Hello folks, I recently picked up a pre-he motor with the intention of building a full drivetrain to swap into my xjs... after a long fight with head studs I finally got the heads off only to find they're likely scrap metal

I'm wondering (hoping) these could be saved with welding and oversize valves, the plan is to build this motor for 15-20psi of boost so my other question is could the head be machined into to form a proper combustion chamber? That would allow for a squish pad to introduce better turbulence and hopefully avoiding the piston-burning problems the folks at Bonner engineering documented back in the 80s
To that end my other question is can the valve seats in the pre-he be recessed into the head a little, .050" or thereabouts?




--
Angel

 

I’d repair it. Then I’d use the stock 7.8-1 compression cast pistons. No need to go to silly forged pistons*. Adjust ring gap to allow the rings to expand under the heat so you don’t pop off the ring land. A forged piston is too expensive, too heavy and needs to expand too much. Just limit the engine to about 7000 rpm.
The short stroke is your friend here. It really helps keeping down the piston speed.
They will stand up to 20PSI without failure. If, if you get the mixture right. I’m conservative I’d go to 9.0-1 fuel mixture with E85 And don’t go too silly with timing. Added timing is a temptation because the power goes up with every degree you add. But there madness lies.
What are your thoughts on intercoolers. If used for road racing. They are almost a must. Drag racing? Not so much with only 20PSI start needing it above that though. Don’t forget, while it cools down the charge, it adds back pressure.
For GOD’s sake do not. Repeat DO NOT use the HE distributor. Tempting as that may be.
In fact I would completely remove the distributor and go to coil on plug. Then instead of wasting lot of dyno time trying to get the timing right, you can change timing with your lap top. And a few key strokes.
If you are here in AMERICA you can buy E85 from racing fuel suppliers. You want the cooling effect of ETHANOlL Not only will it provide a lot cooler running but will add a significant amount of power.
I assume you will be using a pair of Turbo’s. Rather than trying to use a single big one. If this is for the street use the T2’s size. You’ll like the fast spool up time. Racing? You can go to T4’s.
Don’t be afraid of the cheap Chinese ones. They are really good value for the low cost. I paid $130 each for mine.
Yes you can spend a lot of money on expensive ones and while they are better and probably will last a bit longer. It’s a silly waste of money. Turbo’s fail when they are run with too much heat and back pressure.
Make your life easy spend the extra money for the electronically controlled boost valves. But take them apart and carefully tighten all the screws. Chinese ones work fine then.
If this is your first time turboing an engine I can suggest a few Utube sites that really help show you the in’s and outs. Of tuning.
My choice for ECU would be Megasquirt pro 3 it’s got enough pins to handle coil on plug. Plus a lot of people are comfortable with it. Get the prewired version.
MAXXECU. Has been used successfully on the V12 too. A little more expensive. I’ve never used it.

 

Oops, the valve seats are recessed by .020 stock.
Regarding the above, you should probably explain what sort of use you plan for this.
I foolishly thought racing when I started all the above but if it’s street use? In that case use a fuel sensor to select which ignition profile / fuel you’re going to run at.
Second. If you are in ENGLAND without access to E85? I’m out of my element Plus my only experience with gasoline was back in the 1990’s and I limited it to 112 octane racing fuel and only 6 psi. That car is still running around but almost makes 500 hp.

 

Whole lot to break down here but I really appreciate the in depth response!

First of all yes this is going to be kind of a drag-and-drive setup, I want it to be as quick as possible without sacrificing the ability to daily drive it if I wanted to.

Secondly I would love to stick with the stock pistons but according to the research I've done the dish and flat head combo leads to poor air-fuel mixing and hot spots in the flame front (this is why bonner was burning pistons). My thought is to go to flat top pistons.. possibly HE stock, add a combustion chamber into the head, and set the piston to deck clearance much lower (custom rods? 6.0 crank?) to achieve the 'squish' effect that introduces turbulence to the mixture.

Here's what I have in mind for the chamber:

​​​​​My chamber shape is loosely based on the SB2 head used in nascar, I won't pretend to know much about the science or math behind it... Doing this would require recessing valve seats to ~.110" (depends on the valve lift at tdc, determined by cams) ... I believe there is enough material to do this, figure I'll give it a shot on the trashed head. I do think a modification of this sort will make a massive difference to how the engine runs and how likely detonation is.

As for fuel and turbos e85 is available at most pumps here it seems so that's a no-brainer. Definitely not scared of running ebay turbos, I was thinking I'd add some sort of free flowing filter or mesh in the intake to catch shrapnel if they do explode! Supercharger is always an option too but the centrifugal type seems silly for the street and a screw type means chopping up the hood.

