120mm trumpets on ITB's on standard bottom end?

[Rhys Beal]

I currently have 90mm trumpets but wondered if I will gain anything by going 120mm. I have GT cams so basically 428's and 45mm bodies on standard compression.

 

[Tony Hunter]

Torque.

 

[neil a]

How much more torque would these give over 60's also do they give a larger spread of torque ?

 

[MG cup]

From what I have heard and seen on R/R printouts you get more peak torque figures and also low to mid range torque increase, most of your small capacity 4 pots like trumpet length/ inlet runner length. Your not going to notice the difference dramatically but on tracks with hills, torque is your friend and that's why I have decided to switch to 120's before getting mine mapped. I have seen 10lbfts of peak torque increase from fitting 120's and a swap from one performance exhaust to another. How much was the exhaust and how much the trumpets is hard to say.

 

[NorthloopCup]

How much more torque would these give over 60's also do they give a larger spread of torque ?

There are too many variables that come into play, so there's no way of saying how much extra torque it will gain or if it increases the torque spread I'm afraid.
The mapper and cam timing are the 2 biggest variables in it. It's a bit like asking 'how long is a piece of string?' if you see what I mean.

 

[MG cup]

There are too many variables that come into play, so there's no way of saying how much extra torque it will gain or if it increases the torque spread I'm afraid.
The mapper and cam timing are the 2 biggest variables in it. It's a bit like asking 'how long is a piece of string?' if you see what I mean.

True but in pretty much every case I have seen with 120's fitted they have a higher torque output than other similar specced smaller trumpet cars, irrelevant if they are forged or standard internals???

 

[NorthloopCup]

True but in pretty much every case I have seen with 120's fitted they have a higher torque output than other similar specced smaller trumpet cars, irrelevant if they are forged or standard internals???

The point I was trying to make is that you can't just say 'oh 120mm long trumpets will give you x amount of torque' as there are variables that will make that figure higher or lower. Incorrect cam timing for instance can have a really dramatic effect on the f4r engines, even in standard trim.
Forged internals as in high comp, just raises the power/torque band further up the rpm scale.

 

[Cr33do]

Swede Cup. Have you got before and after graphs for 90mm and 120mm trumpets? Would be interested to see the difference.

As part of a little project lately I have been researching runner lengths and reading information found on various sites suggests that generally the longer the runner the lower down the RPM range max torque will be delivered, if no other variables (such as cam timing, inlet lift duration, runner diameter) remain constant. In addition to that, resonant frequencies (good thing) are dependant on all the attributes I just mentioned. Will find out if my basic calculations have worked out on Thursday

Sure Dan did some runner length research last year with some quite long runners but I didn't ever read the final verdict.

 

[Sam@NP]

ARP rod bolts as a precautionary measure.

 

[Tony Hunter]

Tend to give better low down torque.

 

[Rhys Beal]

I will give these a go and will play around on the dyno with the 90's and 120's to see what gives the best overall result on my engine and post the results....won't be for a couple of months though

 

[MG cup]

Swede Cup. Have you got before and after graphs for 90mm and 120mm trumpets? Would be interested to see the difference.

.

No sorry, no graphs of my own just from other peoples graphs and reading I have done. Most sites I have been on wether its 106's/saxo's/honda's they all seem to like more length of runner and its not just know it all mis informed keyboard warriors im taking this from. Info from the likes of sandy brown and other well known engine builders.

As Tony has said above and from my above post, "more peak torque figures and also low to mid range torque increase"

IIRC I may be wrong but Resonant frequencies are redundant in a car with single runner per cylinder i.e throttle bodies with no cylinders joined like standard inlet manifold if that makes sense??

 

[Cr33do]

Yep. I have been trying to gain info from people with real world experience rather than theory. The more you read the more you realise how involved some of the design aspects can become.

I don't know the answer about resonant frequencies and itb's rather than plenums etc. I would still think the same applies off the top of my head as its still a pipe with a tuned length. Take a look in our project thread on Friday and hopefully you will see why I have an interest in this.

Where is Chip when we need him? We need a long winded detailed account of runner length!

 

[Ills]

This makes an interesting read: http://www.emeraldm3d.com/articles/cat/projects/post/emr-adj-length-intake/

 

[Dan519]

This makes an interesting read: http://www.emeraldm3d.com/articles/cat/projects/post/emr-adj-length-intake/

experimented with that at emerald last year. in short, as long as you can fit under the bonnet is better

 

[MG cup]

This makes an interesting read: http://www.emeraldm3d.com/articles/cat/projects/post/emr-adj-length-intake/

Good read, I can see a bulge being made in my bonnet in the future.

 

[Cr33do]

Yes. Really good read that. Refreshing to see it related to back to back practical tests rather than theory!

Dan's pictures above are the ones I remember seeing before.

According to some of my online based calculations 15mm change in runner length can shift torque by 250rpm. All theory of course

For the OP. I know you mentioned just the trumpets but you need to consider the total runner length. Some bodies use a shorter manifold than others so 90mm trumpets to some will offer a different total runner length than others.