Destroking

minorv8 · Post by **minorv8** » Mon Jan 15, 2007 9:32 am

Since everyone wants a stroker I have certain interest in destroking a 3,5 litre engine. I would only have to get around 69,5 mm stroke with std bore. If I offset grind the rod journals, what is the absolute limit in terms of reliability and strength of the journal ? Any ideas ?

kokkolanpoika · Post by **kokkolanpoika** » Mon Jan 15, 2007 10:53 am

I think i read somwhere that wild cat use +45mm journals of their ??-90mm+ stroker crank? Not sure is this true?

HairbearTE · Post by **HairbearTE** » Fri Jan 19, 2007 12:14 am

A common practice in the states now is to use the smaller rod journal of the honda engines. I think its around 1.89" but dont quote me on that! i'll have to check. the main reason for using these rods is the move towards reducing bearing size and thus reducing the overall friction in the engine. Obviously a little strength is lost but they are doing this in sbc'c and bbc's so i'm sure the rover with its much smaller output could handle it. Another reason for this mod is to generate a little extra capacity but it could be used to reduce stroke as well of course. The reduced size of the rod journal on the honda spec rods will also mean the rod weighs less which will be helpful if you're spinning high revs (why else would you be de-stroking?!)

Wotland · Post by **Wotland** » Fri Jan 19, 2007 8:09 am

Hi Here,

On old forum I have opened an topic about machining blank crank :
http://www.v-8.org.uk/snitzforum/topic. ... ,machining

Myself I study the idea to use Nascar/Honda rods journal size 1.88" and Clevite CB1456P bearing or with Clevite CB1664H bearing will allow them to be used on a 1.850" rod journal.

Many stroker kits on SBC use this size of rods journal size. Also it offers the possibility to use Nascar rods aviaible in all sizes.

I think Ian Richardson uses also this rod journal size on some stroker cranks to avoid interference between rods and cam lobes.

But as I know only with forged crank. So I don't know if SG crank are enough strong to accept smaller rod journal size like Nascar/Honda.

Cheer.

minorv8 · Post by **minorv8** » Fri Jan 19, 2007 3:40 pm

Actually no high revs. It´s all due to our silly legislation: we are allowed to increase the capacity of the engine by 25 % compared to the largest engine within the model range. This is a modification that is a simple MoT approval thing. More than +25 % means one has to get a permission from DoT which is very very complicated nowadays, bordering on mission impossible !

The victim is a Opel Commodore GS with a 2784 cc inline six. Apply the magic +25% rule and you get 3480 cc. So, destroking to 70 mm with std bore OR fitting 88 mm pistons with std stroke achieves this. Either option is going to cost. I believe nascar rods have 1,888" big end, I do have my eye set on them.

Post by **katanaman** » Fri Jan 19, 2007 5:52 pm

there is a post doing exactly what you want for the same reasons over in the old forum so have a search there. I cant remember if there was a happy outcome or not. How do you prove that you have reduced the cc or is it just on your say so?

minorv8 · Post by **minorv8** » Sat Jan 20, 2007 7:36 am

I doubt that MoT person would accept the engine size based on "honestly officer"

One needs to supply documented proof, e.g. a record of stroke/bore measurement from a machine shop doing the work. Like I said, a bit silly since the increase in displacement is around 27 % instead of the 25 % allowed.

When I did the Minor conversion (not actually that minor...) 1997-99 I got an approval from DoT. It only took 6,5 months or so. They were not that excited about the idea of replacing the trusty 948 cc with something BIGGER. Anyway, the engine code was recorded in the files during the actual MoT and I had a document from Land Rover UK that a 92 hp V8 engine actually exists. Due to changes in legislation similar V8 Minor conversion is nowadays impossible to make legal.

Post by **katanaman** » Sat Jan 20, 2007 4:06 pm

it might actually be easier for you to replace the liners and use a smaller bore. It could mean you only have to replace the pistons where the crank route could mean changing crank, rods and pistons. Alternative could be to source a Stag 3.0 V8 but then your down on your cc.

minorv8 · Post by **minorv8** » Sat Jan 20, 2007 8:06 pm

Or Tatra air-cooled V8´s or Daimler Sp250. Sadly they are not that plentiful whereas Rovers are quite easy to locate. New liners are indeed cost effective solution. Oh boy, inline sixes make lovely sound but V8s even better. It is indeed worth all the trouble !