Bec TOP SPEEDS??

[JRM Rossi]

HI ALL just went for a blast(on a private rd) my mnr vortex it has all ways been a bit rev happy & sharp,it runs a zx9r lump and on the limiter in 6th its 103 mph (GUTTED!) its getting there very quick...lol... time for some bigger tyres on the rear? i was just thinking what top end speeds you bec guys were doing? the road angel was saying 103mph.yawn yawn! this is way too low hence the wheelspin in 4/5 gear?? the rear tyres are 195/45/15 can any one suggest a larger size or work out the size i need to get another 25/30mph? or will it be a diff change ?

i was going to try 205/55/15 semi slicks

its flat out before the 1/4 mile its ok for car parks & traffic lights !
if any ones after a set of 195/45/15 mine are coming off asap

jason

[Snake the Sniper]

Sounds like you may have a 3.9 diff in there. Mine tops out at 125, with a 3.6 and 195/50/15 tyres. That's with a 10,750 red line. It's quite a simple job to change the diff out for another one.

[robcollingridge]

My Fury R1 does ~130mph flat out in 6th and that's with a 3.38 diff and 13" wheels.

[Timwenham]

I've seen an indicated 135mph (with speedo healer fitted but still obviously less in reality) in 6th with not too many more revs to use in the MK Indy r1.

[JRM Rossi]

Time to pull out the diff ! & hunt down a diff with push in shafts? is it worth going cosworth rear end? as mine has drums? or just change diff ??

[dean100yz]

Snake the Sniper said:

Sounds like you may have a 3.9 diff in there. Mine tops out at 125, with a 3.6 and 195/50/15 tyres. That's with a 10,750 red line. It's quite a simple job to change the diff out for another one.

Yeah mine does similar at about same revs. Ive seen 126 on my DD1. Mine will rev to 11,900 give or take. Not sure if its a 3.6 or 3.38 but 103mph sound very low! Must be manic changing gears!

[JRM Rossi]

yep 100% manic coming home from the meet last month was fun all back roads (1st nighttime run)so it was ok ,got to find a diff now 3.38 push in shafts .i run out of gears in 9seconds just revving too high mind u its a fun 9 seconds (poor engine) roll on the next meet @ the lodge hopefully will sort my gearing out

[hugh_]

My old Fireblade Fury would do 120 on the red line in 6th; 3.54 and 205/60/13s

[singlecoil]

Easy enough to change a diff, problem is finding a more suitable one. They certainly exist, but tend to get snapped up quickly when they come on the market.

I personally wouldn't bother changing rear drums to discs, as drums are more than adequate for this sort of car.

[Furyous]

My old Fury9R would do 127 on the red line in 6th; 3.54 and 205/60/13s

[Kiwi XTR2]

Mine's something like 230-235






Metric

[matt frost]

Our megabusa used to do 122 in 6th and that was with a 3.38 diff. We have since had it rebuilt with a 3.076 ratio and will now do 133mph or 143 with the 6th gear limit increased.

[rhinochopig]

I'm finding some of these sevens claimed Top speeds a little optimistic. The fastest I ever saw in my Blackbird powered westy (~165bhp) was somewhere around 125mph and that was at Elvington, and the aero was the limiting factor - not gearing.

[Busa_Rush]

JRM Rossi said:

Time to pull out the diff ! & hunt down a diff with push in shafts? is it worth going cosworth rear end? as mine has drums? or just change diff ??

The 7" diff from the 1.6/1.8 Sierra is plenty strong enough, has push in shafts. There are two types of drive shafts, you can use the smaller ones from the 1.6. I have 7" diff with ZF LSD and the smaller push in drive shafts on my car. The diff is a 3.14. I have rear discs but only because I have an aversion to drums, don't like the look of them, prefer discs.

Don't be tempted by the 7.5" diff, much heavier and the bolt in drive shafts are much heavier again than the push in type. My car has over 300 bhp and the wheels spin long before the diff gets too loaded.

