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Cosworth YB Tuning Guide

Cosworth YB Engine Tuning Guide

Cosworth engine tuning guide covering modifications to the block, cams, con rods, cylinder heads and injectors

Cosworth Tuning (YB) – Crankshaft

The standard crank can support up to 500bhp without any problem and they are also very well-balanced. Cranks which have been ground are less strong. Cranks in original condition fetch about 500GBP. The standard Cosworth crank can be upgraded to a steel item from companies such as Arrow Precision and Farndon.

Cosworth YB Tuning Guide – Photo: Reyland

Cosworth Tuning (YB) – Cams

There is a massive range of cams available depending on the use of the car. For fast road use with 350-450bhp a BD10 exhaust and BD14 intake cam. For 450-500bhp a BD14 exhaust and BD16 inlet work well.

SCS can make custom profiles for 560GBP.

Cosworth Tuning (YB) – Cylinder Head

The standard cylinder is very good. It can support up to 350bhp without modification. For 350-500bhp the valves can remain standard but the ports need to be enlarged to 22.5mm on the intake side and 23mm on the exhaust. For 500bhp+ the valves can still remain standard but the ports need to be made even larger, 25mm inlet and 24mm exhaust and this works well with BD16 inlet cam and BD15 exhaust or BD15 inlet and BD14 exhaust. For 600bhp+ port need to be taken to 26.5mm inlet and 25.5mm exhaust. At this level the valves are becoming restrictive so bigger item need to be fitted. For bigger valves, bigger cams are required and this means further machining of the head is required.

Cosworth Tuning (YB) – Sump

Often overlooked even on big power motors the sump plays a crucial role in reliability especially if the car is taken on track and/or wider grippier tyres are fitted. There are 2 solutions, either a dry sump system which can be expensive or baffling the original sump with a trap door style type baffle. Julian Godfrey Engineering can baffle your sump for 250GBP.

Cosworth YB Tuning – Con Rods

The original rods are cast steel and are extremely good. If there is one problem with them it’s the fact that they are slightly too short which leads to quite high lateral forces against the cylinder walls. Longer rods with shorter pistons will relieve this situation slightly. This can lead to an extra 8-10bhp and SCS can carry out this conversion for you for 750GBP

Cosworth YB Tuning – Pistons

The standard pistons are Mahle items are fine up to 400bhp with some tuners saying they are good up to 500bhp. Where they do run into problems is when nitrous is used or on high revving engines. Pistons can be upgraded to forged items from many of the major forged pistons manufacturers. As forged replacements cost around 600BGP its hardly worth replacing the original pistons with new standard items.

The verdict on compression ratios differs widely, SCS say for 450-500bhp a 7.2:1  is a nice safe ratio, up to 350bhp 8:1 should be ok.

Cosworth YB 205 block, no the stronger 200 YB block – Photo

Cosworth YB Tuning – Block

2wd Cossies came with the 205 block, the 200block is the stronger version. The 200 block has the advantage of being able to accept longer studs. Fitting longer studs to the 205 block is hit and miss and depends on the casting. The machining work for longer studs can be carried out by A1 Rally Sport and costs 300GBP. Up to 500bhp 6 studs should be fine, for 500 GBP+ 10 long studs is advised. 6 studs can be used up to 700bhp if the exhaust side outer studs are made 5mm longer. 10 studs are usually used with Nikasil coated steel liners but this is usually reserved for motorsport applications.


Liners are stronger and allow higher boost levels but different rings new to be used with them. 10studs and Nikasil wet liner conversion can be done for 2000GBP depending on spec.

Cosworth YB Tuning – Turbo

Standard T3 turbo are good for up to 300bhp. Upgrades such as a GT30 are good for 450bhp and the GT35 for 600bhp plus. GT turbos will need external wastegates. A 44mm external wastegate will cost around 350-400GBP and the manifold and downpipe will have to be modified to fit them.

Cosworth YB Tuning – Engine Management

The are a massive range of options available here and the best advice is to go for what your tuner recommends.

Cosworth YB Tuning – Injectors

Bosch are the most popular. Dark Greens/803s for 300-330bhp and are approx 70GBP each. Light Blues/400s up to 400bhp. Greys/403s for 400-450bhp.  For more than 450bhp and 8 injector set up is an option and brings with it all the nice features of a nice sequential set up. 8 Greens will be good to approx 500bhp. Siemens have started making Blacks which negate the need for an 8 injector set up and a will fit in the original fuel rail.


T5 Gearbox – How to fit a close ratio gear kit.

And now for something completely different. A 3 part guide to rebuilding the T5 gearbox

Part 1

Part 2

Part 3

Find performance parts on ebay

This page was last modified May 11, 2019 @ 10:10 pm

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