Whats Best ? 250 or 221

[Danielson]

Reading through some recent posts it seems the 250 must produce much more power than the 221 although its only 500cc bigger. I have a good 221 with great compression 170 - 180 psi on all pots, 308 inlet valves, stage 1 mild cam, pacemaker extractors, 2.5 inch exhaust system, XE electronic ignition, Weber 34ADM carby onto a enlarged inlet. Diff is 2.92 and tyres are 215/65/14 and single rail 4 speed. The motor sounds good, goes and runs great but there is no way in any gear (unless it's wet or I am going around a sharp corner) that by simply slamming my foot on the throttle that it will break out into a spin.. I also had a good XF with simliar setup and it was the same.. I would like this wheel spinning power and I have a 250 motor that is running but would probably be best with a rebuild. Or should I just get an 8.. :x or change my diff ratio ?
Cheers Dan

 

[2502vxw]

simplest way to get some extra power to the ground would be by putting a 3.23:1 diff under her. That will give you HEAPS better take off and should let you light her up a bit better. You will find that XW's came out with 3.5:1 diffs in the autos and 3.23:1's in the manuals. I wouldn't go to a 3.5:1 unless you put a T5 in there or you have to rev the guts out of the thing for no reason even at 100kph and with fuel the way it is, that's not an option. But if you already have a 250 you could just do it up slowly as you can afford it and eventually put her in and maybe pick up a 2v head for it. The 221's are a better balanced motor though and as such you can rev the knackers out of them in comparison to the 250's with their longer stroke. I have a 34ADM weber on my 2v with a T5 and 2.92:1 disc LSD, but with the 250's greater low down torque it should be quite good. I had an XD a while back with a 200 with flat top pistons, pretty big cam and a 350 Holley which, with a 2.92:1 diff wouldn't even chirp the tyres from startup in the dry. In the wet, however it would be forever sideways and you could get it up to 90 k's an hour in first gear... You'd think with all the work the motor had it would've been great, but the diff ratio was just too low. When I sold it I put a 3.23:1 diff into it and it was a whole new machine, you could light it up at the drop of a hat and it was great. Anyway, I hope this gives you a bit of insight. Cheers, Tony

 

[2v XLE]

I have a 34ADM weber on my 2v with a T5 and 2.92:1 disc LSD,

Going through a similar dilemma at the moment. With the T5 and the 2.92:1, was rpm does it sit on at 100 km/hr? What size wheels you got?

Cheers

 

[Danielson]

Heres the formula to work out your speed.. for a given RPM

1/ Measure your tyre diametre (height from top to bottom) and multiply it by 3.142 mine are 14 inch tyres with 620 diametre so 620 times 3.142 = 1948.04 (tyre circumferance or TC)

2/ Multiply your diff ratio times your gear ratio T5 is .78 in top so .78 times 2.92 = 2.28 (overall ratio or OR)

3/ Divide your TC by OR. 1948.04 divided by 2.28 = 854.40 this is how far the car travels in mm in top gear for 1 engine revolution. (known as rollout in the RC world)

4/ Now multiply the above figure by 60 to work out how far it goes in 1 minute. 854.40 times 60 = 51264.00 then divide by 1000 = 51.26 this how far you go in metres in 1 minute at 1 rpm.

5/ Multiply the above figure by your engines rpm say 2000. So 2000 times 51.26 = 102520.00 then divide by 1000 to give you KPH.

This is for a car with 14 inch tyres and with 13 inch tyres in 5th your rpms at 100 kph will be around 2100 at a guess .

Hope this helps. I learnt this stuff racing RC cars as gear ratios per tyre size are crucial on the track.
Regards Daniel

 

[2v XLE]

awesome. thanks danielson

 

[addo]

If someone really wants a bent eight, they should buy one. I'm not for keeping these things in the closet. To me, they're an insurance risk, and a magnet for idiots - but others may have different opinions!

Ranting aside, the 250 is my choice for a larger body like XR-XY. For the XK-XP, a 221 for sure. That's in terms of non-crossflow motors BTW.

