Four barrel conversion

cobraboy

Well-Known Member
#1
This has been on the cards for a long while, I finally got around to having a crack at it.
Until recently I owned a Ford High Performance Mustang 289 K code, the K code had a unique 4 barrel Autolite 4100 carb, this thing was the mutts nuts, so much nicer than a Holley.
When a friend had one for sale I grabbed it and built it up to be the same as the one fitted to the Mustang, my logic - if it made the Mustang's 4.7 litre go like the wind it would be OK for the 4.6 Rover.
It is not proven yet, but it is fitted and the car seems to like it, finessing the jetting is yet to come, but the hard work of getting the thing sitting on the Rover is done.
Nice and clean inside, valley gasket removed to allow trial fitting of Offy intake and port fettling
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I went for a 1" phenolic spacer to improve torque and reduce heat transfer. The spacer is ducted underneath to the brass stub I tapped into the rear for a PCV system.
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Manual choke Autolite 4100 on Offy 360.
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I made a cable throttle linkage operating off the old auto kick down cable bracketry at the rear of the left cyl head.
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K&N Filter and bling to finish off :)
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Who knows, a set of downdraught's may be the next step ?
 

quattro

Well-Known Member
#2
ooohhh tasty :)

I never did get my weber to run right, it was good, but never spot on :)

Best of luck with it, V8s need a 4 barrel they just look right together

Richard
 

corazon

Well-Known Member
#5
Excellent. From what I’ve read with the Edelbrock/Weber 500, no off the shelf needle/jet combo is spot on, close but not perfect for the 4.6. A custom profile is required. I’ve got an AFR gauge going on my build so I can really see what’s going on at different driving conditions and tune accurately.
I like the spacer, I’ve got similar plans but with a thicker one. Any plans to blend/taper the underside?
Jim
 

cobraboy

Well-Known Member
#6
First test today, had to return home PDQ, AFR gauge off the scale lean. I had fitted jets for a bog standard Ford 289 thinking they would be close, nope ! car would not pull, better fuelling when the secondaries came in.
So I fitted the jets for the 289 HiPo and bingo car pulled well, only a slight hesitation just off idle. so back again and increased the pump shot by re positioning the lever as the shot looked weak, another run and the slight bog has gone. Pulled a plug and colour good. Need to watch AFR at a very light throttle, may need to go up one jet size on primaries. Car pulls like a train, I would say the HS8 match the Autolite for torque, maybe even have an edge, but car feels stronger at high rpm with no sign of running out of puff.
All this with stock ish 3500s exhaust manifolds, headers will really let it run.
Very pleased with the first runs, well worth all the planning and work.

Jim the Offy has had some work and has been cleaned up, I made sure the ports are ok to the head, the plenum is fairly nice corner wise. It is an old fashioned 360, there are better designs now, but this one likes WOT :)

Thanks Richard
The 4100 is not a true 600 CFM Carb, which is why I picked it for the Rover. A 600 is reckoned to be too much for a stock 289 (4.7 litre), the 4100 reputedly flows around 530 ish CFM so ought to suit the Rover.
I did not want to just go and buy a 500 Weber, that would be too easy :rolleyes:
 
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cobraboy

Well-Known Member
#7
Has been quite a saga battling vacuum leaks, jetting and generally try to get the new carb to run good. Vac leak was my fault, I missed a port on the side to the old auto choke. Jetting wise I seem to be at 54 Primary, 62 Secondary, a little up on the primaries from the Ford 289.
I fitted up a PCV set up, but had to restrict the vac line as it was taking too much air and not metering the primary circuit properly.
I have a box of Holley vac secondary springs in various weights so am going to play with bringing in the secondaries a bit earlier, at the moment there is a point at around 4000 rpm that things really light up, I think it would be handy to get that going a little sooner.
Economy wise, not that I'm counting, it seems really good, you can tell when things are a bit scary drink wise, but no, tis alright.
The AFR readings at cruise are very good. So yup I can recommend the Autolite 4100, it is certainly revered Stateside and I do like them very much.
 

cobraboy

Well-Known Member
#8
Well today was a trip to Emerald at Watton to set up the Autolite 4100 on the rollers. The last time I was up there the car was wearing 2" SU's and we managed to squeeze 240 bhp and 276 ft lb
Today I wanted to see how the fuelling was and go through the timing.
It was apparent that the car was quite rich, I had put in 54 primary and 62 secondary jets and had a few spares with me plus some drills.
First run gave 255 bhp.
I also was watching for when the secondaries started to move, this was quite late and they did not open fully.
We had a chat and I fitted the 54 jets that were in the primaries into the secondaries and fitted a pair of 52 spare jets into the primaries. I also fitted a lighter spring in the secondary diaphragm.
The fuelling came good and the secondaries opened sooner, power upped a little.
So I fitted the lightest secondary spring I had and the secondaries then started to open at around 1800 rpm.
The distributor was put back on vacuum, I had disconnected it, and the timing optimised over a couple of runs.

