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Best bottom end for turbo I6 

 

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 Post subject: Best bottom end for turbo I6
Posted: Mon Feb 28, 2005 9:55 am 
Parts Gopher
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Hi guys. My mate and I are going to turbo his XF ute. The 250 X flow is going into the bin and we have 2 possible engines we can use (for sale worked EFI 250). We have already got a EF long motor and a AU long motor. He has a decent buget and this will have a fairly stout bottom end with forged pistons and custom rods etc. Apparently the EF has the best crank but wont fit into the AU block with cross bolt mains. Is the AU crank still good, does it have harmonic probs at high revs? This engine will have a 1000HP turbo hanging off it and will probably rev over 6500rpm. What is the best combo and why?

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Posted: Mon Feb 28, 2005 12:11 pm 
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AU has the better strength wise as the sump etc holds it all together..
For rods and pistons www.rocketindustries.com.au
They don't list the parts but they have them...

 

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Last edited by EBXR8380 on Fri Mar 04, 2005 12:28 am, edited 1 time in total.

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Posted: Mon Feb 28, 2005 2:51 pm 
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The AU crank has better harmonics and revs out easier, overall the AU bottom end is much stronger, the cast sump almost acts like a stud girdle, the EF head breaths better due to larger ports.

 

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Posted: Mon Feb 28, 2005 3:19 pm 
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Thanks guys, keep bringing the info. That is the sort of stuff I want to hear.

What about strength? How strong is the AU crank itself? Will it handle over 6500RPM with 30psi of boost? What sort of strengthening are people doing on these cranks?

 

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Posted: Mon Feb 28, 2005 4:39 pm 
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Absolutly no idea to what limit perple have tested them (au crank), however I have never heard of them breaking, as EBXR8380 said call rocket industries and they will hook you up with Arias pistons and H beam rods that will take a hammering.

Once again I'm not sure if annyone has tested them to the limit.

I'm sure there are people on this forum that know more than me, hopefully they will come out of their hiding places and answer some of your questions.

 

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Posted: Mon Feb 28, 2005 4:44 pm 
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Yeah, thanks anyway man, You steered me in the right direction. Lets see if anyone else knows more. I will give Rocket industies a call.

 

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Posted: Mon Feb 28, 2005 7:11 pm 
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im sure someone said the ED had the best manifold for turboing.
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Posted: Fri Mar 04, 2005 12:33 am 
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After rods and pistons..Then check or think about tuning as this is more important than shelling out on tuff parts if its going to detonate on start up!! The bottom end of the XR6T is much the same crank wise and they have made some serious numbers...

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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Posted: Fri Mar 04, 2005 6:48 pm 
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We are just going to use a EF engine with EA head, standard crank and rods and ACL pistons. All machined etc.. Should be good for 500rwhp.

 

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Posted: Sat Mar 05, 2005 8:50 am 
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Could you explain why you have chose an EF with EA head? Isnt there a better flowing head... AU maybe?
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Posted: Sat Mar 05, 2005 6:18 pm 
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The EA head was not chosen for flow. But it flows OK with porting. The reason is when modified a bit and used with the EF bottom end, the compression ratio will sit at a boost freindly 8.2:1 (or there abouts) thats with stronger ACL race series pistons (which increase CR) If you use a EF of AU head the CR will be way to high to run huge boost. The only other way is to use custom pistons etc, and that costs heaps. The combo I mentioned was uses in 6BOOST, a Zoom cover car (EA falcon) with 556RWHP. I have spoken to the owner and got the low down. The plan is to see how long it takes to get bored with this massive power, then use a full house bottom end with AU head etc etc and 1000HP turbo. This time we will only be useing a 800HP GT42.

 

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Posted: Sat Mar 05, 2005 10:35 pm 
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Yeah he's a good guy, always got good reliable info...

What are the specs on the turbo you will use?
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Posted: Sun Mar 06, 2005 1:04 am 
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See if ACL make the 3.9 piston with lower comp ? As in deeper dish .. If they do you can use a .030 over piston and fit it in your EF block with LESS overbore this way you lower comp...
I know this works with std pistons from Ford...It maybe a good idea to O ring the head also...Helps prevent head gasget blowout...

