47. Engine Build (For our 2022 race season)

This update is a bit delayed as we wanted to see how the engine held up over the course of its first season before making too much of a song and dance. Back in Jan/Feb 22 we decided it would be a good idea to refresh the engine as we didn't know its history, and wanted to minimise the chance of any failure cutting short races.

The original plan was simple - engine out, strip it down, reassemble bottom end with new new bearings/rings/oil pump and arp rod bolts - a relatively proven recipe for a reliable F4R. What we ended up with was slightly different to this original plan...

Here is the engine on its way out - as per most F4R engines, a right grubby oily mess.

First up was stripping it all down - had a bit of a disaster with the dephaser covering plug - so much for the 'reputable' mechanic who did the belts for us back when we first bought the car - they either cross threaded it or torqued it up to the same as the actual dephaser bolt as it was stuck fast - ended up having to take it off with a slit disc, ruining the dephaser in the process.

Having stripped it all down it appeared to be in pretty good condition - bores looked in good condition with the cross hatching still visible and the head/valvetrain didn't have any hidden horrors other than and abundance of sealant in places it shouldn't be and a fair bit of mild scoring to the cam journals (which is again pretty common).

After getting it all apart it was time for some preliminary checks and measurements to confirm that all was order (as it appeared visually). This is where having the right tools, and James being a bit of a data nerd, is invaluable...

From the cleaned up piston markings and lack of markings on the block you can determine which production category the engine falls into (Renault group the blocks/pistons into two categories based on manufacturing tolerances/sizes). The 'B' on the piston crown and no marking on the block mean this engine's nominal bore diameter is 82.71-82.72mm. The images below show ours was measuring ever so slightly over this at 82.725mm (from memory the rest of the measurements were all around this mark too) - just down to wear having done 100k+.

The pistons measured up ok too but I now can't find any photographs of this process to share. 

So, with the block measuring up nicely, and the head just needing the expected refresh it was time for things to take a bit of a detour from the original plan. With the engine apart (and knowing we would need a remap in any event as the original map was pants) it all of a sudden became a bit of a no brainer to try and squeeze a bit more power and out of the thing. A popular upgrade is to fit the pistons and cams out of a MK3 RS which increases the compression ratio due to the increased piston dome volume (the mk3 combustion chambers are bigger so overall the compression ratios are similar between the two 11.2 vs 11.5) and the cams have a slightly higher lift too - they're also pretty darn cheap so we thought we would look into this.

Having sourced a decent set of used pistons and cams we set about checking the clearances - something thats not particularly common knowledge with most seemingly throwing them in and hoping for the best.

Images below and on the next post show the setup to quickly check the valve to piston clearance with VVT engaged, and as you can see it gets close on the inlet side - to a point that we weren't really happy with the clearance given the engines going to see high rpm for most of its life (and this is pre-skimming of the block & head faces too).

So after that little interlude, and having now got quite keen with the idea of more power, it was sort of back to the drawing board for what turned out to be a fairly drastic rethink on the build plans. We had given up on the idea of the 197 cams/pistons due to the clearance issue and the idea of 'simply' putting new rings on the original pistons was feeling like a bit of a half arsed job, so, in the usual fashion with this car, it was now in our heads to 'do it right'.

Enter from left field the 'new' build spec (and the fairly wooly justifications for the same):

- some wossner forged pistons - these are available in high compression (12.8:1 nominal) and a 82.72mm bore size meaning we could hone the block (instead re-bore) and be happy with the running clearance, also they have nice deep valve pockets for plenty of clearance to allow future cam upgrades if desired.
- PEC forged rods - basically because they were really cheap if bought with the pistons and came with arp bolts already - they're not the best but supposedly rated to 220hp per cylinder or something stupid, so we were fairly confident they'd do the job for us.
- ported head with supertech valves - we had been in touch with MS Custom Engineering to have various engine parts painted and decided to 'future proof' the head with getting it ported, Max also skimmed it for us and lapped in the new valves, cracking job and photos of the same below. The valves were basically a bit of insurance against a dropped valve destroying our now rather nice bottom end.
- cat cams 421 - a set came up cheap on ebay
- 197 valve springs - ever so slightly stiffer than the mk2 springs to help with the more aggressive cams and managed to bag a brand new set for a good price
- fully balanced rotating assembly
- new oil squirters
- mix of king racing/KS bearings
- new Renault oil pump, oil chains, timing belts etc etc

So, with that all now decided we got the head and block off to the machine shop and had a bit of a wait whilst the work was done. When we got some progress updates from Max we were chuffed with the decisions we had made:

And after a small wait, we had a lovely looking honed and skimmed block back, and all the parts from Max:

Time to start reassembling!

First off was obviously giving everything a thorough clean and measure of oil clearances (sorry no photos of this), then its bearings in the block and crank in to check the end float which was within tolerance.

After that, the next job is to measure oil clearances again, this time for the rods/pistons and get them all sorted by weight and assembled

Rod bolts torqued up by stretch

Everything checked, re-checked and torqued to spec, we could now have another check of the valve to piston clearance (which we knew would be fine by just looking at the pistons, but always good to be sure!)

Following this step, it was time to bolt the head down and install the new tappets/rocker arms. Then valve cover on and time everything up. Job done! - a bit of an over simplification of the work involved, but detailing every step would take forever!

Then following all that get it back in the hole, ready for running in on the dyno and then the acid test of seeing what power it makes...

I've lost track of how long we had to get the car together to get to EFI for mapping but it was a fairly close run thing. Anyway, we made it, and with some part worn tyres on the front it was time to get the engine run in on the dyno and then properly mapped. Having built the engine, James was looking a smidge nervous for the first few runs to high revs (we'd had it ticking over briefly back at base so knew it ran fine), but with hindsight there was no need - he's built a bit of a cracker as the dyno graph on the next post shows.

So here it is, the final result of the engine build. On the way to Chris' we were expecting the engine to make something in the order of 200hp, as a result of retaining the factory inlet manifold. We sort of shocked ourselves with the power it made in the end, 219hp, being higher than a lot have achieved with ITB's. The second (reduced power) plot actually shows the final map we settled on as the engine would have produced too much power for the race series we were entering which is limited by power to weight.

Overall a fantastic result and now backed up with a seasons faultless running - happy days!