Is it worth going Crossflow?

Discussion in '8-valve' started by madasafish100, Dec 14, 2010.

  1. mr hillclimber Club GTI Supporter and Sponsor

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    Just before we get back back on topic... i.e... is a crossflow head better, or at least "potentially" better than the old style head...

    Consider this....

    If airflow is so unimportant, why do we need more valves?.... a 16v head has more valves, giving more valve area, yes?... this extra valve area gives more/better airflow (71-74cfm average for an 8v from it's single 40mm inlet, 104-110cfm from 2 x 32mm inlets for the 16v). So, what is this extra airflow giving us... hmm... extra power... 112 for the 8v, 139 for the 16v.

    Here's a couple more calculations...

    The 8v 1400 Saxo (sorry for swearing on a VW forum!) I just did made an extra 13.7cfm on the inlet, std valve, just porting, and I deliberately kept the port and throat a sensible size so as not to reduce torque.

    If we go by Superflows calculations of .43hp per cfm gain we come up with... 13.7 x .43 = 5.891hp. Now that is on 1 cylinder, so x 4 for our 4 cyl engine and we have 23.564 extra hp. Now I dont buy that for one minute, so I generally mutiply the 1st figure by 2, or divide the final figure by 2... same result obviously, in this case a potential gain of 11.78hp.

    The car in fact gained 7hp at the wheels (8hp approx extra at the flywheel)... tho we did find a further 2-3hp by removing a substantial kneckdown in the intake pipework... highlighting the potential of the head, or removing the restriction modded head or not?.. who knows, but, in this case, a pure flow gain produced a pure power gain, from 2.5k (+2.5hp) to its power peak @ 5k (+7hp) and holding on better past peak @ 6k (+9hp)

    So in this case, more flow is making more power, with a better spread, and no torque loss anywhere, only gains.

    How about our favorite the 16v...

    Using the same calculation, if we take the average flow difference between an 8v & 16v head (34cfm), multiply by my prefered 0.215 (1/2 of superflows 0.43) we come to a potential extra 7.31hp per cyl for the 16v's superior flow. Multiply this by 4 and we should see 29.24hp extra for a std 16v over a std 8v (GTI)... hmm... 112 + 29.24 = 141.24..... goodnite.
     
    Last edited: Dec 30, 2010
  2. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Who said airflow is unimportant?
     
  3. John Read New Member

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    The other "12" BHP came from.....

    Hi everyone, despite being a GTI owner i am new to the clubGTI forum, i am John Read of JRE Racing Engines, i built 212BHP engine in question, i would like to set the record straight with refference to the 0.43 per cfm theory from superflow, in the real world it takes more than just air flow to attchive torque/ bhp from a given engine, there is other perameters which come into the equation of making torque/ bhp, air flow is a very important factor in this equation, i have learnt this over 25 years of engine building, testing and development. so just to clarify on day one of testing 2.0 8v vw engine we atchieved 198bhp/ 161lb of torque. we were unhappy with this figure knowing the engine had more potential. after two more days of development with exhaust design/ pulse tuning and camshaft phasing and injector sizing, so as a result of our three days of dyno testing, our end result was an atchievment of 212bhp and 171lb of torque through hard work and real world development, flow bench's, rolling roads and engine dyno's are just tools to help us develop our mechanical and not theoretical conclusions.
     
  4. danster Forum Addict

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    Hello and welcome to CGTI John. :thumbup:

    I am sure over the years you have spent building engines there will have been many interesting and surprising results thrown up during all the development work. Both positive and negative in nature I would imagine. Presumably the cause of much head scratching and smiles, hopefully more of the latter I would add.

    That is interesting to hear you mention all the tweaks that gained so much in the final setup of that VW 8v engine you built recently.
    I have always been sceptical that the same after market 4 branch exhaust manifold design could work on all engines in a productive way. ie from a std engine, too a larger capacity, high compression, long duration cammed, open induction engine. Just seems to me that there is no way all the pulsing tuning effects could be working in a positive way on all those engine configurations. I suppose the question is how much are they potentially losing when not working as intended. And the trouble is it can be awkward to manufacture an "adjustable" manifold for a specific car due to space restrictions.
     
  5. Brian.G

    Brian.G Forum Member

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    John, thanks for taking the time to sign up and thanks for making your first post a good one:thumbup::clap:
     
  6. jamesa Forum Junkie

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    Likewise ... welcome John, look forward to more from you in future.
     
