine quite nicely. You can get the book "How To Give Your MGB V8 Power" directly from the publisher at Don't worry about how the swap will effect your handling as the engine is actually 40 lbs lighter than the cast iron engine that you're replacing. An excellent source for advice in the hands-on building phase is Glenn Towery. He's a professional who's built several of these cars and, better yet, owns and drives one himself, so with his help you should have a car that is more than reliable. You'll find him friendly and quite free with his advice. His Email is There are other conversions that can be done, notably using the Chevy and Buick V6's and the Ford 302, but these are still very much in the experimental phase as no books on them have been published as yet.
Stephen Strange

Yeah, call Glen and or D&D they both offer basically "kits" to put the rover/buick in a B. The rover will probably be more $$ up front than a buick due to the name and that thay are newer, BUT they will be easier to find, and have larger displacement..

You should be able to fit it under a stock hood, without modofications (I think) but that will require; block hugger headers and removing the EFI intake set-up and buying a intake/carb/air cleaner type set-up. If you don't mind bulging your hood, then you could keep the EFI set-up. It all depends on how much time a $$ you want to put into it.
Larry Embrey

Just for the sake of blasphemy,... how about an aluminum crate motor from the local GM dealer? My local parts man said the 350 would run about 5 large, and it wouldn't weigh much more than the BOP/Rover. I can't believe it would be any harder to fit in either, seems to me the physical dimensions are smaller. Dan Masten has a shot of one with the factory ram's horn manifolds too. If I was starting over I would try very hard to justify going that route.
Jim Blackwood

Jim, the idea is great, but even a mild 350 would probably twist up a MG. They are major toque monsters.. It would take major work to get it to work, I also hear the rear distributor can be a problem. It can be done, but the rover is bets..

I am in a 302 conversion and while it is smaller than a 215, I am having problems with motor width between the fram rails..
Larry Embrey

Hey Guys I went the 350 chevy route with my car and yes it does take a lot of work to get them in there granted I did go the hard way with the body mods too.My engine is the cast iron version,I could not afford the all aluminum.And trust me this car can KILL any viper,porsche or what have you out there its the best bang for the buck,The ford V8's are the way to go too.

Steve didn't ask for suggestions from people who haven't done what they suggest and don't know what is involved in doing it.

Not only are you having trouble with getting a Ford 302 to fit between your frame rails, but you forgot to tell Steve that you had to put a notch in your cross member to get the motor to go in. He asked for something that doesn't require a lot of modifications, not an engineering project.

I looked at your photos. Steve asked about something he could do that would not require a lot of modifications to the car, so why did you post on this thread instead of strutting your stuff on a new thread? By the way, you chose the right name for the car- Frankenstein.

None of you guys are of any help to Steve at all.

If you go back and read, you will notice that in my guidance to Steve I never once told him he should do anything other than a rover. In fact even recommended he go Rover rather than Buick/olds for simplicity of finding pieces and fewer modifications. For what Steve wants at this point the Rover is the only viable option, there are V6 kits available that are supposed to be bolt in conversions, but I do no know what they require and Steve asked about V8 so I didn't even bring them up. STEVE GO ROVER! That better?

Anyway, you seem to be missing the point disgusted, this entire board is about sharing information, who knows, maybe after getting this info Steve will decide he does not mind doing more modifications. The more information he has, the more informed and intelligent a decision he can make.

Larry Embrey

Very well put Larry we are here to share info.And Thats all I was doing,I am not here to strut any stuff there are guys in here that built WAY prettier cars than mine,I would love to see what you have Disgusted you probablly dont even own an mg.

The BBS is for sharing information that is pertinent to the question being asked. Your second posting had nothing to do with Steve's original question. Jim posted his Email address and you could have used it to communicate your response to him instead of wasting BBS space.

Why would I be here if I "probably don't even own an MG"? Besides, you are in no position to accuse anyone of this. According to the pictures of your car, you don't own one yourself.

Why am I Disgusted? Because only the first three responses to Steve's question are of any use to him. And I know that I am not alone in my disgust. Over the last several months I have seen several postings from people complaining of how the threads on this website get off on irrelevant tangents, resulting in fiascos like this one. One individual even said he was going to stop using this BBS for just this reason. That's sad, and it is all because people are self-centered in their thinking and impulsive in their actions. Either that or they just don't think at all. If readers would just stick to the subject and use the posted Email address of the person that they want to talk to for conveying comments that are not germain to the subject instead of using the BBS people could get the help they need. Last week a guy in England put up a posting trying to get some stolen MGB parts back. Only two of the very many postings were of relevance. Somebody finally took pity on him and reposted it in hopes that he might get some assistance. I guess I'll stop ranting now as I'm sure that this is all far beyond the comprehension of those who are guilty parties.

Disgusted...perhaps you should change your wimpy, whiny-assed, yellow-belly, feeble-minded, cowardly pseudo-name to Disgusting. More appropriate to your conduct here. It's nearly impossible to attach any credence to your comments when you HIDE.

I've been monitoring and contributing questions and answers to this BBS for over three years. I tune in to hear other individuals' input, opinions, experiences, information, failings and successes to use in my own decisions for the '78 that I brought over from SoCA for conversion. That's what a BBS is all about, Disgusting.

