How Much Bhp Do You Think I'll Get ?

[kyepan 291]

Not quite,they might have too much lift at the wrong time.

 

Lift at TDC,top dead centre,where the piston is at its highest point is the thing you need to grasp. As the piston gets near the top on the exhaust stroke, the inlet valve opens to start letting air in, the exhaust valve is closing astrue exhaust stroke finishes. So at this point, TDC, all the valves are open, a small amount, and the piston is very close.Fast road cams often open the inlets a bit earlier, and close the exhaust a bit later. Which means the valves will be even closer. This is what were all harping on about.

 

The cams your "mechanic" is suggesting, have getting on for twice the lift of standard cams.. At top dead centre. Don't confuse this with maximum lift, which happens when nothing else is about and really doesn't matter for the point that is trying to be communicated here.

 

0.047inches for a standard cam vs 0.072 for the one we assume your considering.

 

Read around the subject a bit , start with TDC and then look at timing, this should help you get a bit more savvy.

Edited February 18, 2013 by kyepan

[JakeMathias 6]

Thanks for that information mate. With the 264 cams I wouldn't need to cut out the pistons anymore then standard but I'm now planning to get 285 'ultimate road' cams and therefore I will be having to cut out the pistons more for clearances. Yet again excuse my ignorance !

[camgti 56]

Most of what has been said here is people a little peeved about that face this question has been asked a million times. There is plenty of information on here to both confuse you and teach you things! I came on here 10 years ago knowing nothing, now i believe i know less!

 

What most of the guys are saying, is that the 6 engine as a standard item is pretty good. When you modify it it can go really well or really bad. As you have learnt there is not much room for higher lift cam unless you pocket the pistons as your mechanic is doing which is good! The head flows loads of air without modification, especially for the cams you are using and any mods to the head may actually make it worse. Its a proven head so leave it alone for now.

 

The carbs will only really net you some noise and a bit here and there. The standard inlet on the 6 engine is a pretty nice piece of kit and works very well. Even with the cams your looking at using it will breath plenty, as will the 6 exhaust. The 48-45mm argument has a little merit. Im no expert but what I have learnt has taught me that bigger is not always better. Its like if you open your mouth really wide and try to blow out a candle, you dont have enough velocity/speed of air to blow the candle out. You could if you got really close. But if you have your mouth shut a little more and at the right shape ( head/ports etc ) you can 'tune' the flow of air to be faster/more volume etc and blow the candle out/over!. Im in the middle of building a 2.23 litre 16v and I have gone from 48s to 45s as we want higher port/air/velocity speeds at lower rpm. ANyway, what I have said is not bible, its just some things I have learnt, I check them with an expert and go from there. I hate wasting money and prefer to get as money things right once.

 

At the end of the day, its your choice so do what you like. I would fit the cams dial them in correctly on the standard inlet and then save up for some decent bodies and inlet manifold and stand along management. Way nicer, better Mpg, more power plus plus plus.. Flogging a dead horse otherwise IMHO. Do one thing at a time and see how it feels, works. Do you research so you dont have the wool pulled over your eyes and dont waste your own time and money.

 

Cam

[kyepan 291]

the 254 cams no cut outs needed. The ultimate road ones yes. you can calculate the clearance using a simple formula and a bit of trig.

[petert 600]

The best way to calculate the clearance is to fit the head, with one valve, no springs retainer etc., and drop it onto the piston whilst at TDC, and then again at 5 deg ATDC, and then again at 10 deg ATDC. Measure how far it drops, then subtract the lift at TDC figure for the cam profile.

 

The idea is to only remove what you need. If you take too much material you're only giving away compression.

 

If I was going to the expense of pocketing GTi6 pistons, I'd be wanting some cams with some decent lift at TDC. Something around 0.100 to 0.120" is more like the numbers.

Edited February 19, 2013 by petert

[chipstick 382 1 Cars]

When we will see the confirmed figure?

 

Unfortunately it sounds like you will be disappointed with anything sub 200.

 

I'd suggest closing your eyes when the figure pops up and fold over the print out. Then get it on the road and see how happy you feel with the driveable result opposed to the revealed number.

