Jim, I'm curious about your .0045 cylinder wall clearance. Isn't that bigger than the SRP spec? The literature I have says .0025 to .003, but that seems tight to me for a forged piston.

The cylinder overfilling that you mentioned above is very interesting to me, because most of the stuff I've read makes it seem like you can always increase compression when you push out the intake closing point. Apparently, it's not quite that simple. Great info!

-Joe

 

Lasse, in my opinion the extra $700 for a hydrualic roller is not money well spent. If you desire the best bang for your horsepower buck, use a solid flat tappet design. They'll make nearly all the power of an HR without using stupidly heavy valvesprings to get to 6500. Jsut dont make any sense to me. Solid roller, sure there you'll pick up 10% over a solid, and 15% over a good hydraulic.

Good solid grind, comfortable ramp speeds, great longevity, only requiring 120 seat and 320 open spring pressure = Crane F304-2. 238/248@0.050, 304/314 advertised ( not real agressive ramps), .544/.567 lift. Great all around cam. Its ground on a 114 which might be a bit wide for your low compression, assuming you build it at 9.5:1. But it does work in a 9.5:1. BTDT. The same cam in a 108 lsa ( more suited to your compression) is Crane part number 13F0001. It will lope noticeably however, and it take it a bit to "clean up", around 1800 rpm or so. Although I have not run one, the slightly shorter duration and tigher LSA of the COMP 282S would like your combination better. Tighenting the LSA closes the intake sooner, shortening duration closes the intake sooner. Both serve to keep your cylinder pressure high. If detonation is a problem, then the wide 114 lsa of the Crane will be best.

In hydraulics, I really like Ultradyne grinds. www.ultradyne.com The 280/288 will work excellent. You buy them direct, and that might pose a problem for you. Looking at the Comp line you'll be in the XE 284 I should think. Nice cam, nice idle, and not too big.

The trouble with your rect port heads is low rpm velocity. Dont make it worse by putting a too big cam in there. A moderate cam will keep the velocity up and driveability will be enhanced. It will match your 9.5:1 compression well too.

I or close friends have used all the cams I mentioned.


[Modified by 427TRI, 1:38 PM 6/12/2002]

 

I don't remember off hand what SRP spec'd, but I know folks routinely set them at .0025-.003 or so. I felt considering my HP goals that .0045 was tight enough. I knew it might get a little "pounding" once in awhile so looser is better than tight.

There are many things that affect cylinder pressure under operating conditions. Static is one thing, and the dynamic number that is calculated is a variable to my way of thinking. Definitely a factor, but once you start looking at intake velocities, resonance and tuning frequencies of the entire intake tract there is a point where cylinder filling finally maximizes. Hopefully it is as close to 100% volumetric effieciency as you can get. Wishful thinking anyway!

If, when the cylinder finally fills as much as it's going to, the cylinder pressure is below the detonation threshold, all is good. But if, as the RPM climbs and the cylinder fills almost completely due to the "ram" effect or velocity of the fuel mixture (much more so than at lower rpms) and you get above that threshold of the fuels quality, you got troubles!

If the RPM that this happens at is above what you rev to, then it's no problem, other than maximum power can't be produced.

The goal is to get the cylinder as full as possible, as early as possible in the rpm range and not get into detonation. A big cam naturally bleeds cylinder pressure at low rpm since rpm isn't high enough to out run the leak. Of course this hurts driveability and low rpm power. The big cam also loses pressure at high rpm due to the long overlap and it will keep you out of trouble in most cases. You just have to be careful.

Think about "why" the peak tq range of the big cam is higher in the band. It's because at that rpm, maximum cylinder filling (in relation to all the engines other physical features. Rod length, stroke etc.) has finally occurred. Smaller cams fill the cylinder and trap it in at a lower rpm, but of course choke it up on the top end. The trick to making HP is to make TQ at a higher rpm and not have it fall off too quickly. You just have to decide what RPM range you want to deal in.

Same idea of smaller heads. The higher velocity fills the cylinders at a lower rpm (higher cylinder pressure= more power at that rpm-). Great until they become a restriction. As long as your peak rpm is below that point you are perfect. That's why oval ports are "low rpm" monsters. They fill the cylinder at lower rpm. Big heads don't hit that point until higher in the range. But they keep filling longer without starting to choke it. Thus... higher TQ at higher rpm that equals higher HP.

