I've bought some 136mm long rods to go with my cosworth slipper pistons. What genuine benefits will I see over standard rods on a modified yb. What will it rev like and what bhp gains could I see.

 

if on the std 90.8 mm bore you will still only be a 2 litre so no increase in capacity..

I dont know if there is more power seen from this but i run this set up for about 5 years and was between 540 hp and 640 hp in the end and it certainly revved more freely than a std set up and the bore wear is noticeably better as the pison doesnt come as far down the bore..


cheers danny

 

Cheers Danny forgot to say .75 over size bore too.

 

Rod length is predominantly about optimising piston dwell time at TDC. This is largely related to piston speed which is a direct function of crank stroke and rpm.

On a YB a long rodded engine on std stroke will give negative benefits below 7000rpm. This is due to a reduction in engine torque at lower rpm with no benefit at 7000rpm.

By 10,000rpm there is a benefit due to the increased TDC piston dwell time allowing more effective use of the available cylinder pressure by preventing excessive piston acceleration and descent ahead of the available cylinder pressure.

Edited to add these are my optimum rod ratio against maximum engine rpm for std stroke YB: (i.e these will give the best overall torque spread for that rpm of operation)

up to 6000rpm: 1.5:1
up to 7000rpm: 1.6:1
up to 8000rpm: 1.7:1
up to 10,000rpm 2.0:1

 

Why were they used in a wrc engine then when it was a massive torque engine that didnt need to rev high??


And my own engine that was 600lb ft of torque at 4.8k had peak power by 7.4k and it worked very well ??

The less bore wear i take it is down to rod angle and less piston movement in the bore??



cheers danny

 

I genuinely can't comment with certainty about the WRC engine configuration as I don't know what their development issues were. Development it usually necessary due to issues found during testing that were not forseen during the design stages. Whilst many would wrongly assume that increasing rod length was for a power gain, I would suggest it was more a function of reducing bore deformation due to the higher compression ratios, 102 ron fuel and high cylinder pressures used to optimise the engines restricted power output.

I would speculate that the reason they started to use long rods was not for reasons of best power output (because as Ive allready said a lower rod ratio gives best bottom end torque) but because it was a means to an ends for making the engine more reliable. This is not something that applies to the average cosworth owner because bore distortion is'nt actually an issue for what Id deem a conventional cosworth spec engine running on pump fuel.

 

I agree what you say there probably makes sense but i can assure you as iv used them now on a couple of engines that they make great torque and hold on to the torque longer in the rev range..

I had a 530 hp motor that had ruined its bottom end after a good life and put the whole top end on to a long rod short piston bottom end and then re dyno and we found that it made better torque and held on to the torque just over a 1k more up the rev range and peak power was a little later too..

I under stand the higher cr would of helped also but it was just a better engine after this in every way..

I can say after seeing them in use on a few engines too that the bore wear is deffo better and imo is a worth while upgrade still..



cheers danny

 

I don't know what benefits are yet as I've not run engine in yet I will see when its all running. Cheers

 

danny you must have been running some boost fot 600ft lbs

 

It was when i changed my inlet cam for another one i had made that i went from 580 lb ft to 605 iirc..

It was peaking at 35 psi and held 31-32 at the top..



cheers danny

 

just sounds alot to me .i never got that sort of torque ,with what i would imagine was simular boost

 

What turbo were u running mate and what cams. Bloody hell that's impressive. I'm building mine for drag racing not the road

 

what times you aiming for?

 

I did an 11.8 with 320bhp and road tyres. Got rear suspension and drag radials now so hoping for tens regular no reason why not if its a strong set up and not laggy.

 

well what power are you hoping for now to get in the 10s

 

I think it should do 450ish wheel power depending on boost. Had 398whp with a 34 but never raced it so should see 50 over that with engine spec now. Car only weighs 900kg and is set up for the strip so no reason why not.

 

with 398whp you should be in the 10s on slicks no probs,even with 398atf which is what i think you ment you would be low 11s

 

It had a big port big valve head a custom ball bearin twin scroll .82 ex housing t4oz turbo,8 55 lb siemens f88 life racing ecu

The same spec long rod were talking about with cosworth pistons seanz long rods grp a light weight crank and 8.4 cr

642hp and 605 lb ft the cams were 288 inlet with 474 thou lift and 280 ex with 416 thou and solid lifters..

It was awesome!!


cheers danny

 

arhh theres the answer ,higher comp and less revs explains it ,mine was 7.5 comp gt35r 1,06 ex capped to 8800 rpm

 

that's some special bit of kit what car was all this in.

 

It was in my ex works grp a escort cosworth with a big mix of either grp a and wrc parts all over it and rear wheel drive with a tko 600 box and 9 inch diff..front cover of performane ford and 10 page pull out november 09..

Now over 100 kg lighter as every outer panel is now carbon kevlar and now aiming for a 2.3 tall block 750 hp motor..

I now have seanz sequential box with pneumatic shifter and geartronics paddle shift steering wheel..complete with full wrc front and rear ends


It will be a serious car when finished and i will be entering some competitions next year when all finished




cheers danny