Stock engine?
Performance upgrades?
Remote Turbo Setup & Falcon Sixes?
Performance upgrades?
Bit of an open ended question. i would try looking at similar output engines, then if your going rear mount, go for a smaller turbine housing. Work back for the output requirement you desire, and be realistic, i would suggest you do some study out of A Graham Bells book "forced induction". Ill stick with my first comment above. A stock 250 log head engine would struggle to get to 100bhp, and with some manifold pressure you could double that, so that gives you about 200bhp, so size your turbo for that.
Crustang to Mustang
Well-known member
It will have a DUI style distributor (courtesy of Kritas), a 2 barrel carb (not sure about a complete conversion, I'm still looking for a good machine shop), ideally bigger valves, a cam, and I will of course look into forged internals.
I'm looking for around 400hp, give or take. But I'll take all I can get...
I've also been considering a 200ci crank and longer rods for a higher revving engine. Anybody have any intel concerning builds like this? Is it worth it?
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The biggest turbo for the job will have a compressor inducer of 52mm for a 250 build.
In order to make near 400 hp the turbine housing will need to have an A/R in the .80s
The problem is that you need a turbine housing in the .60s to spool early but that would restrict the exhaust to make HP in the upper end of the power band so you would have to settle for the larger turbine housing and the additional lag the goes with it.
That's the problem we saw with the early STS rear mount systems which used a small housing.
You will need 20 psi of boost to make anywhere near 400 hp depending on the volumetric efficiency of the engine.
At 20 psi the compressor outlet temps are near 300 degrees so an intercooler is recommended.
You will also need to add a Blow Off Valve to the list I made above.
You will need to lock out the distributor and use a boost referenced ignition system like the MSD Ultra 6AL Plus.
In order to make near 400 hp the turbine housing will need to have an A/R in the .80s
The problem is that you need a turbine housing in the .60s to spool early but that would restrict the exhaust to make HP in the upper end of the power band so you would have to settle for the larger turbine housing and the additional lag the goes with it.
That's the problem we saw with the early STS rear mount systems which used a small housing.
You will need 20 psi of boost to make anywhere near 400 hp depending on the volumetric efficiency of the engine.
At 20 psi the compressor outlet temps are near 300 degrees so an intercooler is recommended.
You will also need to add a Blow Off Valve to the list I made above.
You will need to lock out the distributor and use a boost referenced ignition system like the MSD Ultra 6AL Plus.
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This brings you back to a 200ci engine, that means you have to run more manifold pressure to get your result. And, I dont think that swap is possible in the USA engines, it can be done in Australian engines as they shared blocks here. 400bhp is an ask, you would need up to 30psi for that level of output. The 250 is an engine that responds well to boost and gives lots of torque, but less revs. IMO if your really keen, get a alloy head crossflow 250 and start there, the head is sooo much better. Or even better get a turbo Barra, they are 400bhp stock.
Crustang to Mustang
Well-known member
Hermes Motorsports claimed to get 400hp and 500lbft out of his turbo log head 250 at only 15-17psi. Thoughts? He was also using meth-and water though so that helps.
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Crustang to Mustang
Well-known member
Any production cars with turbos that will fit that bill that might could be found at a junkyard?
Yes, It was because he was using meth/water injection which helps cool the air as well as add meth as a fuel.
Not that I know of.
The BorgWarner S252SX-E fits the bill.
Crustang to Mustang
Well-known member
Yes, the engine would only displace 200ci but it would have a different rod ratio. Now whether the rod ration would be better, I have know idea. Nor do I know if it is possible to do the swap, as you have already stated.
Crustang to Mustang
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I'm on a somewhat strict budget for now but that will hopefully change soon. Are there any cheap ebay turbos that anyone knows of that are close in specs? I can always replace it for one of better quality later.
The Toyota 1JZ connecting have been used in the 200 six.
Crustang to Mustang
Well-known member
What are the benefits here? Shaving weight? Better rod ratio? strength? All of the above? Would both the 300 and 1jz rod require a custom piston? How much does it usually cost for a set of custom forged pistons?
Also, if I may ask an extremely basic question: What determines the ideal rod ratio for an engine? Is it safe to say that a longer stroke is more important than rod ratio generally? In other words, is destroking an engine for higher revs and a potentially better rod ratio worth it?
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Aftermarket 1jz rods were relatively inexpensive, a little longer which will decrease piston weight as well as decrease the rod angle and are much stronger than the stock 200 connecting rods.
Same story using the aftermarket 300 six rod in a 250 six.
Yes, in both cases it will require a set of custom pistons.
Last time I checked, custom pistons were about a $1000 for a set of six.
Race guys use 200 rods in the 250s to get a slightly improved rod ratio, it might be worth 5kw at peak revs, not much more, IMO not worth the cost for custom pistons unless your trying for last kw. I run a 200ci crossflow with a blower, it has a rod ratio of 6.27/3.13=2:1. which is too high according to some circles. From my research into this subject it mainly effects vibration. The block height of your 200s would not allow for a much longer rod, so i think this is out of the question for you. PS, our 200 rods are 6.27 long.
From my own research and reading of others work, the ideal rod ratios seems to be around 1.75;1. However there are plenty of examples of VERY succesfull engines with rod ratios down around 1.5, BBC is one. IMO unless you can do this cheaply, its not worth the effort, anywhere between 1.5 and 2;1 seems to work just fine. Displacement is MUCH more determinate, AND Ve is more important than that. Take an example for our Barra dohc six, its 240ci, makes 250bhp in stock form, is dead reliable, whereas the precrossflow 250 made about 125bhp, thats all down to VE, same basic engine!
There is no ideal rod ratio for an engine. Engine specifications such as bore, stroke, block deck height are determined by the desired engine performance characteristics and vary greatly depending on the use and rules.
The connecting rod is there to simply connect the piston to the crankshaft after everything else has been determined.
When an engine is competing in a class that has a specific displacement limit it is generally better to have a large bore and a short stroke to achieve a specific displacement.
Other examples: Those drag racing the 300 six with extremely high rpms found the tortional harmonics to be unbearable and steel crankshafts were breaking every 25 runs.
Destroking from 3.98" to 3.75" greatly reduced the harmonics and saved crankshafts.
A longer rod ratio decreases piston side loading which reduces friction for possible fuel mileage gains.
It also decreases the engines tendency for detonation.
A shorter rod ratio has more leverage on the crank throw just after TDC and could provide more torque for a lower rpm engine.
As you can see the reasons vary.
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Crustang to Mustang
Well-known member
Thank y'all for the replies! I really appreciate it!
So I read somewhere that at least some of the 250ci rods are forged. If I'm working on a somewhat tight budget, should I just use those?
So I read somewhere that at least some of the 250ci rods are forged. If I'm working on a somewhat tight budget, should I just use those?
All Australian rods for these engines were forged.
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