For tuning I was looking at maxxecu, seems to be the only one that supports true sequential injection on a v12 vs waste fuel/spark on most other platforms.. there's also the "speeduino" platform which is completely open source and has a huge community of people I can bother for help..

Sorry for rambling 😅

 

Just to touch on this the more efficient (well mixed) combustion is the less octane and timing you need to make power, from the obscene amounts of timing the pre-he and he both need we can clearly see there is a *lot* of room for improvement.. boost likely helps mix the mixture a little better but if you address the root issue it should help NA performance significantly and performance under boost exponentially.

 

I’m not going to tell you that you are wrong.
This is my opinion working on a bunch of turbo’s V12’s.
E85 is the magic juice. Gasoline has all sorts of problems. mainly a tendency to generate hot spots.
Squish is generated at the edge of the piston. Swirl is generated by the angle the charge enters the bore. The V12 engine is wonderful in that regard.
A smooth flow is more efficient than flow forced
to change direction by obstructions. Every time air / fuel mix changes direction it’s a chance for the heavier fuel to seperate out plus it reduces flow.
That in my humble opinion is what creates hot spots.
The shape you have is exactly what COSWORTH came up with in their racing piston. NLA. A decade ago I spent hours trying to talk them into re-running those. ( unsuccessfully).

Here is my view on your ideas. Anytime you spend porting and changing flow is really hard to duplicate to all 12 cylinders by hand. Forcing the work to a CNC vertical mill Now we are talking painfully expensive work. It eventually was worth it for me to buy a vertical mill never had the knowledge or patience
My first one I did by hand I know I had hundreds of hours on the flow bench trying to get each cylinder to flow similar.
Stock there is significant difference between each cylinder to start with. When you combine the hand reworking it was a massive headache. I cut up 7 heads to try to alter flow enough to get back to equal.
Hopefully you are aware that 2 different casting companies did the cylinder heads ( there is a casting mark indicating which is which.) no I’m not talking about preHE* and HE)
* I call that one the Flathead.
When I finally got things close enough to assemble and dyno there wasn’t much horsepower difference to make all the work worth it. I was hoping for more than 100 hp gain. Instead it was like 5.
My first engines were all high dollar built to the max. But I know that power comes from experimenting. So I Eventually stopped spending for the best and went for affordable.
Yes down a little but not enough to offset the cost.
The biggest gain was in the camshafts. But billet custom cams are brutally expensive.
Crower & ISKY REGRINDS got me 60% there. And a willingness to stay under 7500 suddenly even stock rods and pistons were OK.
SO MY ENGINE’s cost less than $1500 to build. Instead of over $8000

 

Little more background.
Anyway back in the 1990’s there was Chump car racing. $500 limit. My first turbo was a 1975 XJS with just a modest amount of rust in the floor boards. 2 used SAAB TURBO’s @$30 each and a FMU ( device that tricks the computer into going richer the more boost you have) I kludged close to 500 hp out of it and it’s still running around here occasionally.
Later I wanted to get back to vintage sports car racing. ( in the TRANS AM CLASS )
I knew I could easily hide the Turbo’s but the faster guys were well into the 600+ horsepower. The XJS is just too boxy to have low drag so I knew power was an issue.
That’s why I wanted Turbo’s the computer program I used ( engine analyzer) told me I could build an affordable turbo V12 and get to that 700 number relatively easily.
Then I heard about GRASSROOTS $2000 race. Build a race car for $2000 or less
I bought a nice rust free XJS AND A Pair OF $130 T4turbo’s. The rest of the motor stayed stock and I could use the Megasquirt v2 that came with it. .

I went on UTUBE to figure out how to convert the T 400 transmission into a manual shift. Turns out pretty easy and that way I could hold it in whatever gear as long as I wanted.

 

I completely agree with you that e85 is wonderful and helps with a whole slew of issues. The issue I see with the pre-he chamber is that it has no squish area, the outer ring of the piston is .080"+ away from the head at tdc (for squish to be effective it should be at most .049" (1.8% of stroke)).. having a squish area that's slightly too large is much worse than none at all!


​​​​​​Thankfully I'm no stranger to CNC milling, as soon as I find a more permanent workshop location it's pretty much at the top of my shopping list.. I do wonder if one of those cheap CNC wood routers (<$500) could be modified to do chamber work..
I have no delusions about this being a cheap or easy process but I'd rather pick up where others left off than follow their footsteps if that makes sense.. to that end I'd love to see any designs or photos you might have of your builds!

