Zmanco Posted February 27, 2008 Share Posted February 27, 2008 Here's my situation: L28 block recently rebuilt with flat top pistons Mild cam (Delta cams regrind .480" 284/284) 6:1 header and exhaust stock EFI intake manifold with 60 mm TB Megasquirt N42 head My thinking so far has been that to get much more power I'm going to have to begin spending some big $$$ on head work and intake manifold. My inclination has been to stop here with the L28, focus more on my driving skills on the track, and when I eventually decide I need more power, go LS1 and T56 (more bang for the buck). But... I can't run full max spark advance (35 degrees) because of the poor quench characteristics of the open chamber N42 head and high compression. I enjoy wrenching I have a hard time leaving well-enough alone So I'm wondering if maybe I should pull the head and do the following: - replace the valve seals (they could use it, but they're not a problem yet) - unshroud the valves - do some very mild porting of the intake/exhaust passages I've been watching a lot of the threads here on porting and believe I have a good idea of the basics. I have a scrap head to practice on, but don't have a flow bench. My questions to the experienced head porting guys are: 1) Does what I'm describing sound like a stage 1/stage 2 port job? 2) Roughly what kind of additional power am I likely to see? 5-10 HP? more? 3) What is your sense of how much unshrouding the valves will lower the CR? I'd like to get to the full 35 degrees of advance I see others running. (I remember a great thread where the topic of which was more important: CR or spark advance was discussed, and BRAAP made a strong case for advance over CR.) 4) Am I going to see enough of an improvement to make this worth it? Or should I stick with my original plan to work more on my driving skills? I'll stop here and wait for some feedback. TIA! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 27, 2008 Share Posted February 27, 2008 I can maybe kinda help with #3. It's been 6 or 7 years, but I think I added about 4-6 cc's to the chamber volume when I unshrouded my valves, but I also cleaned up the chambers, it wasn't just unshrouding. You can use that as a rough calculation to figure your new compression ratio. If you're looking for general advice, I'd say get a larger cam. Since you have programmable EFI you should be able to make a larger cam work for you, and I would guess that it would allow you to run the advance you want without any of the port/chamber work. If you want to do the other stuff on top of the cam great, but the cam is the fastest, easiest, and best way to get where you want to go in my opinion. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted February 27, 2008 Author Share Posted February 27, 2008 Jon, thanks, I follow your reasoning. A few follow-up questions: 1. Wouldn't a bigger cam move the torque curve higher up the RPM scale? My current cam is still good on the street, but not a lot is happening below 3k. 2. Maybe I should qualify what a "bigger cam" means. If I went with one with more lift (and of course new valve springs) but kept the same duration, then would the shape of the torque curve change much? Seems to me that it would remain about the same with just an overall increase across the rev range due to better flow at all rpms. 3. Since I'd have to pull the head anyway, wouldn't it make sense to at least unshroud the valves? Assuming my personal time is "free", there's no extra cost. It might drop the CR more than required when combined with the bigger cam, so would the extra flow offset the reduction from a slightly lower CR? I guess I'm looking to understand the trade offs of CR vs. ignition timing. I hope I'm not getting to far off into the muck with these questions. I've seen a lot of discussion about how each of these changes can improve performance, but not much about the relative benefits and tradeoffs. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted February 27, 2008 Share Posted February 27, 2008 1) Does what I'm describing sound like a stage 1/stage 2 port job? The stage of a port job and how it sound is meaningless IMO. Generally, you start with one chamber and set of ports, take starting measurements, port ad finish that, use inside snap gauges make drawings with final dimensions and work your way through the head making sure that they are all very close. 2) Roughly what kind of additional power am I likely to see? 5-10 HP? more? ! It'll depend on your cam, how good of a job you do. Port work is an art, if you can't make it blend smooth then leave it to the more experienced. 3) What is your sense of how much unshrouding the valves will lower the CR? I'd like to get to the full 35 degrees of advance I see others running. (I remember a great thread where the topic of which was more important: CR or spark advance was discussed, and BRAAP made a strong case for advance over CR.) I'm not sure why you want 35 degrees of advance, better burn will allow for peak power at lower advance settings. Unshrouding the valves will increase the chamber volume, by how much will depend on how much material you remove which is directly proportional 1:1 with chamber volume in cc. You MUST CC the head after chamber work to balance the CR on all cylinders. The result of that will be a much smoother running engine IMO especially under boost! 4) Am I going to see enough of an improvement to make this worth it? Or should I stick with my original plan to work more on my driving skills?! I'm pretty good at porting and have all the cylinder head tools, IMO it is worth it. