Speed Issue

[Guest Al-Bicester]

I have a series 3a with the normal 2 litre pinto, 32/36 DGAV, 5 speed etc. Sounds good, accelerates like nothing else but the top speed seems to be stuck around 90mph (in a controlled environment of course). The car will easily accelerate to 80 in 3rd at around 6000rpm, change into 4th and the speed will increase steadily to 90 as the revs drop a little, put it in 5th and the speed can actually tail off to 85mph as the revs drop to around 4000. Changing down to 4th brings the revs up a little and the car does pick up but only to around 90 again. A friends S7 has a similar top speed issue.

 

Is this because we have the aerodynamics of a brick and if so how do our posh cousins in Caterhams claim top speeds into the 120+ bracket?

 

Al

[Guest chris brown]

Is this because we have the aerodynamics of a brick

Got it in one any open wheeled car is poor on aerodynamics as you are pushing what are in effect 2 square blocks through the air (wheels). Just look at a F1 car versus a GT racer, even the 2ltr MG LMP2 car is quicker. As for the catering van well it is smaller, lighter and it’s only the higher powered ones that are really fast. As for your top speed I think you may be down on power a bit I can hit 100 and hold it in 5th with no real problem and can cruse all day at 85. 110 well that’s a different matter it gets there but so does christmas.

[Guest salty_monk]

My old car - would go to 115mph with a 3.92 diff in fifth gear.

Same car, engine everything (2ltr pinto, piper 285, no vernier pulley) 38 DGAS, modified dizzy) with 3.62 Diff - 95mph in 4th Gear, 90mph in 5th. Car rolling roaded at 99 BHP wheels (121BHP flywheel).

 

New Car - 2ltr Rs 2000 ported head, Kent Cam, vernier pulley, standard Dizzy, 38 DGAS, 3.62 Diff will pull to 100 MPH easy in 5th Gear. Not rolling roaded yet.

 

As Chris says - aerodynamics are poo. Lose some weight or change for a 3.92 diff or put on a bigger carb & Cam kit etc.

 

Dan

[Guest stu205]

does sound like your a little down on power, my 2B runs a standard 2ltr and 85 is no problem at all in 5th and will pull when you put your foot down from there too (dont know terminal top speed) so your 3A should be doing the same as its lighter

[Guest micky bigthumbs]

I think grim is right there is something wrong in the tune up my 3a will go over 120 in an un-controlled environment although the speedo is wrong the road angel 2 gives a very close reading.have you checked the speedo

[Mat-Moo]

Cycle or clam shell wings?

[Guest timswait]

Likewise, don't expect much over 100, but it does sound like you're a tad down on power. Also it will go faster with the roof on, or even faster if you take the windscreen off.

I think grim is right

You been smoking too many of your funny fags? I don't see Grim on this thread, even though I'm sure he'll be glad to know he's right even when he hasn't opened his mouth!

[BigLee]

Aerodynamics play a big part and those swept wings dont help I guess, if you have those, like I do. Diff ratio will also play a big part.

 

Luckily I don't have any problems on this front, but then I have a lump that weighs the same as 3 small continents. It does help the top end though, which is enough!

 

Although of course I have never tested it on the public highway.

[Guest chris brown]

You been smoking too many of your funny fags?

I wondered that too but didn’t like to ask

[Guest stu205]

maybe he means Dan, we all know what he can be like

[Guest red7]

Going very fast in a 7 is terrifying! Probably my over active imagination but when I am approaching the Ton I feel very unsafe. I imagine what what would happen should a tyre blow or something break. Every nerve in my body and every remaining active brain cell is on full power. Unlike in my Focus where I feel so secure I can listen to the radio, look at the scenery passing by, hold a conversation with my passengers etc. In my opinion 7's are not about top speeds but cornering ability, handling and sprinting off the line. Once you'r in triple figures in a 7 the outcome of the slightest mechanical failure will probably result in something horrible. Am I getting old? Probably.

[Guest chris brown]

I imagine what what would happen should a tyre blow or something break.

I wouldn’t worry too much Steven. You probably wouldn’t know much about it and anyway you go gray if you worry, or so they tell me.

[Guest red7]

When I get the usual question from Joe Public "What's your top speed mate?" I usualy reply "I don't know, I've not been there yet. But I can tell you 90 feels like 220 in your tin top". That get's them thinking.

[Guest timswait]

Mine feels pretty stable and composed at the ton (on track of course), even if a bit blustery! Maybe I just lack an active enough imagination.....

Oh, and I saw 115mph on the speedo at the Ring, but that was down quite a hefty hill. Still felt stable, but I couldn't help worrying whether the clamshell wings would stay attached, so I didn't keep my foot down.

[Guest salty_monk]

For interests sake I should tell you my first car was clam shell wings & my second has cycle wings... Maybe they make that much difference at the top end....

 

Anyone who's done a conversion care to comment?? There are a few out there. Daren F is one but I think he's on hols...

 

Dan