Tony Jones Posted April 14, 2009 Share Posted April 14, 2009 Hi all, Sorry for yet another seemingly daft question but here goes: On the 4.6 litre crankshaft are the con rod large end the same bore as on the 3.5-3.9 conrod large end or are they different? What is the bore to bore length of the 4.6 conrod please? Cheers again, Tony. B) Quote Link to comment Share on other sites More sharing options...
cipx2 Posted April 15, 2009 Share Posted April 15, 2009 The crankpin journal diameter on 4.0/4.6 is 55.513-55.500 mm and on the 3.9 is 50.812-50.800 mm so I guess the conrod big end bores are different. Bore to bore conrod length on 4.6 V8 is 149.68-149.78 mm. Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 15, 2009 Author Share Posted April 15, 2009 Cheers mate for the help. I have a problem (Yeah, no doubt I hear you all cry!! ) I have a 4.6 large journal crank which will be getting fitted into a suitably modified 3.5 block. Yep, i'll have to have it line-bored and new liners installed ....... but I have a set of Stage 2 Heads (Ex 3.5) that will also be fitted. Now, the 4.6 block and std (28cc) heads give a compression ratio of about 9.35:1 which is reasonable for a high torque cam engine but with the 3.5 heads the CR is going to be significantly lower. Ideally i'm looking for a CR of high 9's with the 3.5 heads. The only way I see of that being possible is to fit non OE pistons and if necessary conrods to raise the CR to decent levels. I thought also at the same time if I could increase the bore to approx 96mm which I understand is the accepted safe limit of the liners then I could squeeze 4.8 litres out of it and with a decent CR. My question therefore is does anyone have any idea what is the best piston + or conrod combination to use with a 4.6 crank to reasonably achieve this? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted April 16, 2009 Share Posted April 16, 2009 How is using a 3.5 block & heads going to result in lower compression, unless you have a low-comp setup? The later 4.0/4.6 heads were effectively skimmed a bit to account for the thickness of the composite gaskets - but it's half of naff all difference as far as I'm aware. Certainly my 4.6 is running 3.9 heads with comp gaskets, no problems and no noticeable loss of power. Quote Link to comment Share on other sites More sharing options...
stuck Posted April 16, 2009 Share Posted April 16, 2009 Are you going to modify the block sufficently to accept a 4.6 crank?! Would have thought you could buy a OE block for less £ Quote Link to comment Share on other sites More sharing options...
Quagmire Posted April 16, 2009 Share Posted April 16, 2009 Tony, If you havent found it already, try browsing around here for answers on what goes with what to make what: V8 Forum As for 3.5 heads lowering compression- Fridge is right, the only difference in heads that will impact compression is the fact that the later heads are skimmed slightly more so that they can use composite gaskets with no drop in CR. I am currently using the other way around and have a set of 4.0 10 bolt heads on my 3.5... In the RV8, the factory compression is determined by the pistons. Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 16, 2009 Share Posted April 16, 2009 With modern fuel and a decent EFI setup i'd be aiming for a CR higher than 9... 10-10.5:1 is where i'd be aiming for. Quote Link to comment Share on other sites More sharing options...
