Originally Posted by DazC
Originally Posted by Garage19
Using the specs for the cvh 1600 i could find off the net I have worked out the rod ratios for both engines
CVH 1.65
zetec 1.58
As you can see the ratios are not all that different!
From this we can see that the cvh may have slightly lower piston / bore side loading, but bore wear has neve been an issue on a zetec so no advantage there.
Rod length can effect cylinder filling at different rpms and there for ignition advance figures and camshaft choice and will also effect torque characteristics, but the difference between the cvh and zetec rod ratios will simply not have that much of an effect.
As for bore wall thickness... if zetecs are not cracking bores at 400 bhp i cannot see it being that much of an issue. Bore flex and cracking is not simply effected by bore thickness. I think you will find block design and structual rigidity is has a lot to do wih it!
I got 1.66 for the 1600 CVH and 1.55 for the 2000 Zetec.
CVH
Stroke - 79.52mm
Rod - 131.9mm
Zetec
Stroke - 88mm
Rod - 136.2mm
I agree that the cylinder dwell will not have that much of a detrimental effect at TDC but it can still have a difference. The Zetec is drastically helped with the reduced dwell time at BDC in a turbo application.
What are your views on adverse acceleration/deceleration (and thus increased loading/stresses) on the pistons/rods at TDC and BDC?
The block thickness was inspected by Karl Norris while he was at Jaguar. He disected a CVH and Zetec block to compare them. I don't have the exact figures but I remember at the time the CVH was around 1 point something mm on average thicker than the Zetec.
Bearing in mind, the Zetec is a CVH with a few modifications and a 16v head, the Zetec should technically be better although if I was to build one, I personally would like to ditch the crank and rods for something more like the CVH rod ratio, or maybe even higher.
P.S I was only naming 1 aspect where the CVH is technically superior to the Zetec.
You are right. 1.659 for the CVH. My spreaadsheet was cut at two decimal points with no rounding.
I think you will find the zetec one is right for the later black top engine. They have a longer rod and shorter piston deck height than the early engine. The h beam rods and forged pistons that i use are from the states and out of the later engine. They go straight in the early engine and give it the same rod ratio so that was the specs i used.
The smaller rod ratio of the zetec makes my life easier when it comes to mapping a turbo converted one as it means that the cylinder pressures are more quickly reduced after combustion and which helps in the fight against detonation
Not sure what you mean by "Zetec is drastically helped with the reduced dwell time at BDC in a turbo application". Could you expand on it for me.
Short rods have a higher axial loading at TDC and BDC so i guess potentially more bearing wear.
Nice to find some one that can back up what they are saying rather than make random A is better than B coments to go along with the crowd!