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Build Thread - B GT Miata Swap

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ValveCoverGasket Avatar
Portland, OR, USA   USA
Ive been lurking on here for a while since I got this GT about a year ago, and figured maybe it was time to post a few pictures of the progress, I apologize in advance for the photo size. Anyway, hopefully this is the right forum for sharing...

My original hope with this was to run a set of throttle bodies and fuel injection on the original motor, and get the rust fixed. As things of this sort always have a way of snowballing, thats exactly what happened...
After some looking around online it seemed that a more economical route might be an engine swap rather than investment into the stock engine, so I set about looking for a 4 cylinder that would fit. A late model Miata seemed to be the ticket - after finding the GRM article and seeing the work Eclectic had done - so I bought a wrecked 2000 Miata and tore the engine out.

We're still in the engine fitting phase of the swap, but making steady progress.
The plan will be to run throttle bodies on the Miata engine

Anyway, a few pictures!

The B as originally purchased, with some photos of its glory days prior to being parked






The Miata



Engine out of the B







Generally speaking, it fits pretty well...



Though front pulley/rack clearance is the biggest issue



Throttle bodies should fit with some room to spare




Lots more photos here on flickr


Ive also got a much more rambling thread on a different forum but I'll try to update this with just progress.

We've got a lot of clearance issues to tackle still but should be making new mounts this weekend hopefully.



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guidopazza thomas hartshorn
seattle, USA   USA
1976 MG MGB
Congratulations on your swap. I am interested to see how it goes.

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Benny Avatar
Benny Ben E
San Diego, CA, USA   USA
In reply to # 2419629 by ValveCoverGasket Anyway, hopefully this is the right forum for sharing...

It is.....you'd be whipped with 100 wet noodles if you posted this on the main MGB board.

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kerbau53 Avatar
kerbau53 Gold Member Geoff Morton
Cape Coral, FL, USA   USA
1978 MG MGB V8 Conversion "The Wreck"
That will be a very nice setup. Please keep the updates coming in!

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ValveCoverGasket Avatar
Portland, OR, USA   USA
In reply to # 2420689 by Benny
In reply to # 2419629 by ValveCoverGasket Anyway, hopefully this is the right forum for sharing...

It is.....you'd be whipped with 100 wet noodles if you posted this on the main MGB board.

Hah this is sort of what I figured.
This forum has been a great resource (and I still have a lot further to go in my research) for the car up to this point so I figured I would do my best to make a contribution.

The plans for the engine are some fairly lumpy cams, some mild headwork, as well as TWM throttle bodies, essentially copying a setup done by a couple of Miata folks on other forums.

I'm hopeful that I can help contribute some additional information beyond that printed in the Grassroots Motorsports '73 GT swap series they did - which was informative but missing some photo documentation (in my opinion).

This weekend should be motor mount building and hopefully getting the last details of the swap sorted out. I have a box of Miata crank pullies of various years to see if I can find the thinnest one to use, as well as a small Denso hotrod alternator that others have run on race Miata motors so we can see how well that packages (Im not a big fan of placing the alternator on the hot side of the engine like Ive seen other Miata swaps done).

I'll be sure to keep the thread updated as I get more photos!



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BillC Avatar
BillC Bill C
Huntsville, AL, USA   USA
1977 MG MGB "Lil Miss Behaving"
I hope you get it done soon as I would love to know how you like the performance . I am doing a similar swap using a Duratec engine and a T5 . Should put some zip in your GT and I for one like the idea of keeping the B as a 4 banger . Just keeps the car more sports car and less muscle car to me.



Pretending to be a normal person day-after-day is exhausting.

If at first you don't Succeed try doing it the way your wife said in the first place!

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ValveCoverGasket Avatar
Portland, OR, USA   USA
The swap will likely take some time as the car needs paint and some rust work after we've finished the engine fitting, but to give some idea of performance:

The 2000 Miata engine makes around 100-110 in stock form to the wheels. A similarly built engine as this should land somewhere in the 170-180 range, seen here:
http://clubroadster.net/vb_forum/59-irtb-individual-runner-throttle-bodies/81194-my-172whp-n-engine-stock-bottom-end-no-porting.html
Assuming the weight is similar to the Miata, and the gearing and final drive is very similar between the two, the performance shouldnt be too far off of what others are seeing in 170-180hp Miatas. Not blazing quick, but more than enough for something this small/light and managable for weekend cruising and twisty roads.
Im not trying to build a track car or an overpowered v8 monster that requires signficant other work to the brakes/chassis/suspension (Ive been down that road with other cars and they just end up being no fun to drive on the street).
I agree on the desire to keep the B a 4 cylinder, and I would have prefered to go with a cheaper to modify one than the Miata, but the dimensions were too close to ignore so that ended up being the winner. Most Miata folks who want power go the turbo route, so naturally aspirated modifications end up being relatively rare and expensive.