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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Posted: Wed Mar 09, 2005 7:05 pm 
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I'd suggest going the ACL race series pistons as mentioned above. The reason is that the ACL pistons in my turbo crossflow saved my bottom end when I got the tune up wrong.

I used ACL hyperutectics then got some detonation. The pistons cracked the bottom ring lands but when we stripped the engine I found that the big end bearings were loose in the conrods. This was a sign that the pinging was bad enough to have effected the bearings. If the pistons had held out longer the engine probably would have spun a bearing and made for a more expensive rebuild.

My engine was running the old style ACL pistons then, which had the slot cast into the oil ring groove. Mine aren't even race series and I have 418 rwhp.

I am using the same turbo 6 boost used when he made 556 rwhp with the next size bigger turbine housing. 6boost actually supplied the turbo for me. The only reason I have not made the same sort of power he did is that I cannot get a big enough exhaust under the car and have about 8 psi backpressure in the dump pipe which will be rectified soon.

Definateley forget the worked crossflow and go the OHC engine for many reasons.

-Starter motor located on passenger side allows heaps more room for dump pipe. Seriously aim to use a 4" dump pipe or bigger if you can

-the crank harmonics talked about above actually stem from valvetrain harmonics. The crossflow engine doesn't like to rev past 5500 rpm because of valvetrain dynamics but the OHC engine will happily rev out to 6200 (maybe further but not necesary)depending on the cam selection and the inlet manifold runner lengths. You will need a cam up over 300 degrees total duration if you are serious about running a 1000hp turbo. Also look at using the shorter rocker arms in the OHC head. I have never built and OHC engine but I know the earlier series engine ran a 2.0:1 rocker ratio which is huge and there is shorter rockers available which ease the valvtrain harmonics. See the Crow Cams website for cams to suit different rocker ratios but I wouldn't suggest buying a crow cam.

- Try to use the engine series which ran a crank angle sensor on the harmonic balancer because having to reference the crank angle from the distributor (or dummy dizzy used on the OHC engine) means that your crank angle signal is effected by backlash in the dizzy drive gear and the valvetrain dynamics. Number 1 top dead centre reference trigger still needs to be driven off the cam but the accuracy of this signal is not as important as the ignition trigger signals.

- OHC engine use bigger ports than the crossflow. Due to the long stroke nature of the ford six the ports are undersize and air speeds end up being the limiting factor of the total power output you can expect. If you compared two heads ported such that they flow the same amount of air on a flow bench but one has bigger diameter ports, the bigger port will still make more top end power because the flow losses are proportional to air speed which is proportional to port area. The idea is to port a head to give good flow then also hog the port out as far as possible without losing flow, especially in the lower lift ranges.

- OHC engine are easier to achieve the lower compression ratio. Crossflows have a smaller combustion chamber so need the 27.9 cc dish ACL piston and still need to run the piston 1.5 mm down the bores to achieve 8:1 compression. The OHC engine with the larger chambers are able to get 8:1 compression with about 15 cc dish.

- Another tip try your best to get the pistons to run as close to the top of the block as you can as this hugely improves the squish band aorund the edge of the piston. This makes the engine must less prone to pinging. If your budget allows then custom pistons are good as they allow you to run whatever dish and pin height you want. In my opinion this is the main reason to go custom pistons (not strength). For the custom piston option, chose the head which has the best chamber design to resist pinging then worry about what dish you need to get the compression ratio right. It is best to run the squiah band around the perimeter of the piston flush with the top of the block to reduce pinging, then dish the piston the amount you need to get the compression. This is the downside of the ACL pistons they all run slightly down the bores and you compromise other areas slightly to work around the piston you have available.

- If your budget allows custom conrods then look at using Chev small journal rods. They are the same big end size as the crossflow and can be bought in a range of lengths from 5.7" right through to 6.2" from heaps of places. You will find a set of 8 chev rods will be cheaper than a set of six made specially for the Ford engine. The only trick is the big end needs to be narrowed slightly to fit the crank (or the crank journal gorund out slightly wider) You will also have to mess around with a bush to the right size gudgeon pin or make the pistons to suit the chev gudgeon size if using custom pistons.
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Posted: Fri Mar 11, 2005 4:18 pm 
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WOW some info there 8-) Mind Blow

AU have the best bottom end for turboing but i heard its a real prick to put a Au bottom end in a ED cause thats what im looking at doing to mine when i twin turbo
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