Can some one explain to me the benifits of Trumpets?

912uk · Post by **912uk** » Tue Apr 08, 2008 10:30 am

I have a set here and was woundering the benifits and what are they, more important what are the negatives there are always negatives..

I think there was a section in D/Spencers book.. I will look at that for now..

Nige · Post by **Nige** » Tue Apr 08, 2008 10:43 am

They all about aligning and directing the airflow into the carb. Getting the right length of trumpet can have different effects and gains over the rev range.

912uk · Post by **912uk** » Tue Apr 08, 2008 12:29 pm

do what heights do what?

hot66 · Post by **hot66** » Tue Apr 08, 2008 12:40 pm

the lengths of the trumpets are used to 'tune' the intake pulses .... it all relates to intake manifold lengths, cam timing ( overlap) etc etc . Not a one size fits all scenario when looking at modified motors !

Modern porsches use variable length intakes ( vario-ram on 993's for example)

912uk · Post by **912uk** » Tue Apr 08, 2008 12:53 pm

Ok I just did alittle bit of research I think for what I have standard carbs, 1720 shasta Bursch SX1 cam there does seam to be a set that works for the set up I have. I will have to ask some one for their responce. I just feel if I can get the most from what I have and as the engine is the best of what I can get for the ££ v reliablity..

fourteener · Post by **fourteener** » Tue Apr 08, 2008 1:05 pm

What carbs do you have -did these not come with velocity stacks (trumpets)?

Ian Gunney · Post by **Ian Gunney** » Tue Apr 08, 2008 8:47 pm

not sure you'd want to run the car on the road any distance with trumpets on mind you...I think that one of the Harry Pellow books discusses this (or maybe it was the Duane Spencer 356 book)

Nige · Post by **Nige** » Wed Apr 09, 2008 9:31 am

I ran trumpets on my 912e. They're 40mm and fit under the airfilters which are designed to do so.

912uk · Post by **912uk** » Wed Apr 09, 2008 9:57 am

40mm is what I had in mind. It's certainly not a deal breaker just looking to Max what Ihave

Nige · Post by **Nige** » Wed Apr 09, 2008 10:04 am

I doubt you'll see any noticeable gains other than making the top of your carbs look funky. Obviously only when you remove the filters.

I bought mine of Ebay, was the sellers hobby I think as he made them from scratch. Only cost £20 but this was a few years ago.

Paul @ P R Services · Sat Apr 12, 2008 10:11 am

Hot66 is right but it is even more involved than that....

It's also about pulling air from a perfect hemisphere and in some cases stabilising the air pre-trumpet, which is why you will find trumpets inside air cleaners.

Don't for get that primary exhaust lengths play a huge part and this is a draw back with the 912 and 356 engine. they are not long enough before the tight 180 turn on the rear of engine. This is according to a customer who works all this stuff out for Ford development centre at Dunton.

When we started to go racing with Barry Curtis back in the eighties he cut apart and bench flowed over 15 cylinder heads to work all this out perfectly (imagine the cost

)

The Jim Clark 356 was the quickest 356 at LeMans classic last year and was second quickest Porsche overall in the night session behind a 904.
The guy who drove it had never raced a 356 before...
It has a pushrod 1720cc 356 engine !! built by Barry.

You can only find out what is right for your cars engine by calculations and experimenting.
This means hours on the rolling road...
This is also why engines and especially race engines cost the money they do...

revival-cars · Post by **revival-cars** » Sat Apr 12, 2008 4:02 pm

Barrys knowledge of these 4-cylinder motors is nothing short of exceptional, what a legend!