GT40 Irons, Boost, and Compression Ratio - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 28 Old 08-19-2012, 11:30 PM Thread Starter
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GT40 Irons, Boost, and Compression Ratio

First please do not just tell me to go to aluminum heads. Looking for some useful information for myself and anyone looking to run irons with boost. Thanks in advance guys!

Currently in process of building a short block for a turbo set-up 70mm, intercooled. Was planning on running a -13cc piston with cometics and ARP head studs and cobra iron gt40s (custom turbo cam, PMS, cobra intake ported lower). Should give me right in the neighborhood of .040 quench maybe slightly more. My static compression ratio will be right around 8.5:1 dynamic at 7.6:1 and boost compression ratio at 11.6:1 with 8psi. My goal is 425-450whp.

I am wondering how much boost I can safely run at this compression ratio with the irons. If I need to increase the boost to 10 or 12 psi at this compression ratio to meet my power goal if that won't be a problem at all or if that's asking for trouble. I do not know how much truth there is to this but was told to stay below 12:1 for your boost compression ratio on pump gas. Or if you guys have other suggestions. I hear about guys "lifting" heads but I am beginning to think that is from running too much boost with too high of compression for iron heads or not a straight sealing surface.

Whatever insight you guys have or information would be greatly appreciated.


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post #2 of 28 Old 08-21-2012, 12:31 AM Thread Starter
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Anyone?

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post #3 of 28 Old 08-21-2012, 12:53 AM
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I dunno if this helps but I run a 150 shot with cometic head gaskets with no issues. I have a turbo kit waiting to go on and I will be running it at 12psi, hopefully it will be OK
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post #4 of 28 Old 08-21-2012, 01:18 AM
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You over complicated something simple a stock motor with 10-12psi will make 400hp


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post #5 of 28 Old 08-21-2012, 02:22 PM Thread Starter
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You over complicated something simple a stock motor with 10-12psi will make 400hp
No, not trying to. Just trying to make it so I can have something that will last for a long time at that power level, not trying to break records. Not wondering when a stock bottom end will let go, 100 miles or 3 years.
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post #6 of 28 Old 08-21-2012, 02:23 PM Thread Starter
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I dunno if this helps but I run a 150 shot with cometic head gaskets with no issues. I have a turbo kit waiting to go on and I will be running it at 12psi, hopefully it will be OK
Nice! You running studs then?
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post #7 of 28 Old 08-21-2012, 03:13 PM
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I just blew the head gasket on my gt40 headed motor. The heads were surfaced and gone through prior to installation and I used ARP head studs as well. The car was tuned by a highly respectable tuner in my area. I was running just shy of 10lbs (roughly 9.8lbs)and used fel pro 9333pt1's.

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post #8 of 28 Old 08-21-2012, 04:44 PM
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Originally Posted by AJs94cobra View Post
I just blew the head gasket on my gt40 headed motor. The heads were surfaced and gone through prior to installation and I used ARP head studs as well. The car was tuned by a highly respectable tuner in my area. I was running just shy of 10lbs (roughly 9.8lbs)and used fel pro 9333pt1's.

Sorry to hear about your blown head gasket....Ive been there done that...Replaced 4 sets last year. IMO FelPro 9331pt1's are junk...I had them only lasted about 3 days. Go buy yourself some good cometic MLS gaskets, they cost way more but are worth it. I have ran as high as 17psi making a full pass at the track. I have also flashed 21psi for short bursts when my boost controller was screwed up. Answer to the original post you should have no problem making that kind of power with those heads on a stock short block with 10psi. A good tune, good gaskets and head studs will make it last for awhile.

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post #9 of 28 Old 08-21-2012, 04:55 PM
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Sorry to hear about your blown head gasket....Ive been there done that...Replaced 4 sets last year. IMO FelPro 9331pt1's are junk...I had them only lasted about 3 days. Go buy yourself some good cometic MLS gaskets, they cost way more but are worth it. I have ran as high as 17psi making a full pass at the track. I have also flashed 21psi for short bursts when my boost controller was screwed up. Answer to the original post you should have no problem making that kind of power with those heads on a stock short block with 10psi. A good tune, good gaskets and head studs will make it last for awhile.
Did you have the block machined before going with the MLS gaskets? I have read that before and at this point that is what is keeping me from running them. I just went ahead and got some tw 170s because I didnt feel like going through all that work just to put the irons back on.

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post #10 of 28 Old 08-21-2012, 09:32 PM
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Nice! You running studs then?
Nope, just ARP bolts (the way I got the motor). I am pretty sure if run Cometics with studs there will be no issues.

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post #11 of 28 Old 08-21-2012, 09:49 PM
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Did you have the block machined before going with the MLS gaskets? I have read that before and at this point that is what is keeping me from running them. I just went ahead and got some tw 170s because I didnt feel like going through all that work just to put the irons back on.

