Wondering what the standard 998 A series came with as far as rockers are concerned.
I am running +60 over, 12G295 head (ported) larger valves, twin 1/4 carbs.... and finally a Visard (APT) VP7 cam.
Years ago when the engine was rebuilt we kept the original rockers, and it ran well enough with a HIF44. However, since we added the twins it tends to lose power under load. Timing still needs work perhaps.
Anyway, the cam spec sheet that I found says that it is best suited for a 1.3:1 rocker set up. Calver seems to suggest that rocker ratio for small bore engines as well.
What are my original rockers??
Thanks
If they are the standard "sintered" rockers, then an article on Mini Mania seems to indicate they are about 1.21:1 so the bump to a proper 1.3:1 set would be an improvement.
Article:
https://www.minimania.com/Rocker_gear___General_compendium (https://www.minimania.com/Rocker_gear___General_compendium)
The info is about 1/2 the way down the article where they have a set of pictures of the different types of factory rockers.
I like the 1.3 forged rockers that MiniSpares sells, unfortunately they're out of them right now (at least they were last week when I tried to get some) so I had to order them from Somerford....
But losing power under load doesn't strike me as a rocker issue, but too much carb.....or maybe the wrong needles or even low fuel pressure/volume.
Too much carb eh? I had an HIF44... and it worked well enough, but the needle had to be profiled to get it to work.
With twin 1 1/4 SU, is there a concise list of needle / jet options that one might start with?? For example, this engine would be similar to a 998 Cooper (except for the cam) but the VP7 isn't that dramatic. Twins should be ideal... My guess is that the most recent engine builder that recently added the twins for me used the wrong jets and needles... Any ideas where to start on that?
No idea, you might check with the MK1 forum....I would have thought an HIF38 would have worked better than the 44 unless it's a got a fairly worked over head and a big cam that can use the volume that a 44 can flow.
The best way to get it sorted is probably to get it onto a rolling road.
I know most of the small bore Sprites used 1-1/8 twin carbs, it wasn't till they went to the 1098 and 1275 that they went to the 1-1/4 twins. Twin H4's (1-1/2) would just be too much on a 998 IMHO. With throttles that big it slows the airflow down too much causing the fuel to drop out and cling to the sides of the ports and back of the valve.
It's easy to fall prey to the "bigger is better" idea, but it really depends on what you're trying to build - a high RPM screamer (no low end power till it's up around 6K) or something street drivable, where you're after torque.
Going back to the rockers for a moment - if you can buy them from Minispares they will come already sized to fit the rocker shaft - if you buy them from anyone else (MiniSport, Somerford) they will need to be finish honed to fit the shaft, just FYI. Of course, MiniSpares is out of them right now. I don't know about Mania or 7 Ent.......
Personally, I'd go for the 1.4:1 rockers that Calver sells.
https://www.calverst.com/webshop/cylinder-head/ (https://www.calverst.com/webshop/cylinder-head/)
He might be out of them right now because his old foundry decided to screw him over on pricing, but in a recent phone call to Keith revealed that he's located a new foundry - also in the UK - that appears to be completely viable.
I think the 998's work better with the 1.3's.....again, it depends on the head and cam and what kind of engine you're building.
"I am running +60 over, 12G295 head (ported) larger valves, twin 1/4 carbs.... and finally a Visard (APT) VP7 cam."
The oversized bore and 12G295 head lead my to think that the 1.4's would allow max breathing - but I'm only speculating.
Right, still comes back to high RPM power or street driven torque off the line......the 1.4 rockers are a good compromise, but still are more biased to high RPM power, those are what we used on Dan's engine....same with the larger carbs. It's not just the port and valve sizes, but also the displacement - 998cc will only fill so far - keeping the velocity up is important too.
I don't claim to be the be-all end-all beard of knowledge on these, I would always defer to Vizard or some of the other notable names.
Without taking the trip to our library in the apartment's southern wing to pull the dusty TBASE tome - the bookcase in the living room/dining room/den about 12' away - how big is a +60 998?