Quagmire Posted April 16, 2009 Share Posted April 16, 2009 I thought modern fuel was not as good as old fuel? But then i have no idea about the petro-chemical industry so could be talking poo... Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 16, 2009 Share Posted April 16, 2009 hmm ye maybe your right, i was meaning more that the fuel was more consistent and of a decent quality. Old 4Star did have a higher octane rating than Unleaded, so would resist det a bit more. The main point however is that with a decent EFI system and proper mapped ignition timing, you can run a decent compression ratio and get decent power and efficiency from the engine, sticking it on some scaggy old carbs and a dizzy nailed on the side is just wasted potential, especially when it means you have to run a lower compression ratio as well to stop it grenading. A lot of naturally aspirated modern engines have compression ratios above 11:1, and they manage just fine. Our Audi A4 1.8T runs a compression ratio of 9.5:1, and its turbocharged... Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 18, 2009 Author Share Posted April 18, 2009 How is using a 3.5 block & heads going to result in lower compression, unless you have a low-comp setup? The later 4.0/4.6 heads were effectively skimmed a bit to account for the thickness of the composite gaskets - but it's half of naff all difference as far as I'm aware. Certainly my 4.6 is running 3.9 heads with comp gaskets, no problems and no noticeable loss of power. Cheers for the replies guys. Well first it looks like I got the wrong end of the stick, I was under the false impression that the 4.6 heads were of a significantly lower compression. I'm glad they're not which means I can just go ahead and build her up as normal. As far as the block goes I thought i'd fit the ARP stud kit, line bore the block to the bigger journal size, fit the ARP head stud kit for added protection and run the whole thing with a Viper Stump Puller Cam, my stage 2 3.5 heads and as for the top end well ........... I don't have an EFI set up any more as I somewhat stupidly scrapped it a few weeks back So, I may have to go Carb fed, either dual 2" SU's on a matched manifold or the usual 4 barrel set up. Cheers for the link Quagmire. Will check that out too at work tonight. Got to get ready now though. B) Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted April 19, 2009 Share Posted April 19, 2009 Why go to all that effort then bolt carbs on? Mind you, if we're asking questions like that, why go to all that effort when you could just buy a bigger lump to start with? Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 19, 2009 Share Posted April 19, 2009 Yer i agree, EFI is SOOO much better. You will get more power, better drivability, better fuel economy, infact just about every aspect of the engine will improve. I suggest using a proper mapped ignition system with wasted spark, to go with the fuel, which will provide the optimal all round engine. Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 25, 2009 Author Share Posted April 25, 2009 You are right of course, they are very much plentiful so 4 barrel carb set ups would be as expensive if not slightly more so. It would seem rather daft to bolt on carbs after going to all that effort to get extra power and torque. Optimum EFI set ups though, i've seen bored out 45mm inlet manifolds, shorter carbon trumpets, 71mm throttle plates used single plenums (twin are pretty rare I believe). I also understand if you "megasquirt" it you can delete the airflow meter. I have a few more questions about the EFI set up: Wasted spark would necessitate using coilpack, fair enough, would a pair of ones from the Zetec silver/black top suffiecient or do I need a specific 8 cylinder one? If I went distributor less on my 3.5 small bearing block then how would I resolve the oil pump problem as the pump is driven from the distributor or would I just remove the electrics, physically leave the mechanics of the Dizzy there and disconnect all the electrics, would that work? Could I just fit a set of OE 4.6 injectors to the 3.5/3.9 EFI inlet manifold to meet the correct fueling requirements and will these be man enough for a 4.6 block, Viper stump puller cam, stage 2 heads + the aforementioned EFI tweaks? Lastly, I heard there were some more twin plenum casting made, so how rare are they and in the unlikely event one did come up then what would they typically go for? Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted April 25, 2009 Share Posted April 25, 2009 I have read this thread a couple of times now and still have no idea what your trying to do Twin plenums are rareish and a giant PITA to set up, often they have wear in the spindles and can be hugely fussy when setting up, for all but the highest state of tune engine the std plenum maybe with a bigger inlet as with mine is enough - JED do triple plenums and all sort of exotic stuff is possible but rarely of 3.5 blocks trippe plenums being for 4.9-5.3 V8s normally along with other stuff inside to match Compression - with a wedge head 9.5:1 is fine 10:1 is often something that may result in pinking with modern fuels, the old 3,5s had 10.5 pistons and a mate races with that and it pinks and rattles all the time, even with compo gaskets which drops compression a tad, my engine has 48mm shortened polish trumpets and matched and ported inlet tract heads and Omega pistons and around 9.3:1 comp and with Megasquirt the dizzy has gone and it just has a shortened dizzy base to drive the pump, and a screw top to keep the elements out You'd do worse than to read BBCs Rebuilding a V8 thread, or the A-Z of megasquirting a V8 thread