crazycage

my old cvh did 233@the wheels and made full boost @2600rpm
ported head standard valves
8-5-1 cr
newman can and solid lifters
stg3 t3
tubular manifold
custom inlet
gotech
and front mount

JamboRS

i understand that but by fitting a thought it spec none of these parts can increase lag that would be noticeable on the road.davie k ran a low comp,big valve head on his t28 turbo'd rst along with a custom newman and never encountered lag,Andy R ran exactly same engine/turbo as me with inlet/exhaust manifolds on aftermarket management and gen rs500 cooler with better power and response than mine.fair enough my car had a lot of RR time,probably too much and not everyone can spend that much time tuning a rst,but my point is a decent set up by an experienced tuner can eliminate lag to the point its not noticeable on the road

JamboRS

bet it was lively
i regret not going aftermarket management just to see what i could have really got,my tuner reckoned 250+@wheels possible by running there management,but at 2.5k supply and fit for 35bhp@wheels i decided not too.

what was full boost at 2600rpm and what was boost at 233@wheels

crazycage

i loved it mate my only regret was i never fitted steel rods when i first built it!! so my boost/power was limited .

crazycage

probably less boost than you were running .(1.1bar) i will wait for all the.... oh that cant be done !!

JamboRS

mines spiked at 22,thats all the mfi would let it boost at without det so that limited my top end boost which was 17psi.id could have held 20+ top end if only the mfi would let me mid range.tests showed my cooler was a restriction and would benefit from a single pass as i was getting 4 psi pressure drop.i was happy with 214 as i asked for 210 and since it spent most its time in ava i just wanted it back but fuck me it went and revved like fuck

crazycage

so about the same boost as mine but i didnt have the spike , and i had management so my ignition was optimum.

(zetec is the way forward tho.)

jamieRST

crazycage,so your car had about 270bhp on a standard engine apart from the cam,with a bigger turbo,tubular manifold,modded inlet manifold,efi and a cooler.without the boost on max.id say thats quite an achievement

Karlos G

iTrader: (4)

Yup but it's ported and flowed too which is were the gains come from
What I said about big valve heads is not my opinion, it's what I was told by APT, NMS, and MSD mate so it is a fact.
Running bigger valves and so slowing gas velocity will loose you power and response, it's only advantageous once you've reached the limit of standard valve size and you need the extra flow.
Remember if something is not restrictive in the first place gains will be minimal if at all, and can often be counter productive in the case of porting or bigger valve fitting.

Karlos G

iTrader: (4)

Down to good mapping i'd say, and 17psi on a stage 3 T3 is a fair bit of flow too

crazycage

just over 260 at the fly wasnt a standard engine it was a standard bottom end.it had a proper head and cam manifolds management ect ect was a good little car .

Karlos G

iTrader: (4)

As an example.....
Swapping from a Stock T3 to a Stage 3 on my Bro's engine added 500rpm to spool up time with a peek boost of 15psi (going from .36 to .48 is a big step), then dropped a kent CVH35 into the mix and was making peek boost another 400rpm later...... so went from 3000rpm to 3500rpm and then 3900rpm, this is the only way to really see what difference mods actually make as comparing one car to another is almost pointless.
This was without altering anything else on the engine so is a fair test.

A RR session could have brought it back down by another 5/600rpm (tweaking cam advance, and ignition timing, etc..) but still a noticable increase in lag.

I do not think any tuner can eliminate lag on a RST, newer cars will VVT etc. almost yes but not on a single cam engine!
Still, just my opinion mate!

jamieRST

i thought the factor that determines an engine's ultimate power potential is the total inlet valve area.having it ported and flowed is only half of it.more air into the cylinders is how to generate more power.ie bigger inlet valves.if the work is done badly they can hurt power right through the rpm range.

crazycage

the biggest gains on a cvh head will come from the exhaust side.

jamieRST

and who told you that

crazycage

no one mate im talking from my own experience.

Karlos G

iTrader: (4)

Bigger is not always better!!
You can increase air into the cylinders by turning the turbo up
It's only when you reach the limit of head flow (the point at which it becomes restrictive) that you need to increase valve size, which on these engines is around 250bhp.

jamieRST

but thats just not true

crazycage

please explain then??

think of it this way .. your turbo will force the air in under pressure no matter how small the ports are but it will choke on the exhaust side and give you a shit load of back pressure so you will gain more on the exhaust side on a turbo engine.

