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Max recommended boost on 5MGE with enough fuel?

3386 Views 10 Replies 8 Participants Last post by  Supra Bob
Lets say someone had a low compression (8.8:1) 5MGE from an 83 in his car. They wanted to run Megasquirt to take care of the fuel system, and probably run 440 injectors. Assuming that there was more than enough fuel, what would be the highest boost you would run on a stock engine with 55,000 miles on it?
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Im running 11-11.5psi. It isnt really stock as it has been bored .020 and balanced/blueprinted so I dont know if it helps you or not.
I've heard of people running 12 or 13 on stock internals...

Me.. I'd be a bit leary of running much more than 9 or so without a metal HG at least..
what about on a stock '85 that I'm going to rebuild, what would be max safe boost pressure after the rebuild?
From what I've seen, about 10-11 on the 85. Remember, the 84+ engine has 9.2:1 instead of 8.8:1, and higher compression is rougher on a boosted engine. I'm planning on running about 8 when I do it (85). If you want to run a lot of boost, it would be worth getting a 7M or a 2JZ (2jz, ahhhhhhh.....). Just my oh so humble opinion
I'm looking at probably doing a swap of the 5M-GE into an AE86 GT-S Coupe, and I'll be doing a stock CT26 setup. I've been thinking about which engine to get, a pre-83 or an 84+. Either way I'm looking to run about 9psi boost, not any higher, so I'm thinking the 84+ would be better for me, because the 9.2:1 combined with the 9psi will give me an overall higher effective compression, while still being safe at 9psi.

Just looking for other opinions on whether 9psi is safe on the 9.2:1 engine. I'd assume so.
On a related note, does anyone have and idea how much power can the stock AE86 GT-S LSD diff take?
i dont have any experience here and have never rebuilt a motor before, but i think you'd probably be better off with lower compression *if* you have decent timing control. from what i've read, most turbo motors are of course totally limited by knock. retarding timing to limit knock is a great way to a) save your motor and b) lower the efficiency of your engine considerably. lower compression means more advanced timing at the knock limit, and while overall compression might be lower, there's a decent chance you'll make more power. from what i've read about knock-limited engines, compression is not just a matter of safety.

also, while off-boost performance will be better with higher compresison, there's theoretically a chance lower compression will make spool-up quicker, as more heat goes out the exhaust.

of course with 5mgte engines, it's hard to say because there isn't much data to go on.

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Yes, that makes sense, though I have heard a lot of people extremely happy with the basic CT26 on 84+ 5M-GE engines, and they are making about the power I'd like.

I'm not looking for huge numbers at all, and I'd like to have as much non-turbo assisted horsepower as possible, as it makes it very fun. I'll definitely think on it for a while.
Back in mid '99 I was running a 6m-gte (not sure of the mileage, was told 50k) w/ 2.0 hks MHG, 440's, walbro pump, S-AFC, and a paxton FPR. I had a stock ct-26 pushing 12psi daily and ran 15psi for race. Never snaped a rod or crushed a piston ring land, however I had dyno tuned this thing very well. I ran this set up for almost two years - this motor was pulled in favor of the 7m and is still running fine in a friends car today. Get Corky Bell's book "Maximium Boost" it is a very good read - in short, you can run as much boost as you want, so long as you do not pre-detonate the poor beast to an untimely death.
ONe thing to consider tho Chris, in your case, was that 2.0mm MHG. All other things being equal, that MHG will take alot more abuse than a normal one will... I doubt that on a regular HG you couls run 12 psi on a daily for two years with no problems.

...but you are right about Corky's book. GREAT read, very informative.. I think before anyone even thinks about turbo's, they should read that.

"Turbos=Torque. Torque=Fun" -Corky Bell
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