: L37 vs LD8, actual differences?



venom242
01-11-05, 02:19 PM
I was just wondering what the differences are between these two engines. I know the cams are different, but what else?

Thanks.

eldorado1
01-11-05, 02:43 PM
That's it. As far as powertrain differences, the 300hp has 3.71 gears vs 3.11 for the LD8

BeelzeBob
01-11-05, 10:52 PM
I was just wondering what the differences are between these two engines. I know the cams are different, but what else?

Thanks.


The 93-99 engines have a different intake cam only.

The 2000 and later engines have different intake and exhaust cams.

Katshot
01-12-05, 08:06 AM
I never checked it out but someone told me that the valve springs were different too. It that true?

danbuc
01-12-05, 12:36 PM
The force required to compress the intake valve srings is a little more on the STS I think mostly due to the higher lift of the cam itself. This would put more stress on the springs. This is what I know from my 1998 Service manual, and is probably a little different from other years.

BeelzeBob
01-12-05, 11:21 PM
The valve springs were different on the 93-96 Northstars. The L37 engine had slightly higher tension springs because the L37 engine is set up to shift at 6500 where-as the LD8 shifts at 6000.

The LD8 engine had the softer springs for reduced friction and improved fuel economy. Small but directionally correct friction reduction for the fuel economy car. The softer springs were fine due to the 6000 RPM upshifts.

Interestingly, the stronger springs for the L37 were for the EXHAUST cam lobe action at the L37 6500 shift points. The exhaust cam lobe is fairly radical in it's lift rates/acceleration on the lobe ramps so it needs a stronger spring turn the higher RPM. Remember that the exhaust cam is COMMON between the LD8 and the L37. The intake cam is the different cam with more lift and duration on the L37 engine. The L37 intake cam (more aggressive of the two) can actually work fine at 6500 shift points with the softer springs due to the relatively mild acceleration of the cam lobe lift. The exhaust cam is the one that needs the stronger springs for the higher RPM operation of the L37 package....not the higher lift intake cam...!!!

The L37 needs to rev higher to make the extra HP. That is the only way to make more power with the displacement and such fixed...rev it up higher. So the bigger inlet cams increase lift, flow and valve overlap to increase the RPM capability to make more power but the common exhaust cam going along for the ride needs stronger springs to handle the RPM.

How's that for a little Northstar trivia...???....LOL

BTW....the springs were commonized to the stronger versions mid model 1996....so after that the only difference was the cams.

On the 2000 and later engines there is only one version of the valve spring regardless of the LD8 or L37.

danbuc
01-12-05, 11:30 PM
Thanks for the correction Bbob. I was too lazy to pull out my service manual, so tried to remember what they were. I guess I was a little off. :rolleyes: . I knew it had something to do with the lift on the cam.

STS 310
01-13-05, 08:55 PM
So, the "suttle" differences were implemented for fuel economy? The HP remains the same rite.

Sorry, its BeerThrity and comprehension is at a low.

BeelzeBob
01-14-05, 01:11 AM
The power is the same regardless of the springs mentioned...

The springs actually made very little difference in the fuel economy as it turns out...so they were commonized to the higher performance version.

danbuc
01-14-05, 02:34 AM
Bbob, do you know what it was exactly, that made the newer STS's a little faster than the 1998-99 models? I was just curious, since I think the 2000+ is rated at 6.5 0-60, and the 1998-99 is rated at 6.8 0-60 (mine feals much faster than that though). Is it the new design of the valvetrain, or did they make the tranny more efficient or something? Thanks in advance. :D

caddydaddy
01-14-05, 08:14 AM
Well, in 2000 the Northstar got roller cam followers. That might make a difference.

venom242
01-14-05, 11:03 AM
Is there a difference in fuel economy between the L37 and LD8?

Ranger
01-14-05, 12:35 PM
Is there a difference in fuel economy between the L37 and LD8?

The L37 has a 3.71 final drive and the LD8 has 3.11, hence the LD8 will get slightly better milage.

BeelzeBob
01-14-05, 02:07 PM
The L37 has a 3.71 final drive and the LD8 has 3.11, hence the LD8 will get slightly better milage.


