61 replies to this topic

[ACJ]

Oldjohnno hits the nail on the head “but this sounds like a fun project”
Chopper wants a bigger motor. We have a merlin 560 cub 8/71 running methenol with 1200HP just back from the bank manager shop. Not a lot of fun just money.
We have started. Heads are sandblarsted, ports cleaned up and a little bit removed between the push rod holes. Should flow 480 500 so if its 10% less still should get 430 hp. Should do the job, probley bad (very bad) air speed down low so we will just have to keep it reving.
The 288 cam is a long shot. Its just siting there, one less thing for the shopping list.
Lots of bridges to cross, lots of thing we don’t know about or understand. But if we blow all 5 motors and don’t make 400hp I will be pist about the $10 but more room in the shed and less sh-- laying around.

[EunUCh]

ACL are now Mahle,the poor little 2 fitty 3,i had one for years on ACL duralites,,nothing flash but a sweet little
motor.
The big problem with them is that they actually need slightly less valve size (curtain area,CSA to bore volume,,etc blah blah)
Most engine rebuilders jam big valves and cams in them and it kills them dead in the water,,worse than stok in most cases.
I beleive the blue 253 that Broky had a bit to with went just as hard in std trim as some 308s.
They will spin to 7 with w/out forgies,good cam,good valve springs,,all the boys use up here on the
202 stockies is basic ACL stuff.my 2c worth.

[ACJ]

Yes VN heads. Valves are standard VN size (1.94 and 1.6). Stock VN heads flow as good as heverly ported red head so try to keep them as small as I cam for better air speed.
I have a Torque power but the runner have been ported, maybe to big ? The runners on a Harrap manifold are 1742 square mm T/P 1677. My heads are about 1550 so I was thinking of making one. Using 45mm id pipe (1590 square mm) and rolling the pipe to make oval runners and a bit taller than a T/P ?
Some one from this forum has emailed me with lumpy top forged piston and also AMCA is a 253 powed speedway cay, But still running about 300HP and 6500rpm but do make forged pistons.
And yes people and cars both prefom differently when running on alcohole.
Well, I hope NOBALLSUC is wrong or I am off in the wrong direction ?

[ACJ]

Sorry oldjohnno. Spending no money on testing, flow sheets ect this is nutty professor all the way.
The last set of heads I did took my 40 hours of grinding, lots of mechning, bigger valves ect with flow sheet and cost me over $2000. If I was to do it all agen I would buy alloy heads ready to go.
If we can get it all to fit with the wrght comp and valves not hitting pistons, I think it will make good power up top, but lower rev range way down. So use what we have got, add a little nutty professor then stand back and pull the trigger
I geas its really about are the skills and knowledge we have picked up over the years as good or bad as we think they are ?

[rodomo]

Some one from this forum has emailed me with lumpy top forged piston

Attached Files

•  piston1.jpg   69.76K   6 downloads

[rodomo]

Sterling, Federal Mogul

[greens nice]

off the shelf JE flat top forgings are available for 202's, can you use a scat Holden v8 rod and rebush the little end to the .866 holden pin?

Edited by greens nice, 03 January 2012 - 06:57 PM.

[greens nice]

^^^^ that is if you wanted to overkill it.

[ACJ]

Any chance of a mod number as I had a look at there web site but no holdens.
Maybe overkill but still not many options.
I also sent JE a email but closed for Xmas.
No deadline on build. Sooner the better

[greens nice]

i can but they are at work so not atm, give this mob a ring http://www.precisionintl.com/

[ACJ]

Just a little update. Got a reply back from crane cam who said. I would use the F-280 cam and make sure you have min 11.5 comp.

[makka]

My 253 saw the back side of 7500rpm quite a few times with acl's

A bloke I know ran forged hemi pistons with an offset ground crank and saw quite a few more rpm than mine did in his race boat with quad webbers

[Struggler]

OK this is were it strated. We have a 355 VN heads crane 288 cam and so on we made 500HP. I said if all this is in a smaller motor (253) and you spen it harder you can make near the same power in theory. Reply, Bull sh--, so its on for a $10 bet.

First time I have seen this thread so sorry about the late reply.

Airflow is horsepower. To make your 500HP with the 355 and 288 combo you need to spin it to about 6800rpm. 6800 x 355 ci = 2,414,000 cubic inches of air per minute to make the 580 HP. To get the 580HP from 253 ci we then divide the 2,414,000 by 253 to equal 9541 rpm. OK thats the first problem. To make the same amount of power by moving the same amount of air we have to turn the poor old 253 to 9500 rpm.

Wait, it gets worse ! As someone else mentioned the flow is compromised on a 253 by the restrictive bore size. Also getting any real compression out of a 253 is hard enough with HQ heads, let alone the bigger chamber VN heads. This knocks our Volumetric Efficiency around considerably so we are probably 20% behind the 355 on the big details before looking at the smaller stuff like rotating friction etc.

OK, so you only want to get 400HP. Well your typical 355/288/VN combo will make 400 HP at about 5200rpm. Applying the same airflow maths gives us 7300 rpm, before we factor in the 20% losses in flow and efficiency. You might get close by 8700 rpm.

I don't hate 253's, in fact I quite like them. To get the best out of them requires tiny standard HQ port volumes and standard HQ valve sizes with conservative camshaft profiles.

Good luck !

[ACJ]

400 hp out of a 253 is up there, But I think its achievable, sure I have some hurdles.
I also have VT heads with 58cc chamber for better compression if need.
Not sure about your formula though ? If my 355 is using 2414000 cubic inches of air per minute which ( if I am rite ? ) = 1396.990 CFM. All this threw a 750 carby ?
Thanks