im trying to figure out roughly how much hp per psi i will get going na to twin turbo.

5500 cc engine will remain stock at 10.5 cr
fit 2 t3 ar .48 turbos rated at about 300 hp each
engine is about 300 hp currently

im just curious how much hp i could get per psi assuming engine stays stock

just thinking on 100 hp of boost instead of 100 hp of nos and no lag as cr remains the same.

i was thinking i could run 5 psi without needing an intercooler and engine should take it, but what power woold be achieved roughly ?

 

Rule of thumb is if you stick a bar of boost (15psi) up an NA engine it basically doubles the output.
So for your 300hp V8 it becomes 600hp, working back from 15psi to 5psi you should see a 100hp gain, 10psi 200hp gain. That's my understanding anyway.

 

thatd be great if it is as thats what im after.

question is will a 10.5 cr engine run 5 psi boost on optimax ?

 

There isnt a straight formula that tells you how much power you will get for a bar of boost.

On one hand you probably only have about 13 psi absolute in your manifold currenly (due to intake restrictions) so 29psi from a bar of boost is way more than double, so it looks like you should get more than 100% gains, but then you have to take into account the change in intake temps, which bring it back down, especially if non intercooled.
If you then consider the exhaust side as well, you have to consider what bolting two quite restrictive snails on would do to your N/A power output in the first place.

All that said, I'd expect 5psi to give you roughly the sort of gains you are looking for and some really good torque increases as well, but I would want to put it on mappable ignition at least, and preferably management for the fuelling too, as to get the best from a high cr turbo conversion you do need to be careful about how its mapped, and on a carb and dizzy its hard to get right (although possible of course)

If you can add an intercooler, it would really be worthwhile doing so, even on low boost.

 

Isnt as simple as that. And I would say that those turbos are a bit small unless you're operating over a very small rpm range.

5psi should be ok with no intercooler, obviously will good control over ign timing and fuelling though

If you worked on the theory that 1bar ie atmospheric allows 300bhp, then in theory 2 bar could allow 600bhp ( in that ideal world ), but obviously it wont. I cant see 5psi giving you another 100bhp though. And doing such a conversion for anything less would be a total waste of time.

You could probably get the extra 100bhp through n/a tuning

 

I agree on the turbo size, bigger the better when you are doing high comp n/a conversions really as you dont want the boost till later anyway so small turbos have no advantage and they have disadvantages in terms of EGT and EBP

 

something else ive been looking at is a 383 stroker kit.

id rather just optimax than messing with nitrous all the time if i can.

 

top rev will only be 5500 rpm though chip and 3rd to 4th gear change is gonna drop me down to 3000 rpm.

 

If you are determined to only rev it to 5500rpm, then fair enough on the turbo choice.

Nitrous has the advantage of masses gains that are easy to achieve and dont need mappable management or lots of expensive setup time on the carb/dizzy etc.
Disadvantage is its very expensive on an ongoing basis for anything other than drag racing.

So depends what use it will get if thats a good route or not.

Personally I would nitrous it wether your turbo it or stroker it or whatever, I just dont se the point in having a big strong engine like that to go drag racing with and then not use nitrous on it.

 

im really not sure mate just toying with options at the moment.

id say i have been revving it to around 7000 rpm and not realising, as since ive fitted the omex limiter set at 5000 rpm its a hell of alot lower than i was revving it lol

it has hyd tappets so online they say 5500 rpm max, but my oil pressure is far from standard, when it was built all journals were altered and pump work, upto full temp its 30 psi idle, as soon as i touch throttle it has 100 psi all the time which i guess is holding the tappets up virtually like solids anyways. either way it seemed happy revving high i just dont wana kill it.

the other issue is the mains are just 2 bolt, i dont yet know the limit of the bottom end ?

 

At only 5psi, despite no IC as long as you have proper control over timing and fuel, then pump fuel should not pose a problem. You could maybe even squeeze 10psi in

You could also use water injection if detonation cant be avoided..

But for such relatively small gains, it's hard to see how a twin turbo install would be worth the effort. Spend the money on the stroker, better heads, cam etc. You should easily see an extra 100bhp with that.

Other than perhaps the availability of cheap smallish turbos, I wouldnt even consider a twin install again. A bigger single would be much easier in every way. Well, unless I was buying an already fabricated kit. Twins are pretty much double the work.

