Motor is out, block has been bored, checking clearances and doing a little grinding right now for the stroker crank. 427HotRod has been a big help with suggestions along the way. I thought I would post the combo here to get feedback:

496, 10.2 CR with SRP forged pistons (8.3 DCR). Running a low rise LS6 intake for factory hood, 2" headers, 2.5" exhaust with H pipe, and GMPP alum heads (2.25/1.88 valves).

The cam I want to use is a solid FT 243/243 @ 050 with .586/.586 lift on a 110 LSA. Any ideas on how much vacuum I will get at 800-900 rpm? I want to have enough to run my headlights and brakes.

Gearing is 3.36 with a Tremec TKO500 (hope to finally get it the second week of August). Motor will need to pull smoothly from about 1500 rpm at around 50 mph. Think it will with this combo? I want good low speed response and strong pull to 6000 rpm.

Oh, and I am in the middle of painting the beast-long over due. I may not recognize it when I am done.

 

Jim is a great source of info. Your combo looks good to me, you will have plenty of vacuum for the brakes. My last motor was a 454 with a much biggger cam and the brakes and headlight worked ok. You will also have no problem pulling from 1500 rpms, mine did.

The one thing I would look at is a differant set of heads, the GM's are a good head, but in the last year or so AFR, Brodix, Canfield, Pro-Action, and a few other have heads that are simply better. Look for a small rec. port in the 305 cc range, the AFR 305's are a very nice head.

 

A warmed up 496 could use a 3" exhaust. It fits in there, just.

A 112 degree lobe centre will give you better idle vacume.

I dont know how good the exhaust port is on the GMPP heads but the factory ones are typically weak and I think they prefer more cam timing than intake, particularly with full exhaust. Get a few different recommendations on cam from dif makers.

 

Looks like it's coming along!

I think Doug already has the heads and got a good deal on them. Just for reference another Forum member recently had his worked on. They flowed like 292/201 or so .600 and he got around 330+/260+ after some port work. I think he's going to be posting before and after dyno runs here soon on his 540, so I don't want to give anything away, but I can tell you that he definitely made improvements with cam and head changes!!

Airflow is always everything on a motor, but on these big motors it's just that much more important. They are hard to feed. Even the bottom end increases when you increase it.

You'll be able to get near 600 hp out of those heads with a little work.

But you know me...I'm still voting for more cam!! That is a pretty small one for a solid flat tappet. I can tell you that the hyd roller he is using in his 540 is holding 10.5" or so and works lights and brakes fine. It's a 245/250 on 110 LSA. Plus it cruises fine with Tremec and 3.08's. You could go out to a 255/265 range and do the same. The solid roller cam I had in the 427 held 14" with a 244/244 on 110 LSA. Very streetable.
I'm still thinking that intake you're going to use presents some new challenges in cam design that we can build something special for. You're going to need all the help you can on the intake side! One of the issues you might hit with some of the aftermarket heads is that the LS-6 intake might not cover the ports. You'll be fine on the Edelbrock GM's, but consider doing some serious port work. There's a guy in Dallas doing very nice work and very reasonably priced we can turn you on to.

I know you already have the 2.5" pipes, but some day, 3" needs to be in the plan. Make sure you use the best muffler you can. Looks like the Dynomax Ultraflows are doing pretty well these days.

Stick with 2" headers and you'll be fine. 2 1/8" would be OK, but 2" will work fine for your deal.

Looks like we have another "Monster Vette" in the making. And a sneaky stock looking one at that!


JIM

 

Ya, for sure get those heads ported. My last 454 had the Edelbrock ovals on it and they flowed in the low 280's before and 320 after being ported. The same motor with a Victor Jr, Holley 1000, 10.5 to 1 and a solid roller (255 / 262 at .050, .652 on a 112 LSA) went 123.6 mph its only trip to a 1/4 mile track. With a 1/2. wood spacer it made right at 500 rwhp.

That cam was about as big as you can go in a 454 and still have everything work ok, headlights were a little lazy, but still worked.

I agree with Jim, a bigger cam would be a good idea, particulalry when you consider the tq. multiplicqtion of the Tremec.

