how hard does your 250 rev?
- Thread starter SONNY
- Start date
A
Anonymous
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I know one thing from personal experience......because they don't have a fully conterweighted crank, the flywheel will come loose at 7,500rpm from vibration. but these engines were never designed to work there anyway.
My $200 dollars worth. (I STILL OWE YOU SONNY)
1. the pushrods are the limit on all Falcons after mid 1980. Up till then, 5000 rpm on the 4.1, and reliably up to 5300 rpm with no problems on any 4.1. The 76 to 80 Iron headed engine revs better than the Honda headed Alloy Head I, II's and EFI's. These had the tragicly awefull tube pushrods which are worse than useless. Fords rev limit in 1981 went down to 4800 rpm for the 4.1, then 4500 rpm for the XF 4.1, 5500 rpm still for the 3.3.
2. 5500 or more on a stock XE/XF 3.3. All 3.3's have a rev range 700 rpm higher than a 4.1, but they are renown for chucking pushrods in a 4.1 and especially the 3.3 5-speed. Mainly becasue the 3.3 is the best geared Falcon around, and heaps of fun to thrash. Been there, done that.
3. Personally, 5300 rpm with a rebuilt 250 XE and 256 degree HS20E heatseaker cam reliably.
4. The X-Flow has really heavy valve gear, and the longest pushrods in the business. The cylinder pressures on the 4.1 are much higher than the 3.3, and thats why it carries the 700 to 1000 rpm lower rev limit. Along with the low tesnion rings on the later XF 4.1's.
According to Dynoed 250, the early cast iron XC/XD Iron head pushrods can be fitted on the stock Alloy head engines if you use either a planed head, or perhaps cut down Cleveland 351/US 3.8 Essex 90 degree length valves ( they are 30 to 50 thous shorter).
1. the pushrods are the limit on all Falcons after mid 1980. Up till then, 5000 rpm on the 4.1, and reliably up to 5300 rpm with no problems on any 4.1. The 76 to 80 Iron headed engine revs better than the Honda headed Alloy Head I, II's and EFI's. These had the tragicly awefull tube pushrods which are worse than useless. Fords rev limit in 1981 went down to 4800 rpm for the 4.1, then 4500 rpm for the XF 4.1, 5500 rpm still for the 3.3.
2. 5500 or more on a stock XE/XF 3.3. All 3.3's have a rev range 700 rpm higher than a 4.1, but they are renown for chucking pushrods in a 4.1 and especially the 3.3 5-speed. Mainly becasue the 3.3 is the best geared Falcon around, and heaps of fun to thrash. Been there, done that.
3. Personally, 5300 rpm with a rebuilt 250 XE and 256 degree HS20E heatseaker cam reliably.
4. The X-Flow has really heavy valve gear, and the longest pushrods in the business. The cylinder pressures on the 4.1 are much higher than the 3.3, and thats why it carries the 700 to 1000 rpm lower rev limit. Along with the low tesnion rings on the later XF 4.1's.
According to Dynoed 250, the early cast iron XC/XD Iron head pushrods can be fitted on the stock Alloy head engines if you use either a planed head, or perhaps cut down Cleveland 351/US 3.8 Essex 90 degree length valves ( they are 30 to 50 thous shorter).
dont panic lol
73GreenMachine
Well-known member
What about revving a 250 pre crossflow? My cam supposedly make power to 5500rpm and I was hoping to be able to rev it to 6000. Are the pushrods built more sturdily in the earlier motors? By the way, the motor is a full rebuild with extensive headwork, Crow 282 degree cam, performance springs and lighter retainers. The pushrods are standard though. I have heard rumours that the oiling system\rocker train arent up to scratch above 5000 but I am not sure about this.
There is no real problem with earlier Non Crossflows from what I've seen. Most of the short 4500 to 5000 rpm rev ranges were due to the poor heads and tiny 252 or 256 degree cams they used. Even the 170 HP 250 2v is way undercammed compared to something like an 164 hp 1985 on wards XF 4.1 EFI. In addition, any hydraulic cam Ford before 1976 was likely to have pretty poor quality valve springs and issues with the lifters bleeding the sump dry at high revs like 202 Holdens do when reved. That's why Ford changed the priority oiling with the 250 X-flow. To eliminate the separate oiling system to the head, and use V8 Cleveland style oil through pushrods. On an earlier non cross flow, you've just got to make sure there is enough oil in the sump. The 250 X-flow basically looks after itself.
It is the later X-flows that have all the pushrod problems. Any engine with a rocker shaft like the non cross flow is stronger than with individual sled fulcrums and rocker balls. Why do you think you'd need to option up roller rockers, guide plates and hardned pushrods if the Clevleand or x-Flow valve gear was so good? Becasue it wasn't a patch on the non cross flow, and was designed for ease of building. The 250 log and 2v basically have an FE 352/360/390/406/410/427/428 style rocker arrangement, and we all know how tough that was.
The X-flows have canted valves verse the wedge valves of the non cross flows. These X-flow engines have higher peak cylinder presures, which gives them 10 to 15% more power potential, but a minus is that the rocker gear is much heavier than any earlier 250. By about 20%. The x-flow cam gears have to run an extra wide link belt just to cope with cold start loads and the extra spring pressure required to stop the valves floating at speed. The weght of any two intake and exhasts valves, there rockers, there pushrods and lifters and the resulting spring seat pressure is far higher than the Non Cross flow. It is even higher than a 351C or 400 Ford V8 because the pushrods are so much longer.
In addition, any X-flow is more detonation prone than an earlier 250 non cross flow. The 4.1 X-flow is rougher, and more likely to detonate under load than a 250 log or 2V.
It is the later X-flows that have all the pushrod problems. Any engine with a rocker shaft like the non cross flow is stronger than with individual sled fulcrums and rocker balls. Why do you think you'd need to option up roller rockers, guide plates and hardned pushrods if the Clevleand or x-Flow valve gear was so good? Becasue it wasn't a patch on the non cross flow, and was designed for ease of building. The 250 log and 2v basically have an FE 352/360/390/406/410/427/428 style rocker arrangement, and we all know how tough that was.
The X-flows have canted valves verse the wedge valves of the non cross flows. These X-flow engines have higher peak cylinder presures, which gives them 10 to 15% more power potential, but a minus is that the rocker gear is much heavier than any earlier 250. By about 20%. The x-flow cam gears have to run an extra wide link belt just to cope with cold start loads and the extra spring pressure required to stop the valves floating at speed. The weght of any two intake and exhasts valves, there rockers, there pushrods and lifters and the resulting spring seat pressure is far higher than the Non Cross flow. It is even higher than a 351C or 400 Ford V8 because the pushrods are so much longer.
In addition, any X-flow is more detonation prone than an earlier 250 non cross flow. The 4.1 X-flow is rougher, and more likely to detonate under load than a 250 log or 2V.
73GreenMachine
Well-known member
Thats some good information you've got there! Given the points that you have made, I will be interested to see how the new aluminium head on an old 250 will compare to the 250 crossflow.