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Spotted a L-series
- Thread starter johnymd
- Start date
johnymd
Club Member
Sounds like it's no one on here so I'll give a little more detail.
Built by a company in London and to a pretty high spec. Its a 3.2 with "big" cam but little else known. Running 45's with to small idle jets (1.2 lamda) and not enough air flow to produce the power it should be capable of. Should be a monster with the right fuelling.
Built by a company in London and to a pretty high spec. Its a 3.2 with "big" cam but little else known. Running 45's with to small idle jets (1.2 lamda) and not enough air flow to produce the power it should be capable of. Should be a monster with the right fuelling.
richiep
Club Member
Not necessarily; consider that Steve Kiddell’s 3.0L is running on 45 ITBs and getting 300hp. Obviously ITBs can be tuned much more finely but I wouldn’t rule out properly jetted 45 carbs. Plus, depends on what the intended use is - a 3.2 with 50s might get ultimate hp at WOT, great for the bhp pissing contest, but be a complete dog as a road car.
atomman
Club Member
How do you work guys out what size choke /carb your engine needs ?
I thought it was worked out by how much flow each cylinder needs ? Smaller choke equals faster flow @ lower rev's, bigger choke etc ,
The reason I ask is my dyno guy said i needed bigger chokes, so I'm up to 36mm now but it they are not big enough I've gotta change to 45's , will find out after Christmas when i go back
I thought it was worked out by how much flow each cylinder needs ? Smaller choke equals faster flow @ lower rev's, bigger choke etc ,
The reason I ask is my dyno guy said i needed bigger chokes, so I'm up to 36mm now but it they are not big enough I've gotta change to 45's , will find out after Christmas when i go back
richiep
Club Member
It’s quite possible to go too big on the chokes, when the power could’ve been made through different jetting with smaller chokes.
E.g. the L28 in my Fairlady Z is running Dellorto DHLA 40s with 34mm chokes and is making at least 200hp (I say at least as that figure was from its dyno tuning runs back when it had an MSA header and exhaust, known to be inferior in performance terms to something like the Fujitsubo it has nowadays). The tuning (done by Ric Wood) was more about expertise focussed on jetting and timing, with results judged from the dyno graphs.
My underlying point is that big is not necessarily better once all variables have been considered.
Actually, there will be some change with that engine this year as I switch to a Harada/Kameari intake and a cold air feed system, which should squeeze some more power out. Also, the current N42 is going to be swapped to a JDM E30 head from an L20; the ports will be hogged out to N42 size and N42 standard valves fitted, but that head comes from the factory with 36 or 37cc kidney-shaped chambers for great squish. Should yield interesting results...
E.g. the L28 in my Fairlady Z is running Dellorto DHLA 40s with 34mm chokes and is making at least 200hp (I say at least as that figure was from its dyno tuning runs back when it had an MSA header and exhaust, known to be inferior in performance terms to something like the Fujitsubo it has nowadays). The tuning (done by Ric Wood) was more about expertise focussed on jetting and timing, with results judged from the dyno graphs.
My underlying point is that big is not necessarily better once all variables have been considered.
Actually, there will be some change with that engine this year as I switch to a Harada/Kameari intake and a cold air feed system, which should squeeze some more power out. Also, the current N42 is going to be swapped to a JDM E30 head from an L20; the ports will be hogged out to N42 size and N42 standard valves fitted, but that head comes from the factory with 36 or 37cc kidney-shaped chambers for great squish. Should yield interesting results...
Alphabettispaghetti
Club Member
It’s a shame mr Skidell doesn’t post on here anymore.
Which cold air intake are you going for?
Which cold air intake are you going for?
Alphabettispaghetti
Club Member
richiep
Club Member
The one Mr F sells, ie the fibreglass version of the Skiddell one. Had it on the shelf for years.
Alphabettispaghetti
Club Member
which looks to be a carbon copy(well frp) version of the old r-tune one?
My engine is 2915 and I have 39mm chokes in my Dellorto 45s, and it works well (now!) in all conditions.
I sized the chokes based on a calculation offered in the Honsowetz book, based on cylinder capacity and max rpm.
It's definitely got a fudge factor in it, so not that scientific but the value it comes up with (39 for 7500 red line) is pretty close to what my engine builder friend was suggesting. (he said bigger!). Vizard has a similar calculation.
Here's a pic from the Vizard book (I'll take it down if someone complains) that shows a couple of interesting things - 1) that you need bigger chokes to flow more air and 2) that the air flow tails off rapidly as you go bigger than 38mm choke on a 45mm body.
If you're building a 3.2 litre performance engine, surely you'll expect to rev and produce power up to 7500 rpm (at least) , and if we're to believe Honsowetz and Vizard, then you'll need bigger than 40mm chokes to deliver the air, AND 45mm bodies can't do it.
if you want to have a torque monster and run it in the stock 6500 rpm range then I support 45mm bodies will be fine, but I think you'd still want 40mm chokes.
In the comparison with ITBs, I'm not 100% sure, but I don't think ITBs have chokes, so really I think a 45 ITB should be compared to a 50mm body carb with a 45mm choke. You can't put a 45mm choke in a 45mm body carb.