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted February 27, 2008 Administrators Share Posted February 27, 2008 Daniel, I have found that moderate to aggressive unshrouding removes approx 2 cc per chamber. You can spend more time in the chambers performing clean up as Jon did and gain a little more volume. Just as Jon said, because you are using aftermarket EFI, a cam is going to be fastest, easiest source for altering the attitude of your engine. If you are removing the head and plan to tear it down, then by all means, unshroud the valves. No loss in doing so, only gains to be had, even for stock engine. While the head is apart, work a little on that step in the roof of the exhaust port that surrounds the exhaust valve guide, just as shown in post #15 of your DIY valve unshrouding thread. It is easiest if the valve guide is out of the way, (I just drive the guide part way out as seen in the pics in post #15). Zmanco's "Valve Unshrouding" thread Hope that helps… Paul Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted February 27, 2008 Share Posted February 27, 2008 I'm assuming that removing this material ( as shown in that post) does not measurably weaken the valve guide and/or risk a bent valve in the process? I'm getting ready to port my P90 for my SC'd street engine. I'm looking at a balance of performance and longivity while leaning towards the later. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted February 27, 2008 Administrators Share Posted February 27, 2008 I also shorten the valve guides up the roof of the port, thereby removing even more material out of the air stream. Down side is increased valve stem and valve guide wear as the guide is now shorter, and with big cams, that situation is exaggerated even further. Typically speaking, stock, the valves, guides, and seats will last in order of 200,000+ miles and still have adequate valve stem to valve guide clearance. Add a cam, shortened valve guides, you might get 60,000-100,000 miles out of the valves and guides. Keep in mind that when someone builds an engine with the bigger cam, this sort of port work, (moderately hot builds) the engine will be torn down for rebuild or even further enhancements in less than 100,000 miles, which at that time, the head will be overhauled/reconditioned as well. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 27, 2008 Share Posted February 27, 2008 Sure if you want to unshroud the valves there's really no downside to doing so, and cleaning up the chambers should also help with the pinging issue. The N heads have spark plug threads that are cut into the head where the plug itself will NEVER hit. Those should be removed, as well as all the sharp edges in the chamber. Still, if it were my motor, I'd be changing the cam too. If you're going to suffer the ill effects of a bigger cam, you might as well get the benefits too (no pinging). My street cam was similar to a stage IV Schneider and I had no trouble in stop and go traffic and driving around town. It came on at around 3500. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted February 28, 2008 Author Share Posted February 28, 2008 Thanks everyone for the feedback. What I'm hearing is that the best way for me to gain power is to go to a more aggressive cam. It sounds like just doing the mild porting/polishing won't make much difference by itself (which was my original plan). As I said up front, I have a feeling that eventually I'm going to replace the L6 with an LS1. At our altitude I think that's going to be more cost effective way to gain power vs. continuing to work the L6. (No offense to the turbo guys here, but that just isn't going to do it for me on road courses.) So now I have to decide if I spend "just a little more" on this engine, or just stay where I am until I can make the big jump. I'm just a little afraid of that slippery slope of doing "just a little". It never is Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted February 28, 2008 Administrators Share Posted February 28, 2008 Thanks everyone for the feedback. What I'm hearing is that the best way for me to gain power is to go to a more aggressive cam. It sounds like just doing the mild porting/polishing won't make much difference by itself (which was my original plan). As I said up front, I have a feeling that eventually I'm going to replace the L6 with an LS1. At our altitude I think that's going to be more cost effective way to gain power vs. continuing to work the L6. (No offense to the turbo guys here, but that just isn't going to do it for me on road courses.) So now I have to decide if I spend "just a little more" on this engine, or just stay where I am until I can make the big jump. I'm just a little afraid of that slippery slope of doing "just a little". It never is I think the point was that time invested per HP gained, the cam swap is a couple/few hour process and yields a more significant gain. The port work, if it can be done should be done regardless if you install an aftermarket cam or not. The porting will make a difference, even for a stock engine, though the gains to be had will be greater with the bigger cam as the added lift and duration the cam provides, allows the engine to breathe even deeper. If the head is going to be off and torn down, it will only cost you your time, not much money, and if you have the time, by all means carve on the head. The LS-1 will yield a significant gain in torque AND power everywhere in the the rev range, from idle to redline. Just image double the power you have now, every where in the power band. The ONLY way to do that with an the L-6 is add boost. N/A, even race prepped, wont produce the amount of