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MG MGB GT V8 Factory Originals Technical - 60 degree V6 dream

Visions of a 60* V6 screamer realized so poetically...

Compare that to the beautiful lines of the Mclaren F1...

No one offers a kit that is identical to the lines of either car, but the Ultima GTR offers a very pragmatic mechanical approach...

alright jeg, now i've got to get a new keyboard as mine was ruined from the drool. so where can we get those engines? group purchase maybe? imagine the wind noise in a B with the straight up windshield at 220mph? jim
james madson

The engineering is in and of itself poetic artistry, but those lines have me infatuated..both the Lotus and the Mclaren.

Incidentally, for those looking for a street legal racer, the Ultima GTR has received very high recommendations by everyone who has ever tested it.

This one is more attainable by normal people. That ultima kit is $90,000!


I'll take it!
The motor was special built and i do not believe it was normally a 3 litre, but instead is a destroked or storked version of the newer designed GM 56?(degree) V6 is built in GB and one other place and is used in Caddys and other cars worldwide. GM has actually come out with the 56 degree as well as one other 60 degree motor and continues to build thier current system- all of thier new and old "narrow" motors have multiple bore and strokes that allow for different sized motors right away- not like the old way of starting a motor out as a smaller bore and keep boring and stroking it for 20 years.

Anyways, the biggest thing i see is that they are going with thier own fuel injection and ignition system, thus illiminating the GM systems which are getting very technical- variable cam timing, variable intake runners, blah, blah blah... Anyways, VERY powerful from no displacement, but VERY expensive at this time. Give it a couple years for prices to come down and more systems to come out. ;-)

BMC Brian McCullough

Nice curves, but why bother with just changing the looks? If I were ever to consider a kit car , it would involve a tubular frame and etc., not simply a 'donor car' with a "facelift".
Also, the new GT40 ($65k) is outdoing everything(?) in its class, to the point of being unfairly compared to a Ferrari "out of its class"..namely the $500-$600k Enzo.

Thank you for the input, I was not aware of those nuances.
Incidentally, I hadnít decided between rwd heads and fwd heads for the V6 I plan I having built. Primarily because the FI system is limited at the upper edge of the mid range to top end.
I have a comparison of an engine that was tested with a carb and then with FI that was conducted by Car Craft..needless to say, the 3.4 would actually benefit without losing anything at the lower end..going with a roller cam.

Would you happen to know someone with alloy rwd heads?

Uhm, that car DOES have a tubular frame. It is a completely new car and uses the driveline from the C5 vette, and a porsche transaxle. You toss the vette chassis, body, interior, and everything else.

Take a closer look at it and you'll see what I'm talking about.

Well now, I saw the words Factory Five and "donor car" along with that picture of the vette and did not bother to scroll down further.

I have never liked Factory Fives designs (undercarriage, etc), specifically the Cobra's..there are better Cobra kits out there.
They presented no price, but going by their past work, I would rather go with Fords advanced GT40 for $65k.

Apparently your eyes aren't working too well. The kit is slated to cost about $19,900 and they estimate a completed car will cost about $35,000. It's all in the information. Their ladder type frame has proven itself to be exceptionally strong. Especially in the latest designs of their cobra kit.

The Ford GT40 starts at $141,000. Is someone selling them for 50% off?


Apparently your eyes/brain are not doing too well-little one, there are two links to click on at the Home page BOTH listed as "The Cars and Pricing".
The one listed to the left is what I had clicked on effectively bypassing their "target" cost.

Regarding their chassis, it still sucks relative to what others offer..but that again is me.

As for the GT40, MSRP is 139,995, thus I 'probably' detracted 65k from 165k..I will continue to deter others away from Factory Five.

My memory rarely fails me...

"Conceived with an initial $70,000 price target, the GT40 is now referred to as a $100,000 car".

Seems most likely what I had heard was the price target for the car.

F.I. is the way to go. A little head work either way is going to help with the upper end. Send me your email address and i will send you a dyno sheet of a motor.

There was never any stock RWD Cast Aluminium head cars, but thier are conversions. Aluminium head design is initially better flowing, iron heads do not remove energy as aluminium does (via heat!), so they both have benifits. A rear wheel drive block can be used with less changeovers in parts to complicate the system such as FWD blocks do and can use the aluminium heads and intake at a later time. FWD blocks have a better oiling system, but i have never realy heard anyone with an oiling issue on a RWD block which is what i use. Tradeoffs- its what you get for going either way.

I prefer iron head for ease, but would love to run an experiment one motor against the other for comparison someday.