Think of cams in the same fashion. Thats why the 'combo" is so important. The best runners have a cam, head and intake/exhaust that all combine to peak power in the same range.

There are other tricks to help out. MSD units typically retard 1* per 1000 rpm. That help keep you out of trouble at the top end too.

Then of course there is always the switch on a set of dual points. You run one set of points in normal driving, then throw the switch to bring in the second set at high rpm under load. The increased dwell, retards the timing. You just adjust the second set of points to give you the total timing you need in high gear. Old Grumpy Jenkins trick.

I used this trick years ago on a 68 Nova Pro Street big block. Big cam, heads , compression etc. Plus tunnel ram and 660 cfm center squirters! It needed 55* timing to drive smoothly on the street. Ran great, but of course some of it has to go as RPM climbs. I'd launch (14x32's- wheels in the air!) grab second (wheels in the air!) hit third and immediately throw the "poor mans retard" switch. That sucker would change sound and just lay back and pull like an animal through 4th. It was beautiful. After the pass, put switch back to "cruise mode".

Jim

 

Lasse,

I really think that if you want a smoother idle and very docile personality from your car, you need to go with a solid roller cam. I spoke to Crane and they had some very good recommendations for my 12:1 motor. Not too different from the 288 Comp Cam roller that GDaina has. Just a little more duration to bleed off some of my ultra high compression. I would give them an email and ask for their advice.

That said, I can't tell you how pleased I have been lately with my factory L88 now that I re timed my L88 solid cam to straight up specs. No it doesn't like to idle below about 1200, but the throttle response is now crisp and the engine is very willing to run in the upper ranges. I kind of have you pegged for someone that really likes that high strung personality of a high revving BB. The 91 (R+M)/2 octane I am using is fine around town now that I add 32oz of Real Lead 130 to each tank. 1.8 ounces per gallon is supposed to raise the actual octane to 96. By buying 2 cases (24 32oz bottles) it costs me less than $9.00 per bottle for each tank. I am happy as can be. For racing or dyno test, I will use 114 leaded. But for having fun around town and on the highway, I am not getting any ping, let alone knock whatsoever. Surely much of this is due to the large overlap of the factory cam, cold air package, and aluminum heads with clean chambers.

If you really want the dual personality of a mild around town car and a high revving fire breather, the roller is about the only way to go, but I can honestly say that I am no longer in a hurry to change my solid factory cam. If you ask Crane, I'm sure they would have an even better aftermarket solid flat tappet cam than my old factory cam design that would save you large Kroner and make you one happy Swede!

Chuck

 

I really think that if you want a smoother idle and very docile personality from your car, you need to go with a solid roller cam.

WHAT??? I'm just a visitor here and dont wish to upset any regulars, but this statement is spurious at best. Show me a solid roller that will work good in a 9.5:1 468?? 510, sure 540 sure, but not 468...

Sir, order the Crane F304-2 solid cam. Set the lash 2 thou loose. You'll have a smooth idle, good low end power ( due to the wide centers), and it'll take your 468 past 6500 if you desire to.

Solid rollers are for max effort engines, not street motors. Yeah, I know a whole bunch of guys that run them, and its just my opinion. Its a boatload of cash for something you're not competing with. FWIW, Crane guessed I would gain "up to 50 hp over 5000 rpm" by going to their SR238 solid roller from the F304-2. 50 ponies is a good increase, but for $700?? Naw, I had a custom grind done that will cover most of that differential, ex the 25 hp of the roller lifter. I dont have a race car. Just a street/show/fun car.

Where talking about a nice 468 here, not a drag motor...... M21/3.55 aint no drag combo.....

I GUARANTEE you'll be pleased with the F304-2. Its is nothing more than an LS6 cam opened up to a dual pattern. It will pull from 3000-6500, idle at 900 rpm and 15" Hg. In fact Lasse, for $105 US you can get the LS6 camshaft w/lifters!!! from gmpartsdirect.com, P/N 12364057 which has to be one of the best deals around. Either of these cams would MUCH rather prefer 10-10.5:1 compression btw. A good friend used the F304 in a 9.5:1 454 and ran very good ET's in an A body.