Karlos G

iTrader: (4)

It's for this very reason that fitting big valves until needed is pointless!
It drops Gas velocity, making your car slower!!!!!

crazycage

i didnt tell anyone to fit bigger valves!! im just saying you will choke on the exhaust side before you need to port the inlet side.

and i know of a cvh with 350hp on standard valves.

jamieRST

ok.think of it like this then,the engine makes more power the more air goes into the cylinders.agreed? turn the boost up gets more pressure in,induction kit gets more in,the more the better. now the above mods are actually,if you think about it restricting the standard head,it is not designed to flow this much.so as karlos g says,he got is ported and flowed,to flow better.agreed on the above?so after spending money to turn the boost up,buy induction kit etc why wouldnt you want even more power in,weve already agreed more air in means more power.a proper big inlet valve,i.e 45mm creates a larger area and allows more air into the cylinders,meaning more power.when you mess with the exhaust side,is where you get problems,larger exhaust valves will not help power as they are to large to begin with,unless a little if you have a big power unit perhaps. a lot of people keep saying you dont need it,its not restricted,you dont need it till excess power,just because it is not needed apparently till 250 bhp doesnt mean it wont improve performance below that,the same as a st/st manifold.the better the engine breathes the better the power.

crazycage

do it your way and ill do it my way. i already have over 350hp and running in the 12s on the 1/4mile.

jamieRST

will do mate and get an extra 40bhp from my head

muz

I'd quit while your ahead Jamie. No offence but you clearly have NO idea how a CVH head works.

jamieRST

great another one that thinks if i turn the boost up ill get more power,which is correct but cant understand the same principle,as in getting even more air in again by having a bigger inlet valve,the more air that goes into the cylinders the more power the engine will make.simple. so im not the one who doesnt know how to get the most out of head

Karlos G

iTrader: (4)

HOW MANY TIMES DO I HAVE TO SAY THAT BIGGER VALVES/PORTS SLOWS DOWN THE SPEED AT WHICH THE AIR FLOWS!???!!!
Meaning that if you change nothing else on your engine/setup then you will get LESS air into the cylinders than you did before........ which means what?? LESS POWER!!!
Do you understand?
The slower the air flows the less gets in before the inlet valve closes, the less in the less out, meaning the turbo spools less, meaning less going in again......see the spiral???
If you fit a big enough turbo and use it to take advantage of the bigger valves you will make more power, but if you dont your engine will make less power, or you will have to rag the shit out of your little turbo to make that same power you did before.

Another example...
My first engine had a heavily ported head, a long duration cam, and 1.5mm oversize low comp pistons........ my Stock T3 would only hold 11psi on the RR making 185bhp because it simply could not supply enough air to make use of all the extra available flow..... fit a Stage 3 and I could have made 270bhp (fuelling allowing).
Also it made peek boost at 4000rpm!!! Why?............. Slow gas velocity!!
Had I of had a stock head, cam, and pistons, I would have made the same power (as the turbo was my limiting factor) but would of had a lot less lag hitting peek boost at say 2600-3000rpm, holding 16/17psi, and the car would of driven much nicer, instead I had a wacking great boost spike at 4000rpm and then as the engine demanded more air that the turbo could not supply it gradually dropped down to 11psi the closer I got to the rev limiter (6400rpm).

Do you see now why opening everything right up but without the correct turbo is pointless??

crazycage

we all know that more air and more fuel makes more power but only if your head /exhaust housing and exhaust system can flow the gas out fast enough. so what im saying is your standard head will choke on the exhaust side way before the the inlet side needs porting. all the big cvh heads have more taken out of the exhaust side than the inlet side as the inlet side is force feed by the turbo.

are you getting my point yet??

Karlos G

iTrader: (4)

This is what happens when you make your engine breath really well (increase it's volumetric efficiency) but dont change your turbo.............lag!!!!