This is true...plus...most cars that have the L37/3.71 final drive also have performance oriented tires on them that inherently have much more rolling resistence compared to the tires on the LD8 cars. The tires can make a huge difference in the fuel economy on any of the cars.

Generally, the STS/ETC/DTS packages with the L37/3.71/performance tires suffer about a 2-3 MPG penalty in the city and 4-5 MPG on the highway I would estimate in the real world.

dkozloski
01-14-05, 02:48 PM
bbob, I have heard that some of the Formula I engines use air springs for the valves. Also they have gone to the trouble of regulating the air pressure up and down to relieve stress when the high pressures are not required. I saw a six cylinder Honda 250cc motorcycle engine with torsion bar valve springs that turned 22,500RPM. What an unbelieveable sound.

BeelzeBob
01-14-05, 03:36 PM
The forumula 1 engines have used air springs for the valve actuation for many years. That technology is banned in most all other motorsports due to the cost and complexity.

Any mechanical spring has a resonance frequency and the major struggle with a valve spring design is to design a spring that will perform at the desired lift/acceleration/jerk rates of the cam lobe associated with the desired operating RPM range. Since the F1 engines have to rev near 20K to make the power that they do the use of conventional valve springs is almost impossible due to the spring resonance and surge problems. Air springs do not surge per se...they are naturally damped and therefore work well to actuate the valves. The system to supply the high air pressures required (actually nitrogen is used I believe in the systems...not "air") is very comlex and expensive and not something that will live for years on the street. Works well for 2.5 hour races.....

dkozloski
01-14-05, 06:10 PM
Aircraft engines have multiple valve springs for redundancy with a tight coil on one end that goes toward the cylinder head to reduce the effects of resonance. I had a very expensive twin engine aircraft brought to me with geared and supercharged engines that were running rough at high speeds. The 425HP engines(IGSO-540B1A) had just been overhauled by the Lycoming factory in Williamsport, Pa. It didn't take me twenty minutes to find that the valve springs were installed randomly as if the assembler didn't know about the spring design. I admit that the tight coil is pretty subtle unless it has been pointed out to you but you would think the factory would know better. The customer left a very happy man after I reinstalled the springs and his $55,000 engines ran as smooth as glass. I still haven't figured out why the defect wasn't found in the test cell at the factory.

BeelzeBob
01-15-05, 12:30 AM
Yes, there are lots of techniques used to dampen the valve spring resonance or spring surge. It is amazing to see a valve spring surging at high RPM with super slo mo video equipment. The spring surges just like a slinky back and forth and the effect can be so severe as to actually pull the end of the spring away from the retainer while the spring is on the seat.

Some springs have multiple springs that cancel each other's resonances out. Others have damper coils inside or flat spring dampers that use friction to dampen the surge out. The newer LS1 chevy engine has oval wire and beehive shaped springs that do an excellent job of damping with single coil springs and no friciton coils inside. At 18,000 RPM, however, nothing much works.....so the F1 race teams resort to the pneumatic valve spring setups.

dkozloski
01-15-05, 02:27 AM
Ed Iskendarian of camshaft and valvegear fame thought he had come up with a killer setup for a cam, pushrods, and rocker arm setup. He was amazed to find that the engine would barely run. He got the bright idea of using a General Radio Company stroboscope to see if he could stop action in a manner similar to a timing light. He about fell over when he saw very little movement in the valves but everything else including the pushrods and rocker arms were flexing all over the place. He had to start over and develope the whole package again and eliminate the flexible parts. He must have succeeded because his name became synonymous with high performance cams.

airfuel2001
07-06-07, 10:10 PM
I tried to retrofit a 2000 intake to my 97. its the same design but about 15% larger runners. It would make all the difference in the world I would think, but it is to hard to make fit and work properly

eldorado1
07-06-07, 10:18 PM
I think you beat the record. 2 and a half years. Congratulations.

Regarding the intake... why not make an adapter plate that bolts inbetween the heads and intake? Done all the time for things that don't fit.

clarkz71
07-07-07, 03:22 PM
I tried to retrofit a 2000 intake to my 97. its the same design but about 15% larger runners. It would make all the difference in the world I would think, but it is to hard to make fit and work properly

If the intake is better then 95-99, why do the 2000 and up make the same hp? (LD8 275/L37 300)