tb42 repowering

[y60chile]

Hello!

Im new!!!

Im re-powering my tb42 (have discard change engine for the moment - got a vh45de stored until i have the time.. and money ).

So...the thing is:

TB45 pistons and rings (first overbored size - dont remember size).
Crower camshaft (product number 61392) (has been bought, but not yet received)
Crankshaft + other stuff balanced.
head shaving and block decking (???)
Brand new Nissan president carb (650CFM) with K&N filter (in process)
Pertronic Electronic ignition (done)
headers (done)

Whole price: US$1700

The questions is....
How much must i shave the head or deck the block to get 9.5:1 compression ratio or maybe 9.8:1?
Its necessary to deck the block?

Thanks from chile!!!

Chris

[Brett S]

I am also keen on boring out 4.2 to 4.5. (96 to 99.5mm from memory).
My question that noone could answer was whether the block was thick enough to go out the extra 3.5mm.
I believe the conrods are the same length and the combustion volume in the heads are the same in 4.2 and 4.5 therefore the 4.5 piston will have a deeper dish than the 4.2 to have the same compression ratio.
Also im lead to believe the deck height is the same on both blocks.

[y60chile]

I am also keen on boring out 4.2 to 4.5. (96 to 99.5mm from memory).
My question that noone could answer was whether the block was thick enough to go out the extra 3.5mm.
I believe the conrods are the same length and the combustion volume in the heads are the same in 4.2 and 4.5 therefore the 4.5 piston will have a deeper dish than the 4.2 to have the same compression ratio.
Also im lead to believe the deck height is the same on both blocks.

Hello!

I have seen the manual and the conrods are the same, the volume of the chanber too. The main differences that i have notice between engines are the Pistons, TB45 has jets to oil the pistons and the carter is different (smaller, but has "the thing" to prevent the oil from waiving).

I havent take the head so i have not seen how much the head could be decked. I really prefer to shave the head instead the block.

3.5 mm decking?
Its estimated? or have you calculate that with real values (chamb volume, bore, etc).

Greets
C

[y60chile]

I am also keen on boring out 4.2 to 4.5. (96 to 99.5mm from memory).
My question that noone could answer was whether the block was thick enough to go out the extra 3.5mm.
I believe the conrods are the same length and the combustion volume in the heads are the same in 4.2 and 4.5 therefore the 4.5 piston will have a deeper dish than the 4.2 to have the same compression ratio.
Also im lead to believe the deck height is the same on both blocks.

Hello!

I have seen the manual and the conrods are the same, the volume of the chanber too. The main differences that i have notice between engines are the Pistons, TB45 has jets to oil the pistons and the carter is different (smaller, but has "the thing" to prevent the oil from waiving).

I havent take the head so i have not seen how much the head could be decked. I really prefer to shave the head instead the block.

3.5 mm decking?
Its estimated? or have you calculate that with real values (chamb volume, bore, etc).

Greets
C

Ahhh, the pistons are equal... only the diameter change... (have seen couples of minutes ago on the manual)

[PGS 4WD]

I used to buid a lot of 308 holden engines and to get the comp up without sacrificing the deck or head (too much milling makes them flex and head gaskets blow) I used to offset dring the crank about .015" and use .020 bearings.

You could get longer rods made, this would be the best solution as piston Dwell at TDC increses meaning more torque, about $2000 AUS though.

Am making such mods to a turbo TB45 but with relocated pin height on piston to keep the comp lower and forged pistons.

Could also get the chambers welded up and reshaped, making sure to not shroud the valves however.

In regards to thickness, many engine shops have ultrasonic testers for bore thickness.

Personally I think the TB45 gains are from the head which has far larger intake ports and intake manifold design with a larger camshaft, thin bores flex and cause poor ring seal, oil consumption, low power and high blow by. Be careful.

Joel

[Brett S]

Yes but if they are the same castings the bore wall thickness would be fine for 4.5L (3.5mm o/s) or you could prob get o/s pistons for the 4.5 and get it out to 4.6 or so and that should be instantly 10% more capacity and therefore 10% more power.
I am assuming they are the same casting as the motor was designed for the 4.2 diesel which requires thicker bore walls for the higher compression which is why they could go out to 4.5 for the petrol but not the dirty diesel.

[PGS 4WD]

I am fairly sure they are not the same casting as there is a major rework of the oil galleries, the TB42 runs an external pump (chain driven on the driver side) and the TB45 is driven off the front of the crank, the timing case is not interchangeable as there are different galleries to accomodate the new pump location.
10% in capacity is no assurance of 10% more power as the valve lift and duration has to be increased to allow the additional air volume time to fill the larger cylinder.
If that were so 6.0L LS2 engines would be all +400kw as there are a number 3.0L European cars that make +200 kw
With the same cam lift and duration a larger engine will make some more power but also lower in the rev range due to air flow dynamics. Thats why big power engine have big camshafts that make crap torque at low rpm. Its all a bit technical but basically the valve overlap that is a byproduct of long durations (required for the air to have time to fill the cylinder at 7000rpm) mean that the dynamic compression of the engine is low at low rpm, both inlet and exhaust valves are open at the same time as the piston approaches TDC and the actual running compression is lowered, effectivly like shortening the stroke, this is also why you put higher compressions to larger camshafts.
Hence why manufacturers are moving toward variable valve timing, the best of both worlds.

Joel

[Brett S]

Yes i agree you won't get exactly 10% more power from the 10% capacity increase, the point was trying to make is if capacity increase is available safely go for it as it is free power.
I haven't seen the 4.2 or 4.5 apart so wasn't aware of different oil circuit differences but would imagine it would just be a machining difference or slight pattern change to suit. As for cyl wall thickness finding a definate answer (without being able to take block for ultrasonic) as to whether there is the same amount of material for 4.2 vs 4.5 is all that is needed to know if a safe option.