 

When I had mine mapped I deliberately became realistic and thought as long as it was upwards of where it was before and felt better then I'd be happy. The figure was beyond what I was expecting, but again it's just a figure so when I drove it back from mapping the difference was personally far more rewarding than a number.

 

To put it another way - I drove mine to Sandy after I installed the bodies and DTA with the previous map, and was happy with the improvement over before when standard. I then drove it afterwards and straight away could appreciate the fine tuning and driveability this produced compared to before.

 

I personally think you will feel disheartened because you've spent a few bob and want high numbers. As mentioned, this is nothing apart from a cool number to share at the pub and add reassurance that the investment was worth it. If it feels like it drives better and pulls harder afterwards, you should feel content.

Edited February 19, 2013 by chipstick

[allye 530 3 Cars]

Well summerised sir!

[welshpug 1,666]

unles you bolt it to an engine dyno you'll never know its true output, only a glose calculated guess

Edited February 19, 2013 by welshpug

[GLPoomobile 958]

I'm really not qualified to comment on the technicalities of anything being discussed here, but I would like to make one contribution.

 

Have you given any consideration whatsoever about how you want this 205 to drive and for what purpose the engine is being built? You talk of moving to higher lift cams and seem to want more BHP, but you need to remember that creating big peak numbers won't necessarily make for a better engine, nor a more drivable one. If you take some of the enlarged capacity builds for example, they are making in some cases 220-240 bhp without having to use lairy cams, but what's important is that they are making a big thump of usable torque. The engine doesn't need to be thrashed, so it'll lead an easier life (less stress on it) and you have a more usable engine on the road that doesn't need it's arse wrung out every time you want to get the best out of it.

 

Going ~2.2 litre is of course a different kettle of fish and brings it's own expenses, but I'm simply trying to illustrate the point that you shouldn't get hung up on relying on your cams to try and squeeze out every last ounce of pub-talk BHP unless you are happy to live with an engine that may be more reliant upon revs.

[dcc 855]

'A lad' local to 'me' had a standard gti6 on bodies, was around 150 to 160 whp. Was faster than a 320bhp/400ftlb astra vxr. Was slower than a 1.3 starlet. Either way, the lad was glad he didnt go seeking the figure as he would have been upset. £200 worth of potential scrap engine later he had a grim from ear to ear...

[kyepan 291]

Peak figures, chasing them myself at the moment, realise the futility, but like larry and the light, i can't help it, it's so beautiful.

 

So have a look at this composite i carefully made in photoshop (the graphs match up perfectly)

 

Two Mi-16 1.9 engines, both on throttle bodies, both with cams,

one with more cam than the other..

 

one makes 185bhp, the other about 200.

 

Purple and blue is torque, check out the mid range torque curve in comparison.

I'm gonna have to say it... which is faster?

Edited February 19, 2013 by kyepan

[JakeMathias 6]

When we will see the confirmed figure?

 

Unfortunately it sounds like you will be disappointed with anything sub 200.

 

I'd suggest closing your eyes when the figure pops up and fold over the print out. Then get it on the road and see how happy you feel with the driveable result opposed to the revealed number.

 

When I had mine mapped I deliberately became realistic and thought as long as it was upwards of where it was before and felt better then I'd be happy. The figure was beyond what I was expecting, but again it's just a figure so when I drove it back from mapping the difference was personally far more rewarding than a number.

 

To put it another way - I drove mine to Sandy after I installed the bodies and DTA with the previous map, and was happy with the improvement over before when standard. I then drove it afterwards and straight away could appreciate the fine tuning and driveability this produced compared to before.

 

I personally think you will feel disheartened because you've spent a few bob and want high numbers. As mentioned, this is nothing apart from a cool number to share at the pub and add reassurance that the investment was worth it. If it feels like it drives better and pulls harder afterwards, you should feel content.

It should be all set up on the rolling road within the next month or so.

 

To be honest i think this has all got blown out of proportion as i was just interested as to what people thought i'd get as i've been told so many different figures, i think your completely right its not all about what bhp your running its about the way the car drives and after its all set up properly i'm sure i'll be as happy as a pig in sh*t !

 

I've just today purchased some 285 cams, vernier pulleys, competition cambelt and uprated valve springs... now just to give it to my mechanic and let him do all the hard work ! Thanks again to everybody thats given helpful advice.