What are the good points about am 8.13:1 engine?

#1
I got a random RV8 for a good price - going to use it to convert my Mk2 Cortina. Question is, are there any desirable attributes about the 8.13:1 that would make it a good engine to use in the final build? 3.5's are pretty thin on the ground here and I've been told it's not as simple as a piston swap to make it higher compression....??
 

SydneyRoverP6B

Well-Known Member
Staff member
#2
Hi Rob,

I don't have any empirical data specific to the 8.13:1 engine in 3.5 litre format. I do however have information that is specific to the 4.6 litre engine in both low compression 8.13:1 and high comp format. Whilst it is true that the higher compression engine will deliver a greater maximum power at maximum rpm, it is the torque delivery that is most important for a road car. The low comp engine delivers torque at a greater rate up to peak torque compared to the high comp engine. This means that if your car runs an automatic transmission, it will be more pleasurable to drive as you will require less throttle to achieve the same degree of acceleration. The high comp engines are preferrable if your car runs a manual transmission.

If you decide that you do want to increase the compression ratio, then assuming you don't change the type of head gasket, then changing the pistons is all you need to do to either increase or decrease the compression. It is true that to make the engine tractable, you will need to change the carburettor settings such as needles, and the distributor advance curve will ideally also require changing.

Ron.
 

PeterZRH

Well-Known Member
#3
You can skim the heads (by 0.02" - not sure about more) or fit later heads which can up the CR by 0.6 or thereabouts.

In any circumstances you'll have enough torque for a car as light as a Mk2 Cortina so I'd not worry much about that. What you might want if it is manual is to tune it to make it a bit more lively and willing to rev, there's nowt much beyond 4000rpm. That's just to make it more fun to drive if not necessarily much faster.

I'd say it's probably the least desirable for a conversion but if it's in good order and the price is right.
 
#5
You can skim the heads (by 0.02" - not sure about more) or fit later heads which can up the CR by 0.6 or thereabouts.

In any circumstances you'll have enough torque for a car as light as a Mk2 Cortina so I'd not worry much about that. What you might want if it is manual is to tune it to make it a bit more lively and willing to rev, there's nowt much beyond 4000rpm. That's just to make it more fun to drive if not necessarily much faster.

I'd say it's probably the least desirable for a conversion but if it's in good order and the price is right.
Thanks to all - the car will be a cruiser with an auto, rarely see above 4K RPM, so you guys make it actually sound quite a good fit! The price was definitely right, all I had to pay was freight. I've put the engine on a stand and degreased it - there was a fair bit of dirt and grease on it, but I've been told it was a decent runner before a cabin fire killed the donor 10 years ago, and it's been in dry storage since then. Looking forwards to making it fit!
 

jp928

Active Member
#6
You can change CR simply by changing pistons . In my experience (8.13:1 CR Rangy) the low cr engine is pretty much unstallable - aided by a heavy flywheel - very good low end torque. The 9.25 (or 9.35) engines have their power curve moved up the rev range somewhat, but they are much better than the low CR engines in revvability (is that a word?). Have had a 9.35 Disco 3.9L, currently a 9.25 4 speed P6B. On an auto the low CR should be good. Would suggest an SD1 front cover with its larger oil pump, and SD1 heads.
 

colnerov

Well-Known Member
#7
Hi, As further info, depending what the engine came out of you might find a venturi restrictor between the carb and inlet manifold which can be discarded.

Colin
 

cobraboy

Well-Known Member
#12
It's the model with the flapper injection...but that's coming off as it's incomplete and I hate computers.
The very nice folks at Emerald in Watton, Norfolk specialise in EFI, and ECU's and lots and lots of wiring that make cars go whizz whizz fast. But I did impress them when I turned up with a car fitted with a carb, had a screwdriver in my pocket, and the motor made 270 hp !
 
#15
We're fairly regular visitors to Anglia. Family in Attleborough & friends in the Ipswich/Southwold corridor. Frequent visitors to Norwich too which we are big fans of. We had a few nights there week before last, holiday & stock-hunting.
 
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