ajamesc

I trust my tuners word if he says it's ok and I use what he says is needed to me it will be ok.

smiley

Kool mate

R4N SS

iTrader: (6)

its probably more related to the amount of boost than compression

turbotrev

Thats what i thought , but i dont know why though?
Is it something to do with using more ignition?

Cheers Paul

R4N SS

iTrader: (6)

more heat with more boost and more pressure all around the engine. The head will start lift if too high boost

turbotrev

So less cylinder pressure and less heat with a lower comp engine?

Mark seems to run high boost figures on a majority of his engines though and a lot em are specced at around a standard compression ratio?

Cheers Paul

Caddyshack

Surely if you drop the compression just to achieve the power then you end up with a laggy and lazy engine? There are very few instances where it is all about peak numbers, it is how it behaves on the way to the headline figure, unless you are building a full on drag car.

I think that if you really want 700bhp then you have to be prepared to spend big, like cossy Dave has, engine fails...build it stronger with alloy block and arrow crank....if you plan to do it without the big budget then it could fail and when it does you end up spending more as you have the first build cost and then then the proper build cost.

Jay,

iTrader: (4)

This subject is actually a real arse as some tuners say you can't achieve big power on standard comp ect ect yet Mark has been using high comp on all his builds for few years and Julian Godfrey has run 10.1 on 700 bhp + engines with 2 bar antilag which are driven absolutely flat out so this low comp argument is very much like the world is flat lol

800bhp

If your planning on fitting a twin scroll in the further then go for standard comp going low comp engine will not be suitable for twin scroll if you go that route in the further.

Best to see if you can get a ride out in different setup cars to make your mind up.

turbotrev

Are lower comp engines much lazier/laggier then?

And if so why?

I've heard people mention this before

Cheers Paul

turbotrev

I'm guessing it's dropped to make it more reliable rather than to gain more power??

As mentioned previously less heat and pressure in the cylinders??

Cheers Paul

Caddyshack

The higher the compression the more responsive the engine tends to be, in an ideal world we would run the highest possible, but we lose it to prevent detonation. I think people drop it to allow more boost higher up

Dropping to gain more reliability than more power is actually the same thing, it is a trade off, more power OR more reliability.

turbotrev

Isn't there more scope for ignition advance on low comp engines to compensate for that though?

Do you mean more boost held at high revs?

As opposed to dropping off as revs increase?

Cheers Paul

Rod-Tarry

2.9bar through to the red line making 838bhp/666ft-lb with compression Ratio at 8.5:1 & this was back in 2008. The Latest will be more Boost & the same Compression Ratio 900+bhp/700ft-lb ? . Head lift becomes the problem so you solve that not drop CR & ruin the engine. It was 6.8 :1 when I first got involved making lethargic touring car type engines but state of the art in 1995. Its been evolving since then but most did not follow just excepted the Touring cars must be right. They were stuck around 600bhp in a laggy race car now 900bhp in a car with road manners is possible. Move on lads 2017 is already here Julian & Mark & any other moving on wont be wrong just look at the engines they produce. Having a compromise because your budget wont extend to the expense it costs to solve things like Head lift & Blocks cracking is another matter.

markk

iTrader: (2)

Stop guessing and start calculating.

Its a mathematical equation to see what is and us not feasible for the most part.
Have a look at your expected BMEP then work from that.

stevieturbo

They ain't using pump fuel though

Mark Shead

Rods one makes over 750hp on pump.

Mark

stevieturbo

With 10.1:1 ?

Mark Shead

Rods is 8.5-1 but can go higher as it can loose some ign and still not get in to the window of loosing power.

Mark

Jay,

iTrader: (4)

not ato massive power but 500 600 bhp there is no need to either lower compression or run 103 or above

turbotrev

So how much ignition you can use does come into play depending on comp ratio?

Cheers Paul

Mark Shead

It's mainly what it's all about. Same spec engine and turbo when you go up on comp you have to come down on ignition then you come it to how little ign you can run without loosing power and heating up the egt.
It's a window of knowing how it all will work and how much power you can keep in it when the intake heats up.

Mark

turbotrev

So would a regular comp engine with medium ignition advance drive better/have more power than a lower comp engine with more ignition?

