[Myles]

So I was talking to my boss at work today and he said that he used to have a 1400cc datsun with dual carbies and it absoloutly flew.. Which got me thinking if I could do it to my sierra...? Has anybody here done it? Is it worthwhile? How much would it cost? Cheers

[v.w.dave]

Don't waist your money, Put that money into putting a 1.6 efi in it

[2stroker]

Myles who is your boss, there were not many of us that did the A14GX twin carb conversions, I may know him.

Mate it is not impossible but it is a real lot of work, the problem with a suzuki engine is that unlike the nissan engine the suzuki inlet manifold has water jackets and has the thermostat housing incorporated in the manifold so a very complex manifold will have to be made from scratch. I will post some pics to show you what I mean.

[Myles]

Yeah but 1.6efi is illegal on your p's... You can drive a vitara.. But you can't drive a sierra with a vitara motor it sucks... I can't get any other engine in my car while I'm on my ps.. Otherwise I wouldhave gotten a g13b or a g16 instead of just rebuilding the g13a... So yea I'm just looking at different ways to get more power from the g13a.. My bosses name is John Stamatiou

[Reubs]

Myles wrote:

Yeah but 1.6efi is illegal on your p's... You can drive a vitara.. But you can't drive a sierra with a vitara motor it sucks... I can't get any other engine in my car while I'm on my ps.. Otherwise I wouldhave gotten a g13b or a g16 instead of just rebuilding the g13a... So yea I'm just looking at different ways to get more power from the g13a.. My bosses name is John Stamatiou

A stock coily has the G13BA (1298cc). IMO, you could have put a Swift GTI motor (same block capacity wise) in it if you want grunt for the on-road.

You've complained of carby problems and a gutless car in the past. Have you ever been to a carby specialist? You'll get a lot more than just a carby rebuild for your $$$. A good carby builder needs to check all the engines systems - electrical, fuel delivery, exhaust etc. for problems in order to ensure a good tune. You also might find your new BIG exhaust system is causing you a loss of power.

Do you run 30 or 40 weight oil? Do you run 98RON fuel? Do you run double platinum plugs? Do you have a performance air filter? Does your exhaust maintain correct backpressure? Are you running suitably sized tyres?

Also, have you looked at a new camshaft?

I'm sure there are lots of ways a P-Plater can get a little more power from their engine...

If you still want to go quicker, take the front diff out of your car. Less unnecessary weight = more gusto!

[royce]

fucn backpressure, funniest shit I ever hear

[Rusho]

Just wait and get a 1.6 buddy. Would be your best and more affordable option over the long run

[joeblow]

Myles wrote:

Yeah but 1.6efi is illegal on your p's...

so are twin carbies on a 1.3........p's or no p's.

[ball]

royce wrote:

fucn backpressure, funniest shit I ever hear

You find it amusing like I do

[SuziBlu]

royce wrote:

fucn backpressure, funniest shit I ever hear

What is it with this back pressure idea, I have seen it so many times now, I know people think it has something to do with something, but its got me stuffed why.

No back pressure, more clean air in chamber, better burn, no waste of energy trying to blow out old burnt crap, more broom.

[TZAR]

royce wrote:

fucn backpressure, funniest shit I ever hear

I still don't understand back pressure when you have top fuel drag cars that have very short pipes. Maybe its from the two stroke perspetctive of expansion chambers but I still cant understand back pressure. I cannot even understand were the idea of backpressure came from.

The only explanation I have ever heard is that it helps stop the valve slamming shut, but thats a bit hard when at 6000 rpm ( that is 100 revolutions per second) the valve opens and closes 50 times in ONE second so that seems a bit wierd to me.

Anyway twin carbs on sierra is like turning a goat into a racehorse.. It wastes your time and annoys the goat.

[DMAC]

Thought of a similar thing.
Have a read here might answer some questions.
http://auszookers.com/index.php?name=Fo ... pic&t=8168

Haven't totally ruled it out.

[Rusho]

I think the pipes on a drag car are there to direct exhaust gases out more than anything...3000 to 7000hp doesn't really matter how long they are does it? I don't think tune length extractors and diameter of exhaust really come into here.

Hehehehe Goat....good way to look at it TZAR, I like it

[zacs7]

Forgive me if I'm wrong, but drag cars aren't designed to last long... and generally don't

[lump_a_charcoal]

I had twin side draught webers on my old A15 datto moter in my 1200 ute, used to do good skids.
IMO it would be a waste in a sierra.

