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MG MGB GT V8 Factory Originals Technical - What's so great about the 4.2L Rover?

I keep hearing, on this BBS (Tony Bates mentions it, and Ted something mentions it, Glenn Towery mentions it and Tony Barnhill mentions it) and on the street, about the merits of a Rover 4.2L motor. What's so great about them? Is it the best choice for a BOP/R V8? Easy to get parts for? Can they be made to develop a reasonable amount of power without going nuts?
Todd P. Gormley

Todd, You can make GOOD power with a 4.2 with a mix match of easy to get parts. What I do is pull the 4.2 apart & find a set of 3900 pistons & cut them to fit in the 4.2 & this mod will give you 9.5 to 1 comp. ratio & this is what makes the 4.2 run. If you can find the 3900 9.35-1 pistons this will give you 10.5 to 1 comp. & you will have to run 93 oct. & it runs a good bit better Find some one that knows how to port the heads & it can make real good power. I have a 4.9 that runs real good & I have made a 4.2 that will run with it. I can build a 4.2 long block for $3,200 but f you need a 4.9 it will cost over $6,000. It goes to show you that to go FAST it cost cubic dollars! I like the 4.2 for it is easy when I go to put the F/I on.
Glenn Towery

My engine is the one Glenn built to run with his 4.9...we started with a 3.9 block that was cross drilled for 4-bolt mains & bored, 4.2 long stroke crankshaft, 5.7" 4.2 longstroke rods, A&E Hepalite 3.9L short stroke pistons shaved .080" off top & 1/8" off bottom with moly rings, double roller timing chain, Isky 270° cam with Isky lifters, Triumph TR8 carbureted heads with combustion chambers relieved, oversize 1.625" intake valves & 1.325" exhaust valves, ported, polished, decked & Chevrolet small block valve springs with 95 pounds on valve seats, & oil galleys opened to at least 1/2" to name just a few things...&, there are lots of Glenn's other secrets inside that engine...its probably putting out as much torque as horsepower (in the 300hp range) & shoving it all through an 11 pound aluminum billet flywheel with 10-1/2" Rover SD-1 Borg & Beck clutch into a Towry built Rover 5-speed tranny...we're talking a bore of over 3.7", a stroke of only 3" & compression of 10.5:1....oh yeah!
anthony barnhill

4.2s are nice but I can't imagine how you could squeeze more than 250hp/250ft-lb out of one, unless you used an absolutely huge cam and some other goodies. 300hp? ... NFW!! Besides a Ford 302, which is rapidly gaining my buy-in, a 4.2 would be the way to get the most bang for the buck.
roverman

Interesting to note that in the three seasons 1991 to 1993 inc using an JE engine dyno to verify accurate power with representitive intake and exhausts we started with 262bhp with a 3.9 on standard single throttle Lucas injection a Crane 248 cam and Pete burgess well developed heads, and by the end of the last season power had increased to 312 using the same throttle, but now on a different engine management system, inc ignition control, a Crane 256 and some more head work. Air intake ducting was interesting as it used 3" plastic gutter pipes.

In a TR7 chassis which was also well developed this engine enabled the car to take the overall Cox and Buckles TR Championship for those three years. OK the car was light at about 900kgs, but rev limited at 165mph and acceleration to the ton in around 8 secs depending on tyre temps made for an interesting car that could also take 5th gear full throttle, or any throttle for that matter from 1200rpm cleanly.

Things have moved on a bit since then, especially in terms of engine management control so I expect wilder cams can be tamed better for good road manners.

Rog
Roger Parker

I was able to obtain 260bhp and I forget how much torque at the dyno last year -- I also forget the rpm where max torque was but it was amazingly low -- with a built 4.2 (not nearly as exotic as Tony's) running at 9.5:1 CR, big-valve (i.e. Vitesse) ported heads, very high-lift cam, Carter 400 and Edelbrock Performer intake. Gas guzzler extraordinaire, though. At least within the BOP/R world, dollar for dollar you can't really beat a 4.2 ... they definitely have more grunt than the 3.9 (as you'd expect, since they're just a stroked version of that motor) but OTOH don't spin up quite as easily. The ones I've seen do tend to run a little warm though -- so at least be sure to have a good radiator.
Terrence

The 4.2 has amazing torque and in stock form- mild cam & a bit more compression- 9:1, has powered my GT as a daily driver for the last 5 years. I can come off the beltway at 70 mph in 5th gear, blend with traffic down to 30 mph & still drive along in 5th. At 65-70 mph I can get very good accelleration for passing without downshifting, even though my 5th gear is .63 in a T-5.

The engine does tend to run hotter than my 215, but an oil cooler solved that problem. It does want 93 octane while the 215 runs happily with 87 octane.

In my opinion, this is the ideal daily driver in (mostly) stock form, & as others have said, has tremendous potential for additional power, while maintaining ease of conversion far above the Ford 302. I am not being critical of the Ford, just pointing out the difference of installation difficulty.
Jim Stuart

This thread was discussed between 16/10/2002 and 01/11/2002

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