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I am building a high compression 2v. I was wondering what compression some 2v guys are running on there street/weekend/track cars. I'm thinking about going with some 3cc dish pistons that is suppose to put me around 11.9:1 to 12:1 cr with PI heads. Is there any guys running this cr with (nitrous) on pump gas. I know its all in the tune just seeing if this is feasible. Thanks
 

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I am building a high compression 2v. I was wondering what compression some 2v guys are running on there street/weekend/track cars. I'm thinking about going with some 3cc dish pistons that is suppose to put me around 11.9:1 to 12:1 cr with PI heads. Is there any guys running this cr with (nitrous) on pump gas. I know its all in the tune just seeing if this is feasible. Thanks
I am doing the same build and i have recieved two sets of feedback.

12-1 is too much for 93 octane is the first.

run a big cam and get a good tune and you will be fine is the second.

I'm hoping number two works since that is what I'm rolling with. I don't think you will get away with nitrous and high compression with premium fuel though. I planned on 100 octane when spraying and 93 when not.

I'm sure some others will chime in. I won't have results until april time frame.
 

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Discussion Starter #3
Yea I was thinking probably 100 or so octan when spraying but was hoping i could run pump when not spraying. Thanks for the reply I have heard so many diff. answers too.
 

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depends on how much compression the cam bleeds off.
but yes it can be done... people run 4V pistons in 2V motors all the time, and thats about 11.8:1
That said, from what i understand once you get past 11:1 its diminishing returns. The % gain from 10.5 to 11 is higher than the % gain from 11 to 11.5 and so on...


no way id advise you to spray on top of that though... not on 93.
 

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Discussion Starter #5 (Edited)
Yea I think I'm going to go with the 3 cc dish pistons with valve notches. From what I have read each valve notch adds a cc so It will actually be 5 cc pistons. I should be ok with a tune and 93 octane without spray and race fuel with. Thanks guys
 

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Ported heads too? If so, depending on what the chamber cc is, you could lose a little compression that way. I think stock is 42ish. If that cc increases you could bring that down closer to 11:1
 

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I have the cobra piston npi short block with pi conversion set up. I used a fairly aggressive cam. Without a tune the car would go into detonation after the engine reached full operating temp. With a tune no problem at all. I love this setup the car loves to rev and makes lots of power (no dyno yet). I am considering a small nitrous shot my self just for fun, maybe 75-125 shot? Good luck with the build I think you will love it.
 

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I have the cobra piston npi short block with pi conversion set up. I used a fairly aggressive cam. Without a tune the car would go into detonation after the engine reached full operating temp. With a tune no problem at all. I love this setup the car loves to rev and makes lots of power (no dyno yet). I am considering a small nitrous shot my self just for fun, maybe 75-125 shot? Good luck with the build I think you will love it.
Do you remember what your operating temp was?

I planned on running 2 step colder plugs, reduced timing, and keeping coolant temp at 180 in order to prevent detonation. Those are the things along with gas octane and inlet temperatures that determine whether it detonates according to what I have read.
 

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Discussion Starter #10
Do you remember what your operating temp was?

I planned on running 2 step colder plugs, reduced timing, and keeping coolant temp at 180 in order to prevent detonation. Those are the things along with gas octane and inlet temperatures that determine whether it detonates according to what I have read.
I was wondering the same thing
 

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At first I ran it stock settings, it would run great for about 25 minutes (until the engine was completely heated up or "heat soaked") then it would start detonating badly during acceleration. If I kept my foot out of it I could still drive it without noticeable detonation. As far as temp is concerned I was running a 180 thermostat with no other changes. Of course this was in Florida during the hottest part of the summer (around 100 degrees outside + or -). Before the engine warmed up it was crazy fast, I have never seen a na 2v run this strong before...it would hit the rev limiter before you knew it and you could tell it wanted more (still pulling hard). I took it to a local gut that is pretty good with custom tunes and let him seat of the pants tune it until I can get it to the dyno. He set the fans to 180 and adjusted the timing and fuel charts to control the detonation. He also upped the rev limiter to 6700 or 6800 (don't remember but I shift at about 6500 when I'm getting on it now days). The car did lose some power (cant always run on the edge of detonation :crying: wish I could :rolleyes:) but is still very strong. The crazy thing is I have almost no supporting bolt ons. Only a off road x pipe, that's it. After the tax return gets here I am getting some long tubes, BBK 78mm one piece intake, 90mm mass air and matching 24# injectors and a 410 rear end. And finally a custom dyno tune then we will see what these can do.

On a side note the extra power is way to much for the stock suspension, I can feel the rear end moving around on hard braking corners, and the whole car twists when I hammer it so next on the list of to do's is the suspension.

Forgot about the plugs, I use autolite 103's they are 1 step cooler than stock. Going 2 steps cooler is overkill in a high compression na engine....maybe with the nitro idn but the 103's work great and most of the builders I have spoken to prefer them too.

As far as operating temp the tuner told me that the car was running at about 215ish degrees during the test drives with the 180 thermo and stock fan settings. With the fans set to 180 it was in the low 190's when driving hard and would get down to low 180's when at rest. this was on a 103 degree day with high humidity.
 

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Have you thought about converting to E85? It will support the compression ratio even on spray. I am working on putting together a 13:1 compression motor with 2 stages of spray 200 first stage and a 300 second stage.
 

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I am doing the same build and i have recieved two sets of feedback.

12-1 is too much for 93 octane is the first.

run a big cam and get a good tune and you will be fine is the second.

I'm hoping number two works since that is what I'm rolling with. I don't think you will get away with nitrous and high compression with premium fuel though. I planned on 100 octane when spraying and 93 when not.

I'm sure some others will chime in. I won't have results until april time frame.

12-1 works with the correct cams on 93 octane with the PI heads, its a popular combo.

Nitrous you should run a separate fuel cell with the race gas in that for the nitrous plate. Its the safest way to do a setup like this as mixing race gas in the regular gas tank who knows what the stoich ratio might get moved too.
 

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I planned on running 2 step colder plugs, reduced timing, and keeping coolant temp at 180 in order to prevent detonation. Those are the things along with gas octane and inlet temperatures that determine whether it detonates according to what I have read.

Also add piston quench to the above. If you zero deck the block or better yet run the piston slightly outside the deck you not only gain compression you also at the same time gain resistance against detonation (sounds backwards but its very true) Race engines that are forced to run on pump gas have the pistons just about touching the heads at higher RPM. You can run the pistons to within 0.025" of the heads on these motors if you blueprint everything (and some race motors go 0.020" I know of but they have bigger cahonas than me)
 

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How much do you guys think it will lower my compression going from a .036 gasket to a .065?
If you are running 3cc pistons with a notch essentially making them 5 cc pistons, I wouldn't bother with the thicker gasket. You can use any compression calculator to get your answer.

Your cam selection will be the most important thing.

You should be closer to 11.5-11.8 compression with those pistons assuming you don't deck the block and don't mill the heads to reduce the chamber volume.
 

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I'm wondering if ported npi heads would be a better option for a 4v shortblock, than ported pi's to get the compression ratio more ideal.
 
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