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Engine re-building for high rpm

Engine re-building for high rpm

Engine re-building for high rpm

Hello guys, pretty wide range question, but has anyone on here been directly involved with taking standard inline 4 bottom ends and re-building them for higher rpm? Someone involved in days gone by with the BTCC(cars were 2.0L 16v and made 300 odd hp n/a) perhaps, or other.

A few pointers as to what Im aiming to find more details on,

Possible fitting of crank ladder style girdles to prevent cap walk.

Adjustment, or complete new choice of cranks.

Cylinder bore wall stabilisation using either sleeves, or by grout filling part way up the water jackets.

Bearing choice,

Con-rod choice,possible pinning of big end caps,  and treatments>(could get involved so skip if needs be),

Piston choice, skirt treatments, ring details,

Possible reduction in size of journals to reduce friction, /surface speeds although I know most exists at the rings.

Block in question is a cast iron European block, Inline 4, not lined, two bolts just per crank cap.

Factory limited at around 7000rpm,

Looking to up that by 2000rpm and get it to last for more than 2000 miles on the track.

I have A LOT of studies done, but I just wanting to hear others views, and not really looking for a do this do that list. Just whatever comes into your head that maybe overlooked.

Thanks in advance,


RE: Engine re-building for high rpm

That's a lot of questions.  If you were here in Socal, face to face, I'd be happy to sit down for a few hours...not here.
Perhaps some of the other members are up to it, just not me...sorry.
I can say this much---

Making a 1275 Mini Cooper put out a reliable 150+hp at something less than 8000rpm for around $15k to $20k, a 1600 Lotus twincam (two valve) @ 200+hp around 9000rpm at $40k or, a Cosworth BDA varient (1600-2000cc) up to the 350 hp NA or 750 hp turbo for $50k and up (waaay up in some cases) is all doable, it's been done by me and many others over the years.

'Course, you can do it cheaper, I'm told...I've watched them blow up in front of me on occasion! ;o)


RE: Engine re-building for high rpm

Evelrod, thanks for that, shame Im not nearer you, your one of the few 'interweb' guys Id like to meet. I know its a daunting question, but from the yrs your at it does anything come to your mind thats not ''mainstream'' information as it were rather than a long list? Perhaps something that is not often mentioned or over looked?
Im not trying to twist your arm to talk, so if Ive put you off already I fully understand!!
Ive seen some pretty expensive engines blow up too, as well as the not so expensive ones...



RE: Engine re-building for high rpm

I'm thinking the details will vary widely depending on exactly which engine we are talking about here. Different engines will have different weak points. Generic question means generic answer.

Lightening everything that reciprocates, stiffening valve springs and selecting cam profiles that give consideration to the valve accelerations, thinner piston rings that are less subject to fluttering, balancing everything, etc are all given. Some engines need lighter cranks, some need stronger cranks. Some engines need lighter rods, some need stronger rods. Some need more oil pressure at high revs.

RE: Engine re-building for high rpm

Narrow it down, Brian.  Give us some specifics and perhaps we can do more...No two engines are alike...E.g., my Mini Cooper has a three main bottom end akin to a string of spaghetti and needs all sort of strengthening, in the case and crankshaft.  Some of the pros are using 10,000 rpm for short periods and 8400 regularly with no problems.  No one is bragging about hp, but I've seen 127 hp at the wheels from a 1380 cc and that may not be the best, either. All this in a 1400 lb car!
Our Lotus 1600 is at 197@8100 for a very reliable 1800 lb. vintage Lotus Cortina race car. It needed only a billet crank and billet main caps to make it safe to 12,000 (should one need to do that).  On the other hand, my current build, a 1953 Ford flathead would need a complete girdle, billet everything and still would NOT be reliable much beyond 6500 rpm.  We are hoping for 200 hp from 250 cu. in.---That may prove to be wishful thinking!

I'm retired, many years.  That gives me a bit of leeway so that I can pontificate a bit.  Still, no specifics unless you ask a specific question.  All this is readily available in multiple publications and web sites. You will never get the answers you want unless you ask the questions we need!

Here is something phenomenal---



RE: Engine re-building for high rpm

Very generally speaking as every engine does in fact have it's own weak spots.

