hlee96

Now that an Euro hybrid may be in the cards for me in the near future. What is the expected gain from a 5.0L 85-86 short block with euro S top end? How much more than a 4.5L short block? Would a 5L hybrid produce same, more, or less power than the original euro S 4.7L engine?

Reason I want to ask the experienced people (many threads regarding euro hybrids), is that I have my original 4.5L bottom end cleaned, but with possible availability of an used 85-86 5L short block from 928intl, will the expected real gain in HP/Torque worth the cost and effort?

Danglerb has mention that a 5L hybrid really just needs the pistons fly cut to accommodate the valve reliefs.

Ducman's dyno shows 250hp/280tq at the wheels (so ~290 crank hp).

Thank you for any and all advice.

Ducman82

that was an old dyno run. i hope to have a new one soon. i was getting way higher at the wheels last time (did not keep the log).

GlenL

Like 30 HP. And you have to remove the pistons, notch them, and replace them.

Ducman82

and the notching , from what i gather, if you want a non interference motor... it does not "have" to be done

XS29L9B

I thought this was about the *other* hybrids... Like mine, which burns gasoline AND rubber

mark kibort

thats euro stock vs euro 5 liter hybrid? generally, i think most of the euro 4.7s are in the 270rhp range, correct? a

Ive done more than most and all of them have got the same 40hp over the US with euro stuff on them (but US heads)

it non uncommon for most to get from 290 to 310rwhp.

I think the last one i built was dynoed at 319rwhp, and that was with the US 4.5 CIS system on it, with all euro stuff on an 85 5 liter bottom end. (notched)

mark kibort

it will always be an inference motor, as you cannot get the near .3" valve cuts in the 5 liter piston. (not enough material to match the euro 2valve early piston)
if you do it, and you should , you end up with .3" valve to end of valve pocket, clearance. if you dont do it, you only have about .15" of clearance before the valve can hit the piston. not a lot of room. kind of worth the insurance.

Ducman82

good to know. i have mine notched. did we ever figure out with the notches what the CR is?

GlenL

It'll be slightly less than the straight multiplication of the displacement. The 4.7l Euros are accurately spec'd at 300BHP for 4.7l or 63 per liter. 0.5 liters more will give 30BHP.

My opinion is that it's not worth the costs for a street car.

V2Rocket

has anyone actually tried using 944 NA pistons for this type of motor?
pre-cut 2v reliefs, 100mm bore, it'd sit 2mm down the hole for extra clearance, it would only give you about 8:1 compression (so you could run the cheap gas ) and/or go nuts with ignition timing.

mark kibort

on an AFM version of the euro , its 250 rwhp... on a euro 4.7 with MAF or CIS, i think ive seen 265 to 275 on the high side. so yes, there are larger gains with the US components going to the 5 liter. IIN fact, another data point , is all those components on a US 4.7 , sans the heads, gives 240 rwhp. seems to be about 10hp less for the us vs euro heads..... no other changes.

the bigger displacmement might leverage all the larger ports better (TB, runneers , valves) etc. now, since you have seen 4.7s run 270rwhp. the engine I built that was put on the euro CIS, did 320rwhp. thats a 30 to 40hp gain over the euro 4.7. I dont know of any euros 4.7s that produce more than 275rwhp, do you?

both of my afm versions of the 5 liter euro made 290rwhp.

the notches dont do much for the compression. only 2cc for the both of them
CR ends up to be a pump gas level near 10.7:1

i cant remember our outcome of that evaluation, but it wasnt worth the effort, due to the CR and the need for a different rod. (i think... cant remember).

notching the pistons was a 400 dollar mod for all 8 at the machine shop.

V2Rocket

I'm sure you had your reasons, but the rods are the same length, pins and bushings same size...no reason the piston shouldn't physically fit in there.

But the 8:1 CR may be a deal-breaker for NA street 928s.

mark kibort

well, one of my reasons was one of many!
1. yeahhhh, 8.1CR is no bueno
2. I already have the pistons that came with the block, and 400bucks for mods, is cheaper than 2 sets of used 944pistons i would imagine.

GlenL

Yes, mine does. 284 DJHP a few years back. It may be more, now.

You've gotta compare straight-up. For JUST the displacement adder, it'll be ~30BHP. A bigger engine will add to the value of exhaust mods or porting and other air-flow improvements because it's nearing the limit of what the stock engine has. It's simple mat, really, as the key to engine output is volumetric efficiency.

danglerb

What I've always heard is that the stock Euro S bore limits the intake valve flow due to shrouding, which is reduced with the larger bore of the 5.0L, and results were consistently more on the 45 rwhp side than 30 rwhp predicted from just increased volume.

Regardless of which end it is, where are you going to get 30 rwhp for the cost of a 85/86 short block and $400 in machine work? Porsche doesn't have a lot of low hanging fruit, pick all you can.