Just bide your time and learn to drive respectfully and safely, and have your fun in a few years time when you have the right machine for it.

[ball]

TZAR wrote:

royce wrote:

fucn backpressure, funniest shit I ever hear

I still don't understand back pressure when you have top fuel drag cars that have very short pipes. Maybe its from the two stroke perspetctive of expansion chambers but I still cant understand back pressure. I cannot even understand were the idea of backpressure came from.

The only explanation I have ever heard is that it helps stop the valve slamming shut, but thats a bit hard when at 6000 rpm ( that is 100 revolutions per second) the valve opens and closes 50 times in ONE second so that seems a bit wierd to me.

Anyway twin carbs on sierra is like turning a goat into a racehorse.. It wastes your time and annoys the goat.

Top fuel cars are supercharged, exhaust requirements are a bit different with forced induction. (pic isn't a top fuel car)

Two stroke exhaust design is a whole different animal again. It isn't really backpressure you are chasing, it is the timing of the exhaust pulses reflecting of the diverging cone in the expansion chamber.

I have heard stories about needing backpressure to stop your exhaust valves from burning but I think that would have more to do with the state of the engine tune having a free flowing exhaust.

[Myles]

Reubs wrote:

Myles wrote:

Yeah but 1.6efi is illegal on your p's... You can drive a vitara.. But you can't drive a sierra with a vitara motor it sucks... I can't get any other engine in my car while I'm on my ps.. Otherwise I wouldhave gotten a g13b or a g16 instead of just rebuilding the g13a... So yea I'm just looking at different ways to get more power from the g13a.. My bosses name is John Stamatiou

A stock coily has the G13BA (1298cc). IMO, you could have put a Swift GTI motor (same block capacity wise) in it if you want grunt for the on-road.

You've complained of carby problems and a gutless car in the past. Have you ever been to a carby specialist? You'll get a lot more than just a carby rebuild for your $$$. A good carby builder needs to check all the engines systems - electrical, fuel delivery, exhaust etc. for problems in order to ensure a good tune. You also might find your new BIG exhaust system is causing you a loss of power.

Do you run 30 or 40 weight oil? Do you run 98RON fuel? Do you run double platinum plugs? Do you have a performance air filter? Does your exhaust maintain correct backpressure? Are you running suitably sized tyres?

Also, have you looked at a new camshaft?

I'm sure there are lots of ways a P-Plater can get a little more power from their engine...

If you still want to go quicker, take the front diff out of your car. Less unnecessary weight = more gusto!

Hmmm... Yeah I did complain in the past but that was because my engine was falling to bits lol it literally had less power then my 50cc Scooter. its all good now after the rebuild and everything though.. I was just asking around for what other things i could do to get more grunt withought an engine transplant.. I had it professionally tuned the other day by i guy i cant remember.. dad sorted it all out for me but he put like sensors in the exhaust and checked the timing and ajusted some things on the carby and everything.. Ive only got a 2"exhaust so its not that huge lol. not sure what kind of oil its running at the moment but yes i do use 98% fuel. dunno about the plugs and i want to look into getting a performance air filter.. Dont know ANYTHING about backpressure except that 2 stroke motorbikes need it... i dont think my 235's are too big, I havent looked at a camshaft andddd i dont wanna rip the front diff out of my car WOAH THAT WAS A MOUTHFULL. lol

[ball]

Myles wrote:

Reubs wrote:

Myles wrote:

Yeah but 1.6efi is illegal on your p's... You can drive a vitara.. But you can't drive a sierra with a vitara motor it sucks... I can't get any other engine in my car while I'm on my ps.. Otherwise I wouldhave gotten a g13b or a g16 instead of just rebuilding the g13a... So yea I'm just looking at different ways to get more power from the g13a.. My bosses name is John Stamatiou

A stock coily has the G13BA (1298cc). IMO, you could have put a Swift GTI motor (same block capacity wise) in it if you want grunt for the on-road.

You've complained of carby problems and a gutless car in the past. Have you ever been to a carby specialist? You'll get a lot more than just a carby rebuild for your $$$. A good carby builder needs to check all the engines systems - electrical, fuel delivery, exhaust etc. for problems in order to ensure a good tune. You also might find your new BIG exhaust system is causing you a loss of power.

