Hello! cranking pressure vs. lash?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Cutting .060 is not necessarily bad, you just have to check what that will leave in all areas of the piston. It may get real thin in some areas.

How deep are your valve reliefs? If they are more than .060" you should be safe.

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Official Cookie and Mater Tormentor.

I haven't been ignoring you. I had them set between .016 - .020. I didn't see really any big change. At the time of testing I wasn't aware that I could tighten them up more safely. Basicly I don't have a good answer at this time.
Sorry for not adressing your question.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

From looking at the picture they look like there more than a 1/4" (.250)

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

You should be good them. You know you can mill pistons in the block with a router.

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Official Cookie and Mater Tormentor.

Sounds like exh Y was causing problems, and could cause detonation on the restricted cyls. On your motor, I would run 2X2.25" from the Dutras into AT LEAST 2.5" single, but better would be 3" single all the way back. I can't tell sizes well with your pics.

Best to get the Y intersection all the way back at the trans X member or maybe 2-4" behind it (to rear of car). This will give best low end and not hurt high end.

Lou

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Home of Slant6-powered fun machines since 1988

Just pointing out one of those time that I don't listen.
AANNT- Can not compute AANNT shuting down.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

not saying you were ignoring me, but this topic's so long and we all jump on your back with so many suggestions and questions that I know we're getting you dizzy. I would have checked the same cam with .08 lash, just to see what happened. If I notice great cranking pressure drop, that'd mean fast ramp, I'd go with .005 on the intake .010 on the exhaust.

About exhaust pipe, I don't think dan's advice should be considered for a custom application. He's right if you're talking about a bone stock 225 with maybe dutra duals and a BBD, but throw in a hot cam and other minor changes and his advice is old news. Build a motor like yours and you're just taking his advice out of context...

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I agree, you just built a Monster air pump, and you plugged half of it up by that poorly constructed "Y" pipe that is way to close to the manifolds to develop any useful torque.

The quotes are for stock or near stock motors.

You have just changed the playing rules and must do a little testing to find out what size pipes will bring it into the best tune and provide good street characteristics.

I would use the same diameter pipe as the Dutra Duals and run them way back 36" or 48" before joining them together to help increase low end torque. Then run about 18" collector, then neck it down to a single 2.5" pipe minimum.

If you run the new pipe you just had built, there will be very little to no low end torque.

If I had that "Monster" engine I would run an "X" pipe cross over and duals the same diameter as the Dutra Duals. That is a preference of mine!

Disclaimer: Everyone else will tell you run a single pipe.

So you may want to try your new pipe and prove to your self that it won't get off the line. Then do some experimenting!

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I would run headers, 2x 3 into 1 and all the way back to the end, balancing them pipes around near the tail of your 904. I run 1 5/8 primaries into 2 collectors and 2 2" tailpipes, balanced around the spot I indicated.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Id run the DDs with 2"- 2 1/4" primaries about 31-32" long into a Flowmaster Y thence to a single 3"pipe with a Flowmaster 70 in the stock location......good for 300hp

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Yes... what he said...
I shoot for 36 inches.
How the two pipes come together in the collector is key to the scavenging that takes place, the pipes must be side by side and terminate at the same point, then leads into a bigger chamber. This way, the pulse from one pipe creates a low pressure area in the zone next to it, that is what scavenges the other pipe.
DD

When measureing deck height. Is it normal to have two different measurements from side to side of the same piston? Another words, toward the lifter side I am measureing .053 and the intake side .023 for an average deck height of .038. These measurements are after milling the pistons of course. The valve reliefs where 4cc's and now there 3cc's The current camber size is 64.5cc's. We plan to add 3.5cc's to the camber for a final CR of 9.24:1
I measured the stroke and I think I need to find a different measureing tool. I sware I am mearsureing a 4.35" stroke. Measure piston deck height at TDC and measure piston BDC and substract the two for the stroke, right? I am coming up with 4.403 deck height at BDC. If I had a dial indicator with a 5" travel, that would be nice. I used a slide caliper and its tail stem for these measurement. I have a nice one that I need to bring and check again. If I right about the stroke being longer then it bring the CR to 9.33:1

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

The deck hight should (not really should, there is a right and wrong way to do it) be measured at the front or the rear of the pistons inline with the center, and with a light touch so as not to disturb them. Everything needs to be perfectly clean. Basic procedure is to wipe the faces of a caliper with your finger and check zero every time you use it. A depth mic is the thing to use here, but with some care and skill you can get within .001 with a caliper if the deck is flat. Just make sure the edge of the caliper is not on the bores chamfer.

Measuring from the sides as you did gives results just like what you got. The looser the pistons in the bore, the worse it will be. Really with the piston rocking back and forth there is no way to know what you have, even averaging the two. You can check it several times and it will not be consistant, it is very likely that it will move during the process.

I made a comment in an earlier post about the difference between knowing something and thinking you know something. It was in reference to details like this. I did not say it to be a jerk, but trying to point out that things need to be done right to get the right results. Making up a procedure like averaging those measurements may or may not work. When something like this does not seem right, it isn't.

It is worth noting that the piston REALLY needs to be at TDC. If that is done with some alternate procedure or logic this all may be a waste of time. I would check several pistons, not that you can do much about any variations, but it would be nice to know how close they are.

Like the deck hight, you should be able to check the stroke pretty closely with a caliper. Just do it at the front or rear of the piston and make sure everything is square.

On a 225, I have measured deck heights with a caliper (at true TDC) all around the pistons and never seen more than 0.015" variation. Usually 0.005". These are tall pistons and a small bore.

If you are using shorter pistons, which you might, then I suppose 0.030" variation might be possible, but still that seems like a lot.

If your stroke is longer than expected, that makes your comp higher.

Lou

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Home of Slant6-powered fun machines since 1988