LS engine positioning relative to steering rack and firewall

[lifeprojectZ]

I have searched and can't find good close-up photos or measurements showing me the following in LS Z-car installs:

 

1) Distance from rear face of block to firewall.

2) Fore/aft positioning of OE steering rack centerline relative to engine damper / oil pan.  Is the damper completely behind the rack centerline, or are you lining up the centerline of the rack with the space between the rear of the damper and the front of oil pan?

 

I am working on a full custom chassis install in my 280Z, detailed in the member's projects section, and looking right now at the steering rack positioning and engine mounting.   I don't have the engine yet, but hope to order a long block later this year.  Am curious to know how mine is going to end up relative to others who have kept the OE steering rack position and are using aftermarket designed engine mounts for the LS in the Z car with OE engine bay frame rails.

 

Thanks in advance for any info you can share.

 

 

[Fridge Gnome]

So this isn't entirely helpful, but here's some pics of my LT which is approximately the same dimensions as an LS.

 

 

Done correctly, I believe there is room to get the damper behind the steering rack. The LT didn't have full adjustability on the dirty dingo mounts I'm using, so I would have needed to modify them to move the engine back.

 

Depending on oilpan you may not want to go too low though. Mine is flush in height with the front crossmember.

 

[lifeprojectZ]

Thank you!  Is your car lowered and if so how much?   Another concern I have....I had my chassis built around having the body lowered about 3" from OE spec.   51.5" roof height down to 48.5" roof height.   I'm a bit concerned about fitting the LS in, keeping 4"  ground clearance with the pan sump, and not having to modify the hood any.  Hoping to keep original hood contour.  I forgot to consider engine height before settling on the ride height for the chassis.   I'll have an LS long block within 6 months, but I can't stop thinking and dreaming about how this is all going to work out.

[Fridge Gnome]

There's more clearance under the hood than you might think. Unless you have the truck intake or something there's plenty of room for an LS in these cars without any ground clearance issues. I have a goofy throttle body setup on mine that sticks way up, but it still clears the stock hood.

[fusion]

I don't believe you can have the damper behind the steering rack.  I have a Corvette damper which is the tightest to the block and mine sits directly over the rack.  This is with the engine as tight to the firewall as I was willing to go.

 

Clearance to the hood is fairly good.  I don't think you'll have a problem there.

 

[zboi]

All the kits I've seen have adjustable motor mounts to slide the engine forward backwards. Full back on them will still have damper on or in front of rack. You can put them low enough to have a stock gen IV truck intake clear, but just barely.

[Michael]

Lifeproject, given that you have a sturdy chassis/frame under the car already, would it perhaps be reasonable to cut/notch the firewall, for additional engine setback?  That gives you better weight distribution, and more room under the hood... not just for the harmonic-damper issue, but cooling-room in front of the engine.

[lifeprojectZ]

Really appreciate the responses and would love to see more.   Very interesting to see what others have done and even more to know why.

 

On 9/4/2023 at 8:08 PM, Michael said:

Lifeproject, given that you have a sturdy chassis/frame under the car already, would it perhaps be reasonable to cut/notch the firewall, for additional engine setback?  That gives you better weight distribution, and more room under the hood... not just for the harmonic-damper issue, but cooling-room in front of the engine.

 

I may have to end up doing that for header clearance if nothing else, but am hoping to keep the firewall as original as possible.   One of the big unknowns is how my weight distribution will turn out given the custom chassis, steel cage IRS with the Dana 60 differential, roll cage, etc.   I hope to get it close to 50/50 but I won't know until the car is complete.   Looks like I'll be getting an LS long block within the next 4 months so I'll be able to see more clearly how it will play with the rack position and firewall.  Another benefit of moving the engine/ trans back would be getting the shifter in a better location.   Right now I'm leaning heavily towards the Tremec TKX instead of the T-56 Magnum F as I just learned it is 40 lb lighter, and I don't need two overdrives.  But the shifter is a few inches further forward.    I just don't want to end up weight biased heavily to the rear of the car.....but not completely sure of that either.  

 

[Phantom]

For what it's worth my car ('77 280Z) was used by JCI to develop their LS1 conversion components.  I have an LS1/T56 combo in mine.  I had my280Z axle weighed with 3/4 tank of gas before the conversion and it was a perfect 50/50 with 1400 lbs on each axle.  After the conversion it was 1400 front and 1430 rear but that was with a heavy torque tube design underneath.  With standard transmission & differential mounts the distribution would probably not have changed at all.

Just know that when you sit down in the car about 2/3 of your weight will be on the rear axle. Yup, with a driver, you'll be tail heavy.

[Michael]

On 9/8/2023 at 2:33 PM, lifeprojectZ said:

...One of the big unknowns is how my weight distribution will turn out given the custom chassis, steel cage IRS with the Dana 60 differential, roll cage, etc.   I hope to get it close to 50/50 but I won't know until the car is complete.   Looks like I'll be getting an LS long block within the next 4 months so I'll be able to see more clearly how it will play with the rack position and firewall.  Another benefit of moving the engine/ trans back would be getting the shifter in a better location.   Right now I'm leaning heavily towards the Tremec TKX instead of the T-56 Magnum F as I just learned it is 40 lb lighter, and I don't need two overdrives.  But the shifter is a few inches further forward.    I just don't want to end up weight biased heavily to the rear of the car.....but not completely sure of that either.  

