Marks69BB

Ok guys (and gals, if any care)! Just got off the phone with a guy at comp cams who told me that, due to my PB and the other typical vette vacuum goodies, I will be limited to the hydraulic 274XE cam since any of the more aggressive solids or roller cams will not give me enough vacuum for my brakes and won't be able to handle my AC when I get it working. With my setup, he acted like I had to compromise either on power or on my power accessaries. Is this :bs or what??? Notice in my sig what is already there. I was thinking of the 288AR if I decide to go roller but he said I would need much higher compression and rear gears. I'm planning on going to 3.36s or 3.55s but he said I would need 4.11s or bigger to run that cam. My current cam is a torque monster better suited for RVs and towtrucks, not for high end HP. Did I get the wrong tech or is he right? I am so :confused: !!! I hear about these people running high hp/torque at the rear wheels on 92 pumpgas and can't seem to understand how the hell they are doing it! :cry

Flareside

Well, I'm building an engine like that, but it has to be planned from the start. For a cam like the 288, you really need around 10:1 or better compression. Easy with pump gas and aluminum heads, not so easy with an iron head, low-medium compression crate :nonod:

It sounds to me like Comp is right. The 288 roller together with a Muncie and 3:08 gears is a bit of a mismatch. My first choice would be a transmission with a steeper first gear so you can keep the revs up and still cruise on the highway, and second would be a 3:5-3.7ish rear axle. 4:11's won't work too well on the highway with an M20.

Flareside

Oh one more thing: I think Jim (427Hotrod) ran that 288AR cam in his 427, so you should probably drop him a line.
http://forums.corvetteforum.com/zerothread?id=167880


[Modified by Flareside, 1:37 PM 1/25/2002]

427Hotrod

I ran the 288AR in my 427and loved it. It held approx. 13-14" of vacuum with a Weiand Team G single plane on ported oval port heads and a 1050 Dominator.

It's a pretty healthy cam for sure, but not super radical. I was using 3.36 gears but I had a 5 speed with a 3.27 first gear. As far as driveability goes it was the best one I ever ran in that motor in 20 years. And I ran a bunch of them through there! It would idle down to 800-900 pretty comfortably and you could lug it down to 1000-1200 rpm in high gear without it bucking or surging any.

On the chassis Dyno it made 423 RWHP at 5800 rpm capped up in total street trim. It also went over 7000 rpm on the dyno and was still making 417 rwhp. The rpm spread between peak torque and HP was very nice. It was great that it didn't fall off on the top end. I had 11.2 compression in it and approx. 195 psi cranking compression.

How much compression does that motor really have? 9.5-10.0? Since you're running what looks like an LS-6 crate motor with rectangular port heads and 3.08 gears you are already used to that kind of driveability. It's not a bear down low but starts moving pretty good up top.

I wouldn't be scared of the 288AR at all , especially if you can get compression above 10.0 and maybe stick a little more gear in it.

I ran very low 11's with that cam at anytrack I went to capped up with10X26 slicks.

A solid flat tappet cam that I had great luck with is still sold by Jegs. It's a Crane. Their number is 270-134691. It has .580/600 lift on 110 LSA and an adv. duration of 290/300. It is a little on the hairy side and not as smooth or as powerful as the 288 AR but it is strong. It seems like it would hold 11" or so vacuum. The 270-134761 with 600/620 and 310/320 on 110 LSA was absolutely the best flat tappet I ever used as far as power goes in a streetable setup. It pulls like a bear on the top end, but I don't think it will like your power accessories. The 270-134781 with .567/590 with 314/324 on 108 LSA sounded real healthy but it was a pig in my car compared to the others. I used it to kill some bottom end and it sure did. A little too much duration that never quite got it together on the top end either.

There is also a Comp flat tappet 294-11-604S (Jegs) that I ran and it is very similar in the way it acts to the .580/605 Crane. It has .579/.605 294* adv duration. Not quite as strong up top but still a great cam. Very driveable.


Whatever you do, make sure you get some good springs etc. I found over the years that it took annual spring replacement to keep any of these flat tappet dudes in top form. I drive 'em a lot. Never really run bad or miss, just mysteriously lose some mph at the track. New springs.... right back to par!

By contrast, I ran a set of ISKY NASCAR (only $130 or so) springs on it with a .725 lift roller cam for a year or so on the street and then used +.050 keepers to help lower the pressure for the 288AR and ran it for another 3.5 years on the same springs and never had a problem. The action of the roller is much smoother and was much easier on things.

Hope all of this helps some. At least gives you some first hand comparisons.


Jim

inqbus383

You can run as many accessories as you want, you may have to just turn up the idle a bit. Make sure your ac idle solanoid is working, it raises the idle when ac comes on. If worst comes to worse, you could run a vacuum pump, or convert the power brakes to use the power steering pump, there are several threads floating around about this.

Marks69BB

427Hotrod - The engine has open-chambered heads with CR probably 8.75-9 which I understand may be increased by milling them. Is this correct? If I have them milled, will I have to use octane additives to run the higher compression? Will the 288AR support my power brakes? Questions; always more questions. :jester

427Hotrod

Is that what you have... a LS-6 crate motor? Many of them had 11.0 comp closed chamber pistons and then they had 118cc open chamber heads installed. You're probably right, maybe 9-9.25 tops for real depending on gaskets etc.

Let me know what pistons are in there and we can figure out what you need to do. You can whack those heads and use some .020 or so head gaskets to get compression up around 10-10.5. that would be a good safe range.