1) Forged pistons, possibly with:-

   a) Anti scuff coatings on the skirt.

   b) Insulating coatings on the crown.

   c) Oil rejection coatings on the bottom or crankcase facing surfaces.

   d) Extra thin low tension rings.

   e) Maximised quench pad area.

   f) Minimum piston to head clearance.

2) Forged steel crank, possibly being:-

   a) No twist forging.

   b) 4340 ? Steel

   c) Tuftrited or nitrited.

   d) Lightened by reducing counter weights and hollowing big end journals.

   e) Rifle boreing the main journals.

   f) Increased radii on the journals.

   g) High level of polish in the journals.

3) "H" beam connecting rods from premium supplier like Carrillo, possibly being longer than stock.

4) Steel main caps, possibly with extra bolts into a strong area of the main bearing web or the block near the outer surface of the water jacket to spread the load.

5) A full girdle similar to many Hondas or Nissans or some Toyotas.

6) A cast aluminiun sump designed to reinforce the girgle like on some very new model Hondas of about 1 to 1.6 litres.  

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RE: Engine re-building for high rpm

Brian, points noted, thanks for that. perhaps my pictures will add more info to my first post.

Rod, more, its a 5 bearing crank, 8 counterweights, poor cap structure/surrounding material. The lotus sounds impressive, must be a good block from word go eh?

'' All this is readily available in multiple publications and web sites''

Thats the thing, Im wondering if it actually is though. Ive read most of all I can find on the net. There seems to be a gap in a lot of forum talk as to making ''high'' power/rpm, everyone falls short by about 80hp. Its is this 80hp that I feel is where the extra bit of knowledge comes in, often kept, I suspect, secret by the original 300hp guys.

Pat, your post is a good one, straight off I see the type points Im after,

''hollowing big end journals''

''Insulating coatings on the crown''

''Rifle boreing the main journals''

''Increased radii on the journals''

This being another below, you will see in my picture of the block studies Ive been doing that here lies the biggest issue. Therefore, a ladder style girdle seems a good option. To be fixed onto saw off/milled skirt, level with crank centre, and cast alloy, c/w integrated caps.

''Steel main caps, possibly with extra bolts into a strong area of the main bearing web or the block near the outer surface of the water jacket to spread the load''

On the rings Pat, do you think just 2 would suffice if used with a dry sump vent regulated oil system? Obviously bore flex would effect things, but Im confident jacket grout, poured in two layers using the dry sand method would combat a lot of this, and indeed dampen bores in general.

Another point, The sump could be integral with the girdle Im sure.

Id like to hear peoples opinions on reverse cooling too, something I mentioned on a forum a while back that got 0 response. I feel it important in keeping the top section of bore cooler for reduced det.

See pictures of cap details, I dont know if/how I can insert more than one per post, so Ill post a few below too,

Thanks to all so far, and remember, it is a slightly random 1st post, but maybe someone knows something that has not yet being mentioned.



RE: Engine re-building for high rpm

"a ladder style girdle seems a good option. To be fixed onto saw off/milled skirt, level with crank centre, and cast alloy, c/w integrated caps."

If you mill the skirt off how are you going to attach the girdle to the block? There won't be much metal left to attach to the outer wall of the block. One option I have seen is milling the bottoms of the caps even with the skirt, then you can fit a flat plate and secure it with all the oil pan and main bearing bolts.


RE: Engine re-building for high rpm

I'm not sure what books your reading, Brian.  I must have read all the wrong ones, 'cause everything you need is in them.  Yeah, you may need to actually "go to a library"...Another good source of "hot rod" tech is the multiple catalogs of various speed equipment mfgrs, much of them "on line". Even Hot Rod...I've been a subscriber since the 1950's...Two rings, reverse cooling, gapless rings, skirtless pistons, composite blocks, pistons and, rods, everything that's been tried, good and bad, are there for the effort.










These are just a SMALL part of what is on my "bookmarks"...I have accumulated a great deal of knowledge from books. Not all, mind you, but a great deal.
I have "apprenticed at the feet of the masters" as the saying goes.  Sure wish I had paid attention!