The ta da moment........ 270bhp and 284ft lbs a whopping 30 bhp up on the SU's :cool:

The car drove much nicer on the way home, the pick up from a trailing throttle much better, the torque curve is much wider now with loads more torque either side of the peak. And I didn't need a dust pan or the broom next to the car - phew !
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#10
wow those are pretty strong numbers :) just for reference, can you remind us on the engine spec, obviously the 4 barrel and its a 4.6 on standard P6 exhaust manifolds, but has it any other mods?
 

cobraboy

Well-Known Member
#11
Thanks guys.
Quickly from memory.
Std bore 4.6 top hat linered block by Turner engineering.
Std timing set.
Kent H224 cam
SD1 heads with waisted stem std valves, shortened bulleted guides, nicely flowed, and skimmed 0.040" from std.
Heads fitted with tin gaskets, compression ratio 10.0 : 1
Offenhauser 360 intake matched to heads.
Autolite 4100 1.12 carb.
Range rover electronic dist 35DLM8
Stock flywheel lightened 4kg
Fettled 3500s exhaust manifolds, 2" straight through twin system w/ balance pipe, side exit.
SD1 front cover, uprated oil pressure relief spring.
 
#12
Thanks guys.
Quickly from memory.
Std bore 4.6 top hat linered block by Turner engineering.
Std timing set.
Kent H224 cam
SD1 heads with waisted stem std valves, shortened bulleted guides, nicely flowed, and skimmed 0.040" from std.
Heads fitted with tin gaskets, compression ratio 10.0 : 1
Offenhauser 360 intake matched to heads.
Autolite 4100 1.12 carb.
Range rover electronic dist 35DLM8
Stock flywheel lightened 4kg
Fettled 3500s exhaust manifolds, 2" straight through twin system w/ balance pipe, side exit.
SD1 front cover, uprated oil pressure relief spring.

thanks, i had it in my head that it was more standard than that, but at the same time thinking it couldnt be
 

cobraboy

Well-Known Member
#13
Well its nothing outrageous or high dollar.
If i get to take the heads off I would go for bigger valves in the stock seats and a better 3 angle seat job. I made good gains on another engine by opening up the diameter of the valve seats and the bowls below. I did not do much with these heads as they were nicely prepared, but stock sized.
I find that the RV8 does not give up extra power easily, you have tease it out bit by bit, but hey that is what dark winter nights are for !
 

cobraboy

Well-Known Member
#15
I must admit It was a shock to me. I am going to have to ask why there is 71 bhp of drag this time, when previously it has only been around 50 odd bhp, I am sure the handbrake was off.

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#16
I must admit It was a shock to me. I am going to have to ask why there is 71 bhp of drag this time, when previously it has only been around 50 odd bhp, I am sure the handbrake was off.

View attachment 14411
could be loads of things, do you have different tyres or even a fairly small change in tyre pressure, if you had done a fair bit of running on teh rollers it may be the tyres were much warmer softer and thus stickier.

your revving it on further so if nothing else changed you would see a bit more loss.
by way of comparison my bmw 325 race car makes 285bhp and looses 60bhp on emeralds rollers
 

cobraboy

Well-Known Member
#17
You are bang on.
It was explained to me that more rpm = more drag, both on the way up and on the way down. Interesting that the SU's were done at 5200, but the Autolite was good at 6000.
A Mustang will rev to 7k + with that carb so I guess now the focus has to be on exhaust.
 

Gargo

Active Member
#20
I like this..... very interesting, good to see a thread with numbers to back up the claims.
You've certainly got the 'In' side working, as you say to work on the exhaust next, reducing the power required to pump the burnt gases out, should be a fairly cheap way of gaining power at the wheels. It is all about making the engine more efficent, by using all the power released by the fuel.
I've promised myself to build an exhaust from scratch this winter. If I had to explain my spending, I'd say the purchase of a TIG welder will be repayed by the gain in MPG ;) , Or by cutting the commute time, take your pick. But she wouldn't even notice the TIG welder; I don't know if I find that sad or if it makes me happy. Then again I probably haven't noticed the new veg in the veg patch.

Your figures are impressive for the engine spec. You are someone who is doing this development correctly, I.e. keeping the engine well serviced and properly setup. I still not sure that the standard manifolds are anything to savour, but you have proved they can't be that bad.

Please don't go and change your avatar to a photo of them.
G.
 
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