Steve from MI stated that he was THINKING of converting to a V8. Thinking, Disgusting, gathering information to make a determination. Am I using words too large for you to comprehend? Steve is obviously seeking help and information from others to move forward. He didn't place any limitations on the responses. Oh, there's another big word Disgusting. Got your dictionary handy?

Harry, Stephen, Larry, Jim and Dave are attempting to help out with their respective experiences and views on the subject. Who are you to begrudge them their input, or Steve's reception of that input? Man, more large words Disgusting. This must be tough on you.

Steve, please don't become disenchanted with this BBS due to the rantings of a mental midget. There is a wealth of information here from the archives and the contributors. Good luck in your decision. I too am wrestling with the engine decision.

Disgusting, go away.
Michael Willis

Dear Disgusted,
Why didn't you start a new thread for your rants? What do your comments have to do with swapping engines or choosing a good candidate? I noticed you didn't leave an e-mail address so anyone could respond to you directly either.

Now back to Steve,
I hope you're getting some good ideas from this. As you can see your options are pretty wide open and there are a lot of people you can contact to get more specific information about the finer points of any particular engine swap. Don't be discouraged by comments such as those made by "dis-cuss-ted" since he's probably a pseudo-purest anyway who thinks it has to be British(Rover) to be considered. You can use anything from a BOP to a Ford to a SB Chevy to a W*nkel or anything else and it's all up to you. Some of those V-6's make a sweet swap too.
Jim Blackwood

I am one of those doing a V-6. It works out to be a no weld conversion. You can contact Bill Guzman at He makes a kit that is complete with motor mounts trans mount and headers to fit right in.
Write him and get his web site to look at the kit. He is both helpful and wise when it comes to conversions.
Garret Koster

FYI, I think even in all aluminum trim the small block chevy is quite a bit heavier than the rover aluminum V8. I wanna say around 500 lbs, grass roots motorsports did a comparison of motors that are good for swapping (in all cars) and they compared weight, power and power potential, price and parts availability. The Chevy can definitly make gobs of power and is readily available, but it will make the car a bit nose heavey from what I gather.
Bill Mertz


Just to show that I'm not one of those "pseudo-purists" referred to in an earlier post, I have a Factory 1974 GT V-8 but I still like well-executed conversions. The Rover/BOP 3.5-3.9 engines are your best V-8 choice from the standpoint of minimal modifications and aftermarket conversion support. The advantage is due to the head start provided by the Factory, and with a rubber bumper car your firewall and fenderwell mods are already in place. Your biggest problems are going to be getting the engine low enough for bonnet clearance (if you want a stock look), and engine cooling because of the problems with getting hot air out of the engine bay. Fuel injection is great but it poses its own problems with gas tank and fuel supply mods. All these issues are documented very well in the BBS Archives. Go for it - hope to see you on a show field some time.


That's a great looking car - looks like a lot of work went into those fenders (and everything else). Don't worry about hotheads like Disgusted. Even though I am an originality freak with my own car, anyone who puts as much work into a car like yours is OK by me. And I bet it rumbles the pavement a lot more than my Factory car too!

Paul Kile
"V-8s are great, both transplanted or innate"
Paul Kile

Thanks Paul,I really appreciate the kind words and I do appreciate all V8 MG's they are really neat cars and fast.

Just for an example of how far some people will go, I did see a 66 MGB with a 427 BIG block chevy once. It was a little "rough around the edges" and pretty much a drag race only car.I woud'nt recommend doing it, but I'll bet it was an "interesting" car to drive!

bill jacobson

IMHO when considering the Rover 3.5/3.9/"4.0"/4.2/4.6 litre engine you should:-

Be aware that the propensity of the block to crack with age. I am told the 3.9 & 4.2 are most likely to suffer this, and that the newer "4.0" and 4.6 are almost immune.

Compare the prices. Here in the UK you can buy a new 4.6 at very reasonable prices; about the same as buying a used 3.5, 3.9 or 4.2 and doing a full precautionary rebuild. Don't forget the cross bolted block on the 4.6 & 4.0. No connection other than a satisfied customer, but try John Eales for the best deal.

Remember that there is no substitute for capacity. I have three cars with these engines a 3.9, a 4.2 & a 4.6. If I was starting again I would go with 4.6 in every case.

Safety Fast
Nigel Steward

I'm almost afraid to ask this question in fear of the "hall monitor" finding out I own a midget instead of a B, but here goes. Does the rubber bumper factory mods help with the swap of say a ford 302 or chevy, or would you be just as well off with a chrome bumper car?
Stan Williams

The mods do help. The 302 is actually physically smaller than a 215, but not by much. The Chevy I have no info on. the problems with the 302 over the rover are

Weight, oil pan width and depth, front distributor.

Weight is obvious. Oil pan issues are 2 fold, requires notching crossmember due to hieght, and can be tricky getting motor mounts to clear frame due to the width. Front distributor can cause hood clearance issues up front.
Larry Embrey

This thread was discussed between 13/04/2001 and 19/04/2001

MG MGB GT V8 Factory Originals Technical index

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