The transmission in question is a 700R4 out of a wrecked '88 IROC 5.7L
My 'vette is a 1980 model with L48 engine. It's supposed to have a TH-350 transmission that has a lock-up converter, but I've never noticed any converter lock-up, so maybe it was disconnected at some point before I got my hands on it. If it has the wiring for a lock-up converter, maybe I can use it with the new transmission?

Scotty

 

Hi Scotty, enjoyed this post a lot.

Im from the era you speak, I don’t know if I ever heard of a Flat tapped camshaft going wrong in the 1960’s and 1970’s . it was done all the time by less than experts .

The past decades tho, seems like new flat tapped cam install and break in is a 50-50 gamble at best and then many don’t survive for years of service, like the ones 50 years ago.

So …what do you think is the cause for all this bad luck or failures . I’m guessing poor quality steel for cams and lifters.

 

Its a combination of that, more aggressive cam lobes made to mimic the better performing roller lobes as much as possible (violates the 47% rule the older single pattern cams all followed) and different oil formulations sometimes play a role. Also back in the 60s I'd venture to guess stiffer springs were less common, now they often come on aftermarket heads and if a person doesnt do their homework they can have issues there as well.
Flat tappet cams and lifters are just classic car parts now for hobby markets, lots of these types of parts have taken a hit on quality, distributor points for example, are not as good as they used to be. Mainly because better performing options are available now and less people actually rely on them.

 

Good evening Scotty,
I also have a 1980 Corvette- 4 speed with an L48 350 with about 41,800 miles. I wanted something with a little more get up and go, so I changed the following:
Edelbrock E Street 64cc heads, Edelbrock 2101 intake manifold, Avs 2 Edelbrock Carb (650), Retrofit roller Comp Cam Xr276, Flowtech Headers into 2.5 inch straight duals with H-pipe. The car runs pretty good and am about appx. 380 HP. As far as your question on Octane you are going to have to bump it up to 89 minimum.

 

Wait a minute, wait a minute! If a cam with an advertised duration of .272 @ .004" were measured at .006". it would have LESS advertised duration. The lift @ .050" is 216, and that is apples-to-apples comparable to other cams with duration measured @ .050". which makes me think the 272H10 is just a scosh smaller in duration than the good ole 268 High Energy cam, which has a duration @ .050" of 218. Other than that, same lift, same LSA, so the cam should work very similarly to the 268 High Energy. (The Energizers and the High Energy cams came out around the same time, and were direct competitors to each other) What do you guys think a Comp Cams 268 High Energy cam would do in my car? (Just to get an idea what a similar cam like the 272H10 would do) It weighs in at about 3,150 lbs. with a full tank of gas, and has a 3.07:1 diff gear, but with the lower 1st gear ratio on the 700R4 tranny, my final drive in first gear will be 9.4:1. Not the "ideal" 10:1, but pretty close. Better than the 7.74:1 with the TH-350 tranny, anyway. Stall speed around 2200 rpm, Will I have plenty of power and throttle response taking off from a stoplight?

Scotty

Scotty

 

 

Just throwing that out there. High energy flat tappet cam info. XE268

 

I have a broken in 268 high energy cam and lifters with like 2,000 miles on them im looking to get $150 for if your interested. they came in the shortblock I bought and tore down to built the engine for my car. I went with the voodoo262/268 cam at the time (which I also still have with matching lifters)

 

thats the "extreme energy" 268 cam... different than the old single pattern retro 218/218 -.468/.468 grind... the High Energy 268h (for hydraulic) is a lot safer to run without risk of wiping the cam. The XE268 is a lot like the voodoo 268 cam. both break the 47% rule for aggressive lobe angles but have better performance.

 

Yes, I had this one.(XE268) But I assure you it is easy to wipe a lobe. I have now switched to the XR276hr, same sounding note but faster reviving, better vacuum, quicker take off, but a little on the pricey side.

