Engine Block and Head Data
 

Folks,

I'm looking to mod an AJ27 and need to play around with the compression ratio and bore.

Does anyone have the cylinder head, deck clearance and other volume-related figures to hand?

I know it's a square 86/86 bore and stroke - I'm planning to up this to around 93ish bore and perhaps reduce compression slightly to allow a modern screw-type SC to be installed, amongst other things for my first stage mods.

Thanks in advance.

93mm is not safe for SC engine asn specially if you have AJ27 block. Same later blocks allow up to 92mm SC and up to 93mm N/A. 4.0 safe is max 90/91mm. Depends on block castings. There is no need to lower CR.

Thanks for his XJR-99.

With a bit of care, I've known the later heads to take a 94mm bore but a good quality metal layered gasket is called for + thorough testing. That said, I am going to heed yours and other sage advice to not go beyond 92, and of course a layered steel head gasket, new valves, guides and seats.

I'm commissioning a new 416 steel alloy crank, so the next port of call is to maybe increase the stroke slightly to something like 89, so a 92/89 engine is the result. Forged pistons and their hardware will go with that, as well as new con rods.

The M112 SC is also getting a porting, bearings and pulley upgrades.

I'll keep this thread updated with results - I'm looking forward to see what sort of torque and HP numbers come out at the other end of the dyno. What I really want is to take it to 550Hp+ and some serious torque.

Thanks again.

There are several other engine build threads where you can find a lot of engine build details. Perhaps you have read them. I started my "High HP super build" a couple years ago and stalled out due to technical difficulties. My block is bored/sleeved to 92mm. This is the limit! Do the math. 98 bore spacing, give you 6mm max between cylinders for the heads to seal, not much for a SC engine.
I 3-D modeled the stroked engine I wanted to build and ran into a challenging and expensive problem. I wanted my engine to be balanced for 7000 rpm operation. What I found is that with 92mm pistons, standard pins/rings, combined with custom steel rods, I could not get the cross-plane fully counterbalance masses on the crank to balance unless I went with heavy metal inserts or went with custom Ti rods. Due to our 98mm bore spacing, the counter balances are narrow and are limited in OD by the walls of the block.
To some degree, increasing the stroke helps with rod weight/balancing, but you will have to run the calculations for a complete custom engine build. Don't just try to throw in a custom stroked crank, without having the rods, pistons, and masses of the flywheel and front lower crank pulley included.

At 550+ hp you can probably get away with the standard crank design, (no center counter balances, but then you better pay close attention to engine harmonics. (The count has written abut the 4.2's harmonics.)
I was designing my engine for 700+ hp, so I had to pay more attention to rod strength (added mass) and engine balance.
My limit for the stroke was 90.2 before my rods or block would have to be modified

I believe that the Arden kit claims a 92mm stroke. If you are only wanting 550hp, might be more cost effective in the long run to use their kit. (if they still offer it.)

On the other hand, good luck getting much out of the M112. If you are spending the money to build up the engine go with the KB twin screw.

Arden kit stroke: 95.6mm .

Which I agree with. Coming to think of it, 94mm is too scary, with or without good gaskets

Precisely what I'm intending to do - I've contacted a 3D scanning outfit here in Manchester and gotten prices on the job of providing a fully editable, CNC-accurate CAD model. Not cheap, mind you, so a cost to be added to the final build.

I envy the American mods available for legends by the likes of Ford and GM, whereas the next-to-nothing available for our babes. That said, if I get my way, then I'm releasing all this work to the masses, versus keeping it close to my chest.

Out of interest, how did you go on about your 3D modelling? did you go to nuts and bolts measurements or 3D scanning?

You open a very wide door for prudent argument. No way am I doing this by bolting together six of one and half a dozen of another stocks. I'm under no illusion that this is now firmly looking like a full custom engine build ( i.e. expensive and time consuming)

On the plus side, this will give me all the data necessary, and missing, to apply whatever else mods and designs for now and the future for these engines.

All hail the Count .. I've read his articles and they make for some amazing work Yes, absolutely right about the harmonics, so modeling all the way.

I'm commissioning a new 416 steel crank, so have a lot of room for mods and stress testing.

I'll check Arden, though I'm not impressed by how little they available for the AJ27


Absolutely. I'm considering the KB 2.8L and 3.2L. I'm also looking at the Edelbrock E-Force which is made for the Coyote. So far, the dimensions add up with the stock bonet.

One other area I'm looking at is ECM and TCM - the stock ECUs are both rubbish and too old to mod.

A final, and crooked twist, is to integrate a fully supercharged Coyote engine :icon_twisted:


Thanks again for your feedback and any contributions from anyone.

Just checked Arden. Can't find any performance upgrades for the X308.

Check X350.

Had a look at that too. For the money, I would go my own way.

I thought the 3.900 euro for the forged crankshaft, rods and bearings, was an ok price. For what do you think you could do it?

4640€ VAT included when shipped to the UK - actually the parts are manufactured in the UK... It's actually pretty cheap kit when the quality is the highest possible. Of course those parts are just a very, very small part of the whole engine/car upgrade project Maybe Trump's 25% steel tariffs hit to the kit if ordered to the USA :)