 

100psi will not pose a problem to the lifters and they certainly wont be like solid lifters.. Worst case with a pumped up lifter, is the valves will no longer close properly.
But no way in hell would I want 100psi of oil pressure in any engine when warm. So something isnt right there.

 

whats the limit of 2 bolt main small block bottom ends steve ? thats my only other concern.

its all just cheap stuff im looking at, manifolds are Ł130, both turbos Ł300 for the pair, i reckon i could do the whole job for under Ł1000 intercooled aswell complete twin t3 turbo set up like 2 standard cossie turbos.

or a 383 stroker kit is about Ł1000 aswell but i think just the stroker would just add about 50 hp. im currently on the double hump heads aswell 64cc i think but pretty sure on soft valve seats so running millers with the optimax at the moment.

 

If you were building an endurance racer, perhaps you could be concerned about many things. Ive no idea on your specific engine, but Ive turbocharged plenty of other engines, and never worried too much about things like main caps. It's unlikely boost will create any problems there. High rpm's maybe, but not a little boost. I assume it's already a big heavy strong iron block ?

And what are the heads made from ? Surely nearly all American engines will be fine for unleaded ?

Certainly at less than Ł1k, yea go for it. it would be a waste of money to do stroker and turbos though, and a stroker will place more load on the main caps than a bit of boost.

But dont forget to budget in for proper fuel and ignition control. Although a carb/dizzy could be made to work to a degree as well. No idea what you're using at present ?

Even if you had to stick to a carb, I'd still go for mapped ignition with boost. And fix that oil pressure, it's far too high.

 

it was originally built that way by doug harvey about 35 years ago, it was built soley for grass tracking, it had a 1050 dominator carb on it, used to go well ive seen cini camera footage he used to just drive around the outside of everybody and they all had small block chevys or jag engines.

i questioned the pressure myself as it seems excessive, cold start its right of a 100 psi gauge its bent the needle so 0 is now 15 psi lol.

but it was purposely done this way, i could see the journals had been messed with when i built it up they have a massive lead on them.
heads are the high performance double humps with the larger valves of the 60s and inlet is performance of the era.

not sure on cam but doug also removed vac advance and bolted it down it just runs mechanical, i think it runs about 20d mech advance as best i could measure, the one thing i did notice is not much vac at idle around 9 psi and a very small window of dizzy adjustment to get it running right ?

 

its all iron no alloy here fella not even the inlet mani !

currently on edelbrock 600 cfm performer, if i turbo will run a blow through carb built for the job with mech advance altered to suit.
i want something i can tune myself, wideband is on its way already as current jetting is just a guess

hadnt thought about ignition guess i should look into a better control of spark.

 

Big cam = crap for turbo. ( no vac at idle, could be down to big cam )

Big carb = crap for turbo.

Vac advance, purely for driveability, economy etc. Not much need on a grass track engine.

To turbocharge it, you're going to need to make big changes. Fit a mild cam with very little or no overlap.
It will either need a new carb, or fit fuel injection.
It will need proper mapped ignition if using high CR, no IC and boost to get sensible and safe results.

For fuel injection, best bet is one of the carb style setups. Certainly it should be easiest and cheapest. Just slap it on top of the carb manifold.

You could still work with a dizzy and boost. But I would not recommend it with high compression ratio.
Especially when you could do the likes of Megajolt so cheaply

 

what sort of idle vac would it be stock mate ?

 

If you want something you can tune yourself, a mappable system is a LOT easier than carbs and dizzy IME

 

my plan with the carb is just jet it for 14 afr on the primarys and 12.5 on the secondaries. ign im just running it fairly safe id guess around 30d total advance, all earballed and driving up the road but its close on.

if turbos go on though id need a new carb anyways so i guess i could put that money to an efi set up instead.

i guess id need a whole new ignition system aswell though then with coilpack etc then management soon gets in ŁŁŁŁ and complexity which i want to avoid.

 

You can run a dizzy on EFI no problem at all.
No real value in swapping to coils for your particular application IMHO

 

my brain is an empty book when it comes to mappable ignition mate lol

so could my dizzy be modified so ignition timing could be mappable through it ?

i should have a good idea where im at this week, just waiting for a couple more parts then il put the gtech in and run up 100 metres or so and see where im at currently power wise.

 

You dont need to modify the dizzy itself at all mate.

At the moment your ignition works by:

Ignition module -> Coil -> Dizzy

Instead of the ignition module triggering the coil, you get the ECU to do it instead. Not sure on yours if its points or electronic, but same applies either way really.

