Question:
I have rebuilt my engine with all the same parts and now have got 25bhp less, what could be the reason?
Answer:
One tiny thing could change the characteristics of the engine causing the bhp loss.
Certainly when we are testing and designing engine kits on the dyno, it is important that only one component or adjustment is made for each test otherwise the results will be confused.
—Is the engine exactly identical in every single way.
—If you have changed anything, e.g. cam timing, air filter, air horn length, cylinder head design, all of these will affect the performance of the engine and sometimes components that you have been told work better, need to be proved on a single test.
—If you have a combination of changes, some might give a loss, some might give a gain. Sometimes the results would give no change in performance because the combined losses and gains cancel each other out. If however all the changes give losses, then you have an overall loss in performance. Sometimes you may find one component such as pistons give no change, but the combination of other small adjustments, which seem like nothing at all give a loss and therefore you suspect that it is the piston you have changed because that is the only physical part you have changed, when it is actually everything else combined that creates the loss.
—If you have bought the design for our exhaust manifold, this must be duplicated exactly. We have seen in the past where customers eventually confirm that their exhaust manufacturer could not make it quite as designed and have told them it will be ok. Sometimes even fitting a different size exhaust system or reducing the size, even small changes can completely destroy the output.
For any of the above, we have seen performance losses of in excess of 70bhp and anywhere up to the level with the smallest of changes or errors. Even things that you would think are unimportant; testing on a different rolling road, different tyres, change of gearbox or airbox, can all have unexpected results.
Category:
Engine Build