If you were ok with a little bit less power, or willing to go a little more wild on the engine modifications to make up the difference, the engine fitment would have been made easier by using the shorter 1.6l Miata engine.



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ValveCoverGasket Avatar
Portland, OR, USA   USA
Here are a couple more shots from this weekend, engine is in and sitting on its mounts. We still need to finish the trans mount but its basically locked down.

I think we ended up with it a little lower than the grassroots swap.




You can sort of see the front mount arrangement here



Ill get some more detailed shots of the front end setup next time.



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NOHOME P P
O, ON, Canada   CAN
1967 MG MGB GT "Maggie (GT From Hell)"
I would have been tempted to blend the Miata chassis to the MGB tub keeping as much of the Miata as possible.

Kinda like this:

http://forum.miata.net/vb/showthread.php?t=449226

This example is of a Sabb receiving the graft, but it does allow for the entire Miata suspension to be retained as the engineers meant for it to work.


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ValveCoverGasket Avatar
Portland, OR, USA   USA
That idea was thrown around by some folks I mentioned the swap to, but would involve significantly more fabrication than I was interested in doing.
Would be a great setup - especially if it included the Mazda rear end parts so you could run the entire Mazda drivetrain complete with the aluminum girder they use to tie the whole mess together - but again a fair bit more work than I was after.


Heres a closer shot of the frame to alternator clearance. I think we'll be doing a mild notch here to give room for alternator adjustment





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NOHOME P P
O, ON, Canada   CAN
1967 MG MGB GT "Maggie (GT From Hell)"
Vedran:

I agree that it looks like more work up front, but in terms of less and better engineering, it is a good option.

The other thing I like about the subframe graft is that your future repairs will come from a Miata Repair manual, not the manual the you would have to create to cover the less integrated approach.

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ValveCoverGasket Avatar
Portland, OR, USA   USA
No question, and if I was a more capable fabricator that would be a great way to go!
I think in either case you'll always have some "custom" pieces where the MG and Miata meet - in your example they'd probably be less so, but its tough to avoid some non standard parts when doing these conversions.


My goal was to use all MG suspension/steering parts - which we've met - and to use all the Miata engine/trans/clutch parts - which we've also met. The cooling will also be all rubber bumper MG with some custom hoses, and the rear end and rear suspension is also all original MG. The driveline will obviously be a hyrbid though, as with most swaps...

From the inside it should be imperceptible that the engine has been modified - the plan is to use all original gauges/switches/dash parts.



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SWS 911 Stephen Stack, Jr.
SAN ANTONIO, TX, USA   USA
Any updates? I sure do like this build, thinkin' about doin' the same.

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denvermgb Avatar
denvermgb Brad Carson
Aurora, Colorado, USA   USA
You might get in touch with Keith Tanner. He works at Flyin' Miatas in Western Colorado and he has an MGBGT with an LS7 motor. He used a lot of Miata suspension/parts in his conversion, and I think he knows most of the Miata workings. I know he posts on the BritV8 site, I think he might post on here occasionally. Either way, keep us posted on your conversion. Good luck!

Brad

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ValveCoverGasket Avatar
Portland, OR, USA   USA
In reply to # 2447166 by SWS 911 Any updates? I sure do like this build, thinkin' about doin' the same.

yup!
Sorry I dont get on this forum as much as some of the others I frequent, but there has been a fair bit of progress in the last few weeks.

I ripped out all of the front end metal in prep for the rubber bumper style radiator panels...





And the ITBs arrived - so they got a test fit to check firewall clearance before being hidden away in their box again hah







We reworked the alternator clearance frame notch a bit, I was getting kind of worried and figured it might not hurt to have too much room rather than too little there



And then this weekend the new front end panels went in after a bit of massaging...
















I still need to clean up the front end area a bit now that the welding is done, and take some updated shots.
But the next big step is going to be stripping it in prep for paint work. Still a ways to go, but Im glad to be near the end of the grinding and cutting, my shops becoming a mess haha

And theres a few more pictures of various bits and pieces here in the Flickr album (which gets updated a bit more frequently)



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