You can run 10-10.5 with iron heads on pump gas without additives pretty easy. You just have to keep overheating down and tailor the advance curve properly. The addition of the larger cam and a little more comp. will add up to much more power than a little cam /less comp. and still maintain street manners on pump gas.

Jim

Marks69BB

427Hotrod - Yes, I have the open-chambered 118cc rect port heads that are supposed to flow 325ccs. The previous owner told me he was told there are large dome TRW pistons in there but I haven't had the heads off yet to verify it. As for cooling, I have an aftermarket AL rad that never lets the temp past 210, and that's with no seals around the rad, shroud, or the hood. I've got the seals and am waiting to put them on when I pull the rad for the cam install. Never had the AC hooked up yet so not sure what impact it would have on idle or temp. Any more comments? Keep em comin! :cheers:

427Hotrod

I'm in favor of pulling the heads and looking at all that porting and polishing and checking the actual pistons and deck height and chamber cc.

It seems like the old 11.0 compression closed chamber pistons have around 30 cc domes. If you actually have a real 118cc chamber (most of these heads are pretty close) and I assume the pistons are down inthe hole .020 and you have a .040 gasket in it you would have around 10.1 to 1 compression. That would be just about perfect. The real issue is what pistons are in there. Did they give you any engine building pictures? During all that balancing/blueprinting did the original owner lower the compression by changing pistons? The factory pistons are TRWs which is good. There are some small dome 454 pistons with about a 16cc dome that would knock you back down to 9.0 range. That's a big difference and not good.

By the time you get so far into it you are doing a cam change, it's really not that much harder to pull the heads or just pull the engine to check it all out and make sure.

Jim

69ttop502

Hey guys jumped on this thread a little late but this is some great reading. Great info 427 Hot rod. Mark and I have compared notes as we are contemplating similar buildups. My question is this. I was looking at a book called Crate engine buyers guide and LIngenfelter has a whole section where he runs a few different engines with the 288 solid roller and they all have 9.2 to 1 compression and they all make at least 615 horsepower. My question is this, since the Lingenfelter motors were all 496's or 502's can you get away with less compression for a given cam with more displacement. Incidentally all thes combos also featured the ported cast iron rectangle port heads.

427Hotrod

The bigger cubes, whether it's by stroking or boring in those two cases will automatically add some major power. A 502 is typically 20-30 hp stronger all things being equal due to the better breathing of the large bore.

But the relationship of the cam and compression ratio is critical to make it a fun responsive to drive motor. Dyno testing is great but there is definitely a "seat of the pants" dyno that has to be satisfied or you will never be happy with just dyno numbers.

Getting 600 hp out of one of these is pretty easy. The difference between 9 and 10 to 1 compression is probably only 15-20 hp. Percentage change seems to diminish as you get higher, but it would be a shame to me to assemble it with 9.0 and leave all that on the table when it isn't necessary. Plus compression equals throttle response and driveability.

A 9.2 one is going to be a nice reliable strong motor,but a 10.0 one will be just as reliable and run much better.

Lingenfelter has been a proponent of that cam for years, and after using I can see why. It does just about everything pretty well on the street. I'm sure the newer Xtreme Energy versions are even better. The GM iron rectangular ports really start to come alive on a 454 and a 496/502 for sure if you are going to rev it to 6000-6500 rpm. They need rpm to work. Otherwise you might as well put together some real nice oval ports and turn on strong down low.

mountainmotor

Mark,
More than likely to make the power you are looking for the cam needed will require the intake valve pocket on the piston worked for axial and radial clearance depending on LCA and the centerline the intake lobe is set on when installed.
Just makes sense to get the motor down to see what you have and make changes as needed.Compression = torque which will help offset some of the drivability problems associated with a somewhat small cubic inch"for these times"motor such as what you have and allow you to run enough duration to get the job done.

More than one member here has installed a power brake set up from a GM truck on their cars as mentioned previously.

Marks69BB

Mountainmotor - Thanks for the info! As a sidenote, since the 454 Bowtie block I have has siamesed cylinders, another forum member told me I can bore and stroke it up to a 540 if I want too. Is this true and if so, should I consider doing that to get the power and street manors I'm looking for?

Marks69BB

[Modified by Marks69BB, 11:56 AM 1/28/2002]

Flareside

Uh oh, another 454 bites the dust :lol: Just think, you'll lighten that block by around 50 lbs. with all that metal removed! I'm building a 540 right now because that's the easy path to getting big power and good street manors. Let me know if you need more info.

Are you sure it's a bowtie block? I didn't think GM sold crates with the bowtie. (Maybe yours wasn't a crate?)

-Joe




[Modified by Flareside, 11:20 AM 1/28/2002]

Marks69BB

Joe - Numbers don't lie: Casting #10051107 = Gen IV 454 Bowtie CNC prep 4 bolt mains. I'd prefer not to bore this block until I have to and can't afford to plop a 540 in there. :nonod: Heck, I'm probably looking at a couple of grand in cam kit plus head work to pull this off! What cam are you going with and would it be different for me since you are going with EFI vs a carb?


[Modified by Marks69BB, 11:33 AM 1/28/2002]

Flareside

Sounds like you've got a great block there, Mark! Lots of options in the future. Are you planning to take the motor apart? I probably wouldn't go the 540 route if I were you, since you already have a decent 4" crank and set of rods (540's use longer rods). You can make the same peak HP with the 509, they just seem to give up around 40-50 ft. lbs. of torque at lower rpms. Not really a big deal with street tires. A bore job and a set of pistons will get you to 509 relatively cheaply. See how easy I spend your money :lol: :lol:

-Joe