Jenvey DTH Throttle Bodies

yes , but if it doesn't deliver , it's very easy to blame the Cam , the Carburation , the manifolds , the ignition , the weather , the Horoscope......

 

My mate Bargate has an old BRM 16V big valve head ! who will have done that head.

he is running 241 bhp weber 45mm throttle bodies 2.1L 16V

 

The BRM man wasn't the Shed - Rob: know the name?

 

I'm told there's a Dialynx golf running close to 240 bhp with a shed head (std valve sizes), but I haven't seen it.

 

see what mine runs when i fit 45mm DTH Jenvey's on my shed head! Won't be that much tho

need to get a price of Badger for a kit.

 

That will be interesting actually. What other spec will you be running?

 

I'd love to see all these engines on the same rollers on the same day.

 

I think it was a Shed head + more on top, but may be in a single seater.

 

This is just a comparison of a diy head on std. valves running 45 carbs. The old mk1 was208.8bhp@6564rpm.
On the day at Stealth, the crank was blamed for not revving any higher, not the cams lol.
It's just a shame flow benches aren't easily accessible. Would be interesting to see what could be done by the home boys, and in what ways they could be improved.
As said, the likes of the man in the hut haven't got a flow bench, so not all heads are going to be equal, some being better than others.

 

i have an 027 Head ready to go down to the shed, and i have 051 shed head at the moment.

would be interesting to see the difference between both on the rollers.

 

260 schrick cams 11.2mm lift, Microsquirt management , 4-2-1 exhaust manifold, 2" stainless exhaut.

only need a Kit with the 45mm DTH, throttle Linkages, injectors, i have everything esle, don't want to go for the DTA as i want to programme and tune myself.

 

true, but its very easy to do some theoretical calculations of how much power omething will make given X cfm air flow......yes airflow isn't everything but it wont make the power if it doesn't flow the air

 

Jim Knifton

 

I parked next to it at a sprint was fitted in a Ralt F3 car but now in a red Mk2 golf. It managed 115mph / 53.59 secs. Quick car. I did 120mph / 52.14 secs

there is no way on this earth that that car has the same spec head as was tested by Neil.

 

i also have an ABF Head is it better to change the exhaust valves to 28mm KR ones when the head is re-built?

 

Fair point mate . What are the calculations ? And where did you pick up all this knowledge ? What little I know is all from building quick FIAT TwinCams as a nipper wi' me Dad , and from studying A. Graham Bell's Tuning Book.. Every day's a school day!

 

The figures above are from the CNC website.

But its quite easy to calculate - cubic ft / min airflow can be used to calculate mass of airflow at a given airpressure and temperature. Air : fuel ratio is something like 12.5 to 14.7:1 depending how you have tuned it so from this you can calculate the amount of fuel you can burn / min. Engines have different efficiencies to turn fuel into power (brake specific fuel consumption) and from this you can work out power.

try this
http://www.stealth316.com/2-air-fuel-flow.htm
http://engine.firebirdv6.com/formulas.html


Bell is a good book - I have his modern engine tuning, forced induction performance tuning and two stroke performance tuning books

 

Basically, it depends, on how much inlet flow you are looking to get, I know from test that 27.5mm exhaust valves will flow at least 113 cfm, good enough to match an inlet flow of 141 cfm, a pretty respectable inlet flow number. Obviously, if you are looking for more inlet flow than that, you will benefit from the bigger exhaust valve area.

 

I'm not sure that the KR valves will fit. I guess anything's possible.

If you want to change the valves, you need to insert bigger seats in the head to get the best out of them.

 

You need 0.5mm outboard of the valve as a minimum seat diameter for sintered valve seats, though you can get away with less for copper-beryllium inserts.

Just taken a look at a standard head, not really any room to manoeuvre for larger valves on standard seats.