both have a wealth of info nige Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 25, 2009 Author Share Posted April 25, 2009 Thanks for the info. As to what i'm trying to do well i'll try my best to explain: I want to build a nice V8 that will give bags of torque and power all the way through the rev range. I have a 3.5 block in the garage. Want to rebuild it to a larger capacity. I had a 71mm stroke crank and was going to just overbore, reliner and make a 3.9 out of it. I bought a set of stage 2 heads from e-bay. Wasn't sure what carburation/fuel syetem I should go for so I asked the professionals here as I want to build a very capable engine but for the least (reasonably) possible. I started asking about the EFI system as I have seen lots of references to megasquirting V8's and high performance V8's in general. You answered my question about the single plenum as it is therefore more than man enough for my needs with a high torque engine and from the sounds of things, simpler too Perhaps I should have asked straight but I like to know why too that's how one learns. You guys have done all this before, this is all virgin territiory to me mate. Forgive me but I have enough common sense at least to ask those in the know, albeit sometimes in a roundabout way I'll look up the threads you suggested too, the more info the better. Cheers again. B) Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 25, 2009 Author Share Posted April 25, 2009 Just been reading that thread(4 out of 26 pages that is), the A-Z of megasquirting - that's some serious peice of work, amazingly detailed too. Shame i've got to go back to work. It makes excellent reading superbly informative. B) B) B) Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted April 25, 2009 Share Posted April 25, 2009 ...........I have a 3.5 block in the garage....... Ah one of those projects Serioulsy the 3.5 is very limited and expensive to get the bigger BHPs and Torques from IMHO one of the few sayings from the land of "Hell yeah Boy" (USA ) that is true is that there is..... "No substsitute for Cubes" Thus a 3.5 in the V8 stakes doesn't help. However from a bore / stroke point a view the 3.9 is a great engine and not as prone to liner probs as a 4.6, and a 3.9 low mileage V8 can be had for F all £s. You have decent heads - so they will help, and a bottom end rebulid / clean up with say rings deglaze and a dynmaic balance and decent cam etc will see the basis of a decent engine MS is the way to go IMHO now, I am won over, and esp with any tuned V8 the way you can tweak and tune a otherwise touchy tuned engine is amazing, also the 3.9 is "Squarer" than a 4.6 so will rev higher and freeer although for grunt and BHP the 4.6 wins. Key points whichever engine you go for / build is ARP main and Head studs Decent Steel timing gear / roller chain Composite Genuine Head gaskets Glue the sump on no nasty cork gasket use quality oils, if pre serpentine Valvoline VR1 racing is the baby Decent camshaft - can help if you give idea what your planning power wise new followes and check or repalce valve pushrods New Genuine oil pump drive gears The V8 engine build and the MS thread will do the rest Nige Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 26, 2009 Author Share Posted April 26, 2009 Cheers Nige once again for the additional info and help. B) Most of the last I knew with the exception of the Valvoline oil - cheers for the tips B) For some reason i'm having trouble getting hold of a 3.9 block, you see over here the Tdi'd are the most popular choice of engine, not many people run them. If I can eventually get a 3.9 block for cheaper than a set of top hat liners + the cost of the machine work to fit them then i'll use one otherwise i'll just have to use the AE block I have which is meant to be better (of the 3.5's) to use as a competition block or so, it says in david Hardcastle's book. Anyhow the search will continue. Cams wise I was looking at Real Steel, at their Viper Stump Puller Cam making it's power in the 1500-5500 rpm bracket. This motor is going into a lightweight which is just a tarted up street machine, not a serious offroader but the idea is to keep smart with the mods and squeeze as much power out of her that the R380 box will take so as not to make her unreliable. She will be running no more than 33" tyres on all terrain tyres., and keeping either the 4.75:1 CW ratio or maybe going up to 4.11:1, not sure which yet. I thought this the best all round cam to give a bit of extra oomph without making it too "cammy" if there is such a word. Is this a good choice of cam do you reckon or should I got for something with longer legs? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted April 27, 2009 Share Posted April 27, 2009 All your megasquirt questions answered in Nige's thread in the Tools'n'Fab section Personally I really would not bother spending big money on a Rover V8, especially a 3.5. I'm sure someone such as my mate who breaks Range Rovers would ship you a good 3.9 / 4.2 / 4.6 on a pallet for much less than you will spend tarting about with a 3.5 and then it's fit & forget. A Landy is not an F1 car, you'll lose more power through fitting chunky tyres than you'll gain spending hundreds on bling engine parts. Quote Link to comment Share on other sites More sharing options...
Tony Jones Posted April 27, 2009 Author Share Posted April 27, 2009 Could you ask your mate please what sort of money are you talking about for a 4.6 engine then and how much for shipping to Northern Ireland? Cheers for this + the link. B) Quote Link to comment Share on other sites More sharing options...
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