Lee Connor

Hey Guys,

This is a bit of a technical question for a none honda turbo engine, but since its a 80mm bore and 89mm stroke its pretty close to a b18 so im hoping guys with a fair bit of experience can offer their opinion.

Anyway this engine is called a Rover K Series and is a british engine.

My question relates to static compression verses peak cylinder pressures, we all know with E85 becoming more avaliable there is benefits to be had by raising compression to become a more effecient engine.

With the raise in compression you can get to the point of having head lifting issues, normally in that case you would simply put head studs in and clamp it down.

I do not have that option and my head bolts are 16" long M9......to save going over it with everyone multiple times, they cannot be replaced with anything larger or stronger period.



The head isnt the best for flow, similar to a non-vtec LS head.

On pump fuel(93) we make 400ftlbs and 562bhp(8000rpm), using a hx40 turbo with a compression of 7.8:1 and 36psi of boost




We monitor coolant pressure coming out of the head and exhaust manifold back pressure

With that in mind I need to raise this up to 700bhp and the only way i can see this is by raising the compression and switching onto e85.

We dont want to increase the turbo size as the powerband is already fairly narrow and again pulling overlap out of the cams while does help with peak power, massively hurts spool and anything up to 7000rpm.
Due to having 131.1mm rods which means the rod/stroke ratio is awful so while i have been revving it to 8500rpm, its pushing it.

The potential problem with this is that it may lead to an increase in peak cylinder pressure which since i cant change head bolts could lead to head lift issues.

Since this isnt an engine anyone really turbocharged if i need 'off the shelf' pistons my real only other choice is 11.1:1 which is a big increase in compression, this combined with e85 should widen my powerband, also one advantage through is it will allow me to the run the 133.1mm rods, meaning the extra 2mm of rod length will make me more comfortable revving to 9000rpm.

I suppose my question would be has anyone increased compression on their engine and run the same peak torque but suddenly had head lifting issues from the change in compression?

Sorry for the long post but ive spent alot of time researching this forum but of course generally you guys have head lifting pretty much sorted by now.

K7-1Ktrevor

Chance EG

What ft-lb are you able to torque your OEM studs down to? Like K7 said, O-Ring with a receiver groove in the head would be a good idea.

Other option for more power, or at least more spool on the bottom end would be a 100 shot of nitrous. Could either carry it all the way into the upper RPM band for peak power, or go to a larger turbo and then use the nitrous in the lower end to help spool it up.

Not very ideal, but it looks like you're a bit limited on options.

Lee Connor

The liners are ductile and actually just drop in by hand, ive set them 8 thou above the deck surface to allow extra pressure around the fire ring area, which while not exactly the same, does emulate partially the O-ring approach.

The bolts are stretch bolts which are 20nm then 4 x 90 degree turns, looking at the data of them you can probably get another 45 degrees onto them before they risk going from elastic to plastic stretch. the normal 360 of turn normally puts them about 52-53ftlbs.

I would rather not carry the extra weight of nitrous to be honest as im trying to keep the weight as low as possible, but i do understand the benefits from spool and power of nitrous, im not really after a massive amount more torque, we can easily make 450ftlbs at 6000rpm but i would be unable to make that torque at 8500rpm as i will run out of boost before reaching it based on my current setup.



at the moment its around 650kg(1430lbs)

My target is 9.5s to take the lotus record from Kings k20 turbo lotus which if I can get there purely on boost I feel that would be more of a respected record.

K7-1Ktrevor

Chance EG

Nice looking car, very neat.

You don't have any option of getting custom headstuds made? Just something that followed the same diameter/length/thread pitch of your OEM studs, but in a better material?

extremeracer

Wow have never seen an opened Rover K-series engine. It has a fairly unusual block/sleeve arrangement. I'd be worried that with more cylinder pressure you'll start encountering sleeve-shift like the EJ257 Subarus and B-series Hondas which then lead to cracking.

Your 'step deck' method is a good bet, and like the other members have added, o-ringing is your other option. Could you run a thinner headgasket or skim the head to try bump the CR into the 8's ?

What are you using for boost control ?
What are your turbo manifold specs ?
What size turbine housing ?
What compressor wheel ?
Are you intentionally ramping in the boost with rpm ?

I have a fair amount of experience with Holset HX40 turbos so I'm trying to understand your boost curve and possible reasons why you only reaching 36 psi at 7500 rpm. I'd suggest switching over to Ethanol to take advantage of the increased fuel mass and try get the turbo up to peak boost pressure to give you a broader powerband. As a patch you could also inject methanol via a water-meth system to help bring the turbo up sooner and avoid any possible detonation.

The cams look pretty well suited to the combination, as it holds the Torque flat to ~7800rpm

Lee Connor

ARP actually make a headstud kit for this engine, which caused alot of engines to fail.

But once you understand how the engine works you can see why this is an issue.

The engine doesnt have the traditional head bolts and mains bolts seperate like 99.9% of engines.

How they work is the crank girdle is bolted on underneath via m8 bolts around the outside of the girdle(torqued to 20nm)

Then the long head bolts travel down the block, through the girdle and into a 'ladder' that has threads in it, which is held to the girdle with a couple of m6 bolts

You then torque the head bolts which pulls the ladder into the girdle and hence girdle into the block itself and finally head into the block.....basically making a big sandwich.

So this is a compression engine being squished together rather than a tension engine where the bolts are trying to pull itself apart.

