Anyone used forced induction on a Twin Cam

[bigvalvehead]

Hi all

I am currently working on a turbocharged twin cam

Spec as follows

1900cc , steel 82mm crank, 5.23 BD n/j rods, JE forged pistons

CR 8.5:1 running a T4/T3 hybrid turbo with Megasquirt EFI with boost control and wideband Lambda sensor. Intercooled and water injection fitted.

Has anyone else built a turbo engine running FI?

I built a turbo 1700 motor 30 years ago but the was a suck through system with 2 1/2 inch SU carb so things have moved on a bit since then!!

The engine will drive through a T5 gearbox similar to the set up used by Tom (thanks for the info) but will use a bellhousing made by RWD Motorsport and my own concentric clutch slave cylinder system.

Any experiences would be very helpful, good or bad.

Cheers Dave
26-R-9

[rgh0]

Looks like an interesting challenge - never turboed a twink but thinking about the issues faced in getting a load of hp from a twink I would consider the following

The biggest radiator and electric cooling water pump you can fit would be advisable with maximum possible water circulation rate and maybe some thought of how to best optimise the water flow distribution though the block and head. Maximum oil circulation rate and cooling also needed together with Redline oil - dry sumping would not hurt to achieve all this.

Ceramic coating of pistons tops, valve heads and cylinder head combustion chambers to limit heat into the engine cooling system also would help. Finding a head gasket that will work may also be a challenge at the peak combustion pressures you will be getting. The head you are using better be in good condition before you start - good hardness and not to thin.

Dont know what block you are using but a good check of all the bore wall thicknesses would be needed. I would want about 120 thou as a minimum.

I presume you are aiming for around 230 to 250 hp - not much point actually turboing if not at this level. I dont know what happens to the bearings and crank and clutch at this hp but everything downstream from there to the rear hubs will also probably need replacing as they dont last with much above 170 hp used regularly.

cheers
Rohan

[john.p.clegg]

Dave

That box looks like it's going to be a tight fit???

John

[Galwaylotus]

The biggest radiator and electric cooling water pump you can fit would be advisable with maximum possible water circulation rate and maybe some thought of how to best optimise the water flow distribution though the block and head.

I agree with most of Rohan's comments but have some reservations about the water circulation. There is a point where too high a circulation means the coolant hasn't enough time to absorb or release the heat from the engine. I don't have the calculation but I believe there is an optimum (as opposed to maximum) coolant flow rate to maximise heat rejection. IMHO.

[rgh0]

No disrespect but heat transfer system design has been an area of my professional engineering work for the last 30 plus years and in general terms increased circulation rate is better and achieves a greater rate of heat transfer at the same or less driving temperatures ( LMTD - Log Mean temperature Difference is the technical term for the temperature difference that drives the heat transfer in an engine to the coolant or radiator from coolant to air).

In simple terms 3 things control the rate of heat transfer from an engine to it coolant

1. The surface area of heat transfer - fixed for a specific engine and head casting
2. The average temperature difference ( LMTD) between the flowing fluid and the metal surface - This is relatively fixed maximum for a twink as limited by maximum metal temperatures in the head and minimum and maximum desirable coolant temperatures. Increased coolant flow rates will limit the heat rise in the coolant as it flows through the engine from its allowable min on inlet to allowable max on outlet.
3. The heat transfer coefficient - this is driven by a number of factors but increasing fluid velocity increases heat transfer coefficent all other things being equal. This is due to increasing turbulence (as measured by someting called the Reynolds number) in the fluid transferring heat from the metal surface to the bulk of the fluid quicker and keeping the boundary layer next to the metal surface cooler and closer to the bulk fluid temperature. Strong viscosity variation versus temperature variation in the flowing fluid can confuse this situation as you can end up with better heat transfer coefficent at lower flow rates due to a higher fluid temperature and lower viscosity but that is an abnormal situation and not a concern in a car coolant system design using usual coolant mixes.

Boiling heat transfer adds another layer of complexity and there are situations where lower circulation rates are better but again is not relevant in a car coolant system. Overall not a simple analysis and I shake my head in frustration that university training non longer produces engineers with any understanding of this stuff - they just plug numbers into a computer

cheers
Rohan

[Galwaylotus]

Rohan, thanks for the update. I, too, have been an engineer (for 40 years) but admit that engine cooling has not been one of the areas of my work. As I said, I had reservations, not hard facts. Your explanation has been very helpful
-Bill

[bigvalvehead]

Thanks for input Rohan
The engine is to be drysumped and the head is in excellent condition having been removed from an S4 early in its life and just sat on a shelf in the garage.

When fitting an electric pump would it be best to remove the innards of the original pump and block the bearing hole?

