How far to push the engine back in the chassis.

[Guishnu]

As some of you will already know, i have a 200sx S15 which i am putting a VH45DETT into. The question is, how far do i have to push the engine back in the chassis to make it handle as "close to" an SR20 powered S15?

Does anybody have any experience with this? Im guessing it's actually going to be a question of mathamatics...

[maxnix]

Not only back, but I bet down also.

[Mettler]

Yep... custom sump it so you can bring it right down.

[Guishnu]

ah right,so down and back...

Any idea how much?Does anybody know how much an SR20DET weights fully dressed with turbo and box compared to a VH45DETT fully dressed with a pair of turbo's and a Z32 box?

[Mettler]

That's some pretty hard maths to figure out, because having a gearbox bolted to the back of the motor biases a lot of the weight towards the rear of the assembly.

The weight either goes into the front crossmember through the engine mounts, or into the gearbox crossmember (and therefore roughly the center of the chassis) through the gearbox mount.

While I don't think you'll be able to perfectly match the SR20's weight distribution, if you set it up so the motor's both as low and as far back as you can possibly get it, with minimal clearance, then you probably won't notice much of a handling difference at all... Something that after a few laps, you will soon grow accustomed to.

Are you concerned that you're going to radically change the handling? You can always counter that by retuning your suspension damping settings etc.

[Guishnu]

So do you think it's worth pushing the engine back through the firewall a tad? I don't want to go "too" far back as it will end up handling like a mid engine car (which i really don't want, although others seem to favour)

Do you think back and low within the standard engine bay may be the way to go then?

Chris

[Mettler]

Seemed fine in my car... but then, mine's not built for the purpose of sustaining sideways slides.

Why don't you put your car on a weighbridge that can measure the weight distribution, and then when you drop the V8 into it, do it again and judge from there whether you need to move the engine.

There's an S13 Silvia here in NZ fitted with a VH41DETT putting out around 800HP, I've seen a video of the driver sustaining a very long sideways slide at a local racetrack, and I think all he did was fit the engine into the bay as best as he could without recessing the firewall.

Oh, found it, here:

http://www.youtube.com/watch?v=-O2ZIBme ... OKqf_EnqnI

[David Steele]

This is something you can never ask on a forum.

You need 4 corner weight scales and you compiling what items your are going to use.

Everything your going to use from hood to subframe to wheel and put it all on the car.

[ZedZillaZ32]

That's some pretty hard maths to figure out, because having a gearbox bolted to the back of the motor biases a lot of the weight towards the rear of the assembly.

The weight either goes into the front crossmember through the engine mounts, or into the gearbox crossmember (and therefore roughly the center of the chassis) through the gearbox mount.

I must complain about your choice of words here, its sounds like you are trying to say that the position of the engine mounts or gearbox mounts has some bearing on the weight distribution of the engine/gearbox... that is not true, simple moments the engine and box will act the same regardless of the offset of engine or gearbox mounts. Further more i'ld like to say that the "SR20 handling" will never really be obtainable with a TT'ed Vh45DE and z32 box. your are simply adding too much mass in front of the vehicles COM (centre of mass).

However if you want to get a similar weight distribution it could be done with a recessed firewall. But why?, the "amount of SR20 handling" (<-- I use this as a very loose term) you will loose by only mounting the engine as far back and low, without cutting the firewall would be minimal. If you want a road car then rear mount the battery, use FRP gaurds and bonnet and use a light weight turbo manifold with bracing and make up a sheetmetal inlet manifold use the shortest thinest intercooling set up possible.

With +700hp why are you so worried about the handling? if its a race car and thats why the concern for the weight distribution, then cut the d@mn firewall easy!

Its not hard or complicated really, its just expensive to get someone else to do it thats all

(BTW i dont mean to rain on your parade)

[Mettler]

I must complain about your choice of words here, its sounds like you are trying to say that the position of the engine mounts or gearbox mounts has some bearing on the weight distribution of the engine/gearbox... that is not true, simple moments the engine and box will act the same regardless of the offset of engine or gearbox mounts.

Nah I wasn't talking about offset/positioning of mounts, I was talking about the weight distribution of engine & gearbox assembly between the front & middle mounts. If the engine was lighter and the gearbox was heavier, then more weight would be biased towards the rear of this assembly and would therefore place more load on the gearbox mounts, changing the overall weight distribution of the car.

I hope this clarifies what I was saying a little.