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Bigger valves vs. bigger cam
https://www.slantsix.org/forum/viewtopic.php?t=7933		 Page 1 of 1
Author:  Buddy [ Wed Dec 24, 2003 9:54 pm ]
Post subject:  Bigger valves vs. bigger cam
I'm thinking that for a street/performance engine a properly prepared head (ports) with larger valves will allow the use of a less radical cam and provide similar peak power while maintaining a wider torque band and better overall driveability, compared to the opposite approach.

I. E., if I use MP 1.70/1.44 valves, as a convenient example, in a head that was ported for good low-lift flow, combined with, say, an MP 244* cam, wouldn't that offer better wide-spectrum performace than, say, an MP 268* cam with a stock head? All this assumes I'm talking about using both setups on the same engine, with each setup tuned for max performance.

I realize that, ideally, the cam profile should match the flow characteristics of the head, but things in this world are seldom ideal.

Anyway, perspiring minds want to know...
Author:  Doctor Dodge [ Thu Dec 25, 2003 10:51 am ]
Post subject: 
A small increase in valve and port size will help a 225 without a cam change. To really make more power with a SL6, you need to spin it to higher RPMs, that is where a cam change comes-in.
You have to flow air / fuel to make HP, removing intake track restriction(s) while keeping good mixture velocity is one way to do this but it has limited affect at low RPMs.
DD
Author:  Buddy [ Fri Dec 26, 2003 9:41 am ]
Post subject: 
Makes sense, I reckon, since HP is a measurement of torque vs. time. At the same time, I understood slants to be more torque efficient at low RPM, compared to other more RPM-friendly engines. Consequently, I thought it might be easier to improve on that torque than to try to ring out the revs.
Of course, I reserve the right to be wrong. :wink:

Heck, if seeking some rpm's will actually produce the desired performance, I guess there ain't no sin in that.

Am I on the right track, though, trying to max out low-lift flow on a street engine, even with a more aggressive cam? Seems like that would effect low-speed driveability a lot, no?
Author:  lgu32 [ Sun Dec 28, 2003 3:28 am ]
Post subject: 
I have some experience with big valves in SL6 where is also 244 deg MP cam. The valve job is the latest improvement. All other mods like D-Duals with 2.25" secondary exhaust, Super Six intake with 318 BBD and milled head was there before. I have used big valves because they made things simple at cyl head rebuilt job. This is true because the original valves were really dee...eep in the head and good cores are not so usual here. The valves are custom made from 300 cid inline6 Ford material. Intake is now 1.725 and exhaust 1.42.

This engine is the pushrod eater I have wrote to the forum before. Too tight bronze quides at the exhaust side. Some hits to the pistons, so it was close to the real damage.

How the valves change it? I have found no noticeable high RPM gain after the valve job, but the overall performance is now better. From the rpm meter is easy to find that there is no power increase above 4500 rpm (225 cid +0.060"). It seems that the 2 bbl carb is the limiting part now, but because I have used stock parts when rebuilt the base engine, I know it is not a very good idea to go over 5000 rpm and so I stay with this (for a while...)

This slant is now a very good street engine. I have 1:3.55 gears and the car a light weight '66 Dart. Low gears help me to get 0-60mph @ 8+ seconds (G-tech measurement) but I have to pay for it in the highway.
Author:  Bruce Johnson [ Wed Dec 31, 2003 10:49 am ]
Post subject: 
My machinist recommened cast iron valve guides, he warned me that bronze guides can sease up and I have not had a problem,(stock pushrods,oversized stainless valves, custom from Eggy. .100 milled off the head,rev limiter set to 6000 rpm) Bruce Johnson
Author:  Buddy [ Wed Dec 31, 2003 1:22 pm ]
Post subject: 
That's interesting, Bruce. I was under the impression that bronze guides are supposed to help reduce valve seizure and last longer, being self-lubricating and all.
Author:  bud L. [ Wed Dec 31, 2003 6:00 pm ]
Post subject:  ?
There are pros and cons to each. Cast iron is somewhat "self lubricating" because of the graphite(carbon) content. Bronze also has some graphite content. But the only real self-lubricating bronze is "oilite" bronze, which, interestingly enough, as I recall, was developed at or by Chrysler before WWII. I have had no problems with bronze guides or guide liners. Cleanliness, and lubrication on assembly is crucial. It is also important to use valves with straight (no taper) stems. The stems can very easily be nicked by careless handling, which will gall up a snug guide in no time. For exhaust valves I use guide liners with a smal helical groove for extra oiling. Also excessive heat & poor rocker geometry can exacerbate a tight clearances situation. There's alot more that cause things to go sideways on you, so examine your situation closely.
Author:  Bruce Johnson [ Wed Dec 31, 2003 6:39 pm ]
Post subject: 
Bud, Hope to meet up with you some day,going to have to catch a few meets next summer in Washington. If I'm understanding all the input correctly... If the valves are correct and geometry is not excessively out of wack, bronze guides will slide easyer? and free up some HP , but will wear faster? And because of the lower melting temperature, will more likely sease in a situation where demensions aren't right or oiling is lacking, I've been following the posts on this sight a couple of years and I don't belive this area has been covered in any detail. Also what about the compatability of stainless valves with eather iron or bronze and what about the advantages of stainless valves? all I know so far is that they are good because stuff doesn't stick to them. interrested in opinions. :?: Bruce J.
Author:  DusterIdiot [ Wed Dec 31, 2003 10:00 pm ]
Post subject:  Caravan...
Bud is a great guy, I got to briefly talk to him last year...hope he stays a bit longer next time. (I still owe you a beer for the ebag Hpak incident... :roll: )
Bruce, maybe we should 'Caravan' up, I think Matt also wanted to go, his hi-po 6 should be done and 'tuned' by then...


-D.Idiot
Author:  bud L. [ Thu Jan 01, 2004 2:35 pm ]
Post subject:  ?
Thanks for the endorsements, guys! :lol: Some of my neighbors may not share your sentiments. :lol:
I don't have a huge amount of experience with SS. But I did( & redid) a set of heads for a circle track Mopar guy a few years ago. He bent some valves over-reving it, and I believe if they had not been (Manley)SS, they would have busted the v. heads off and done alot more damage. On the downside, SS stems are even more prone to nicking, as I mentioned before. There's a funny story that goes with that car(and me), but I'll save that for some other time. :wink:
'Bout the bronze guides. I don't know if there is that much benefit from them from reduced friction. I think their biggest advantage is once the machine work is done to install them, you can easily punch them back out and reinstall new ones again and again. It may also be easier machining them to the tight clearances car guys like to reduce oil burning, improve vacuum seal. They used to make cast iron replacement guides. They seemed to be rather thick-walled, though, and maybe that was a problem for installers.
Author:  Bruce Johnson [ Fri Jan 02, 2004 1:11 pm ]
Post subject: 
Thanks for the info I'll be doing anouther head (4.0L) for the Gremster it all helps. A caravan north sounds good Rob, hope Matt can make it, thats three bet we can work the events page later on and turn it into formidal convoy. Bruce J.
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