SVA form help with Q13

[davidcot]

I have nearly completed the SVA form. Just one question...left

Q13 Max road speed.............?
Max power engine speed............?

Can anyone shed light on the correct numbers to use?

I have fitted a chevy 350cu 5.7ltr V8.

Thanks in advance .. hope to have the SVA mid/late April

David

[Andy S]

Originally Posted by davidcot

I have nearly completed the SVA form. Just one question...left

Q13 Max road speed.............?
Max power engine speed............?

Can anyone shed light on the correct numbers to use?

I have fitted a chevy 350cu 5.7ltr V8.

Thanks in advance .. hope to have the SVA mid/late April

David

Havnt done the SVa mine was built before I got it.
However my estimation would be max road speed 110 that will determine what rating of tyre you fit.
max power engine speed, it appears from other recent posts that this refers to revs at max power and for your enging which is the same as mine I would plump for 4800-5200. the lower you can give the better as this, if I am right, is used to calc the revs used in measuring exhaust Db.

As I said these are on experience not SVA fact and I am sure someone will be along soon that can set the record straight.

Good choice by the way, to coin a well known phrase on here........

[wilf]

Do a search on this. 110mph top speed was rejected recently as being too low for this type of car. The reason for that question is so they can check that your tyres speed rating correspond to the likely max speed of the vehicle. Check what tyres you have (and if they are not rated to 140mph you should change them) and maybe put down 125+mph.

Again - a lot of people were putting down artificially reduced rpms for max hp because " its a big yank engine mate, develops max power way down low" - they are wise to this one, but you are in a cleft stick - put down too high a figure (and they use 2/3rds of that figure for the rpms for the noise check) and won't get through the noise check. Put down too low a figure and again it will get rejected.

3000rpm is about the rpms you want the noise to be checked at, - I'll leave you to work it out.

[tsearle]

Hi, just sent a post on this myself, currently in discussions with Vosa over maximum RPM, the Technical Officer I have is a real jobs worth, I put down 3500 RPM, he is suggesting within his right to insist on a Dyno test? I need to call him back tomorrow and still not sure what I am going to say yet! Who knows if I put 4000 or 4500 RPM maybe would of just gone through?

[JohnWoodman]

Turning the cat on its head, you could get hold of a DB meter and measure the engine rpm that is below the magical pass limit. And as long as its not stupidly low rpm stick that on the form. If it is too low you are going to have to silence the exhausts some more

[wilf]

See also SVA Application Problems

[JohnWoodman]

Hmm....

Reading my previous post I'm not sure I explained what I was intending very well.

What I meant to say

1) Setup db meter as per instructions in SVA test manual.
2) Gradually increase engine speed until the db meter reaches 101db limit.
3) Note the engine RPM at the noise level.

This will give you exactly what engine rpm yields 101db. The SVA test is conducted at 2/3 of engine max power. So you can now work out at what rpm you car will pass the test. Obviously don't go over reving the engine just to get to 101db, generally it is not an issue to get this much noise with a reasonable size v8 at lowish revs.

Example
Say you measure 101db at 4000rpm you can put 6000rpm on the SVA form as 2/3rds of 6000 is 4000. So the test will be conducted at 4000rpm. However, you may want to allow a bit of a margin for error.

If you calculate it this way but find, to get your car through the test, you need to put a really low number on the SVA form then you may have to add some more silencing to your exhaust. If you don't the examiner may question why the rpm is so low. You may get away with telling him that you have a cam that causes the engine to generate power at low rmp but at least if you test the car yourself before the SVA you will know where you stand.

Cheers
John

[Purple AK]

Originally Posted by JohnWoodman

Hmm....

Reading my previous post I'm not sure I explained what I was intending very well.

What I meant to say

1) Setup db meter as per instructions in SVA test manual.
2) Gradually increase engine speed until the db meter reaches 101db limit.
3) Note the engine RPM at the noise level.

This will give you exactly what engine rpm yields 101db. The SVA test is conducted at 2/3 of engine max power. So you can now work out at what rpm you car will pass the test. Obviously don't go over reving the engine just to get to 101db, generally it is not an issue to get this much noise with a reasonable size v8 at lowish revs.

Example
Say you measure 101db at 4000rpm you can put 6000rpm on the SVA form as 2/3rds of 6000 is 4000. So the test will be conducted at 4000rpm. However, you may want to allow a bit of a margin for error.

If you calculate it this way but find, to get your car through the test, you need to put a really low number on the SVA form then you may have to add some more silencing to your exhaust. If you don't the examiner may question why the rpm is so low. You may get away with telling him that you have a cam that causes the engine to generate power at low rmp but at least if you test the car yourself before the SVA you will know where you stand.

Cheers
John

Unless things have changed? Noise is tested at 3/4 Max Power Speed! Not 2/3

[Happy Jim]

David,

Here's a pretty naff Dyno graph that might help...
Gilbert Chevrolet

But if you've got the Centre and Back boxes you should be OK anyway

(Chicken wire up the pipes worked for me by the way!)

Can't believe you're nearly finished, feels like years

Cheers

Jim

[JohnWoodman]

Quite correct the SVA manual says "Run the engine at a constant speed of 3/4 of its maximum power speed. Check the level of sound emitted."

However, there is also a foot note which reads

"Where the engine maximum power speed is not available, the test may be carried out at 2/3 engine maximum design speed."

Sorry got my wires crossed substitute 3/4 for 2/3 in my previous post. Also, it will be better to state a value on the SVA rather the using 2/3 of max engine speed. 2/3 of max engine design speed will definately not get you through the test.

Cheers
John