Engine and Transmission Tech

Gentlemen,

Wanted first .... some advice.

Are there Rover 3.9 blocks with factory 4 bolt mains ? Or must I start with a 4.2 block AND with liners, reduce displacement down to 3.9 - in order to build a new 4 bolt main 3.9 Rover V8 ?

I'm in the process of convincing the SCCA that a GT 2 MG Rover RV8 should be allowed the Rover 3.9 block/displacemement.

The CRB (Competition Racing Board) of the SCCA will probably allow the change from the now required 3.5 size ro the 3.9 size, for the RV8 originally was sold with the 3.9. Rover sold 2,500 RV8s. They were all equipped with the Rover 3.9 engine size and
the Rover factory RV8 shop manual shows only the 3.9 size Rover V8 in the RV8.

any advice will be much appreciated

keep them on the track,

phillip g

Phillip, you should probably be looking for a later-model "4.0" block. 3.9 and 4.2 versions of the engine differ in stroke (2.800" versus 3.030"), but they have the same bore. They were produced simultaneously.

It's not intuitive, but 3.9 and 4.0 engines actually have the exact same bore (3.702"), stroke (2.800"), and displacement (3947cc). From the SCCA's perspective, they're the same engine. Don't confuse them by focusing on the names "3.9" and "4.0". They have the exact same bore, stroke, and displacement. Once more for emphasis: they have the exact same bore, stroke, and displacement.

Page 23 of the book "How To Power Tune Rover V8 Engines" breaks down all of Rover's production to eight distinct block types. By that book's definition:

Type 4 are the 3.702 bore blocks produced from 1989 through December 1993. These 3.9L and 4.2L engines have the same 2-bolt main bearing caps as the 3.5L engines.

Type 5 are the 3.702 bore blocks produced from January 1994 through April 1994. Although the Type 5 engines have the more heavily ribbed later-style block castings, these engines were assembled with early-style 2-bolt main bearing caps.

Type 6 are the 3.702 bore blocks produced from April 1994 through October 1998. These engine have the heavier duty block castings, and they also have the bigger main bearing caps, but the caps haven't been drilled and tapped for 4-bolts. You COULD have a machine shop update one of these engines to four-bolt mains... but it would be easier to just start with a later model engine block.

Type 7 are the 3.702 bore blocks produced from September 1994 through 2004. They have four bolt main bearing caps.

Since they're the newest and since they were produced in greater numbers, the Type 7 blocks will almost certainly be easiest to find in your area.

Next subject: ignition. I can't imagine that SCCA would forbid any GT2 car from running crank fired "direct" ignition. You should verify that. (Vintage racing rules typically forbid crank fired ignition which is why the vintage guys will be on the look-out for the the front cover from a Type 5 or Type 6 engine. These "interim" engines had camshaft driven distributors.) - but if YOU are allowed to run a crank fired ignition system such as "Electromotive", you should certainly plan on it!



Edited 3 time(s). Last edit at 09/14/2012 01:41PM by Moderator.

Phillip, From that same Rover book, it presents that "all" of the later 4.6L blocks were sonic checked, for cylinder wall,(aluminum) thickness. This is because of the persistant problem of "core shift", during the aluminum casting process. The best blocks had" pink" paint code, for use in 4.6L engines, only. The thought here is larger engine, higher cylinder wall loading = more likely to crack the aluminum, behind the liners. I suggest a 4.0 or 4.6L block, only, for better durability than a 3.9L/4.2L. Whichever block use choose, pay very close attention, that NONE of the liners have migrated below the deck surface, in the slightest. This would be your easiest way to suspect cracked aluminum behind the liner. Since this is to be a real race engine, only FLANGED liners should be used. Your race block is saying, "you can pay me now, or you can pay me later". Do you feel lucky ?? You know my take on using a dry sump, for this application. As per David Vizard, regarding a "restricted inlet" motor: All effort should be made to reduce air inlet tempeture through the intake manifold, as in thermal barrier on manifold/inlet ports, to reduce thermal transfer from lifter valley, the cylinder heads and engine compartment." Stand-off inversion and heat are enemies of power, here. Enhanced plenum volume in a "single plane" manifold, with a thermo insulative "shear plate", under the carb, should help. Mushroom lifters,(legal), should be used. The engine will definately need to sorted-out, on an engine dyno. Good Luck, roverman.

Philippe,

only TVR Tuscan Challenge Blocks were factory 3.9 X-bolted block (3.702" bore and 2.3" main journal).

This blocks are based on TWR/ARG 3.5 X-bolted block casting.

Later 3.9/4.2 block with full main caps and side boss provision for X-Bolted (called interim blocks Post sept 1994) are based on 38A block casting like 4.0/4.6 blocks but they use 2.3" main journal size.

If ever I should have parts to build race 3.9 engine.

Cheers.

There are a number of brand new Rover/TVR V* engine blocks on Ebays UK site. They are about $2000 but US buyersshould get the VAT back reducing the price to about $1600. Some are cross bolted and other are not but can be modified to be done. To find them search "Rover V8 block" on the UK site

Ok, so $1,600., and NO flanged liners. Buy a seasoned 4.0/4.6L for $150. ? roverman.

Main large journal blocks are not the best choice for full race application IMHO.

Main large journal block = more friction on main crank journal = more oil temp.

But in all case you need to change stock side bolts of main caps as they can brake under heavy duty load in race application.

Racers,

Thanks everyone - for your input on this engine block choice.

The RV8 GT2 car needs another 100 hp to be competitive in class and a new engine - maybe built over the winter months - might just be possible.

keep thm on the track,

phillip g

Using the "small" mains may/or not reduce bearing drag, vs. 2.5" dia. Using a "cast" crank for this kind of racing, is marginal, at best. The 2.3" crank might actually "grab" the bearings more, in a race application. Stronger crank will flex the main webb area less. Stronger is better. Stronger = race reliability, a good thing indeed. sbf and sbc are all using 2.5" mains. No one is complaining about the extra drag. If cranks were breaking, we would hear about it. Onward, roverman.

Phillip, You might ask Bill Jacobson about the benefits of using a mushroom lifter/cam assembly. I'll be using one in my "legal" 4.0L, for the Huffaker TR8. Cheers, roverman.