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Nope.....Block is untouched...Heads were decked...Haven't had a problem yet, knock on wood...lol

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post #12 of 28 Old 08-21-2012, 10:49 PM Thread Starter
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Sorry to hear about your blown head gasket....Ive been there done that...Replaced 4 sets last year. IMO FelPro 9331pt1's are junk...I had them only lasted about 3 days. Go buy yourself some good cometic MLS gaskets, they cost way more but are worth it. I have ran as high as 17psi making a full pass at the track. I have also flashed 21psi for short bursts when my boost controller was screwed up. Answer to the original post you should have no problem making that kind of power with those heads on a stock short block with 10psi. A good tune, good gaskets and head studs will make it last for awhile.
I am building a short block right now. It will be a built mexican block. Trying to put together a engine that will live for ever at the 400-450 range 6k rpm redline.
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post #13 of 28 Old 08-21-2012, 10:54 PM Thread Starter
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Originally Posted by AJs94cobra View Post
I just blew the head gasket on my gt40 headed motor. The heads were surfaced and gone through prior to installation and I used ARP head studs as well. The car was tuned by a highly respectable tuner in my area. I was running just shy of 10lbs (roughly 9.8lbs)and used fel pro 9333pt1's.
Could be other issues. What fuel system are you running? Do you know what total timing he ran on your tune? Is the deck of the block warped?
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post #14 of 28 Old 08-22-2012, 02:04 PM
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I have 9333 pt1's ARP studs i do run TF heads...and i make 14 psi..i do run meth tho that mite help a little...AND from what im told you want a fuse and Cometic head gaskets wont let go so guess what the pistons or rings might go i would rather blow a head gasket...IMO...

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post #15 of 28 Old 08-22-2012, 02:59 PM
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You should have NO problems making 4-450 with that setup. Seen guys running a 70mm with an E-cam making around 500. I have am running a stock block, GT40 irons, E-cam, and a 150 shot. Have a 76mm billet wheel, ceramic BB kit waiting to go in, but need to check valves first. Have a strnge noise coming from around #3.
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post #16 of 28 Old 08-22-2012, 05:18 PM
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I have 9333 pt1's ARP studs i do run TF heads...and i make 14 psi..i do run meth tho that mite help a little...AND from what im told you want a fuse and Cometic head gaskets wont let go so guess what the pistons or rings might go i would rather blow a head gasket...IMO...
Too much timing and boost with crap fuel and or lean is what makes things go boom....

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post #17 of 28 Old 08-22-2012, 05:23 PM
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Could be other issues. What fuel system are you running? Do you know what total timing he ran on your tune? Is the deck of the block warped?
Walbro 255, 60lb injectors, block was checked when I had it out of the car. Not for sure on total timing but he said it was conservative. And I always filled up with 93 octane from co-op. Which where I am from is supposed to be the best quality.

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post #18 of 28 Old 08-22-2012, 08:56 PM Thread Starter
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Walbro 255, 60lb injectors, block was checked when I had it out of the car. Not for sure on total timing but he said it was conservative. And I always filled up with 93 octane from co-op. Which where I am from is supposed to be the best quality.

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I was told by a tuner from this forum that the 255 alone isn't really enough for boosted set ups and you should either use the 340 or 255 and trex. Do you have a wideband or fuel pressure gauge in the car? I know some guys are doing it but it seems to be hit or miss. Heard people running out of fuel at 400whp with the 255.
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post #19 of 28 Old 08-22-2012, 09:04 PM
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I was told by a tuner from this forum that the 255 alone isn't really enough for boosted set ups and you should either use the 340 or 255 and trex. Do you have a wideband or fuel pressure gauge in the car? I know some guys are doing it but it seems to be hit or miss. Heard people running out of fuel at 400whp with the 255.
Hmm, I am sure the tuner knows way more than myself but I have read quite a few threads with ppl having zero issues with the 255 on boost up to 500hp. I may be wrong tho. I know my injectors were only roughly 50-55% duty cycle. Yes I have both gauges in the car. At WOT, 11.2-11.4 on the wideband. Never paid too much attention to the fuel pressure while I was on the throttle hard to see what it was doing.

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post #20 of 28 Old 08-23-2012, 03:05 AM
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Currently feeding a 351 windsor 14lbs of boost on 9333pt1 head gaskets and stock head bolts re used, single 255 in tank pump, adjustable regulator 39lb injectors... car put down 487 on 12psi, running 14 now.

On the 302s we used 9333pt1 gaskets and arp head bolts, never really could take much more than 12-13 psi for very long before it would push coolant.