The block is a thick wall AX block so should have no issues at 85mm bore.

The engine from years ago was giving over 220bhp so with injection, intercooling and water injection I was hoping for around 280bhp with pretty mild cams but the torque is what I am really after.

I'll check out the ceramic coating availability in the UK as I intend to get the manifold coated as well.

I'll keep you posted on progress.


The gearbox fits as per Toms detailed post from some time back.

Cheeers
Dave

26-R-9

[rgh0]

Yes i would remove the impellor and shaft and seal plug the hole in the front casing.

Even with a "thick wall" AX block the amount of extra material if any that can be in the walls is limited by the sand casting techniques used and you need to check that the bore is centred in the casting before you take it out to 85mm. Doing an unltrasonic wall thickness survey and offset boring to maximise and equalise the wall thickness I would strongly recommend especially given the meachanical and heat loads you are going to be putting on the block.

Getting the water passages in the block as clean as possible to maximise heat transfer would also be desirable so a very thorough chemical clean to take them back to bare metal is needed.

The high torque aim means very high combustion pressures around twice the original design so sealing the head gasket and the life of your big end bearings will probably be the biggest issues assuming you get the cooling to work OK. You may want to look at higher torque on the head bolts and larger washers under the bolt heads to help carry the loads in the head and keep the head gasket sealing

cheers
Rohan

[bcmc33]

I'll check out the ceramic coating availability in the UK as I intend to get the manifold coated as well.

Check with this company - http://www.camcoat.u-net.com/

I was quite impressed with the range of performance engine work they did when I took my manifold in for ceramic coating.

Camcoat also do a treatment for radiators to improve heat transfer.

[bill308]

I'd like to add that high strength fasteners and hardware be used, especially if higher torques are being considered to handle increased combustion chamber pressures. Larger and thicker and maybe even harder washers could be used for the mains and head bolts.

Does anybody know what kind of peak combustion chamber pressures are seen on a normally asrpirated TC, say with a 10.3:1 static CR? How about a forced induction TC running 10 psi boost and a static CR of 8.5:1?

There is also the question of what to do with the turbo heat? Perhaps a local shield to protect adjacent body surfaces would suffice. I believe engine bay heat is already an issue on Elans?

Bill

[bigvalvehead]

Hi
Just an update on the Turbo project.

The Jenvey injector adaptors arrived today.

They also do a throttle body to the same configuration which would be ideal to FI a Stromberg T/C.

The other pic is of the pattern in foam for the plenum chamber.

I intend to go the Camcoat route on cylinder head and pistons as well as the ex manifold.

Cheers Dave
26-R-9

[S2Jay]

Hi All,

I have not checked if there is a Head Stud kit available for the TwinCam Block, but using Head Studs in place of the standard Bolts may help with gasket sealing. The stress on the threads in the Block when a Head Bolt is being tightened would be removed from the threads in the Block and taken by threads of the Stud, which is typically a higher tensile strength material. This could also allow the use of a higher Torque setting.

Another possibility would be to machine O-Ring grooves into the Block or Head surface. This can improve the sealing effect at the gasket, if the O-Ring matches up well with the gasket. Some years ago, before the improvements in gasket design, there were racing applications with high boost levels that used fine-wire O-Rings on the Block surface against a soft copper gasket. This was usually seen in Drag Race or other short duration use, and was not considered generally practical for street use due to possible water leaks if water passages were not also O-Ringed. Machining all water passages was usually not practical due to space or configuration limitations.

Jay
26 / 5009
______________________________________________________________________________

[Tahoe]

Keeping boost levels at reasonable pressure shouldn't be a problem for the head bolts or for the engine in general. With the right CR, and mild boost, I believe the twincam would do very well. Maybe someone has experience with Turboed Twin Cams can prove me wrong, but in my experience with other engines it's not an issue. If I did a Turbo I would go with fuel injection, and probably a Garrett ball bearing, water cooled center housing, limit boost to around 9 psig max, and do an air to air charge cooler. You could easily get 150-175 HP.

Anyone interested in learning more on how to select the correct turbo should check out this site, http://www.turbobygarrett.com/turbobygarrett/, I also have a few books I can recommend on the subject.

[burgundyben]

Will the megasquirt EFI accept a knock sensor input?

I'd been keen to have a knock sensor in place to ease back on the ignition advance if it senses knock, it might prevent an unfortunate engine disaster!

[rgh0]

Hi All,

I do not know if there are any Head Studs available for the TwinCam Block, but using Head Studs in place of the standard Bolts may help with gasket sealing. ______________________________________________________________________________

ARB make studs - just ordered a set to try - but getting the head off may be an issue as the studs will have to come out due to the chain guide in the front cover

cheers
Rohan