Trumpet size for 20v

[kiwi]

After reading hundreds of forum topics about the length of the trumpets i should run i think its better to just ask if anyone is running a 20v on trumpets and what size are they using. I am after high rpm power upwards of 4,400rpm.

thanks

[Sam_Q]

100 or 110mm. Multiple customers report and mid and top end gain over 70mm stacks.

[xero]

as above.
if cant fit those, 50mm seems to be a decent compromise at some sort of mid range while having plenty above 4500rpm.

[kiwi]

Thanks guys. The Silvertop is just begging for trumpets.

Looking at some 100mm ones, seems an good option.

[Sam_Q]

kiwi, what model car is it going in?

I can supply velocity stacks if needed

[kiwi]

kiwi, what model car is it going in?

I can supply velocity stacks if needed

Its a Silvertop 20v in a 1984 FXGT hatch. Would prefer them to make power above about 4,000rpm as the VVT operates on the TPS and not at a set-rpm range.

The trumpets will be mounted in a sealed box that will fit secure against the bonnet and have a vent feeding it with cold air.

[Sam_Q]

looks like you have lots of room, I suggest the 110mm length

[kiwi]

Why would you recommend 110mm? How do the lengths work?

[rick q]

FWIW, I started with parallel sided ram tubes 115 long, but for packaging reasons had to change to 75mm tapered, and was pleasantly surprised to pick up 3-4hp as a result.

I think there are many many variables in this, and that sometimes the maths [which suggested 115mm] sometimes throws its hand in the air!!!

[kiwi]

Yeah somepeople swear by short tubes and others by long ones.

The engine has had the following work done:
Blacktop Intake Cam
7afe headgasket
Blacktop ECU
2.5inch free flow exhaust no cat

Basically i need it to make peak HP as it will be a hillclmibing/rally car and it wil spend most of its life in the 4,000rpm plus side of the rev guage.

[Hiro]

Yeah somepeople swear by short tubes and others by long ones.

That's because different lengths have different effects - long tubes tend to improve low- and mid-range torque, short tubes top-end power. The problem is that since most people tend to quote peak power figures, a set of long trumpets might look like completely ineffective mods on paper since peak power doesn't change, but the mid-range benefits are massive. I know of some 2ZZ guys with aftermarket cams and ECUs where the peak power figure has barely moved but there are ~30% gains in the mid-range, completely changing the nature of the engine (no longer need to wring every single rpm out of it to ensure you land back in lift when you change gears, for instance)

[knightrous]

I've been making proto types with my 3D printer to see what lengths provide the best results for my AW11 with it's 20V ST.

[Sam_Q]

I have sold many stacks from a radii in flat plates to 150mm. Now I normally don't like making a judgement from feedback alone however I had quite a few reports now to get a rough idea. I am sure it would happen for some however I didn't have a single customer report of losing power in the top end. I had a back to back dyno run organised with the head of a Clubbies group but it was cancelled, a pity. I do have a dyno run of a BEAMS engine with 70mm VS 110 that's rather interesting but a very different engine.

Of note a friendly customer of mine is using 100mm small bellmouth stacks on his high power 20v, it does displace 1.8L progressively till high revs with a 83x83 bore/stroke which likely changes things quite a bit. I should ask him why he chose that length.



knightrous: nice work, going to make four of each and do some test runs?

[knightrous]

knightrous: nice work, going to make four of each and do some test runs?

Yes, that is the plan. Currently I have 80mm and 120mm designed units and will do a few in between designs, but mainly I want to test to see if the ABS plastic will survive the harsh environment of an automotive. If it does, these are super cheap to produce, using only $6.00 of ABS filament and 15hrs to print per 120mm trumpet.

[allencr]

Cut yours & use hose&clamps to find what you like best.
Dyno or off road or road race or hydroplane or rock crawler or bling or just a fun DD?

ah somepeople swear by short tubes and others by long ones.
That's because different lengths have different effects - long tubes tend to improve low- and mid-range torque, short tubes top-end power. The problem is that since most people tend to quote peak power figures, a set of long trumpets might look like completely ineffective mods on paper since peak power doesn't change, but the mid-range benefits are massive. I know of some 2ZZ guys with aftermarket cams and ECUs where the peak power figure has barely moved but there are ~30% gains in the mid-range, completely changing the nature of the engine (no longer need to wring every single rpm out of it to ensure you land back in lift when you change gears, for instance)

X2