Thanks for the good words on our Twink...Actually, it's pretty conservative, kinda state of the art 1980ish...I have seen almost 220 from the same engine with much more aggressive camshafts and Lucas slide-throttle injectors.
It really is pretty much "straight forward" stuff, no magic.

The photo is of the "old" wet sump Twink bottom end...new one is much the same except dry sump with a multi plate 5" clutch and "flexplate" flywheel.


RE: Engine re-building for high rpm

Very general ideas.

High speed requires a very light rotating mass.  You actually want to use thinner bearing surfaces (less friction).  Do not overlook the windage tray/oil "scraper" (Mercury outboards picked up about 10 hp by redesigning their scraper and a few offer things on their new 4 stroke engines).

Of course, you need to start worrying about the top end !

Below is an excellent summary of Ford's new 5.0L Coyote engine (5.0L, 400 hp naturally aspirated).  Lot of good pictures.

RE: Engine re-building for high rpm

That link needs it's own thread.  I doubt it can be linked to the OP's "bottom end" question.

Start your own thread...I'd be interested to see where it goes.


RE: Engine re-building for high rpm

Rod, late getting back on this one, snowed under, Thanks for the links, came across many snippets of said info before, so dont shoot me when I say I didnt read anything that raised my eyebrows. I guess its a combination of everything, a very big everything of course, but exactly that. I guess the links do confirm that it is also just that, and that there is no 'secret magic' involved, just planning, testing, money, and hard work.

Pat, spotted the girdle alright on an s2000 unit I had in for failure investigation, its meaty surely, see picture attached.

Big thanks to everyone who took the time to post.



RE: Engine re-building for high rpm

There two kinds of tuning that are separate activities but intimately complementary: 1) tuning for power and 2) tuning for survival and durability at said power.  You said above, "There seems to be a gap in a lot of forum talk as to making 'high' power/rpm, everyone falls short by about 80hp. Its is this 80hp that I feel is where the extra bit of knowledge comes in, often kept, I suspect, secret by the original 300hp guys."

Girdles and much of everything else fall under #2.  Very important to be sure, but at the end of the day, you can build a bulletproof engine at 9000 RPM but still be 80 HP short of target.

Let's start with some background:  Judging from your description of a European cast-iron I4 block with 2-bolt capped mains, I speculate that you're working with a VW engine.  Good background for me.

To get 300 HP at 9000 RPM naturally aspirated from, say 2L displacement, your engine will need a BMEP at that operating point of just shy of 15 bar, not a short order.  Reading a comparison of contemporary F1 and Nascar Cup engines here:
you see that this BMEP level exceeds both engines!! That is not to say that it cannot be done, but it's not going to be something that can be achievable with just bolt-ons.  Formula 3000 and Super Touring classes have had NA engines in that level.  To get 15 bar BMEP, you need to focus most of your attention first-and-foremost in cramming as much fuel-air mixture in the engine as possible, burning it as completely and efficiency as possible and getting rid of the spent gasses as effectively as possible as well.  Then you need to go over friction reduction with microscopic detail.

Let's look at another important engine parameter.  If my assumption of a VW 2L block is correct, the stock stroke is 92.8mm.  At 9000 RPM, you're looking at a mean piston speed of 27.8 m/s, higher than either an F1 engine at 19000 RPM and a Cup engine at the same 9000 RPM (on account of the shorter stroke).  Indeed, this is even higher than the record-setting 1st-gen Honda S2000.  Running this kind of MPS, no less on plain, uncoated cast-iron cylinders is murderous for tribology and getting any semblance of durability.  You'll want to de-stroke that engine, run a higher L/R ratio than the stock VW engine and run a crankshaft, equal or even smaller than the VW 1.8L's 86.4mm, yielding an MPS of a still-high-but-at-least-not-stratospheric 25.9 m/s.  Larger bore pistons will also permit larger valve diameters, essential for volumetric efficiency and deshrouding said valves.  For reciprocating and valvetrain parts, lightweight and high-strength rule the day; for valvetrain components, stiffness is also important.

You must understand and respect physical limits of BMEP and MPS before you go any further on your quest.