I've read many forum threads about people that have struggled to get their triple carbs working well with big chokes. in my experience the problem is that the progression hole spacing is fixed and so it's a compromise with the choke sizes; My Dellorto 45s at least seem to have been designed with lower revving, higher capacity engines in mind (Jag 4.2 anyone?) and aren't ideal for high revving lower capacity engines.
The problem is that as the choke sizes go up, smaller movements of the throttle allow the same amount of air in and so the progression holes are effectively stretched apart which can mean that the engine can go lean between progression holes. Mine used to. (Just FYI, you're on the progression holes rather than main jets most of the time, even cruising in excess of the speed limit on the motorway).
the effect of this is that with big chokes, most of the time when you go to accelerate from cruising you get a really irritating lean stumble.
Reducing the choke size does cure it. At the expense of top end, which I accept is fine for many people.
However, you can also solve the problem by putting your progression holes where they're needed. It just involves bravely drilling some holes in your carbs
I sized the chokes based on a calculation offered in the Honsowetz book, based on cylinder capacity and max rpm.
It's definitely got a fudge factor in it, so not that scientific but the value it comes up with (39 for 7500 red line) is pretty close to what my engine builder friend was suggesting. (he said bigger!). Vizard has a similar calculation.
Here's a pic from the Vizard book (I'll take it down if someone complains) that shows a couple of interesting things - 1) that you need bigger chokes to flow more air and 2) that the air flow tails off rapidly as you go bigger than 38mm choke on a 45mm body.
If you're building a 3.2 litre performance engine, surely you'll expect to rev and produce power up to 7500 rpm (at least) , and if we're to believe Honsowetz and Vizard, then you'll need bigger than 40mm chokes to deliver the air, AND 45mm bodies can't do it.
if you want to have a torque monster and run it in the stock 6500 rpm range then I support 45mm bodies will be fine, but I think you'd still want 40mm chokes.
In the comparison with ITBs, I'm not 100% sure, but I don't think ITBs have chokes, so really I think a 45 ITB should be compared to a 50mm body carb with a 45mm choke. You can't put a 45mm choke in a 45mm body carb.
I've read many forum threads about people that have struggled to get their triple carbs working well with big chokes. in my experience the problem is that the progression hole spacing is fixed and so it's a compromise with the choke sizes; My Dellorto 45s at least seem to have been designed with lower revving, higher capacity engines in mind (Jag 4.2 anyone?) and aren't ideal for high revving lower capacity engines.
The problem is that as the choke sizes go up, smaller movements of the throttle allow the same amount of air in and so the progression holes are effectively stretched apart which can mean that the engine can go lean between progression holes. Mine used to. (Just FYI, you're on the progression holes rather than main jets most of the time, even cruising in excess of the speed limit on the motorway).
the effect of this is that with big chokes, most of the time when you go to accelerate from cruising you get a really irritating lean stumble.
Reducing the choke size does cure it. At the expense of top end, which I accept is fine for many people.
However, you can also solve the problem by putting your progression holes where they're needed. It just involves bravely drilling some holes in your carbs
Here's that Vizard chart.My engine is 2915 and I have 39mm chokes in my Dellorto 45s, and it works well (now!) in all conditions.
I sized the chokes based on a calculation offered in the Honsowetz book, based on cylinder capacity and max rpm.
It's definitely got a fudge factor in it, so not that scientific but the value it comes up with (39 for 7500 red line) is pretty close to what my engine builder friend was suggesting. (he said bigger!). Vizard has a similar calculation.
Here's a pic from the Vizard book (I'll take it down if someone complains) that shows a couple of interesting things - 1) that you need bigger chokes to flow more air and 2) that the air flow tails off rapidly as you go bigger than 38mm choke on a 45mm body.
If you're building a 3.2 litre performance engine, surely you'll expect to rev and produce power up to 7500 rpm (at least) , and if we're to believe Honsowetz and Vizard, then you'll need bigger than 40mm chokes to deliver the air, AND 45mm bodies can't do it.
if you want to have a torque monster and run it in the stock 6500 rpm range then I support 45mm bodies will be fine, but I think you'd still want 40mm chokes.
In the comparison with ITBs, I'm not 100% sure, but I don't think ITBs have chokes, so really I think a 45 ITB should be compared to a 50mm body carb with a 45mm choke. You can't put a 45mm choke in a 45mm body carb.
I've read many forum threads about people that have struggled to get their triple carbs working well with big chokes. in my experience the problem is that the progression hole spacing is fixed and so it's a compromise with the choke sizes; My Dellorto 45s at least seem to have been designed with lower revving, higher capacity engines in mind (Jag 4.2 anyone?) and aren't ideal for high revving lower capacity engines.
The problem is that as the choke sizes go up, smaller movements of the throttle allow the same amount of air in and so the progression holes are effectively stretched apart which can mean that the engine can go lean between progression holes. Mine used to. (Just FYI, you're on the progression holes rather than main jets most of the time, even cruising in excess of the speed limit on the motorway).
the effect of this is that with big chokes, most of the time when you go to accelerate from cruising you get a really irritating lean stumble.
Reducing the choke size does cure it. At the expense of top end, which I accept is fine for many people.
However, you can also solve the problem by putting your progression holes where they're needed. It just involves bravely drilling some holes in your carbs
