Need help to understand what to do reach max speed on 91 SHO+

[mavericksav]

Hi everyone! I tried to reach factory announced max speed of 230 km/h (143 mph). But I had only 139 mph. To tell the truth I would like to reach 160-165 mph. What is surprised me that at top speed (225 km/h) engine has only 5400 rpm but max power is at 6200 rpm. I guess it's deficit of air or fuel or both. So I ask by what upgrade should I start.
P.S. Sorry for my english.

 

[luigisho]

Did you go by speedometer reading or other means to clock top speed?

 

[zoomlater]

Did you have the light bar on top of your car during your test pass

 

[Irish Pride]

What have you done to it already? Any mods or factory?

 

[mavericksav]

Did you go by speedometer reading or other means to clock top speed?

by GPS not by speedometer

 

[mavericksav]

Did you have the light bar on top of your car during your test pass

non

 

[mavericksav]

What have you done to it already? Any mods or factory?

nothing

 

[luigisho]

How many miles/km on the engine? compression good? clutch not slipping?

 

[mavericksav]

How many miles/km on the engine? compression good? clutch not slipping?

138 000 ml, 5000 ml after rebuild all parts of std size. compression is good. it runs 15,5 for 1/4 ml.

 

[sperold]

You need that last thousand RPM in high gear.

At the speeds you are considering, drag is your foremost enemy. You can not change your frontal area and the shape of the car is difficult to alter, you have to settle for skirting the wheel openings.
A few years ago, a member (Dirk37 I believe) got amazing fuel economy numbers by doing this and a few other easy mods. I remember whoever it was did a lot of experimenting.

Next issue is rolling resistance. And that is mostly tires, hard as rocks, high pressure, slender tires are best to overcome rolling resistance,

Since those barriers are difficult to change, you have to consider more power, to allow the engine to overcome the barriers that keep it from full rpm in high gear.

 

[luigisho]

Did you have alot of road to try and reach top speed? You got close. What's your relative elevation? Is it enough to make a small difference? To get over 160 you would need forced induction I would think. You can get some higher end hp from regular bolt on stuff but not enough to make that much extra speed.

 

[sperold]

You can research Ernie Groce on this forum who was trying to challenge the F Production record of 167 mph at the salt flats in Utah. This happened around the year 2010. Ernie is now deceased.

I believe he experimented with Weber carburetors. He de-stroked a 3.2 down to 3.0 to fit in the class.
Rather severe modifications, but it shows what lengths people go to, to increase the power output.

 

[luigisho]

His engine work and car were bananas. Never met him but I miss his project posts. His online obituary had a few car pics on it.

 

[mavericksav]

Did you have alot of road to try and reach top speed? You got close. What's your relative elevation? Is it enough to make a small difference? To get over 160 you would need forced induction I would think. You can get some higher end hp from regular bolt on stuff but not enough to make that much extra speed.

I had 6-7 ml, Elevation is about 200m from see level. Forced induction you mean cold air?

 

[luigisho]

Boost. turbo/supercharger etc

 

[mavericksav]

Boost. turbo/supercharger etc

yes, but I would like to keep it N/A

 

[luigisho]

ok. well you can lighten it, do alot of custom machine work on internals, look at a little aerodynamic tweaks. There's not alot of room to reach your stated top speed goals without reworking the characteristics of the engine. and when you do this you will want access to a spare in case something goes wrong. This isn't a motor that left a ton on the table you can tap into with a few bolt on modifications and a tune.

 

[itwonder]

What kind of shape is your exhaust system in? Wind can make a big difference; Did you run your top speed pass in two directions to check to differences?

 

[zoomlater]

What tire size do you have on the car (stock?), that can affect the speedometer reading

 

[kevinspann]

Aerodynamics. You don't have enough power to push the car through the air any faster.