Nope this is news to me, here's a photo of the markings on mine

 

Yeh, that’s the “better” one. I found slightly thicker wall thickness ( about .060 in general and in some of the corners .120. Unfortunately it tended to be more on the inside of the radius. So I couldn’t take advantage of it. The other seemed to have a slightly thicker “ bottom” and it was too easy to grind through the walls if I was slightly off course.
If you are good at CNC THERE IS NO COMMONALITY BETWEEN PORTS. It seems that each one was ever so slightly different .
I at first tried to equalize them by volume and thst threw the flow numbers wildly off. Then I went for flow number similarity and volume was wacko.
I know CROWER CAMS MASTERED IT BUT THEY MAY HAVE HAD SPECIAL CASTINGS?
CROWER CAMS DID ALL OF GROUP 44’s head and valve work. ( and got some serious horsepower numbers.
You will find BRUCE. CROWER very Knowledgeable about that V12 engine.

 

If you haven’t worked with EFI On the V12 enough to be comfortable I would build a cheap stock engine don’t worry about worn pistons bearings etc. I even reuse old rings. Just open up the end gap enough.
Then build a stand ( not a dyno, just a run in stand. ) using a radiator & oil cooler
Put a big box fan in front of the radiator.
Make sure you have 4 good O2 sensors in the exhaust pipes and just get it running and tuned decently so you get pretty well sorted. If you blow up something you really haven’t lost anything. I regularly buy engines like that in the $300-500 range although a lot of times I have to pull them from rusty and damaged cars. I buy non running ones because most of the Time ( all in my experience) they just have ignition or fuel issues.

One “trick” I found that works well to keep the engine cool is the water outlet on top of the heads doesn’t flow the same temp water to the back of the block as the front. I throw the stock ones away have new flanges made ( send cut send) without holes then I drill my own h sized holes the one at the front of the engine is smal and the one at the back the size of the opening.
Then collect that coolant in a tank at the back and run a tube up to the radiator.
Check a stock engine the back cylinders are always hotter than the front.
Hopefully that makes sense. The goal is to Keep the whole engine even temp.

 

good to know, I imagine that's because of whatever the factory did to 'machine' the ports after casting.. on mine it almost looks like it could've been done by hand!

yep, I haven't had any luck finding the older stuff but the HE motors are easy to come by.. could even use one of the 6 pots, v12s just two of them after all. I'll probably end up just getting it close enough and taking it to a professional tuner with a dyno and all that jazz.

Makes perfect sense, I'll probably try to make something similar to this setup I came across online, albeit probably a little lower profile


since we're on the topic of cooling anyways what else can be done to prevent another valve seat falling out? Maybe stake the surrounding aluminum after installing them? I can't imagine it'll be a big issue with a proper cooling setup but it would be nice to put in a little extra effort for some peace of mind

 

Kitte
FYI, a well known Australian engine guy recommends a method that can take care of the cooling circulatin problem rather more easily. Known s the Lutz method, attached are some data and explanations, and a photo of doing stage one on my road car.

Frant water manifolds Lutz mod modified. The idea is to ensure the cooled water from the rad does not "short circuit" through the front manifolds, but is pushed equally to the rear ones.

 

nope just the stock interference. Staking won’t work. The seats on a 9000 hp top fuel engine are held in the exact same way. Chill the seat and heat the head. tap in place. The only reason seats drop out is the engine was dramatically overheated.
Either neglected maintenance or hose failure and driver didn’t stop.
Group 44 never had a problem.
The photo has tubes that are silly high. I used 1 inch length and had to radius around the tube. So there was only about 1/2 inch high. ( plus the thickness of the flange.)

 

I assume you’ve checked CAR-PARTS.com? Do not bother with EBAY silly asking prices. I used to have alerts in Facebook and Craigslist list But stopped buying 10 years ago.
The other source is the insurance auctions. It seems like whole early cars are there mostly sedans. But I’m not afraid of wrecks or fires I can usually estimate how far into the engine compartments the damage extends Those all tend to sell for scrap metal prices. Same with theft recovery,, vandalism and not running.
Here’s the ones you’ll want. 1971- 1980 all are the flatheads( pre HE ) sedan and XJS are basically the same the early blocks 1971- mid 1977 all use the BORG WARNER bell housing bolt pattern from then on until 1993 they used the GM turbo 400 pattern which is an easy adaptor away from a Chevy bell housing for a manual transmission
the 6.0 liter starts out 50 horsepower more than the 5.3 because of the added 1/4 stroke and bigger bore. Oh, it has a bigger oil pump as well and better rear seal. but there is a serious premium for those v

This is a easy mornings work

 

The Jag aluminum 6 cylinder has 4 valve heads and would be easy to get to 7-800 hp. Plus it’s lighter, several hundred pounds lighter. InENGLAND the six often beats the 12 because of the light weight.
They continued the six for years after the V12 and there are supercharged ones out there that according to rumor are built stronger.