  7. wippy748s Forum Member

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  8. Whittle Forum Member

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  9. wippy748s Forum Member

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    no power is gained from using the mk4 bottom end so where is the cheating ? i thought we were talking about the flow of the crossflow head
     
  10. danster Forum Addict

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    And you are about to use a mk4 head!! ;)
     
  11. mr hillclimber Club GTI Supporter and Sponsor

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    Ahhh... seeing this it all makes the final bit of the jigsaw fall into place.

    I was'nt aware of further dyno testing after what I saw, appologies to all if I've mislead anyone in reader land on here... I was'nt knocking the product in any way shape or form... why would I do that after 16 years?

    We were talking about possible airflow required for power achieved... we all know it's theoretical, I've never said anything other than that and always try to make things as clear as possible... hence thinking I was correcting someone else's missunderstanding of the numbers... I read between the lines (a dodgey thing to do as "many" who have done so in the past have missed points and caused arguments) and I missed the advert... I dont look at every link.. I pressumed the numbers others had mentioned in other posts on this thread were a possible error or chinese wisper.

    Perhaps the kind sole who pointed out my error can point this post out too... or maybe they'd like to join in the discussion or make themselves known to me privately if they're a little shy after now stirring up a hornets nests?

    If not, this is "my" last word on the above.
     
  12. Whittle Forum Member

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    Ha ha yeah fair enough!
     
  13. madasafish100

    madasafish100 Forum Member

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    Sorry to revive this argument thread lol.

    Had my counter flow headed engine rolling roaded today. It is running a bit lean through out the rev range, more so bottom end and top end. So scope for more power if the fuelling is richened up.

    Result was 156bhp with 162lb/ft.....quite good for an 8v I,d say seeing as it's only 1lb/ft less than smudges 16v.

    X flow head is due to be finished mid summer so see what is in store now I have a baseline figure.
     
  14. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Post up your TQ and Pwr plot with rpms.
    This is now your baseline for your reference in case modifications are done elsewhere without the benefit of baselining there.
    Smudge's engine was tested by me on a different dyno, that did not baseline your car, in a different part of the country after 15mins WOT tuning so difficult to compare thump for thump (TQ) unless both cars were on the same machine at some time. Very strong pulling 8vs on that same dyno achieved maximum torque of near 150 lbft@4500rpm, with more to come from further optimisation.
     
    Last edited: Jan 22, 2011
  15. g60gerry Forum Member

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    :clap::clap:
     
  16. madasafish100

    madasafish100 Forum Member

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    I will do when i get around to it, im not up with all the tech gadgets, so i dont have a digital camera of my own. Will take a pic of the plot and post it once i can.

    Its basically a smooth curve with a peak torque of 162 lb/ft @ 4460rpm and peak bhp of 156@just over 6000rpm. Its running a touch lean at the mo with more room for improvement :)

    Time for me to look like a complete tool!!...............what does WOT mean?[:$]
     
  17. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Your dyno run would have been in Wide Open Throttle = WOT.
    Yes get those pictures up!
     
  18. mr hillclimber Club GTI Supporter and Sponsor

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    Thats on the money for the spec Sam... with a little tweeking to the fueling and cam it may top 160hp. The torque is very strong... you not going to see much up on that.
     
  19. madasafish100

    madasafish100 Forum Member

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    Ahhhhh i see, well atleast now i know! [:$]:thumbup:

    I am trying to get a pic of it so i can post it up, out of interest toyo, where is your rolling road? if its not a million miles from me would be interesting to see what it pulls on yours......just out of curiosity really, didnt know RR's could read so differently (ive got so much more to learn lol)

    Tried to PM a reply but inbox is full.

    Yea im pretty happy with that figure to be honest, i think 160bhp would be possible if i got the fuelling optimised.
     
  20. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Yes they do for a number of different reasons, hence the reason I suggested to use this current test as a reference. Worst case scenario is you make modifications elsewhere, which genuinely change the feel of the car and the performance of the engine in most conditions. You test there and the peak numbers are the same or less than your original local baseline. Not possible you would say as you feel your emptied wallet! Then you head back to your local reference and see that the performance has improved peak number wise or overall through a engine speed range, and then you can start justifying your investment.
    The peak chassis numbers and they correlation to a "fast car" will always be open to debate as they are not absolute but it will become a bit clearer when you post up the plots for torque, power and any other data during the test.

    Garage Streamline is in Wandswoth, London. They are one of the forum sponsors. Maybe a bit of a journey for you but you are more than welcome to come down and join the growing list of enthusiasts who have tested on there. Only then can you then have a fairer comparison to smudge's itb thing when it was tested that night.
     

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