It must be pretty darned close to or just over 1100, isn't it?
999? ;D
Hahahahahaaha - :D
I found this on The Mini Forum -
Quote from: John Gervais on June 03, 2020, 04:29:55 PM
Without taking the trip to our library in the apartment's southern wing to pull the dusty TBASE tome - the bookcase in the living room/dining room/den about 12' away - how big is a +60 998?
It must be pretty darned close to or just over 1100, isn't it?
I think its about 1050cc... Last time it ran with the HIF 44, it was more of a higher rpm drive rather than lower end torque. I suspect this is the same... I found this on the interwebs about needles...
Thinking that I am going to check and see whats in the carbs, and maybe start where the 998 Cooper is in terms of carb set up... and go from there.
I assume you're confident about your valve clearances and timing etc?
If so, seeing what needles are in there and comparing to a 998 is a good place to start
I've always read don't do 1.5 on 998s. A true 1.3 or potentially even Calvers 1.4 would be ok.
Quote from: Hercplt on June 03, 2020, 06:51:43 PM
Thinking that I am going to check and see whats in the carbs, and maybe start where the 998 Cooper is in terms of carb set up... and go from there.
Depending on what air filters you are running i have had good luck with the M needles with pancake/cone filter set ups, i believe it is the rich needle for Cooper S's.
The trouble with sorting needles it can get expensive.
Quote from: Hercplt on June 03, 2020, 06:51:43 PM
Thinking that I am going to check and see whats in the carbs, and maybe start where the 998 Cooper is in terms of carb set up... and go from there.
I just added some SU needle charts (dimensional, sorted by name for fixed and biased-type, 0.090 & 0.100) to the 'Media' resource library - hope they help.
I can't believe how much info I've got on this computer...
Quote from: Jimini II on June 04, 2020, 04:25:35 PM
Quote from: Hercplt on June 03, 2020, 06:51:43 PM
Thinking that I am going to check and see whats in the carbs, and maybe start where the 998 Cooper is in terms of carb set up... and go from there.
Depending on what air filters you are running i have had good luck with the M needles with pancake/cone filter set ups, i believe it is the rich needle for Cooper S's.
The trouble with sorting needles it can get expensive.
Agreed... It has K&N Cones on the carbs...
Quote from: Hercplt on June 05, 2020, 09:47:56 AM
Quote from: Jimini II on June 04, 2020, 04:25:35 PM
Quote from: Hercplt on June 03, 2020, 06:51:43 PM
Thinking that I am going to check and see whats in the carbs, and maybe start where the 998 Cooper is in terms of carb set up... and go from there.
Depending on what air filters you are running i have had good luck with the M needles with pancake/cone filter set ups, i believe it is the rich needle for Cooper S's.
The trouble with sorting needles it can get expensive.
Agreed... It has K&N Cones on the carbs...
With cone filters stock 998 Cooper needles will not be rich enough imo.
Quote from: Jimini II on June 05, 2020, 05:07:11 PM
With cone filters stock 998 Cooper needles will not be rich enough imo.
Any suggestions?
There's a FANTASTIC needle comparison tool available here:
http://mk1-performance-conversions.co.uk/technical_carb.htm (http://mk1-performance-conversions.co.uk/technical_carb.htm)
You'll have to download 'Libre Office' to make it work, but only need to activate the 'Excel' equivalent. It's a great tool which allows you to compare the annular area of different needles, including 0.090 to 0.100 capabilities. You can also see what would happen if you were to modify a needle and test it against an unmodified needle.
Not to boast, but when Ian needed someone to help him test and refine it, I was there - ;D
Do you mention compression ratio now? even a compression test number would help.
I build 1050 units with press fit flat tops and mild cams. The heart of the builds is the 295
cyl head. I'm very reluctant to do much port work other than exhaust matching to the small
bore header. I do use the late multi groove O/S valves and match bowls. I zero deck the
blocks and surface head for 10.2 to one street engine. I have tried off set bushings and 1.5
rockers and each trimmed low end and add at top only. I also use the Org. Cooper S rockers.
Steve (CTR)