The benefits of this is the block doesnt take the load of the cylinder pressure so can be heavily lightened(the empty block weighs 20lbs...really), this is done by the ductile liners and bolts, this is great for NA application(what the engine was intended for) but when you start cranking up the cylinder pressure there will be a limitation.

So with all this your still wondering why studs cant be fitted.

The reason being is when the head bolts are torqued down the mains are out of round, to the point you cant turn the crank, once torqued up the crank can be turned.
By fitting larger bolts/studs you change the torque the mains are subjected to and pull them out of round....easy, you just torque and then line bore.
The problem occurs in that because the bolts are so long they are designed to stretch slightly between the engine being cold and 100c(remember 16" height of aluminum will expand a fair bit) this means if you use stronger/thicker studs they wont expand and pull the mains out of round....if you line bore the engine hot you have problems with clearances when its cold and vise versa......this caused alot of race engines to fail from destroyed mains when people tried to use them(but perfect big end bearings) so this practice was quickly stopped.



you can see how they are assembled and the 'ladder' under the girdle i spoke about

You cannot fill the block with metal to convert it to a tension engine as the block wasnt designed to deal with any real load so there is no strength in it, effectively its only there to keep the water around the liners.

Hope this answers your question

Lee Connor

Mine is the most powerful rover k series in the world(previous record was someone with 470bhp with a rotrex supercharger with less torque obviously) so im in a new world effectly and have to use engines to work off rather than simply asking for a spec and everyone knowing what to put into it(like b18/4g63)

the liners are ductile and arnt pressed in, they can be spun by hand so i doubt they will fail, but potentially the block could crack if the liners are really moving about(i would expect coolant pressure spikes before we get to that level but happy to be educated)

I actually developed with a company in the UK called Omega Pistons a new set of 8.2:1 pistons with thicker rings and friction coating(as thrust loads are bad with 89/131.1 rod/stroke) which may give a little bump in compression but this was more for strength over the heavily machined out NA spec Wossner pistons im currently running.

I use a 4 port boost MAC valve connected to my Adaptronics ecu.
Exhaust manifold is a twin scroll T3 flange with a pair of 40mm turbosmart gates
12cm twin scroll housing
compressor wheel is a 60/86 6 blade turbolab billet wheel with a normal hx35 turbine wheel.....so a 6060 turbo if thats americans view sizing
Yes i was intentionally ramping the boost to maintain a flat torque curve, thats not its natural torque shape, i went for 400ftlbs initially as again thats the most a rover k series has ever seen and i was concerned about head lifting(slowly watching coolant pressure for spikes)

Now as you can see if i let it have the 36psi in the midrange i would imagine it will make around 450ftlbs....at which point it maybe fine with that, it may not, in a 1430lb car with an expected usable range while on the drag strip of 6000-8500rpm im not really looking to chase massive midrange torque.

My concerns are....say we want 430ftlbs which will probably be at about 32psi(compared to 27psi now)....but to maintain that until 8500rpm, i will have to ramp the boost, mirroring the current boost shape(VE was dropping off), but i will simply run out of boost before reaching that high an rpm, now im not scared of boost but im starting to get to the point even at this lower level where the bhp/psi ratio is really dropping off, for example it took 6psi to go from 520bhp to 564bhp(30psi to 36psi) exhaust manifold back pressure for the last 1000rpm of the rev range was 39-40psi for reference.

So while ive developed new mechanical cams with more duration and lift from the current hydraulic versions(280/276 12.5mm from 274/274 11.0mm) and going larger valves and better porting....the overall head gain may only give another 8-10% improvement(as i already have 1mm oversize and porting) while im needing around 20% increase.

Ive thought about meth injection but dont like the cylinder distribution of it unless your doing direct port so would rather stay with a fuel change rather than rely on external electronic addons as such

Chance EG

Wow, that's super weird/interesting. I've never seen an engine that's configured in such a way, thank you for the great explanation.

extremeracer

Thank you for the comprehensive reply to my questions. I've never been a fan of HX40/HX35 Hybrids, as the compressor wheel outflows the capability of the turbine wheel and housing (much like a GTX3076) so you run into backpressure issues before you reach the max flow of the compressor wheel. Switching to E85 is going to exacerbate the backpressure issue as well.

To take advantage of the E85 and bigger cams you plan on switching to, I would ditch the HX35 turbine side and go to a 10-blade HX40 turbine wheel with a 14cm2 housing (I usually run 16cm2) which will give you more flow at high rpm and probably require less boost pressure to achieve the numbers as well. The loss in spool won't be as bad as you may think on paper.

When cylinder pressure is your constraint, you need to maximise the efficiency of the complete setup in order to keep boost and ign timing as low as possible. Reducing backpressure and increasing high rpm VE like you doing with the cams and headwork seems to be the right path to follow. You'll see gains with the switch to E85 even on the current setup, I've seen 20 - 30 kW just by retuning AFR's and leaving ign advance and boost the same.

Lee Connor

Strangely enough I started with a normal 56mm 8 blade hx35, on the dyno we made 428bhp at 25psi, anymore boost didnt make anymore power, turned it up to 28psi and gained nothing, at the time i didnt log exhaust manifold back pressure so i dont know the IMAP/EMAP ratio but I it appeared that i had run out of compressor flow, we hit MBT at 14 degrees.

Then when changing to the 60mm hx40 we picked up 40bhp at 25psi which I thought confirmed the compressor was out of flow, it also showed a reduction in EBP because on the same fuel we were able to run 19 degrees of timing.

There may have been a cross over point where moving to the hx40 turbine wheel again becomes beneficial, im guessing we are potentailly getting to that stage now