Along with all the internal upgrades to the engine, we’ve also decided to do something a little different with the inlet. The manifold we currently have is as short as it can be and as such, this gives us peak power, but not necessarily a huge amount of torque. Also, due to the inclination of the engine and the fact that the manifold is dead straight, the tip of the trumpets and bonnet almost collide. Therefore, the plan for this manifold is to create a slight bend (approx. 25 degrees) which would then allow us to extend the length as it would then fit in to package space just above the radiator and below the bonnet.
Before fabricating the inlet manifold, Ryan whipped out the die grinder and set to work porting the head. He got rid of the small steps, creating a nice smooth transition to the back of the valves. This has even saved us a few grams!
There are a few different pieces to the intake manifold puzzle and we start with the flange plate that mounts to the head. We were able to get hold of a laser cut steel piece from Danst Engineering, so that bit was easy. Next up, we needed to source the perfect sized tube which wasn’t quite as easy. Eventually, we settled for a section of tube that matched the aluminium throttle bodies both internally and externally, this did make the tube a little heavier than we ideally as it was steel, but at least it would be a tight fit.
First step is to get the file out and match the flange plate perfectly to the head, this took a while. Then, we cut all 4 tubes to length and shaped the ends to match the plate. Once this had then been tacked up, the file was out again along with the die grinder and after many hours, all edges were smoothed off and matched up.
Final steps now and all that’s needed is a few brackets and a little bit of alignment before getting it all mounted up and in place. Once that was all done, a lick of paint finished it off. Then, it was time to mount the throttle bodies, filter backing plate, trumpets and filter. We’re very proud of this creation, we’ll just have to wait to find out if it actually gives us any performance benefit.
Next up on the shopping list (last of the big items) is a set of forged pistons. We’ve gone for the highest compression pistons we can get and with metal head gasket we’ve chosen, this should give us a compression ratio for a little shy of 13:1.
Finally, it’s time to put this engine together. With less than a week until we’d scheduled a dyno session, Ryan got to assembly. After the first dry build, it was clear that it wasn’t going to be as simple as we’d really wanted. The high compression pistons obviously get a lot closer to the valves and it’s important that we ensure the correct amount of clearance between piston and valve. After a number of measurements, using random springs and self-built solid lifters, we determined that the exhaust valves needed an extra 1mm of clearance to be safe.
Unfortunately, this means we have to push back the dyno booking a week, but fortunately, our friend Tom had a great contact who runs a machine shop in Nuneaton and he was able to skim the pistons on quite a short time frame. So, a couple of 5am drives to Nuneaton and we had pistons with adequate valve clearance. A final push by Ryan and a few helpers got the engine together, back in the car and running the night before the dyno booking! A super effort by the boys.
And so, dyno day. The last time we mapped the engine, we went to a hub mounted dyno down at Silverstone. This time, we were off to Northampton Motorsport and their rolling road dyno. The guys there did a great job and for a great price too. The final results were 223 bhp and 175 lbft, with a nice flat torque curve.
If we go on the numbers alone, it’s actually a little less than we were expecting, simply using the last engine as the comparator, which, as I mentioned, was recorded on a totally different dyno. However, there is a lot of discrepancies with dynos and even the same dyno with the same car can measure different day-by-day! The true measure of the car’s performance will be the Silverstone race, which is coming up in a few weeks, after a nice little shakedown which we’ve planned at Snetterton on a trackday.