Do you run 30 or 40 weight oil? Do you run 98RON fuel? Do you run double platinum plugs? Do you have a performance air filter? Does your exhaust maintain correct backpressure? Are you running suitably sized tyres?

Also, have you looked at a new camshaft?

I'm sure there are lots of ways a P-Plater can get a little more power from their engine...

If you still want to go quicker, take the front diff out of your car. Less unnecessary weight = more gusto!

Hmmm... Yeah I did complain in the past but that was because my engine was falling to bits lol it literally had less power then my 50cc Scooter. its all good now after the rebuild and everything though.. I was just asking around for what other things i could do to get more grunt withought an engine transplant.. I had it professionally tuned the other day by i guy i cant remember.. dad sorted it all out for me but he put like sensors in the exhaust and checked the timing and ajusted some things on the carby and everything.. Ive only got a 2"exhaust so its not that huge lol. not sure what kind of oil its running at the moment but yes i do use 98% fuel. dunno about the plugs and i want to look into getting a performance air filter.. Dont know ANYTHING about backpressure except that 2 stroke motorbikes need it... i dont think my 235's are too big, I havent looked at a camshaft andddd i dont wanna rip the front diff out of my car WOAH THAT WAS A MOUTHFULL. lol

Wrong, read my post above yours

[bigrig91]

just put a new engine in, as if the cop will know the difference!!!! I would be interested to look into a new cam though as i was talking to an engine builder the other day about a mates turbo petrol patrol and he mentioned how important a well ground cam can be.

[zacs7]

bigrig91 wrote:

just put a new engine in, as if the cop will know the difference!!!! I would be interested to look into a new cam though as i was talking to an engine builder the other day about a mates turbo petrol patrol and he mentioned how important a well ground cam can be.

Careful. There's a reason why the police like to hire ex-mechanics.

[steak_knife]

zacs7 wrote:

bigrig91 wrote:

just put a new engine in, as if the cop will know the difference!!!! I would be interested to look into a new cam though as i was talking to an engine builder the other day about a mates turbo petrol patrol and he mentioned how important a well ground cam can be.

Careful. There's a reason why the police like to hire ex-mechanics.

So when the ex-cab's with disco light's on the roof stop working thay can fix em??

[2stroker]

bigrig91 wrote:

just put a new engine in, as if the cop will know the difference!!!! I would be interested to look into a new cam though as i was talking to an engine builder the other day about a mates turbo petrol patrol and he mentioned how important a well ground cam can be.

It's not the cops I would worry about, it is the insurance if you crash it and the Qld transport inspectors who just love to wave you into their roadside inspections.

Myles, mate you own a suzuki, i don't agree with tzar that it is a goat but i do agree that it is no race horse. take it easy mate, slow and steady is the way to go.

[royce]

Rusho81 wrote:

I think the pipes on a drag car are there to direct exhaust gases out more than anything...3000 to 7000hp doesn't really matter how long they are does it? I don't think tune length extractors and diameter of exhaust really come into here.

Hehehehe Goat....good way to look at it TZAR, I like it

on the contrary, they are looking for every little bit and you can bet the size and length of those pipes is the absolute best they can be

[2stroker]

This makes sence:

When contemplating a modified exhaust system there are those who want the biggest diameter pipe that can be had. Their idea must be that fatter pipes are more effective at venting than narrower pipes. This sounds reasonable but it is not quite correct. Sure wider pipes have greater volume and higher flow capacity, but that is just half of the story. Capacity is one consideration but gas velocity is the other factor.

An experienced exhaust designer knows that the best exhaust is one that balances flow capacity with velocity. A given volume/time of gasses will travel faster through a 2" pipe than the same volume of gas passing through a 3" pipe. So when taken to its extremes we can see that a too narrow pipe will create backpressure (restrictions to positive flow) problems and a too wide pipe will cause a very slow flow with no backpressure.

The optimum is where the fastest velocity is achieved with the least constriction possible.



This situation will arise when the pipe is wide enough so that there is the least level of positive backpressure possible whilst achieving the highest exhaust gas velocity.

The faster the exhaust gas pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The scavenge effect can be visualised by imagining the high-pressure pulse with a trailing low-pressure area behind. The faster the high-pressure pulse moves the stronger the draw on the low-pressure gasses and the gasses behind that. The scavenge action is like (but not exactly) suction on the gasses behind.