The only real weakness would be the torque to yield head bolts but I’m sure ARP has something available.

 

Well your approach will work. ( hiring a tuner) but only one time. Changes or updates will rely on him.
That’s why I’m urging you to build a stand and learn for yourself. It’s really not that hard once the light comes on. ( I assume you can tune carbs and points).
There are plenty of HOW TO’s on U TUBE. I’ve got one site when a guy twisted a few wires together on a V2 of a Megasquirt and got it running in a few minutes. Megasquirt is self learning. And over time will get the whole engine pretty decently running.
But for what you want to do go the Megasquirt V3 pro prewired and get yourself a lap top. Up and running will be quick enough to not be bored tuning once the lightbulbs come on really isn’t that. Hard I can point you to a guy who really helps make it understandable. He pulls 830 hp out of a nearly stock Chevy 6 cylinder ATLAS engine ( Chevy trail blazer ) using E85
The advantage of that is you don’t need to wait for an opening in his schedule or for most things even go back on the chassis Dyno everything is just a few key strokes into the lap top.

 

Don’t keep the JAGUAR EFI STUFF except the manifold. Use stuff from the CHEVY ATLAS.
THE THROTTLE BODY IS BIGGER and you can adapt the fuel manifold and Chevy injectors which are a lot less expensive and come in more sizes and types than you can shake a stick at.
it’s also set up in the original program so you won’t have to reprogram that part of the Megasquirt.
The injectors on a Chevy just click in place and the JAGUAR INJECTORS ARE A FINGER TEARING ASSEMBLY PROCESS YOU NEVER WANT TO DO TWICE. ( oh, easy to have leak if things aren’t exactly correct.).
Yes there is a little fabricating but only one time then your life is a ton easier.

 

One final question I use my pickup and lately just rent a U haul trailer to drag home any Jaguar car or parts home. If I’m buying an engine I have my own knock down engine hoist to pick it up and put it in the truck.
I assume you have something similar?
It allows me to chase all over the country for the right pieces. Although often I spend more for gas to go get something than I paid for the car.
For long distance hauling the Chevy bench seat is really the best. Plus when I’m tired I can pull into a roadside rest, lock the doors grab a blanket and get enough sleep in a few hours to make it the rest of the way. My current FORD ISNT AS COMFORTABLE. But I can still cover 2000 plus miles with only a couple of hours spent resting.

 

I'm familiar with some of lutzs' work, need him to make those 305 liners again... I wonder if this method of different sized passages could be expanded on to use all the available ports, or perhaps that is pointless with proper flow

Really good to hear, I doubt I'll have issues then considering I find myself watching the temperature gauge more carefully than the speedometer 😉



Locating a 6.0 short block with the forged crank is definitely something that's on my to-do list, not only does the 6.0 have slightly more horse it has significantly more low end torque (I read 30% somewhere).. pairing a better low range with turbo supplemented mid-range would make for a beast of an engine! As for transmissions I've settled on a ford 6r80, parts are plentiful and with modification they can hold more torque than I could possibly make. Plans for the rear end are still uncertain, I'd like to keep the irs but I'd love to not twist axles regularly or rip the cage out/apart.. I do have the dana 44 axle so maybe I'll ask an offroading forum for ideas, those folks do some crazy stuff with practically the same pumpkin.



Certainly going to be a long term project so I'll probably end up learning to tune for myself one way or another.. I've never had any luck getting carbs to run right, I'll bet that's an altitude thing though (~6k above sea level)



I have no intention of even keeping the manifolds, especially with redoing the fuel/spark system there is no reason not to switch to a central intake manifold.. perhaps 2 LS manifolds frankenstiened together? Chevy throttle bodies and injectors are a dime a dozen



Unfortunately I made the mistake of buying a 90s dodge so in typical dodge fashion I have been fighting with transmission issues and don't dare venture more than an hour or two away.. my xjs I actually took a taxi to and drove it home (crazy right!?) and the engine I'm working on was loaded with a forklift, dismantled, and brought inside in hand carriable pieces.

 

Kitte,
I sent you a private message.
Rob