Imagine how much worse it would have been if I had bigger valves and even bigger ports!!!

jamieRST

ok karlos is this what youve been told is it?dont see how having bigger inlet valves,and your inlet valve throat/exh valve throat flowed,will slow the air down.it has a bigger and smoother area to flow through and your getting more air in,so its increasing the airflow,and creating more power,enabling you to run less boost for the same power.im not on about touching the exhaust valves.and yes you would need a cam to make full use out of it.its got nothing to do with the turbo as that works as a by product of how much the head flows into the exh manifold.its clear we arent going to come to an agreement but il happily give you sites for reference if you dont believe me.

jamieRST

and the reason for your first engine is incorrect spec as you said,thats not the heads fault.

jamieRST

crazycage.most of the big valve cvh engines ive seen for sale shouldnt even be classified as a big valve head.and the exhaust valve is big enough as it is,only work would be matching the exhaust side to a st/st manifold

crazycage

have built a big power engine or is this your first go at it ?

Karlos G

iTrader: (4)

Jamie it is exactly because of how my head flowed that I had that massive spike and lag!
Close the ports up and fit a stock cam and I would have spooled up at least 500rpm quicker, and made the same power!
Thats the point...........

jamieRST

i think it would of been the low comp pistons and incorrect cam that would have made it laggy,not the head.if it was done well.even a PROPERLY ported and flowed head produces only a slight performance gain.its when the valve work is added to it you get the most gain.so it could have also been poor work on the head.opened the exhaust side up and messed the pressure up,which would have caused the lag. and you are increasing the flow from where it begins when you do the inlet valve,in the cylinder.so therefore thats more pressure from the start going through the engine,so increased pressure through the manifold and quicker spool up on the turbo.

Karlos G

iTrader: (4)

Read all of this article and you may understand, noting the caption for the BIG PICTURE IN THE MIDDLE!!! lol ........

crazycage

no more input from me here good night.

Karlos G

iTrader: (4)

Yeah enough said......... lol
Laters........

jamieRST

but i am not on about a massively ported,badly worked head.here is some info ive found for you too.Most 2 valve per cylinder heads are capable of being modified for between 10% and 15% power increase without increasing valve size. Some heads, like the CVH, have even more potential and 20% is possible.Properly done with due consideration for port sizes and valve seat profiles, a modified head will increase power throughout the rpm range. Low and mid range torque increase significantly as well as peak power.The exhaust valves are actually far too big as standard. 37mm is a huge exhaust valve for a 1600cc engine. The 2 litre Pinto has 36mm ones, Peugeot 1.9 Gti are 34.5mm, Golf Gti even smaller. Under no circumstances fit larger exhaust valves and any tuning firm that does this can be safely avoided as they have no clue how to modify this engine properly. There are certain things that absolutely must be done to portshapes to get the CVH head to flow to its full potential. The area around the valve guide where the port bends is critical and this must be straightened out and shaped to blend nicely into the valve throat. You MUST remove the valve guides to get at this area so any head which just has a bit of polishing and no real constructive port work will not show much of an improvement. That means most off the shelf heads you are likely to buy. Every head I do has the guides removed first so that the ports can be modified to the correct shape for high flowThere are some very common misconceptions out there about tuning turbo engines. In particular whether improving flow through cylinder head and induction system porting makes any difference to power or whether all you have to do is turn the boost up. The simple answer is that improving flow can be even more important on a turbo engine than a normally aspirated (N/A) one. All engines make power in proportion to the amount of air they can breathe and anything that increases air flow into the cylinders increases power. To generate a pressure difference there has to be a resistance to flow. Try blowing as hard as you can through a straw and then do the same just through your open mouth. You can generate enough pressure through the straw to puff your cheeks out and almost no pressure without the straw. The amount of airflow is much greater without the straw of course. All the pressure rise is telling you is that there is a resistance to flow but it doesn't tell you how much flow is taking place. The same thing applies to a turbo engine. What the boost gauge is telling you is how much pressure it takes to generate a given amount of horsepower through the restriction of the head and induction system that the turbo is pushing against. If you reduce the restriction you'll get more airflow and power at the same boost level or alternatively the same amount of power at a lower boost level.a big valve head with the correct spec,is good imo

muz

Of course if your chasing massive figures like Christian, Tim etc larger valves will be needed eventually, but on a 200 even upto 250bhp they simply aren't! That's like saying bolting a T5 truck turbo to your 1600 CVH will make it 400 BHP becuase it will shift more air. Everything is relevant to the rest of the engine. I'm no CVH tuning wizard admittedly but it's tried and tested stuff.
Someone with proper, in depth knowledge needs to come put the hammer down here ...