The greater the clearance burned fuel from the combustion chamber the less diluted the incoming air/fuel mix is. Scavenging can also aid intake on overlapping valves (where the exhaust and inlet valves are open at the same time) by drawing in the intake. These are good things to happen.



So instead of going for the widest pipe possible we should be looking for the combination of the narrowest pipe that produces the least backpressure possible. In this scenario we achieve the least restriction on positive flow and the highest gas travel speed.

[royce]

thats 100% for correctly designed extractors, after that it doesnt matter

[2stroker]

I'm not convinced that it doesn't matter, I think you would see a significant difference in dyno sheet figures if you ran a car with a good sports exhaust and then took the exhaust off behind the extactors and dyno it again, and I would bet that the first set of figures with the exhaust on would look better.

[MacDaddy]

The myth of exhaust backpressure !

I Just googled for " exhaust backpressure myth or fact ", and the very simple answer is, drum roll.....

YES exhaust backpressure is a myth !!!

One of the most misunderstood concepts in exhaust theory is backpressure !!!

A good or performance exhaust system, is one that has very little or No backpressure, with High velocity exhaust gases !!!

And i learnt that with better exhaust gas flow, you get a much better and cleaner air fuel mix into the cylinder chamber, and that you should have the engine re-tuned for that better flow in and out, because with a restrictive exhaust system, you get some burnt fuel left in the cylinder chamber, and when your engine is tuned to run like that, when you get a better flow with less or no leftover burnt fuel in the cylinder chamber, that your engine can run leaner, and that will cause the valves to run hotter, and can burn the valves, so the fuel air mix needs to be adjusted, so the valves dont run hot... so as long as you get the engine/air fuel mix re-tuned, it really doesnt matter how big an exhaust you have, or even if you have very short exhaust pipes...

Other than that, the whole exhaust backpressure is a 100% myth !!!!!

[royce]

2stroker wrote:

I'm not convinced that it doesn't matter, I think you would see a significant difference in dyno sheet figures if you ran a car with a good sports exhaust and then took the exhaust off behind the extactors and dyno it again, and I would bet that the first set of figures with the exhaust on would look better.

any gains after the extractors means they arent designed properly and arent scavenging as much as they could, the pipe lengths and diameter decides how much of a pulse there is and the collector design does the work of using this pulse to create a vacuum in the corresponding cylinders pipe, after this is jsut a matter of getting rid of the gas

look at some of the tuned systems for Peripheral ported rotarys, they extend well past the halfway point of the car, such is the length needed to make them work

So yes in real world with real budgets pipe size can make a difference, if you can work out the correct size to get teh right amount of intertia in the gas to syphon off the collector point of the extractors (and thats exactly what it will do) but its only at 1 point, any slower in gas speed it will do nothing and you are relying on the extractors, any higher and you get pumping losses and lose power due to there not being enough flow, but then if you are smart enough to work out the pipe size needed you can probably work out some decent extractors anyway

to hark back to more mini stuff the perfect exhaust for them is a specific design extractor with pipe sizes to suit your engine and a megaphone type exhaust so the gas isnt slowed along the length of the pipe

[SuziBlu]

Insulating helps as well, as when the gasses cool, the get denser and slow down, thus loosing terminal velocity.

Probably not something many 4wders will contemplate but.

[2stroker]

Anyone who has driven a car even for 5 minutes without an exhaust will know what I am talking about. Completely removing an exhaust will make he car loose power at certain rev ranges and run poorly, backfiring when you back off etc as the cool outside air licks back up the pipes and then is expelled by the next pulse of hot exhaust gas. So what I am saying is that what comes after the extractors is as important as the extractors.

MacBear, I have already posted that 3 posts prior to yours, probably from the same google search. In actual fact what you are saying contradicts itself because you say backpressure is 100% myth but then say:

"A good or performance exhaust system, is one that has very little or No backpressure, with High velocity exhaust gases !!!"

To obtain air speed or "high velocity exhaust gases" you need to have some restriction in the flow and restricting the flow means that the flow is backed up to some degree and this creates pressure and that pressure is commonly refered to as backpressure. So you cannot have one without the other.

It is old terminoligy and probably doesn't properly describe the process but so are terms like vacuum which is used to describe suction when the word actually means "a volume of space that is essentially empty of matter"