7/16 bolt and small deck surface just wont hold it, not to mention a block that twists up under power like a fox vert without sub frames lol



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post #21 of 28 Old 08-23-2012, 06:36 AM
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9333's are great gaskets, just not with GT40/GT40p's. The thin decks on the GT's is what makes proper sealing a chore, as they like to lift under any significant amount of boost. Most any other aftermarket head will do great with 9333's, as it is a proven combo.

As for the 255 pump, as long as it's a HP Walboro or similar, with a turbo...you won't need anything else before needing to upgrade the stock rails. 500-600rwhp seems to be the max for these running stock pressures. An inline T-rex will allow the 255 to push more fuel as will running more voltage via. a KB boost-a-pump (or similar).

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post #22 of 28 Old 08-23-2012, 11:39 AM
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9333's are great gaskets, just not with GT40/GT40p's. The thin decks on the GT's is what makes proper sealing a chore, as they like to lift under any significant amount of boost. Most any other aftermarket head will do great with 9333's, as it is a proven combo.

As for the 255 pump, as long as it's a HP Walboro or similar, with a turbo...you won't need anything else before needing to upgrade the stock rails. 500-600rwhp seems to be the max for these running stock pressures. An inline T-rex will allow the 255 to push more fuel as will running more voltage via. a KB boost-a-pump (or similar).
And what would you recommend for head gaskets on GT40's(I'm currently putting a mild Explorer motor setup together for my wife's Fairlane)?

FWIW, mine put down 510 wheel with only a 255 pump. Stock rails, etc...

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post #23 of 28 Old 08-25-2012, 02:10 AM
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You should have NO problems making 4-450 with that setup. Seen guys running a 70mm with an E-cam making around 500. I have am running a stock block, GT40 irons, E-cam, and a 150 shot. Have a 76mm billet wheel, ceramic BB kit waiting to go in, but need to check valves first. Have a strnge noise coming from around #3.
I have stock block, GT 40s, and E-cam.
On the 150 shot with too much gear for the AOD(4.10s) it went 11.7. I changed to 3.27s and a masterpower 70mm with a kit I built and went 11.2 at 128 with a 2.0 60ft and killed the AOD pretty quick. I have seen 14lbs of boost briefly and the headgaskets are okay with 1011-2s and apr bolts. I have a walboro 255 with 42# injectors and the rails that came with my BBK SSI intake. I also run mixed 93/110 octane.
I will get my goal of 10s when I get another transmission but I know the motor could pop any day. Thats the risk we take and Im okay with it.

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post #24 of 28 Old 08-25-2012, 03:09 AM
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Originally Posted by AJs94cobra View Post
I just blew the head gasket on my gt40 headed motor. The heads were surfaced and gone through prior to installation and I used ARP head studs as well. The car was tuned by a highly respectable tuner in my area. I was running just shy of 10lbs (roughly 9.8lbs)and used fel pro 9333pt1's.
Have you talked to your tuner since, all though every thing sounds good on the set up, maybe mentioning it to him might spark something. For the most part you should have had a few more #s before it went. Where are you at with it now?
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post #25 of 28 Old 08-26-2012, 10:09 PM
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Have you talked to your tuner since, all though every thing sounds good on the set up, maybe mentioning it to him might spark something. For the most part you should have had a few more #s before it went. Where are you at with it now?
I just put some trickflow 170s on and just bought a used s trim that I am gonna put on. Im just tired of messing with the turbo and I can never seem to iron out all my issues with it so I'm going a simpler more reliable route.

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post #26 of 28 Old 08-26-2012, 10:43 PM
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What's more simple than a stock motor with a turbo? Btw I have an s trim for sale... My combo does great and I tuned it myself what issues are you having other than the head gaskets?

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post #27 of 28 Old 08-26-2012, 10:59 PM
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What's more simple than a stock motor with a turbo? Btw I have an a trim for sale... My combo does great and I tuned it myself what issues are you having other than the head gaskets?

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It's mainly stuff that if I could fabricate on my own I would be just fine. It seems people have a lot better luck on the fox kits vs the 94-95 ones. My crossover had to be redone because it wasn't close to fitting and it still causes issues. In order to fit correctly, its maybe a quarter inch from the harmonic balancer. I can't get A/C to fit without custom lines. The pipe going from the turbo to the intercooler is the lowest point on the car by a landslide and scrapes everywhere. I burned a hole through my lower radiator hose, replaced it with a cool flex hose and the lower silicone coupler tore in half spewing coolant absolutely everywhere. There is other little things. My car was completely reliable and now it is issue after issue. Not to say that it can't happen with other mods. And truthfully, I just dont want an on3 product on my car after the fuel injector issue I had.

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post #28 of 28 Old 08-29-2012, 07:39 PM
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I apologize I incorrectly assumed we were talking about a foxbody car. My bad man.

I'm not a magazine racer, my car is actually fast.
I also have a Honda civic but, mine has a bigger, uglier driver.
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