BMC Brian McCullough


Just out of curiosity, why did GM come up with a 56 degree design? I'm sure they had a good reason, and I'd like to know more. Can you direct me to a web site or other source for more info on this?


Dan Masters

I have read and heard that most FI systems are very limited primarily due to the throttle body (very constrictive) and the injectors themselves.
In Fact, the manufacturers purposely do this for "smog" and insurance reasons, and have realized dramatic gains with later engines (same)with this correction.

I have corresponded with KillerBeeV6, and in the past he has used a FI system from a 3800 engine with mods.

FI does not scare me (not much does, hehe), in fact I was very much intrigued initially, but have found that carbed may be the best overall route.
I also have aesthetical concerns and would prefer to expound on the original theme..I like the fact that I can still utilize the original choke knob for the same purpose.

I discovered at the 60degree web site that there was a company (Potter Racing) that used to manufacture alloy rwd heads but no longer offer them.
I had considered the "Bow-tie" block as it has improved oil circuitry among other advantages, but see no point if no one offers corresponding alloy heads.

I will most likely opt for the rwd engine which would require a mechanical cam..roller of course. A roller cam in and of itself will boost the lower end and do wonders for its mid to top end.

I will contact you regarding that power graph.

I cannot say. I believe they use this in the Saturn- probably the Large one and in one other GM car- Caddy? I have not kept up with those recently. I remember seeing a cutaway block at the car show here in Mpls/St.Paul a few years back but never got any deeper then that. I believe the bellhousing bolt pattern and flywheel bolt patterns turned me off as i realise that if there isnt a cheap and readily available bellhousing/flywheel setup, then these would not sell well to the masses for conversion work.

Dont know if that was your email earlier or someone elses that i answered, but the dyno sheet was sent. It is my belief that the 3.4L RWD fuel injection looks the most at home in the bay of the MGB- more then the carb or FWD injection, but thats my opinion...!

A few of those RWD aluminium heads have shown up on eBay now and then- keep watch.
The aluminium blocks are $3K NEW! and are the 2.8L bore which with a stroke and a max overbore can maybe be safely put out to 3.2L. Save your money and purchase one of my aluminium flywheels for RWD motors and balance/lighten the rotating assembly and the moving parts with tubular push rods, aluminium rockers and the cool stuff. The power you gain would be more reliable and far outweight (pun intended) the benifits of a 50+ Lbs lighter block.

Use the choke knob to control a starter switch like the REAL MG's (like my Spridgets) LOL! See- then you would use it Every time you start the car up, just like originally!!

BMC Brian McCullough

Yes that was me, I received the graph.
I have considered modifying the choke knob as an override switch for the electric fans. The insignia on the knob even resembles a fan..but hardly a decisive factor.

Below is the test I mentioned which I will post here for the benefit of others.
It is a comparative test that Car Craft conducted of the same engine with FI and without (carbed)...

RPM--- CARB------- FI
2600 375 179--- 425 210
2800 377 193--- 434 231
3000 387 221--- 435 248
3200 396 241--- 440 268
3400 400 259--- *448 290
3600 403 276--- 443 304
3800 407 294--- 437 317
4000 410 313--- 429 327
4200 414 331--- 421 337
4400 *419 351--- 410 344
4600 417 365--- 400 350
4800 413 378--- 386 *353
5000 408 389--- 368 351
5200 403 399--- 344 341
5400 396 408 - -
5600 388 *414

This was obviously done on a V8 engine (small block).

With a motor like the F.I. unit above, a wider ratio gearbox can be used as is and actually increase your 0-60 times doing less shifting staying in a power band longer and there are more performance items that i am not naming in this. In our V6 conversions, we have used the V6 T5 which the ratios I find are better with the likings of the motor that i sent that chart on... as long as you have a differential matched to the gearing of the said unit.

having a motor that has 100 bhp more for 500 RPM is no good if it is highly peaky like a bike motor pulling a large trailer- neather of these appears to be, but something to look at. Big numbers are great, but steady is better in my opinion.
BMC Brian McCullough

My criteria is a bit different..I want more.

The 3.4 V6's really drop off at just over 4000rpm's, thus a carbed system would really prove beneficial.
A nice street port job performed on the heads, complimented with a higher compression ratio (10.5:1), along with a roller cam that I plan on having grinded to my specifications.
This cam alone not only will BOOST the lower end, but will unleash the mid to top end tremendously.
Thus, with a short ratio trans, along with either a 3.76 or the original 3.9 rear end, you have a package that is more productive.
I also appreciate the subtleties characteristic of a true vintage sports of them being a close ratio trans.