torque a stock LS-1 does and that Race prepped L-6 will be not pleasant on the street, and require frequent tear downs and rebuilds, and still might not even perform to the level the stock LS-1 does. The LS-1 will be much more street friendly, the wife could use to get groceries, comfortably, and MORE POWER all the time, at any time, for 150,000+ miles... My $.02 Take care, Paul Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted February 28, 2008 Share Posted February 28, 2008 Daniel, When I installed my new cam I felt an immediate difference.. and I noticed my seat of the pants weee factor felt strong up to about 6,100 RPM.. before it would fade off around 5,400 RPM or so (turbo probably helped lol) I have not touched the port work on my P90... when I installed the new camshaft, I went ahead and changed the valve seals and springs.. why not since your in there.. Im sure Jon and Paul would recommend installing some new heavy duty valve springs while your at it.. now you can finally rev your engine wayyy up there! Hope all is well.. cant wait to see ya at the track again! Ryan Oh yeh.. with my new cam and this awesome pressure altitude.. I idle at 800 RPM and 12 in hg Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 28, 2008 Share Posted February 28, 2008 If you get a cam over about .470 lift you need valve springs to go with it to avoid coil binding the springs. A little more lift and you start running the valve retainer into the seal, so you need seals as well. There are posts regarding these things in the stickies of this forum, read them and you'll know what needs to be done and what seals to use. I ASSumed that he had already changed springs. Not a safe assumption. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted February 29, 2008 Author Share Posted February 29, 2008 Thanks again everyone for the further feedback. Just to clarify, I already have a reground cam that is spec'd at 284/.480". I've been very happy with its driveability too. I just got off the phone with Delta Cams and they have another profile they call 325R and describe as a "hot street cam". It's 250/250 at 0.050" and .475" lift. They don't have any profiles with more lift than that. This is pretty appealing to me from a cost point of view because I want to pull the head anyway to try porting, and the extra cost to do the grind and resurface rockers is only around $150. He thinks it's likely that I could use the same lash pads and could continue to use my stock springs since the lift isn't any greater than what I have in there now. As I said above, I don't want to go down that slippery slope of "just doing a little more" and find myself with another $1k or more in the engine. (If I buy a new cam with more lift, new springs, rockers, lash pads, I think I'm going to be bumping up agains $1k by the time it's all done.) But this seems like a reasonable approach that would net me more power up top, give me a chance to begin to learn to port, and still keep the engine streetable. My question to you is you think this cam is still reasonable for a car driven mostly on the street? (Remember, I have an 81-83 5 speed and 4.11 diff, so keeping the revs up is easy). Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 29, 2008 Share Posted February 29, 2008 I thought Delta had larger grinds than that. I would go bigger. Delta isn't the only grinder around either. Might try American Cams or someone else and see what they have available. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted February 29, 2008 Author Share Posted February 29, 2008 Jon, by bigger, do you mean more duration, or more lift? How much? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 29, 2008 Share Posted February 29, 2008 I had something comparable to the Schneider stage IV and that worked really well on the street. It was great for SU's, when I went to triples I wished it were a little bigger. I don't know how a stock EFI manifold will relate to my experience to be honest. My cam was .490/280, but with a fairly aggressive lobe shape as described by American Cams. A lot of it has to do with the lobe profile which is hard to determine from just the lift and duration, but just by the numbers I'd be looking for something around the specs of .500/290 or .500/300. I think duration (really its the overlap and a narrow LSA) is more important than lift in getting the car to run on pump gas without pinging. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted March 3, 2008 Author Share Posted March 3, 2008 Jon, this is the only thing I've been able to find for "American Cams": All American Cams 810 Ashmore Drive Charlotte, NC (North Carolina) 28212-6111 Phone: (704) 567-0069 It's Sunday so I can't call them, but does this look like the guys you were referring to? I can't find a website for them either. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 3, 2008 Share Posted March 3, 2008 No, the guys I'm talking about were in LA. It's been ~10 years ago since I got my cam, maybe they're no longer in business. Quote Link to comment Share on other sites More sharing options...
jdarkme Posted March 3, 2008 Share Posted March 3, 2008 There's also WebCamshafts: http://www.webcamshafts.com/ Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 4, 2008 Share Posted March 4, 2008 I checked with the guy who ordered my cam for me way back when, he isn't 100% sure that this is the same company because he thought it was American Cams too, but he thinks this might be them: http://www.americancustomcam.com/ Quote Link to comment Share on other sites More sharing options...
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