"Stage 1" is far too vague a cam description. You need to know where it's torque peak is specified, and whether it was degreed in. If the dizzy curve is correct. How the carb's fuel curve measures up to the motor's demands.

Otherwise it's like saying "I've got all the paints, some canvas and a brush but it still doesn't look like a Renoir"...

Go with your cam specs to one of the online calculators to figure out ideal diff ratio. Mine came out at around 3.25 as well!

 

[2v XLE]

Well its the 250 for me. I'm slowly building up the cortina, have just picked up a 2v head

 

[2502vxw]

Hi Corty1975, I haven't as yet started it up. I have just rebuilt the motor and finished installing it along with the gearbox... I should be firing it up later in the week or early next week. (so many other jobs to do to it and I may as well get em all done now) I will be running 215/65/14's on it and I did the calculations a while back for what revs I'd be doing at various speeds, but I'll be buggered if I can find them at the moment. I'll try and hunt them up, or just redo them.

 

[lyonsy]

hey
put skinyer tyres on
nah serious the 221 is a great little engine and can probly make more power then a 250 will but not the torque.
a 2v head will go a long way or the chi head thats in development at moment
you can also buy m90 super charger kits for the old log motor which whould be awsome to put on
id stick with the 221 till she's worn out just stick a 2v head on it or get a supercharger like the m90 or mount up a 1ggze charger from toyota.
skid

 

[SONNY]

i have had both and i belive the 250 is a beeter engine for a few reasons,however if you have a 221 inyour car i would wack a 2v head on it and blast off,if you want to change the motor latter just keep the head and bolt the 250 in and its set up easy

 

[Danielson]

The problem is, all the info I have on the cam is thats its a watson 20/60. I looked them up and gave them a call to try and find more about it but they weren't to helpful. Basically he said it's a stage 1 cam which is a replacement for the original. I have wondered if this may be my motors weak point in performance as everything else seems to be good. I have aslo been looking at replacement cams. I like the specs on the ones from Mike at FSP but wondered whether they either have too much lift 268D: 268/274 - 208/218 - .455/.480 - 108* - 1500-5200. or duration 264D: 264/274 - 214/224 - .450/.450 - 110* - 1500-5000. They seem to have bigger numbers than anything else I have found such as crow crane isky etc.. Anyone tried one of these FSP cams here in OZ.
I know what you mean about have everything working together and in sync, however i am trying to work with what i have and make the most of it. The motor at present pulls well down low and its possible to go as low as 35 kph in top and acclerate steadily without any drama ie it's easy to drive. I don't mind if it's a bit harder to drive but don't want to have to rev the crap out of it to make power..
Regards Dan

 

[lyonsy]

hey
yeah your cam is basicly a stock replacement so something like this from crow whould be a hugh improvement
636662
IN.25/65
EX.74/26 270
280 204
214 .420"
.442" 1500
4500 K6301 Increased mid range power with good fuel economy and idle quality
if you put that with a 2v head the thing whould fly
skid

 

[addo]

Well, the advertised duration is 180+60+20 which is 260. Pretty mild. It also implies single pattern grind. Crow's closest is the 613 pattern. Depending on the valve lift, that's a torque cam which runs out of puff at or before 3800.

To me, sounds like the issue! Talk to Crow. A 603 pattern might be the ticket if you are keeping the 221. Otherwise run that present cam in a 250 with the stock rear gears, higher lift rockers and low-geared tranny.

 

[Danielson]

I have just aquired a new crow 60603 camshaft for the right price. 636032
IN.32/68
EX.72/28
280 280
214 214
.442" .442"
1800- 4800 Gives performance and driveability in street modified engines.
Looking at the grind it is not the dual pattern cam that seems favorable in these old sixes. Would it be advisable to have the profile changed in order to make it a dual pattern or am I better to go with something else ? :roll:
Thanks Daniel

 

[addo]

With light port work on the exhaust you should be fine. Could probably oversize the exhaust valves if you're keen. It'll like a bit extra carburetion than stock once you get over 3500.

Use the Crow single valve springs or equivalents - no need to overspring it.