Some engines will never make much power or like revving.  The example of the spaghetti bottom-end of the original 3-main bearing Mini Cooper is a good one.  Some cylinder heads simply have such poorly shaped ports, combustion chambers and valve positions, with so little extra material in the castings to do significant reshaping, that you have your hands tied right from the get-go.  People more experienced than myself will be able to shed light as to whether whatever platform you are actually working with suffers from such a fatal flaw.

RE: Engine re-building for high rpm

The below links to pictures of a girdle for an engine build project for a VW TDI engine in which I'm involved that will see BMEP of 40 bar and peak firing pressures of 225+ bar.  This uses modified OEM main bearing caps, but the stepped girdle rigidly constrains all the caps.  A new iteration will replace the caps altogether with a single piece.

VAG girdles I've seen on offer made of thin sheet metal will do next to nothing to stiffen the bottom-end and prevent excessive main bearing cap movement.


RE: Engine re-building for high rpm

You have wounded me...My poor Mini may never be the same...;o)

Actually, my current "bottom end" is quite capable of 9000 plus should I choose to use it. I've seen 126.9hp/ltr with one of these (not mine, mind you. I'm at 115hp/ltr).

Our twink (Lotus twincam) makes 125hp/ltr but I've seen four valves at the 140hp/ltr level several times, all NA, of course.

I watched a test on a NASCAR engine at 133.9hp/ltr, a Ford.

These power levels are available to anyone willing to work 25 hours a day in testing...there is no 'black magic' anymore.  Just careful, determined and, intelligent engine builders.  All spelled with a lot of $$$$$$ signs, of course...smile



RE: Engine re-building for high rpm

LOL no wounding intended, evelrod.  We're all talking about relative weaknesses in each particular engine, and every one has them.  I don't think anyone perfected an inline engine with fewer mains than pistons, which is why 5-mains I4s are ubiquitous today in mainstream passenger car engines.  

RE: Engine re-building for high rpm

When we scale down to motorcycle engines, >150 HP/L are fairly routine.  By the key is, and my point was, that they still obey the BMEP and MPS limits I described above.

RE: Engine re-building for high rpm

The Forumula Atlantic 4AGEs put out over 240 hp.
That's pretty impressive for a little 1.6 liter but like evelrod said those motors cost alotta money.
9000 doesn't seem like a high mark to me but that may be because of the engines I am more familiar with.
Like people have said what needs to be modified completely depends on the engine.
A 4AGE of any generation could be made to spin to 9k with very little effort or modification though though the earlier 16 valves wouldn't make any power up there without some work.

RE: Engine re-building for high rpm

Without a doubt, the 4AGE is a good engine.  The Cosworth BDA that it replaced was the engine I saw at 250hp, some years ago.
9000 is just a number...my little Mini is limited to 7800 simply because I want it to live longer than just one race.  Our Lotus twink is limited to 8800 for the same reasons even though it should be "safe" to 12000...back in the 80's I came in with the telltale stuck at 10500 (the max) and the engine seemed fine.

Now, what IS impressive is watching a NASCAR V8 holding 9800rpm for hours on end, 500miles plus qualifying and testing...Unbelievable!
Sure, F-1's can pull 20,000 at probably a million bucks each...but a cast iron, flat tappet cammed pushrod American V8 with a single four barrel?  


RE: Engine re-building for high rpm

The RPM can't be considered in isolation from the stroke.

Friend of mine has a Yamaha FZR250 4-cylinder 4-stroke motorcycle, 249cc, with a nominal 19,000 rpm redline. But, the bore and stroke are only 48.0 x 34.5 mm, and if you work it out, the mean piston speed is only 21.85 m/s at that speed, which is well within the normal range.

15 bar BMEP for a normally-aspirated spark-ignition four-stroke engine running on normal unleaded pump gasoline is in a realm that is difficult to achieve.

For an American Nascar V8, no doubt the stroke is somewhere near 3 inches, I'm not sure of the bore and stroke that they are using in Nascar (I don't follow it). If it's 3 inches then 9800 rpm = 4900 feet per minute = approx 25 metres per second. That's near the upper limit of what's normally seen. The remarkable thing in that case is that the pushrod valve mechanism survives and the air going through the two-valve head can keep up with this.

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