By now most understand how weak a Chevy 350 is compared to a Jaguar V12.
Some don’t realize that the average Big Block Chevy makes less power than the average Jaguar V12
It’s the confusion about Gross or advertised power and Net power. In the mid 70’s power ratings were standardized to Net installed.
So 400 horsepower big block became 230 SAE net and the Jag became 262 by American rules and 291 for everybody else.
Let’s talk about exceptions. The famous LS 6 for example was only sold under the old gross horsepower ratings. So “it had” 425 horsepower. But supposedly 325 Net. Except I’ve never seen how that was rated. SAE net installed? Or did they just subtract 100 horsepower?
now all I can find is 4439 or 4475 sources disagree were made. Should we include the Lister and TWR versions of the V12?

 

Wrong. Most don't understand that. You are polluting the interwebs again.

Even during the darkest days for the SBC, it still performed better real world.

In the late 70's both the Covette and the XJS ran a 15.9 seconds 1/4 mile. By the mid 80's even lesser cars with the SBC were out gunning the silky smooth V12.

1/4 mile times for 1983 XJS was 16.30 Seconds
1/4 mile time for 1983 Monticarlo SS was 16.10.
I chose the Monticarlo SS becasue both the XJS and the Monticarlo were personal luxury Coupes at the time.

If you compare the XJS to other GT 's with a SBC of the same era its not even close, like the 1984 Corvette despite only having 220HP was over a second quicker in the standing 1/4 mile.
After 1984 the gap widens until about 1992 where the SBC runs away with it. Even the mighty 1994/5 6.0 V12 with it's 4 speed auto could only muster a 15.7 second 1/4 mile about where the HO SBC 350's was a decade earlier.

If you factor all the back yard tuning of the 350 it's not even close. Back then we did simple things like grab a 9/16's wrench and loosen 1 bolt to advanced the distributor a few degrees. Weekends were spent installing alu intakes, rocker arms and headers. Those upgrades were good for 25+ hp and that tinkering was part of the fabric of car life in the 80's. If you were well off you could get a set of camel hump or aftermarket heads and a cam, good for 100HP at least. 350 life was totally different … why compare?

 

Please tell the truth. Your $20,000 swap to a Chevy small blocks made 160 Net SAE horsepower. Jaguars made 262 Net DIN horsepower. In America and 291 in the rest of the world. ( except 1980 when it was 299).
Speaking of changing cams, if you know what you’re doing it takes 1/2 the time to change cams on a V12 than it does to change the one cam on a Chevy.
Most Chevy’s have a cast Iron Crankshaft.
Jaguar has a Forging of EN 40 steel and then it’s hardened. Etc etc etc. in other words stuff you have to pay extra to get on in a Chevy is stock in every V12.
Then there is aluminum. You pay a lot extra for aluminum on a Chevy. The whole V12 engine is aluminum. The factory never made a small block Chevy in Aluminum. You have to go aftermarket if you want that.
Finally with regard to the “famous” double bump Chevy heads. The last they were used was 1965. 55 years ago. The chances of finding an unmolested set is extremely rare. Don’t worry some of the Vortex heads work well ( most don’t but if you know which casting numbers to look for•••••)
Same with aftermarket aluminum heads. Depending on what else you’re using. Certain heads will improve things but some will just be awful. In the right combination those awful heads will be great. But you can’t just grab a pair and expect better performance.
But carbs? Simple right? Well the optional carbs for the V12 are bigger than the big Holley dominator. Something almost no small block Chevy can use successfully. But those lawnmower simple carbs on a Jaguar make the Holley look like the wiring diagram of a Jaguar in comparison.
Oh by the way swap the motor all you want and you’re still stuck with that wiring and HVAC.
Finally explain the top speed of your SSMonteCarlo. 120? 125? Doubtful. That Jaguar XJS is capable of 150.

 

OK guys ,so it starts AGAIN!
get over it!
i have owned and modded both engines ! and i do know which responds to basic engine mods!
# 1 if you gonna change just pistons ,you gotta buy 12 / not 8,!
if you gonna change cylinder heads /and valves , you gotta buy 24 custom valves , NOT 16 valves, etc.,etc,, etc!
the cost of the V12 is astronomical compared to GM stuff!
MG ,you must be getting bored ,bringing this stuff up again!
ron

 

as far as the GM 454 BBC , i have owned at least 1/2 dozen, all of them modded for preformance !
pic of this one dynod , 624 wheel HP, 630 torque! thats why they called them TORQUE MONSTERS!, many made more torque than HP #>

82 Camaro, custom 454 engine,(actually 467")

4" exhausts

 

Ron you and I know that big power is made by the combination of the right parts. Not just grab stuff off the shelf or swap meet.

