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Best Small Bore Exhaust Spec


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#1 ads7

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Posted 19 November 2019 - 09:24 AM

I currently have an 850 fitted which is still running the exhaust setup from previous 1293, medium bore LCB + 2 inch single box stainless system.

I'm looking to gain a little more power by fitting a small bore 3 branch manifold and 1.75 inch mild steel system leading to either a Sprite Mk1 box or an RC40 can.

Two questions to see if it's worth bothering

First will the power gains be marginal or worthwhile?

Second, has anyone fitted a sprite box how does it sound?

Cheers

Edited by ads7, 19 November 2019 - 09:30 AM.


#2 luismx123

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Posted 19 November 2019 - 10:16 AM

I cant speak for a 850 but i recently swapped the exhaust and manifold on my 998 from the smallbore LCB and rc40 to a maniflow cooper freeflow and maniflow center exhaust (the small diameter one).
Instantly worked better, sounds better. Its a noticable increase in performance and i know this may sound weird, but standing behind the car and holding my hand to the exhaust - the new maniflow setup blows a lot more air out than my old setup did (i used to be amazed by my friends 1100 exhaust system blowing wind out for meters and my tame rc40 998 would just fart some air out the back. Now there is serious pressure coming out. Not sure if this is a valid measurement but it seems to have free'd up the exhaust....Also the manifolds diameter change is quite substantial as the lcb before was quite a bit smaller...I think the rc40 and center exit maniflow are pretty much similar)


Hope this helps



#3 Daz1968

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Posted 19 November 2019 - 10:20 AM

I have gone for a freeflow maniflow manifold and twin box rc40 side exit on my 998, should be better than a 2" system, although retaining your manifold and fitting a rc40 should also benefit the car.

#4 ads7

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Posted 19 November 2019 - 03:55 PM

Thanks guys for your input. Maniflow freeflow seems the way to go agreed.

I'd still appreciate some viewpoints on the sprite back box

#5 nicklouse

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Posted 19 November 2019 - 03:56 PM

Thanks guys for your input. Maniflow freeflow seems the way to go agreed.

I'd still appreciate some viewpoints on the sprite back box

what is it?



#6 gazza82

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Posted 19 November 2019 - 04:53 PM

Thanks guys for your input. Maniflow freeflow seems the way to go agreed.

I'd still appreciate some viewpoints on the sprite back box

 

Do you mean an Austin-Healey Sprite Mk I? The "Frogeye"?



#7 ads7

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Posted 19 November 2019 - 05:03 PM

Thanks guys for your input. Maniflow freeflow seems the way to go agreed.

I'd still appreciate some viewpoints on the sprite back box

 
Do you mean an Austin-Healey Sprite Mk I? The "Frogeye"?


Yes the frogeye. It's a bit old school but I noticed Clive Trickey recommended this.

#8 rww

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Posted 19 November 2019 - 07:01 PM

 

 

Thanks guys for your input. Maniflow freeflow seems the way to go agreed.

I'd still appreciate some viewpoints on the sprite back box

 
Do you mean an Austin-Healey Sprite Mk I? The "Frogeye"?


Yes the frogeye. It's a bit old school but I noticed Clive Trickey recommended this.

 

    Old School, I should say so. The first mod I did on my Mum's 1964 850 was to cut off the single side exit silencer and fit a Sprite Mk1 rear silencer, making a centre exit system. The entry pipe diameters were the same for both silencers and at £3  10 shillings for the Frog Eye silencer it was cheaper and sounded far better ( quite muted) than a Peco or similiar. Followed that with a Downton Stage 1 head and carb needle mod ( £23.00 exchange), Armstrong dampers ( £3.50 each) and the car was transformed. Not sure my Mum appreciated it but it started a lifetimes love/hate relationship with The Mini. 



#9 ads7

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Posted 19 November 2019 - 07:19 PM

Ok so it's quite muted .. quieter than an RC40 single box I imagine.

Food for thought

#10 rww

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Posted 19 November 2019 - 07:28 PM

Ok so it's quite muted .. quieter than an RC40 single box I imagine.

Food for thought

 

  The inlet pipe to the Sprite silencer was the same as the main pipe dia on the 850 Mk1 , approx 1" - 1.25" from memory, and was a direct fit. I think you will find the o/l pipe dia of the 3 branch Freeflow will be larger.


Edited by rww, 19 November 2019 - 07:33 PM.


#11 absx2

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Posted 19 November 2019 - 08:36 PM

I currently have an 850 fitted which is still running the exhaust setup from previous 1293, medium bore LCB + 2 inch single box stainless system.

I'm looking to gain a little more power by fitting a small bore 3 branch manifold and 1.75 inch mild steel system leading to either a Sprite Mk1 box or an RC40 can.

 

Crikey, the exhaust is so big i`m surprised all the gases don`t crawl back into the engine and choke it to death  :lol: 

On a serious note the cast iron manifold separated from the inlet and that`s only to get rid of the hot spot is all you need on an 850 and most 1000`s to be honest.

You are losing power with a 2" system as you really need to keep the gas speed up to slow reverse flow on valve overlap or half your cylinders will be filled with exhaust gas instead of fresh fuel.

I have had some " quick " and brilliant fun 850`s that would " pull " 73 mph in third gear, that`s 6.5 - 7000 revs with nothing more than a bit of porting and deshrouding of the valves, 10:1 CR, air box ( big plastic ) and needle change and the washer being knocked out of the middle box of the standard exhaust system.

An 850 needs gas speed going in and coming out so the standard inlet with a bit of cleaning up is as good as you will get, separating the exhaust manifold will help torque and allows a higher compression before detonation and an 850 needs more compression.

I believe somewhere in the Vizard bible it states that the standard manifold is actually quite good so unless you are going to be pushing out 50+ bhp I don`t believe there will be any gains with a 3 into 1.  An LCB is not the thing to use on any small bore other than full race, that`s not to say it won`t work but a 3 into 1 is better.



#12 nicklouse

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Posted 19 November 2019 - 09:05 PM

 

 

Thanks guys for your input. Maniflow freeflow seems the way to go agreed.

I'd still appreciate some viewpoints on the sprite back box

 
Do you mean an Austin-Healey Sprite Mk I? The "Frogeye"?


Yes the frogeye. It's a bit old school but I noticed Clive Trickey recommended this.

 

Would not bother a# you would be hacking it up to make it fit. 
 

you want a sensible diameter and with no changes in diameter along its length. Less bends means greater noise.



#13 ads7

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Posted 19 November 2019 - 09:23 PM

Bingo! Brilliant forum :)

So your answers leads me to this; today I dragged an old standard twin box system which had been stuck down the outside of my garage for 3 years rusty outside but still solid. I've already cut the pipe three inches or so to the rear of the middle silencer - all I need to do now is knock the washer out of the middle box(never knew there was one in there) then attach Mk1 sprite back box which I now know will fit the standard pipe to make a centre exit which I prefer the look of.

So all I need now is the standard cast manifold to improve performance, lose the annoying resonance from my existing setup and save myself a few quid in the process.

Happy days

Edited by ads7, 19 November 2019 - 09:26 PM.


#14 ads7

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Posted 19 November 2019 - 09:28 PM

Sprite box

https://www.ebay.co....4fffb1aa2|iid:1

#15 rww

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Posted 19 November 2019 - 10:52 PM

   The Frog Eye Sprite was 948cc. It says  this one is for the 1098 cc engine.

 

 

This looks a smaller dia inlet pipe

 

https://www.frogeyes...ild steel 948cc


Edited by rww, 19 November 2019 - 10:56 PM.





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