I'll happily help you with the mapping if you go down that route, looks like comedy so Im sure it will be a good laugh anyway, me and Tank Mike are round as far as Junction 25 of the M25 relatively often anyway, so not too much extra hassle to pop up to yours one evening for a late mapping session

 

Ps

Rob DOHC on here sells megasquirts, you could put one of them on it while its still N/A to get it up and running on it, then when you turbo it you know that you are already onto a winner management wise

 

Throw a 36-1 or similar onto the front pulley and run off that. Dont bother with the dizzy at all. There is just no point.

Then stick a couple of 4 tower coil packs onto it. There is nothing expensive or difficult about either of those, and it opens you up for a proper setup.

then as Chip says, Megasquirt or similar, maybe VEMS will be about the cheapest efi you can use, and work easily with boost. Obviously when it comes time to inject fuel, your fuel system will need adapted/upgraded to suit though.
But you can very easily run it ignition only to start with.

 

I cant see any real point in going to coilpack when it works fine as it is and has the leads already on there etc to fit the dizzy, but like Stevie says, its very easy to do if you want to.

 

top man

im on electronic ignition, a module in the dizzy with an eye that a plastic ring passes through, when the slots pass the eye makes contact and fires, then charges while blocked til next slot then fires again.

 

whats a 36-1 ? do you mean some sort of crank sensor ?

 

Well all you need to do is find out what signal it sends (normally its just an earth) and then make sure you get an ECU that does the same (including handling the current draw if applicable) if you want a really easy fit rather than going to coils, although like Stevie said, its very easy to do so anyway.

Good thing if you keep it on the dizzy, is you can just cut the wire from that module to the coil to run mappable ignition with, but always reconnect up the current setup to get you home if you have a problem with the management, not that you should ever need that.

 

Yes, add a disk to the aux belt pulley and retrofit a sensor.

 

Just to remove the dizzy cap, rotor arm etc. All ancient stuff really. Becomes zero maintenance then, although just as messy with long leads everywhere.

A couple of coilpacks with normal HT lead fitments wouldnt be expensive, and are generally much much better. There arent really any downsides, and existing leads should be able to be re-used or adapted.

Guy selling a pair of 4 tower here for Ł50

http://trigger-wheels.com/store/contents/en-uk/d8.html

 

is this the sort of ecu id need then ?

http://www.ebay.co.uk/itm/Megasquirt...item4aaf0046ed

could i just get a couple of coil packs from a scrappy of a zetec or similar then what just a crank sensor and wiring ?

 

On my clio im on aftermarket and ive converted to a 60-2 wheel (when I changed clutch I put a 172 flywheel on) instead of the 44-2-2 which now means I can run a coilpack without need a cam sensor, but as the dizzy works ive just left it for now, its one of those jobs i'll do when either I have some free time and am bored, or when I next need a new rotor arm or dizzy cap.

I definately agree overall its better, but if he is trying to just do the bare minimum for now its not actually required.

 

that is a bargain fella far cheaper than id of thought

i spent double that on a new module lol

 

Yep thats the sort of ECU you would need, although if you talk to Rob he can probably do you a full MS3 for similar money to that microsquirt, not that it massively matters as either will work, just got more features for later on like boost control.

Yeah any old coil really, just make sure that you get amplified or non amplified as suited to whatever ecu you want to run, fiesta turbo ones are non amplified for example, vauxhall corsa ones are amplified though, so thats a readily available source of each type, cant remember off hand which type zetec are.

Any old crank sensor will do if you go for microsquirt or megasquirt as they support every crank sensor I have ever seen, they even can handle the 44-2-2 renix setup on a clio williams that almost nothing else does (even my autronic SM4 cant for example!)

 

The link above seemed to be for 2 coil packs, and a crank sensor. So you'd just need a trigger wheel.

But do not just randomly go out and buy some bits here and there.

It will make good sense, if you can to buy everything from one person, AFTER you decide which ecu you will use.

Do not buy anything until then or you could have compatibility issues.

 

Agreed, better to spec out exactly what he needs first rather than buy random stuff and hope it fits.

 

i will try and restrain my itchy trigger ebay finger boys

i am seriously considering it though if i go turbo as its much cheaper than i thought.

 

Have you thought about a draw through supercharger setup ?

They give good results and are very simple.

 

Just a case of finding the right injectors and inlet etc cheap secondhand is the biggest issue.

Is there a later revision of that engine that the inlet will bolt on from that runs injection?