I get tired of seeing Jaguar’s with Chevy’s swapped in them languishing unfinished in garages or the back of shops.
At the peak the con jobs with shops selling engine swaps for perfectly good Jaguar engines because the mechanic couldn’t figure out how to fix the Jaguar is criminal.
I took engine after engine apart and there would be nothing wrong with the engine. No spark? Did you check the ignition module? It says Lucas on the plastic cover but turn it over and there is a GM module that any parts house sells for $10-15 bucks. ( dealer gets at least $300 ).
Not running right? Any leaking vacuum hose? Has the distributor been maintained?

It’s an engine. Works the same as any 4-6-8 cylinder motor except it has 12. All of those early EFI engines were hard to figure out before they standardized on OBD2 and a little plug in gizmo told you what part to replace.
The transmission is a GM turbo 400 or it’s overdrive replacement. Hesitation in shifting. It’s a standard mistake someone put the plastic tube in upside down. Drop the pan pull it out turn it right side up and put the pan back on. You don’t need a $5000 overhaul.
Read the free Kirby manual. Don’t listen to the guys trying to sell you the Brooklyn Bridge.

 

Mother Chevrolet has sold more Bullshit to the American car enthusiasts, then any other company out there. The SBC is the most outdated, and crude engine out there, in as produced form. I remember in the 70's. Hot Rod magazine always talked about "Blueprinting" a SBC. Back then I was just really getting into engines. so I read about them religiously. Having a father who built, and drove sprint cars through the 40's, and fifty's, didn't hurt anything either. So what the heck was Blueprinting??? well that's going through an engine, and cleaning up all the rough edges, the flash, and misalignment form the sloppy manufacturing process.
In machining a part, a tolerance is given. IE. Zero is spot on, a 30 thousandth tolerance. is 30 thousandths either way from zero. That's a total of 60 Thousandths. now everyone that understands engines knows the closer parts are kept to zero, the better they fit, and perform. Chevrolet was notorious for if it was in tolerance, it was used. It's cheaper that way. So you got some great engines, (closer to zero) and some that were slugs, ( on the outside edges of tolerance). Right out of the Factory! Case in point. There wouldn't have been a need to "Blueprint" an engine if they had done it right in the first place. So with all the crap engines, hotrodders blew them up constantly. Many were caused by misalignment of the oil pump, and main bearing cap oil passage. Causing a swirling, and foaming of the oil. Reducing it's volume to the rear main, and causing a rod bearing failure due to reduction in oil flow. All these blown engines contributed to an abundance of extra parts, that people could sell off cheaply, and swap back, and forth furthering parts availability for the average Joe. Ford engines didn't have such crude machining, much closer tolerances, so they were far more durable in stock form, and when hot rodded. They didn't scatter as easily, as stock Chevy's were prone to do. Hot Rod Magazine, never said anything about needing to "Blueprint" a Ford engine. So fewer extra parts. and the price of stock Ford, and aftermarket parts have always been more expensive. So it made it easy for any hillbilly to run a Chevy, cause if he blew it up he could go down to the local junkyard, and pick him up another one for a 100 bucks, and was he going again. which they did regularly. As I've said a million times an engine is nothing but an air pump. The more you stuff in the more you get out, the harder it will run! regardless of what's on the valve cover. In the head department Chevrolet has sadly lacked as far as the SBC was concerned. 2.020 or 2 inches and 20 thousandths, were the biggest valves Chevrolet ever put in the SB heads. The stock Ford 351 C valves were 2.080 for the 2 barrel head, and 2.190 for the 4 barrel, and the ports were oval, and pretty much double the size of the best, Chevy rectangle port. So guess which one ran better. Chevrolet has tried, and does control 90% of the media, so everyone has been led to believe that Chevrolet is the Greatest. Then along came a man named SHELBY, took a SBF, and kicked Chevrolet's and the word's ***! Then he took a 427 CI. (truck engine) and won Le'mans. What has Chevrolet done???? I Forget.
As far as the SBC in Jags to each his own, but I agree with Mguar. A SBC Chevy isn't the cure for what ails a Jag!
Oh and as Far as the Big Block Chevy??? The 427 Grand Sport. They couldn't beat the Cobras either

Just My Thoughts.

Jack (Shelby)

 

Jack what you say has some merit, but why has most of the world of Hot rod engines has been GM, far more than Ford!?
or Chrysler!
and to make over 500HP from a Jag V12, would cost a fortune, Grp 44 last of there engines to make 700hp cost over $20,000. back in 1985.
and i personally seen a number of them blow up at Daytona 24 races, and by far most because of cooling systems!
exerpt from there race program , from the book of building the TWR cars!
simply put the Jag V12 was not a great engineering design, READ IT carefully!

V12 cooling, it says spend time and money on OIL cooling system! TWR

Tullius from Grp 44

 

How often are you gonna flog this dead horse?

Give it a rest!

Cheers
DD

 

This topic had been raised, discussed and argued many times before on the forum. It is second only to "best oil" threads in terms of being resurrected with tedious regularity.

THREAD CLOSED

Graham