head flow

vwfye · Post by **vwfye** » Thu May 12, 2005 3:04 pm

all the charting i have been doing of hp to rpm to head flow cfm show some really amazing numbers (theory)... like the T4 head only flows about 88cfm @ 28 inches water!!!! if you could get that number to 110cfm (on the 1.8L) you could be turning 115hp @5800rpm... i know the exhaust port issues are extreme compared to other systems, but what is needed to get 110cfm flowing through these heads?

raygreenwood · Post by **raygreenwood** » Fri May 13, 2005 1:47 pm

What valve diameter is that for...and at what lift? A little porting goes a long way on these. Outside edge of the exhaust tract before it enter the header....and smooth and widen the intake tract before the valve, to the runner size of a 914 2.0 (42mm).
Also, unshrouding the valves carefully goes a long way. With careful tuning and good FI work...you can get 100 hp from a 1.7L. Fuel mapping, cam, compression and exhaust are the main restrictions.
HP is not made by flow alone. Ray

the_addoniss · Post by **the_addoniss** » Sun May 15, 2005 12:34 pm

Sorry to interupt but i just read your post and figured you might be the right person to ask?

My question is how much HP difference would you expect if you had a 78*96 type iv engine and the only thing you changed was the heads?
(For example put the engine with stock heads on a dyno then unbolt the stock head and bolt on a ported head with 914 relocated sparkplug.)

raygreenwood · Post by **raygreenwood** » Sun May 15, 2005 10:31 pm

I'm not an expert, but there is not enough information there. What was the cam...exhasust...etc. Changing one thing about the way an engine breathes....will force you to change other things. Most esepcially, the fuel imxture and possibly the ignition tuning. Those two adjustments alone.....which may only be allowed by getting freer breathing, may be more significant in themselves, than just porting the head.
I have no way to answer. maybe someone who has built that combo can help. But the would have to know every piece you installed...anmd know exactly what you did for porting. Many times porting can hurt more tha n it helps. Ray

the_addoniss · Post by **the_addoniss** » Sun May 15, 2005 11:09 pm

Thanks for the reply. I did realize you would probably have to re jet carby, reset rocker geometery and re tune engine. The engine combo isnt that important, what i was getting at was what HP increase would you expect by porting the heads?

At the moment i have almost all the parts for my engine rebuild except the heads so i was trying to decide to put standard heads on or go with the extra cost of porting.

raygreenwood · Post by **raygreenwood** » Mon May 16, 2005 12:29 am

Thats a really tough question to answer. The results...depending on what the other other parts are in theengine....can span the galaxy. Heads are extremely important.
A for instance. In a bone stock 1600 bug....all stock ...exhasut, cam, carb, valve size......if done well...maybe 3-5% increase in output. Thats all. But whats limiting it...is all of the other stuff I listed.

Now take my last 1.7L type with D-jet. I could only tune it out to about 90 HP with a LOT of FI tuning, better cam,slightly better exhaust, better ignition. The last changes were valve unshrouding, adding 42 x36 valves, better dialing of of rocker assemblys, polishing, port matching. That bumped it up abouit 8HP. But....all of the fuel systems settings needed to be totally retuned.. And...they had no further tunability to them before working the heads. The minor port work and larger valves chanegd the flowrate and teh vacumm signature and the combustion efficiciency.

there are some engine combos...that can have nearly 50% more power output available to them in head tuning. It really depends to what extent....the heads are a limiting fcator for your engine combination. Not trying to be cryptci. But if you are asking if its worth it....YES! Some head work is considered less of a porting issue and more of a direct upgrade. Plug angle...yes. Valve unshrouding...yes. Larger valves....yes. Proper port matching and polishing....yes. Iwould say those things alone.....just a guess....on a stokish engine....could be 10% improvement....but much more important to longevity an cooling. Ray

the_addoniss · Post by **the_addoniss** » Mon May 16, 2005 7:00 am

Thanks for the reply the information you have given me is enough to go and spend the extra money.
Thanks for your help will let you know how the engine goes when it gets built.

raygreenwood · Post by **raygreenwood** » Mon May 16, 2005 7:40 am

For real answers...Contact HAM on the aircooled technology forum. Ray