4k GT86 Gets a Rocket Bunny Kit & LS3 V8 Swap!
Discussion
I seem to be in the habit of letting quite a thick layer of dust settle on this thread between every up date lately..
But happy late new year everyone and believe it or not I've got a few updates for anyone still listening!
I cracked open the engine a bit further since my last check in, taking off the sump and heads and removing the rods and pistons to get to the bottom of what actually happened and (un)fortunately it was rather obvious.
The engine experienced a major rod bearing failure on rods #5 and #6 which share a crank journal with other bearings not being much better.
Various glittery pictures and even a video to follow:
https://www.youtube.com/shorts/M6W7xxiu6iw
But my next question was where to go from here? As you know I want to buy a stroker kit but obviously the farm is no place to build an engine and so that lead me to suck it up and pay someone to build the engine this time round (A recent job change with a better salary definitely helped this decision!).
I say suck it up but this is probably for the best as clearly my engine building record isn't particularly clean and if i'm going to spend all the extra money on a stroker kit I'd want an engine that doesn't "Just work" as was the previous goal but instead makes a decent chunk of power.
A friend pointed me in the direction of Hurley Race Engineers based outside Cambridge, not exactly local to me but I took the LS up to them and needless to say amongst a slew of race engines, Ex-f1 Engines and the like my rinky dink yank lump should be a piece of cake.
During my chat with them their thoughts on the failure were that I've unfortunately been a bit of an unlucky one when it comes to a "simple" rebuild, advising that electing to replace the rod bearings without polishing the crank means that the crank surface was likely crowned which when paired with brand new bearings lead to premature failure. This was a very basic diagnosis on their part based purely on my previous description of the engine history.
I then ordered the Stroker kit itself. Not wanting to fly to close to the sun I opted for the marginally safer 416ci/6.8L displacement over a massive 427/7.0L which i'm sure is pleeenty for a little 2 door Japanese coupe and landed on going for this kit from CNC Motorsports in the states:
https://cnc-motorsports.com/compstar-416-ls3-strok...
I specced it out with a 4.070 bore, giving us room to take the bores out slightly and start from a clean slate and with the original head combustion chambers this should give a nice 11:3:1 compression, or a bit more if the heads need skimming down.
After a number of weeks the stroker kit showed up, unfortunately these are the only pics I have as I didn't want to take it out of the packaging but i'm set to take it up to Hurley on the 22nd Jan so might be able to get some more pics/info from them then!
Aside from that i'm going to spend this winter downtime to get a couple of other bits sorted on the car, the first and simplest one is sorting out the melted look to the paint on the chassis rails. Once upon a time I considered getting the exhaust parts coated but with the costs involved I compromised by wrapping them, eventually the un-wrapped parts melted the paint on the chassis rails so those exposed parts have been sprayed with DEI exhaust paint and the chassis rails heat protected.
Another is that I want to get the A/C Lines sorted as i've had an Air conditioning kit for the longest time but never fitted it originally! and that slightly ties in to the other thing to fix which is removing the brake booster to go back to manual brakes, reason being that the original brake booster is so massive and space is as a premium around the LS so for want of changing the spark plugs one day as well as better line/hose routing I want this gone!
There is a couple of fairly expensive kits from the states to do this, at first I thought with enough time I could find a suitable master cylinder from an OEM application but I figured i'd simply pull the trigger and purchase the "bolt on" kit instead. It's quite a simple setup featuring a firewall adapter, an appropriately sized tandem Wilwood master cylinder and a pedal linkage adapter which has a couple of options for pedal ratio.
My plan is to fit the new master and while i'm messing about with all of this also change the brake line setup to be hidden in the wiper motor cowl to tidy up the engine bay a bit and save some extra space around the back of the engine.
But happy late new year everyone and believe it or not I've got a few updates for anyone still listening!
I cracked open the engine a bit further since my last check in, taking off the sump and heads and removing the rods and pistons to get to the bottom of what actually happened and (un)fortunately it was rather obvious.
The engine experienced a major rod bearing failure on rods #5 and #6 which share a crank journal with other bearings not being much better.
Various glittery pictures and even a video to follow:
https://www.youtube.com/shorts/M6W7xxiu6iw
But my next question was where to go from here? As you know I want to buy a stroker kit but obviously the farm is no place to build an engine and so that lead me to suck it up and pay someone to build the engine this time round (A recent job change with a better salary definitely helped this decision!).
I say suck it up but this is probably for the best as clearly my engine building record isn't particularly clean and if i'm going to spend all the extra money on a stroker kit I'd want an engine that doesn't "Just work" as was the previous goal but instead makes a decent chunk of power.
A friend pointed me in the direction of Hurley Race Engineers based outside Cambridge, not exactly local to me but I took the LS up to them and needless to say amongst a slew of race engines, Ex-f1 Engines and the like my rinky dink yank lump should be a piece of cake.
During my chat with them their thoughts on the failure were that I've unfortunately been a bit of an unlucky one when it comes to a "simple" rebuild, advising that electing to replace the rod bearings without polishing the crank means that the crank surface was likely crowned which when paired with brand new bearings lead to premature failure. This was a very basic diagnosis on their part based purely on my previous description of the engine history.
I then ordered the Stroker kit itself. Not wanting to fly to close to the sun I opted for the marginally safer 416ci/6.8L displacement over a massive 427/7.0L which i'm sure is pleeenty for a little 2 door Japanese coupe and landed on going for this kit from CNC Motorsports in the states:
https://cnc-motorsports.com/compstar-416-ls3-strok...