It is going to be a great motor, and I think the only 496 on the forum ?

 

As usual, thanks for the thoughtful feedback. The heads were a great deal (less than $1500 brand new, fully assembled, delivered to my door). If I were putting the motor in a different car, say a Chevelle, I would be all over the AFR's and a solid roller. As it is, I think I will be traction limited and will likely start breaking parts in the rear with bigger tires. I am learning that unless you have major resources, these cars are full of compromises when searching for more power, but I wouldn't have it any other way.

My friend and I checked some clearances tonight. We have pistons hung on the four corners, and have one spot so far that hits. Here is my concern. We checked the rod bearing diameter on the crank and it is coming in a little light. This is a new Scat 4340 stroker crank. Getting averages of 2.189 instead of 2.200. This gives me a clearance of .031. That is on the upper end of the acceptable range. The mains come in at .025. I have left an email with the outfit that sold me the crank. Should I fool with undersized bearings? I have a high volume pump, 6 quart LS7 pan and will run synthetic. What is the concensus?

 

Not following the math Doug....

A std rod would be 2.200 as you wrote. If you have 2.189 then that is .011 undersize....that should give mucho clearance issues unless you have .010 undersize bearings?

Any chance that crank is a "second" and has been turned undersize? No big deal if it has really.....just you need to know what you have. I find that the SCAT stuff is generally cut to the high side of specs on cranks and you end up a little tight. Mine was .0024 on rods and .0022 on mains at first. I left rods alone and they always look perfect even after my abuse. I opened main clearance up to around .003 or so for a little insurance. No problem with oil pressure...stays pegged on 80+ all the time even in TX heat. I'm using a Melling HV pump with a couple of extra shims under spring.

I'm assuming you mean you are getting .0025 on mains and .0031 on rods? Don't forget that extra "0".....gets me all confused!

What are you using to measure inside diameter of rod bearing with? Do you have a bore mike? Snap gauges?

If it all works out to be .0031 and .0025..don't worry about it. It will be fine for what you are doing. General rule of thumb is .001 per inch of bearing diameter. So that is .0022 on rods and .0027 on mains. Anything under .0035 really won't cause any issues. A little loose is better than a little tight.

The .001 bearings will put you in sticker shock..they are like $17-$18 each on rods!!

How's deck height looking? You can use a feeler gauge and a straight edge if you don't have mic's and get pretty close. Just measure in the middle above the pin bore on the side of piston to deck surface.


JIM

 

Jim, you are correct on the missing "0". It is .0031 and .0025. I realized it this am brushing my teeth! I don't know the name of the gauge we used, but it used a dial indicator, with 7 or 8 different lengths that screwed into the end, and had a three point support to center it inside the big end of the rod. My friend across the street has all the good mics, and tools and it was his stuff we were using.

As far as deck height. We got .010 on both sides on the front of the block, and .007 on both sides on the rear of the block. The plan is to clearance everything, then hot tank, and zero deck the block.

 

Sounds good.....you'll be fine. Just use HV pump for insurance or even the stock pump with a high pressure spring that comes with it. You don't have a huge pan there, but it is a good one overall. Don't want to suck it dry. Make sure you use the windage tray too and make sure that you bend it up slightly at the front of it as needed so it doesn't rest against pan at the front of sump. helps drain back.


JIM

 

Hi Doug,
I am the person Jim is referring to about the GMPP heads. I do plan to do a large write-up on the forum soon about all of the mods I have made and the power gains after each mod. I would encourage you to go for a set of AFR 335's if you haven't purchased your heads yet. You are going to be dissapointed with the flow results of the GMPP heads. They can be made to flow, but you will have to spend some money to get them to where they should be. I will post before and after flow numbers when I do the write up.

Jim is giving you very good advice, so continue to listen closely. He has been a huge help to me and others on this forum in reaching their power goals. It is good that you checked the Deck Height of the block. Please make sure to check it again when it gets back from the machine shop (regardless of how much you trust them). My block was supposed to be decked to .005, but that didn't happen, so now I am running special high dollar gaskets to get decent quench.