(If both had same turbo, inlet, cams, etc?)

Cheers Paul

Mark Shead

Yes raising the comp raises the efficiency of any engine and most turbo engines are dett limited so its managing that correctly.

Mark

turbotrev

Gotcha, thanks

Cheers Paul

Jay,

iTrader: (4)

Turbo and cam choice are a massive influence to like t4 for instance is a very laggy turbo and if most tuners are honest they will tell you surge is a massive issue along with the gt range so imo you are recruiting not only your power through the rev range but response to due to heavily managed boost curve so it's not just about raising the comp imo

PAUL S

iTrader: (8)

Dick Johnston ran one of his 550 plus bhp engines on a dyno without the turbo strapped on, it made 80 bhp! back then I believe they were down to 6.7 to 1 compression with the basic old ecu they had 30 years ago so you are spot on, think how much more responsive those beasts would have been with todays technology running far higher compression but the same boost.

cossiedave

iTrader: (1)

im at 700 bhp on pump fuel bp to lol

Adam-M

Was the it fuel qaulity or crap ecu's that limited them to run low comp all those years ago?

I seen a video of him saying that, I'm sure it made 680hp with the turbo connected and 80 without lol

Jay,

iTrader: (4)

the fuel was more kind to turbos back then as not many restrictions and the the turbo was a t4oz that's why it did that power so quite a bit bigger than the usual t4

stevieturbo

Anyone can make the power...and anyone can do it easily on race fuels.

But nobody is making 750hp on a 2.0 on pump fuel at over 10.0:1 CR unless it's pulling over say 10krpm

stevieturbo

At or over 10:1 CR ?

nope.

Again, look at the specific comment I was quoting. There is nothing difficult about making 5, 6, 700hp etc but the comment was specifically at Jay's comment about Julian Godfrey making 750hp at 10:1 CR

Very easy with the right fuel.

Caddyshack

I think we are hanging on to the 10.0:1 here, jay is just saying that you don't need to drop from standard on a 500 bhp car, we are not trying to build a 10:1 700 bhp car.

We all understand that if you want to build a 700 bhp plus engine with big boost you are not going to start with higher than normal comp ratio.

Jay,

iTrader: (4)

Lol toby you correct arrogance seems to have a wide band on this forum and also not listening. My point was that the average person and some tuners say and believe that at 500 -600 you need to go lower comp than standard to achieve this which is bollocks and Mark and dave have stated 700 bhp at 8 5 on pump an yes at 10.1 race fuel and higher revs do the job but that's comon sense lol

stevieturbo

You can very easily start with higher if the fuel/build allows it.

likewise for a 500hp car you could very easily go higher even on pump fuel.

All that nonsense in the past about mega low CR's was always insane.....although for the touring car side of things could perhaps be slightly justified given they ran very long races and low rpm performance was never even a consideration.

Although pretty sure they blew up often even back then ? lol

Mark Shead

Rods could easily be run at 9.5-1 on race fuel if I wasn't looking to max out the pump fuel.

Mark

cossiedave

iTrader: (1)

​​​​​​​no im not at that comp lol just saying i was at 700 on pump

PAUL S

iTrader: (8)

He used the motronic ecu from the RS200 program and managed to crack the code on them before anyone else but it was still a pretty basic set up.

Mark etc are far better placed than me to confirm why they had to run such low compression back then, down to det I believe.

They all ran special brews to a degree, remember the story about Brodie storing toleune in the roll cage tubes of his and adding it to the fuel during the race!

markk

iTrader: (2)

Head gaskets were a big problem in the touring car days, a lowered static cr contributed to a lowered dynamic cr when in boost.
on boost the change of ve becomes huge as does thermal efficiency, you have to manage all elements.

cossynut2

Whether the RS500 touring cars could have run better with todays technology is not important to me. At the time they made for very exciting racing and were at the top of that periods tuning level.
This thread has turned into a low comp v high comp argument. If the guys who are running low comp big power engines are happy and the guys who are running high comp engines are also happy does it really matter?
Budgets are also important to a lot of people, everyone would love a 700bhp road going Cossy but not many can afford it.