I specced it out with a 4.070 bore, giving us room to take the bores out slightly and start from a clean slate and with the original head combustion chambers this should give a nice 11:3:1 compression, or a bit more if the heads need skimming down.
After a number of weeks the stroker kit showed up, unfortunately these are the only pics I have as I didn't want to take it out of the packaging but i'm set to take it up to Hurley on the 22nd Jan so might be able to get some more pics/info from them then!
Aside from that i'm going to spend this winter downtime to get a couple of other bits sorted on the car, the first and simplest one is sorting out the melted look to the paint on the chassis rails. Once upon a time I considered getting the exhaust parts coated but with the costs involved I compromised by wrapping them, eventually the un-wrapped parts melted the paint on the chassis rails so those exposed parts have been sprayed with DEI exhaust paint and the chassis rails heat protected.
Another is that I want to get the A/C Lines sorted as i've had an Air conditioning kit for the longest time but never fitted it originally! and that slightly ties in to the other thing to fix which is removing the brake booster to go back to manual brakes, reason being that the original brake booster is so massive and space is as a premium around the LS so for want of changing the spark plugs one day as well as better line/hose routing I want this gone!
There is a couple of fairly expensive kits from the states to do this, at first I thought with enough time I could find a suitable master cylinder from an OEM application but I figured i'd simply pull the trigger and purchase the "bolt on" kit instead. It's quite a simple setup featuring a firewall adapter, an appropriately sized tandem Wilwood master cylinder and a pedal linkage adapter which has a couple of options for pedal ratio.
My plan is to fit the new master and while i'm messing about with all of this also change the brake line setup to be hidden in the wiper motor cowl to tidy up the engine bay a bit and save some extra space around the back of the engine.
Completed this install last week but never got a chance to write it up!
Finished the brake lines to go along with the new brake booster delete unit.
Used AN-3 lines throughout, Teflon steel braided hose with Stainless steel fittings as recommended to put up with Braking pressures.
Originally started with plastic coated line which i've used before for my fuel and clutch master line without any problems but for some reason due to the smaller form factor or perhaps with the stainless lines I just found it impossible to work with and get the fittings over the hose despite plenty of swearing and lubricant!
That's 4m of AN-3 hose wasted..
Once I ordered the naked stainless braided hose it all went together far easier, managed to make up all 6 lines in a matter of a couple of hours.
So what we have is:
2x Lines from Master to wiper cowl bulkhead fitting
2x Lines from bulkhead fitting to bulkhead fitting within the wiper cowl
2x line from Wiper cowl to ABS unit.
Once fitted I filled the reservoir, dropped the lines going to the ABS unit in to the reservoir and pumped some fluid through to get the whole system pre-bled.
Once I plumbed the lines back in to the ABS unit the brakes felt great right away! might even get away without having to bleed them too much but i've got a bottle of fluid left over so it wouldn't hurt to do!
Excuse the messy pics... do I class this car as a barn find yet?..
Quite pleased I managed to complete this, only been completing small jobs on the car over the past few months while I wait for the engine work and this was one that very much "completes" the improved engine swap for me, i'll have more room for the coolant lines, to swap spark plugs and so on!
Speaking of the engine build i've not been pestering for updates too often as I'm not keen on rushing people but I heard from Hurley race engineering a little while ago and there's a few extra bits and tasks needed:
Unfortunately the Sump face wasn't flat, likely leading to an oil leak, good to catch and sort this now
The Cam bearings are past tolerance so need to be replaced
The Oil pump and front belt pulley weren't suited to the Crank timing sprocket and therefore all 3 are damaged and need to be replaced.
All add time to the build sadly but hopefully being an LS some of these parts can be quite cheap.
Finished the brake lines to go along with the new brake booster delete unit.
Used AN-3 lines throughout, Teflon steel braided hose with Stainless steel fittings as recommended to put up with Braking pressures.
Originally started with plastic coated line which i've used before for my fuel and clutch master line without any problems but for some reason due to the smaller form factor or perhaps with the stainless lines I just found it impossible to work with and get the fittings over the hose despite plenty of swearing and lubricant!
That's 4m of AN-3 hose wasted..
Once I ordered the naked stainless braided hose it all went together far easier, managed to make up all 6 lines in a matter of a couple of hours.
So what we have is:
2x Lines from Master to wiper cowl bulkhead fitting
2x Lines from bulkhead fitting to bulkhead fitting within the wiper cowl
2x line from Wiper cowl to ABS unit.
Once fitted I filled the reservoir, dropped the lines going to the ABS unit in to the reservoir and pumped some fluid through to get the whole system pre-bled.
Once I plumbed the lines back in to the ABS unit the brakes felt great right away! might even get away without having to bleed them too much but i've got a bottle of fluid left over so it wouldn't hurt to do!
Excuse the messy pics... do I class this car as a barn find yet?..
Quite pleased I managed to complete this, only been completing small jobs on the car over the past few months while I wait for the engine work and this was one that very much "completes" the improved engine swap for me, i'll have more room for the coolant lines, to swap spark plugs and so on!
Speaking of the engine build i've not been pestering for updates too often as I'm not keen on rushing people but I heard from Hurley race engineering a little while ago and there's a few extra bits and tasks needed:
Unfortunately the Sump face wasn't flat, likely leading to an oil leak, good to catch and sort this now
The Cam bearings are past tolerance so need to be replaced
The Oil pump and front belt pulley weren't suited to the Crank timing sprocket and therefore all 3 are damaged and need to be replaced.
All add time to the build sadly but hopefully being an LS some of these parts can be quite cheap.
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