[matt frost]

rhinochopig said:

I'm finding some of these sevens claimed Top speeds a little optimistic. The fastest I ever saw in my Blackbird powered westy (~165bhp) was somewhere around 125mph and that was at Elvington, and the aero was the limiting factor - not gearing.

In case you are referring to my original post, may I just add that those speeds are theoretical....i.e. what the gearing will allow, not what it has actually done.

Also, Elvindon being an airfield I would imagine that air resistance is much greater than on a track as it is so open. Therefore you would probably hit a higher speed on a track if the straight length allowed.

[LaurenceFrost]

rhinochopig said:

I'm finding some of these sevens claimed Top speeds a little optimistic. The fastest I ever saw in my Blackbird powered westy (~165bhp) was somewhere around 125mph and that was at Elvington, and the aero was the limiting factor - not gearing.

Top speeds in the BEC kit car world are always written as what the car is geared to, instead of what the car will actually do.

I know for a fact that the Megabusa that Matt and I share would hit the soft-cut limiter at Brands Hatch indy by the end of the straight (122mph), so optimistic or not, I would much rather have the car geared to 133mph. If the car manages to hit that top speed or not is irrelevant. What it does mean is that you don't sit on straights bouncing off the rev limiter.

This does not mean I would quote the top speed of the car at 133mph though - I just know that this is the most it would do.

I would rather hit an aerodynamic wall than a gearing wall. It's better to sit at the same speed and be 1,000rpm lower on revs IMO.

[Kiwi XTR2]

matt frost said:

Also, Elvindon being an airfield I would imagine that air resistance is much greater than on a track as it is so open. Therefore you would probably hit a higher speed on a track if the straight length allowed.

Ummm ? ¿ ?

[matt frost]

Kiwi XTR2 said:

matt frost said:

Also, Elvindon being an airfield I would imagine that air resistance is much greater than on a track as it is so open. Therefore you would probably hit a higher speed on a track if the straight length allowed.

Ummm ? ¿ ?

I thought that on an open and totally flat area such as Elvington airfield, there would be more likely more air resistance due to more common crosswinds along a flat unsheltered area than at say a some tracks which wouldn't suffer so badly. But I guess this wouldn't be the case for every day of the week and every track, its a bit of a generalisation.

I am guessing you think different, if I am wrong, please tell me why rather than just question marks so I know for the future.

[custardtart]

matt frost said:

Kiwi XTR2 said:

matt frost said:

Also, Elvindon being an airfield I would imagine that air resistance is much greater than on a track as it is so open. Therefore you would probably hit a higher speed on a track if the straight length allowed.

Ummm ? ¿ ?

I thought that on an open and totally flat area such as Elvington airfield, there would be more likely more air resistance due to more common crosswinds along a flat unsheltered area than at say a some tracks which wouldn't suffer so badly. But I guess this wouldn't be the case for every day of the week and every track, its a bit of a generalisation.

I am guessing you think different, if I am wrong, please tell me why rather than just question marks so I know for the future.

I think you just answered him yourself - "it's a bit of a generalisation" in some situations one will suffer more wind than another

[andygtt]

matt frost said:

Kiwi XTR2 said:

matt frost said:

Also, Elvindon being an airfield I would imagine that air resistance is much greater than on a track as it is so open. Therefore you would probably hit a higher speed on a track if the straight length allowed.

Ummm ? ¿ ?

I thought that on an open and totally flat area such as Elvington airfield, there would be more likely more air resistance due to more common crosswinds along a flat unsheltered area than at say a some tracks which wouldn't suffer so badly. But I guess this wouldn't be the case for every day of the week and every track, its a bit of a generalisation.

I am guessing you think different, if I am wrong, please tell me why rather than just question marks so I know for the future.

on the flip side you may also have a higher top speed on the airfield due to tail winds....