Building a high reving engine

ppyvabw · Post by **ppyvabw** » Wed Aug 22, 2007 10:17 pm

What combination of parts would I need to build a high reving engine, maybe 7000 rpm+What can be acheived on a limited budget.

I can't stretch to a billet crank, maybe able to get fancy conrods and possibly forged pistons, but I'd like to do it as cheapily as possible. Also will be looking at solid lifters and roller rockers etc.. but want a bottom end that can cope with it to.

What parts combination could I use. Sorry if this is a bit of a vague question.

ChrisJC · Post by **ChrisJC** » Thu Aug 23, 2007 6:49 am

Silly question - why do you want to do that? I say that because if you build a bottom end that will do that, then of course the top end will have to breath very well, not something the Rover heads are renowned for....

Chris.

ppyvabw · Post by **ppyvabw** » Thu Aug 23, 2007 7:18 am

Well, its only a 3.9 I'm thinking of building and will also do some work with the heads.

ChrisJC · Post by **ChrisJC** » Thu Aug 23, 2007 8:49 am

I think that the crankshaft is the problem - a V8 needs very heavy counterweights to be perfectly balanced, and it's them whizzing around that keeps the revs down.
In a flat-plane V8, it doesn't have the counterweights (or at least, they're nowhere near as bit), so the bottom end will withstand higher revs at the cost of poor engine balance (same as a 4 cyl), and a lack of V8 burble!

Chris.

Wotland · Post by **Wotland** » Thu Aug 23, 2007 10:13 am

Hello,

If you are interested by high rev engine J. Eales offers an special short stroke 63mm crossdrilled and tuftrided crank to put in 3.9 block to give you an 3.5 engine capacity.

kiwicar · Post by **kiwicar** » Thu Aug 23, 2007 10:33 am

Chris is right about the crank being a major issue, but there are alot of SBC drag engines pulling 10k plus revs and NASCAR engines sit at 8 to 8.5 k for about 500 miles a race, neither use flat plane cranks.
What you need to do is is get the thing ballanced and all the deck heights the same , and all compressions matched, then it is a case of making it lighter (light weight fly wheel) and try to get the reciprocating weight down (light pistons and rods) use a smaller big end Journal on the crank and a rod to match (if you have the money) could look at ebay for 6.1" chevy nascar rods (used) and machine down the sides to fit the rover crank, there can be some great bargins or go for chevy 6" rods and find some pistons with the right deck height. Fancy chevy rods are cheep compared to preping a set of rover ones.
The real issue is to keep the bottom end stable as possable (all of the above help with this) the next bit is to bolt on a nice heafty bottom end brace, or better still make up a bottom end girdle with billet main caps made as part of it (or a cross bolted block).
7000+ revs are not alot for a well prepped bottom end but the real issue here is the top end, the standard head casting cannot suport the necessary flow without needing alot of cam timing, net result peeky engine. You can go to good aftermarket heads like the real steel ones but though these are very good value they are not cheep, however getting the standard castings to flow enough will also be expensive.
A valve train to get this to work can be built, if I were serious about 7k+ then I would go mechanical roller (actually I just did on my chevy build) you can build most of it using chevy bits but this ain't a low cost option (I have just spent £1800 on my valve train and springs etc and I still have to buy roller rockers and I think I bought it cheeply), and you are into changing a full set of valve springs every 6K miles or so.
good luck
Mike

ppyvabw · Post by **ppyvabw** » Thu Aug 23, 2007 11:19 am

But 7K is certainly possible yes? Just got to throw money at it. Is the standard crank strong enough because there's no way I can fork out, what, £2000+ for a billet crank. I was thinking a cross bolt 3.9, and 4.0L crank, then either have the mains machined down, as per, what gav said on another thread I think.

I appreciate the top end is a limiting factor. Was going for mecahnical lifters, roller rockers etc...

Why are the deck heights important and getting the compressions the same. How does this effect the stability/balance of the reciprocating assembly? It's usually something I would over look because I'm lazy.