Dont get crazy with your cam. Those rect ports run best from 3500-7500. If your rpm band is lower you WILL LOSE pull by putting a too big cam in there..Plus, if you get a set of alum ovals at 110cc , bumping your compression to 10.5:1, you can use the same cam.....

I have an L88 cam on my shelf. $120 from gmparts. Guess what, my 10.75:1 aint enough to run the darn thing. I'm dropping to 246/258 @ 0.050 on a tigher 110 lsa. ( and much quicker ramps as advertised is in the 288/300 range) . Cylinder pressure issue

Lastly, I would use the Speed Pro forged slugs and , unless you can't afford to lose the numbers off the front engine pad ( numbers matching), deck the block to get those slugs no more than .005 in the hole. This should get you up in the 10:1 range. Both those solid cams will please you. GUARANTEED. The F304-2 will feel almost docile until you nail it and the tach crosses 3200. HANG ON TIGHT! Its is not a max effort cam. Easy on springs. I've logged over 30,000 miles on one. Frequently taking it over 7000 ( smaller motor). And I mean frequently. ;)

Much fun, but it wont idle like a race car.




[Modified by 427TRI, 9:03 AM 6/13/2002]

 

Interesting post, counterpoint....idle with the Comp Cams 288 is 800-850, vacuum is 14". The 288 is NOT an all out race cam, but is designed to be used on the streets, is cut from the same stock as flat tappet cams, does not require the bronze gear, and spring pressure is tolerable, 460 # open.

Power range is from idle to 7000, response is on demand.

Think this cam gives more that 50 hp over stock, maybe close to 100. Anyway, h.p. cost $$$$$. Another thing, the stock L-89 gave me 15 mpg cruising at 70mph, with the heaviest springs in the secondaries, now the mileage is 13.5 with the lightest springs and bigger motor. Will have to see what it is cruising at 70 w/heaviest secondary springs, but so far, no complaints on performance.

Oh, one more thing...was cruising through the parkway, speedlimit is 30mph, was obeying the limit, had no choice, was behind a dude who was poking along, and time to exit the park, still in fifth gear, and going up a steep hill, yep, still at 30mph, rpm is 1000, not a bog, no bucking, going up the hill, half way up the hill, I nailed it so I can catch the green light, did not downshift, still in 5th, the 533 cubes took off like a bat out of purgatory. No miss, hiss, no bog, just took off. Torque and the cam, what a wonderful mix. BTW, this cam is so streetable, it's unbelievable.

 

427TRI,

I thought I had made it pretty plain that a solid flat tappet cam can give very good performance from idle to 6500+. I encouraged this choice suggesting that a good cam grinder like Crane could dial one in for Lasse if given all the particulars. That this would end up being an even better cam than my L88 and save a lot of money compared to a roller setup.

GDaina's post, as much as I ever hate to compliment him ;) , makes my case regarding the extremely docile nature of a street solid roller. They really can be the best of both worlds.

I guess I just don't understand what was intended by calling my statement spurious. There was nothing false or phony about it.

Chuck

 

I am running the Comp xr280r solid roller .646 / .653 242 and 248 at .050 in a 454 +.030. I can't call the cam unstreetable, especialy when you consider the cam Lasse used to run.

How streetable is a 33 year old car in the first place. My little Saturn has over 60,000 miles on it and have poped the hood to change oil only. I work on my Vette at least once every two weeks or so.

Chuck: Glad to see the L-88 is running better. I got some of the lead stuff, glad you are having good luck with it. I knew your motor would be the test for that stuff. :chevy

 

awwwwwww Chuckster....now see what ya done? Ya made me drop a tear in my beer.

 

Chuck:
Just out of curiousity what are the specs on an L88 cam?

 

Sir, 264, 269 @.050, seat is very wide 320-ish or so, 560/580 on a 112 lsa. BTW the cam is IDEAL for the old L88 o74 head castings assuming you squeeze it greater than 11.5:1. Those old heads love wide durations and moderate lift.