 

 

One of the perennial debates is (or rather was, when this Forum was more active!) about front-rear weight distribution vs reducing polar moment of inertia.  If the really heavy components, namely engine and transmission, move aft, then presumably the polar moment of inertia is reduced, even if the weight distribution becomes aft-biased.  So, suppose that the car comes out to 47/53.  Is that necessarily a disadvantage by itself?  If so, is it a disadvantage if in combination with lower polar moment of inertia?

 

Many people prefer the aesthetics of wider tires in the rear.  Doesn't that actually lend itself to good remedy for being tail-heavy?  I mean, it's just an aesthetic thing... but for a tail-heavy car, it might also turn out to be of practical value.

[Phantom]

Mine ended up 48 front/52 rear with the LS1/T56 combo.  The LS1 obviously has a lower CG than the L28 and it sits farther back with everything but the accessory drive behind the steering rack. Having driven the car for 31 years now (20 years with the LS1/T56) I'm confident that the handling is at least equal to if not a bit better than the L28.  It does require more finess as the L28 never gave me lifting throttle oversteer which I can get with the LS1.  The Ls1 also improves throttle steering in corners once you get the car figured out.  One thing - it does not forgive stupidity with the throttle.

[lifeprojectZ]

On 9/17/2023 at 9:42 PM, Michael said:

 

One of the perennial debates is (or rather was, when this Forum was more active!) about front-rear weight distribution vs reducing polar moment of inertia.  If the really heavy components, namely engine and transmission, move aft, then presumably the polar moment of inertia is reduced, even if the weight distribution becomes aft-biased.  So, suppose that the car comes out to 47/53.  Is that necessarily a disadvantage by itself?  If so, is it a disadvantage if in combination with lower polar moment of inertia?

 

Very interesting to think about that.  I've not seen the topic discussed before, but haven't been with this forum for very long.   I would think that the change in polar moment of inertia with setting the engine back would be very minimal and have an unnoticeable effect.   The Z cars are already extremely nimble with such a short wheelbase.   Personally, I can understand and appreciate much more the effects of understeer / oversteer that go along with front or rear weight bias, respectively.   However, I'm not sure that I would notice it myself in a 47/53 car or a 53/47 car during normal or even moderately aggressive driving.  Maybe?   I am sure someone who track drives a car regularly and then makes a change affecting that car would notice it.    In my case, I am just shooting for a target that I think is worthy, but I will end up dealing with whatever it turns out to be, and hopefully enjoying it regardless!

 

On 9/17/2023 at 9:42 PM, Michael said:

Many people prefer the aesthetics of wider tires in the rear.  Doesn't that actually lend itself to good remedy for being tail-heavy?  I mean, it's just an aesthetic thing... but for a tail-heavy car, it might also turn out to be of practical value.

 

Definitely a consideration for me.  I went with 255/40/18 on front and 295/35/18 on rear.  Both sizes are 25.0" diameter, and I felt that was extremely important for the balance of the car lowered 3".  I like the tire width proportions as viewed on the bare chassis, and I think I will like them even more with the Datsun body over top.   My biggest concern at the moment is my scrub radius at close to 3".   Is the car going to scramble out to either side when I step on the brakes at high speed?   I could reduce that somewhat by using 295/35 on the front as well, but I am not ready to do that until I drive the car quite a bit and find that change necessary.  I am however leaving enough inboard space to fit the 295's in case I want to do that in the future.  More on that in an upcoming post on Ackermann measurements in my project thread.

[lifeprojectZ]

Got my own tire sizes wrong.  They are 255/35/18 on front and 295/30/18 on rear.

[JMortensen]

You can mod the shifter if you get the shorter trans, may require some surgery on the center console if you're running with an interior. Sounds more race car based build though.

With regards to weight distribution I can tell you I went from the L6 and 49.5F/50.5R to the LS 52/48 and having changed the spring rates and alignment, etc that the "nose heavy" LS version turns in WAY harder than the L6 version ever did. I moved the engine to the right 1.5" and have the right head about 3/4" from the firewall, had to cut part of the trans tunnel to fit the bell housing. Spring rates are 600/700, no rear bar anymore. The point is you can work around the weight distribution issues.

In a more extreme example, I used to autocross against the Mustang guys at Maximum Motorsports. Fox body Mustangs have a ridiculously bad distro of something like 60/40, and MM made those pigs fast. 

EDIT--will be harder to avoid understeer with staggered tire setup.

Edited September 23, 2023 by JMortensen

[christianmoller]

LSA works, 5/8" to the hood and engine/driveline center as I6.

A tight fit but it does work 😀

Have a nice evening

Christian

Gothenburg

Sweden🍻