Lewis · Post by **Lewis** » Thu Aug 23, 2007 11:34 am

Buy Lexus 1UZFE and be done with it. 4 litres, V8, tough as anything. Standard ones will rev happily to 7000 all day long. IIRC the factory limiter was something like 7600RPM on some variants anyway, but I may be wrong there

Post by **katanaman** » Thu Aug 23, 2007 11:35 am

Anything can be done but it takes money and lots of it.

Everything being equal is important because it keeps the engine in balance which it really important on a high revving engine. Your engine will need to be blueprinted to perfection. Not sure forged pistons is the right answer here as they are heavy and heavy is bad when your revving. Depends what you mean by 7K as well. Do you mean running at 7K or changing gear at 7K. The latter is easier (Ian S does this) but running at those revs is going to cost bucks.

ppyvabw · Post by **ppyvabw** » Thu Aug 23, 2007 11:40 am

So what then, hypereutectic pistons?

Maybe I had better set my sights a little lower then. I can't imagine I will run at 7K very often, but will change gear at 7K

kiwicar · Post by **kiwicar** » Thu Aug 23, 2007 11:47 am

Ballancing up the compressions the same means all cylinders fire in the same way and accelerate the crank the same amount, results in less crank whip and less strain on the crank, more stable bottom end. getting all the deck heights the same means as you will be running much closer head to piston clearences and spinning the whole thing very fast means more rod streatch means things start hitting sooner, if everything is matched you can set the whole thing up and know you are not going to get things hitting (and then there is piston to valve clearance to check, if the deck heights are the same you don't have to check all 8, it takes long enough to do 1!).
Remember to get this to work you are going to need alot of cam timming (260 ish deg at .05 on a roller cam more on a flat tappet) and therefor run a high compression (11.5 to 1 at least) hence everything gets closer.
Best regards
Mike

ian.stewart · Post by **ian.stewart** » Thu Aug 23, 2007 1:17 pm

I have run 7k on my limiter on a regular basis, Normally doing burnouts, and only recently after 5 years of giving it big had a not related failure,
The recipe is as follows.
Block, Is a early 3.5 rope seal, non stiff block, P5 wobbly item, linered and bored to 93.5, the history is a bit on an unknown, and may have been done by JEs many years ago,
all fixings are ARP, studded top and bottom,
ARP rod bolts as well, which dictate having the rods checked for roundness, are standard injection rods,
Pistons are Omega flat top forged,
Crank is as far as I know a stock non balanced SDi crank.
Steel flywheel, My preference over a factory item,
Camshaft is a bit of a unknown as its a TWR European touring car item, its mechanical and starts to run out of puff about 6500,
Heads are V8Dev stage 4s ported a wee bit more by a mate of mine. Thet are supposedly TVR race items, but I have never been convinced.
Induction is done by 45mm Jenveys, but I don't think that has much to do with the way it revs.
What is a important thing, is a good free flowing exhaust especially at the manifold,
Well that's just about it, nothing special really, but its held together so far, its out for a freshen up at the mo after the cam gear problem, so a bit more compression is in order, and may even fit a bit more aggressive cam as well

Just a an afterthought, Just after I built the engine, I took the rev limiter off by accident, I missed a gear, and I still have the the event on my old ECU, ----------------------8275rpm

and it stayed together, But I would not like to keep it hanging up there for too long

Ian

ian.stewart · Post by **ian.stewart** » Thu Aug 23, 2007 1:32 pm

Talking about High reving engines, I was talking to a mate last week at Brands who did my porting, He also did a lot of the prototyping on the AJP TVR engine, what he said to me about going faster would be a flat plane crank, as mentioned earlier, and then dropped somthing that has had me thinking, "When I did some of the machining on the AJP, a lot of Rover dimensions were used."
Now I wonder with a bit of tweaking, will a AJP flat plane crank fit in a RV8 block, with a new cam, Mmmmm a 9k rover, now theres a thought

kiwicar · Post by **kiwicar** » Thu Aug 23, 2007 2:00 pm

Hi Ian
"9k rover" and how do you intend to keep your fillings in?
Mike

ian.stewart · Post by **ian.stewart** » Thu Aug 23, 2007 3:32 pm

Do flat plane cranks have an inbalance then

the just rev better, sort out the exhausts, and you could have an engine sounding like a 8 cyl Scoby??