But I agree, for some it may be best for them to take your route..for several reasons.


Most gearboxes are pretty wide ratios, such as the original MGB. If you wanted the setup your talking about, with only 10.5 and a good cam, you could probably still get away with a wide ratio box... but a close ratio (V8 T5) with a 3.7 would be great for that setup. the OEM 3.9 is a bad coice because you cannot hook up without a LSD and some wide tyres, so a different rear end in teh range of 3.4 to 3.7 for most V6 conversions is in order for optimum everything and what you are talking about is in need of a 3.7. 3.9 or 4.1 in a GM r Ford or any other rear end is going to give you something that would probably leave you very unhappy for just about any kind of driving you are going to other wise use the car for..

How soon are you going to start? :-)

BMC Brian McCullough

My intended reference was to 'sports cars' with a substantial powerplant.
This of course does not make the others including the MGB any less of a 'sports car', only a different kind.

As to when the conversion is going to take place, there are other more pressing things that need to be done first.
Next on the list are the floor pans, and then welding in reinforcing channels extending from the front spring mount, which will then incorporate a pair of anti-tramp bars.
I have even been looking for a particular style of split spoke alloy wheels..good news though, I think I was finally able to find someone who offers an identical style.
Apparently, some of these wheel manufacturers just purchase and place their names on a particular style of wheel, then sell them as their own creation.
I so far found 3 different "manufacturers" who did this with this particular wheel...

So as you can see, I prefer to do things in the proper steps. In the mean time I continue to refine with research and revaluation.

Incidentally, your response seems to indicate that you feel the compression ratio of 10.5:1 is a little low. Have you ran 11:1 successfully without detonation?..I wouldn't be surprised with a car as light as the MGB.

Not in any 60 degree myself, but for a careful planning of engine timing, compression and so on, i would think that bumping to just about there could be done if everything else is up to par. My main thought is the higher the compression ratio, the bigger the cam can be and the more 'peaky' the motor can become and i would think still streetable around there which sounds like what you want. Sorry, 12 to 1 is probably out of the question for just about any motor that is not completely computer controlled! :-)
Also, nice looking wheels.. Maybe time to go 4 wheel discs when you convert the rear axle.
BMC Brian McCullough

OK, thanks.


I look forward to your progress. I'm curious to see what can be accomplished with these engines in a built, ported & polished, high compression, cammed, carbed configuration. You can certainly make the argument that carbed is more in keeping with the spirit of the car. A happy revving high compression engine cerainly has its place in a "true sports car."

I'm still leaning toward fuel injection though for a couple of reasons. Good cold starting, better mixture control, Knock sensor with computerized timing control...and a better platform for a street driven turbo car. The only downside is the relative inability to modify the computer control without going to an aftermarket ECU, or swapping another GM ECU more suited to any planned mods. My other current project car is a miata with a diy turbocharger setup - a T25 off an eclipse, a WRX intercooler, Weld El tubular manifold and 440cc injectors, a Haltech E6K, and a 3 inch exhaust. Wicked good fun. It is a happy little autocross car.

Right now the 72 BGT is in slow motion. Still finishing the welding on the driver's side sills, floor and fenders. My garage is full so it resides 250 miles away in my brother-in-laws spare garage in Ithaca, NY. Frustrating to be moving so slowly, but I get to watch you guys and learn from the collective experience. Good luck with your build and let us know how you make out.


Brian C

Brian C 72mg

Not sure exactly why you guys are talking about going retro and using carbs on the GM V6. The injection i svastly superior.

300 bhp 3.2
Bill Spohn

You must be using a 2.8 or 3.1 litre block with about a 0.030" overbore to get your 3.2? What else have you done to give 300 BHP?

I have a 3.4L Camaro motor in my 80 MGB and 82 S10- both sequential port injected and DIS ignition.. Good stuff in stock form.
BMC Brian McCullough

I just found out that those wheels I was after are still offered by someone, so I am getting ready to purchase a set --before they discontinue production, hehe.

My questions to you are, on your complete rear ends, what are the bolt patterns offered? Also, do you offer larger rotors to take advantage of a 16" wheel?

Finally, I currently have the banjo spoke wheel rear end which allows for a 2" outside with a 3/4" gap for sidewall (to unmodified inner fender lip) and up to 5" backspacing.
So I like the length of the spoke wheel rear end, which is supposed to be 44.5" measured from "brake drum face to brake drum face"...

Do I have my choice there as well?


This thread was discussed between 10/07/2005 and 04/08/2005

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