2.3 I4 forged engine fueling and exhaust questions

[freddy686868]

Basically my standard 2.3 (2.3 engine with rs2k cams) I4 snapped a rod a week back so i'm going to build a forged motor and i'm looking for 220/240bhp and i need a couple of questions answered to guide me in the right direction. The engine will be revd to around 6.5k maybe as far as 7k but i doubt it The spec will be roughly as followed:-

2.3 scorpio head ported and polished
Forged pistons (hoping for a 90mm piston instead of the standard 89.6mm and around a 12.1 cr)
Forged rods with arp bolts
Lightened and balanced bottom end and maybe a knife edged crank
Standard rs2k cams
Twin weber 45's
Tony law exhaust manifold
And a 2.25"/2.5" exhaust system.

Basically i'm abit worried about the webers being too small to cope as i see alot of people running 48's on the 2.3 I4s but they are on rally cars were mine is going to be used on the road and driven to shows and track days and i don't want it to drive like a pig.

Also i need to change my exhaust system because when i had the engine set up the 2" system stoped flowing at 5k and that in turn killed the power down to 190bhp instead of the 200bhp i was expecting. So my question is what will be best for my spec of engine ? I'm thinking 2.25 as i love the low down grunt of the 2.3 but i don't want to spend all this money for the exhaust system or carbs to not flow enough gases. Thanks in advance for all you answer, John

[exboyracer]

If you want the power you need to size the carbs appropriately. For 240bhp you'll need 48s.
If it's gonna be mainly for road use, fit 45s and sacrifice a few top end BHP for more driveability.

You will need at least a 2.5" exhaust system.

[freddy686868]

If you want the power you need to size the carbs appropriately. For 240bhp you'll need 48s.
If it's gonna be mainly for road use, fit 45s and sacrifice a few top end BHP for more driveability.

You will need at least a 2.5" exhaust system.

Well that answered my 'dilema' in one i'll go for the 2.5" then and one last thing how much bhp will the 45's run before they can't flow enough? Also am i right in thinking 45mm throttle bodies will flow more air than 45mm carbs?

[Darbo]

ive just put some gsxr 750 throttle bodies on mine
they cost £30 the butterflys are 46mm ish
home made manifold etc will have under £100 for the finished bodies and manifold and fliters
so should flow like twin 50's
got a k6 ecu but im waiting on working out how to narrow my capri axle for the right money so cant say how it will all perform as yet

shame it went pop by the way but the power you had was very nice

[exboyracer]

Well that answered my 'dilema' in one how much bhp will the 45's run before they can't flow enough? Also am i right in thinking 45mm throttle bodies will flow more air than 45mm carbs?

IIRC 45s are good for about 190bhp. Yes you are right, 45mm TBs will flow more air than 45mm carbs, mainly because TBs don't have to have chokes in them.

Having played about with both carbs and TBs I would never go back to carbs. They might be a little more expensive up front, but the driveability that the ITB injection system gives you is well worth the extra IMO.

[freddy686868]

IIRC 45s are good for about 190bhp. Yes you are right, 45mm TBs will flow more air than 45mm carbs, mainly because TBs don't have to have chokes in them.

Having played about with both carbs and TBs I would never go back to carbs. They might be a little more expensive up front, but the driveability that the ITB injection system gives you is well worth the extra IMO.

Well i did buy the dta s40 pro so i could eventually go over to bodies so i might do that with this new build. But then i have to mess about with trying to find the correct size injectors. Will 45mm bodies flow enough for my spec? I might be on the look out for some jenveys now then! It just never ends. lol

[exboyracer]

I would think 45mm bodies would be sufficient for 240 ish bhp

There are injector size calculators oon the net if you look, here's one I have used before
http://www.rceng.com/technical.aspx

[packman]

I built one about 5 years ago now , it made around 227 hp fly @ 185 @ the wheels with 187 ft , as far as i can remember ,

Balancer shafts removed.
Stock internals with ARP rod bolts.
x amount of the top of the pistons
10/5/1 cr
Piper cams with verniers
CTM head with standard valves & 3 angles
Tony Law manifold
Webcon 45 mm throttle body kit

Will see if i can find some pics , it did go rather well ;D

[freddy686868]

ive just put some gsxr 750 throttle bodies on mine
they cost £30 the butterflys are 46mm ish
home made manifold etc will have under £100 for the finished bodies and manifold and fliters
so should flow like twin 50's
got a k6 ecu but im waiting on working out how to narrow my capri axle for the right money so cant say how it will all perform as yet

shame it went pop by the way but the power you had was very nice

I was going to go down the bike carb route but 45 webers came up cheap and i had an inlet manifols made to fit them so i wouldn't wanna go for bike carbs now :-( thanks for the reply any way.

[freddy686868]

I built one about 5 years ago now , it made around 227 hp fly @ 185 @ the wheels with 187 ft , as far as i can remember ,

Balancer shafts removed.
Stock internals with ARP rod bolts.
x amount of the top of the pistons
10/5/1 cr
Piper cams with verniers
CTM head with standard valves & 3 angles
Tony Law manifold
Webcon 45 mm throttle body kit

Will see if i can find some pics , it did go rather well ;D

How long did you use the engine for and what mileage did the donor lump have on it? You must of had a nice free flowing exhaust system on it as the bhp is high and the torque a little lower than mine. Have you got a graph of the power plot? thanks john

[caprimentle]

ive just put some gsxr 750 throttle bodies on mine
they cost £30 the butterflys are 46mm ish
home made manifold etc will have under £100 for the finished bodies and manifold and fliters
so should flow like twin 50's
got a k6 ecu but im waiting on working out how to narrow my capri axle for the right money so cant say how it will all perform as yet

shame it went pop by the way but the power you had was very nice

I was going to go down the bike carb route but 45 webers came up cheap and i had an inlet manifols made to fit them so i wouldn't wanna go for bike carbs now :-( thanks for the reply any way.

he said bike throttle bodies fella, not carbs , much much cheaper than a set of jenveys, i plan on using them on my na pinto build, great if your on a budget

[packman]

How long did you use the engine for and what mileage did the donor lump have on it? You must of had a nice free flowing exhaust system on it as the bhp is high and the torque a little lower than mine. Have you got a graph of the power plot? thanks john

The last i heard the engine was well past 20k with no trouble , the donor engine did have @ 80k on it but was mint inside in the bores and crank i had a Tony Law Manifold and a 2.1/4 inch system , Harvey Gibbs said i would have got 5hp more with slightly smaller primary's it did go very well thou.

[Graham]

i would go with a 2.5 inch system, as for your carbs, a big cc 16v will make more use of a pair of 45's than a pinto will so i recon you could get a fair bit over 200bhp on them IF the cams allow

[dangerousdave]

You could always drop in the kent rs2001 cams if your feeling flush

[freddy686868]

Well thanks for all your replies guys but i am affraid i have wasted all your time (for now any way) as i have just bought a shell in need of a full strip down and building up so i will be building the forged lump up for that in around 3 years. T hanks for all the advice any way!

[RWD fords rule]

I would think the std cams you are planing to use would be more of a limitation than the 45mm webers

Since you have an ecu why not convert those 45mm webers to throttle bodies instead, get some injector bosses welded into your inlet manifold, make a fuel rail, buy a weber tps, maybe run it with carbs for now and convert then to 45mm TB's later on, but with steel rods, forded pistons a decent head etc there is no point running std cams imho, that is throwing away a lot of usable power and torque vs a good pair of cams