 

I went from the lunati flat tappet to the xr270hr myself for the same reasons.I did the upgrade for $550 which I didnt think was bad but the retro roller lifters I used have been on backorder at rock auto for a while.

 

I think that is also a good cam, and you got a pretty good deal on it. I paid a little closer to $900 for cam and lifters not including the roller rockers and the new hardened push rods which had to be replaced, since I needed to get shorter ones.

 

Concerning the "47.5% rule", the 268H comes in with 218 / .454" = 48.0%, while the 272H10 comes in at 216 / .454" = 47.6% (Juuuuust barely over the 47.5% rule) The stock "929" camshaft comes in at 194 / .390" = 49.7% (int.) and 204 / .410" = 49.8% (ex.) just to give some perspective. You can also subtract the @ .050" duration figure from the advertised duration figure, and the resulting difference is known as "hydraulic intensity" or something like that, and can be a good indicator of how extreme a cam lobe is.

Now, the stock "929" cam has an LSA of 112 and an ICL of 108, meaning it has 4* of advance ground in. If a cam that is too big can be crutched by advancing it, can a cam that is too small be crutched by retarding it? Suppose I get the heads and intake manifold off, inspect the lifters, and they are fine. I could retard the camshaft 4* and get a little more top end out of it, at the expense of some low end torque, of which there should be plenty to spare? I think it will be an interesting experiment. We'll see how this "Big head, small cam theory" shakes out in practice. I'm hopeful. Have you ever looked at an LS engine and wondered how they make such a wide, flat torque curve, and then look at the head flow numbers and the size of the cam? Big head, small cam. (Or, could this be my subconscious excuse for being a lazy cheapskate?)

Here's the thing: Not only am I scared of breaking in a new camshaft, I don't want to over-cam this engine. I only like high-revving engines with a manual transmission. With an automatic, I want it to drive like a truck. I'd like to keep the power range characteristics close to where it is now, just more. Anyway, thanks for all the help and advice, see ya!

Scotty

 

I'm using this theory currently. AFR 180 heads, 55.5cc heads angle milled for 10.6 CR with D dish pistons, 1.6 rr with .549" lift on a 270/270 advertised 219/219@ .050" cam on a 108 LSA.

Goes like h**l. About 440 HP. Revs freely to 6300 RPM. This is with a TH350 with 3000 stall and a shift kit. Don't miss it not being a manual trans. Shifts hard and fast at WOT.
If I wasn't @ 4000 ft to 8500ft DA I'd be using a 195cc AFR for even more flow. The cam would still be relatively short with a narrow LSA and lots of lift.

 

I am about to find out the difference between 180 heads and ported "195" heads on my engine. I am really hoping it doesnt cost me low end torque. The dyno results ive seen on engine masters were promising in supporting my decision but ive been told dynos dont show part throttle driving conditions very well. I also have 10:1 compression and 1.6 RRs but with the 270/276 cam and flat tops.

 

interesting... I didnt do the math myself, I made a foolish assumption thinking the "High energy" 268 cam being such an ancient grind would be less aggressive than the newer dual pattern "Xtreme Energy" version

 

How much had to get milled off the heads to get to 55.5cc chambers? Did you just go with an extra thick intake gasket or did you have to do more to get the intake to fit?

Adam

 

Theres a couple of things that I think makes comparing SBC to LS intake port volumes a bit misleading:

1. Port velocity is largely driven by airflow per the min and average cross sectional area. Because of the reduced valve angles in LS heads and their raised and straighter Ports they can often flow more air at the same avg CSAs vs 23 deg heads.
2. The intake port centerline lengths tend to be a bit longer which means that some of that volume that they’re getting is from the LENGTH of the port which doesn’t increase the CSA and doesn’t result in air speed reductions. (If you have a 5” intake port length with a volume of 195cc and a 6” intake port centerline with a volume of 195cc, the 6” length port will have a smaller cross sectional area and if they flow the same, the one with the 6” port length will be faster and have less issues with low speed torque.

I do think a big port with a small but aggressive cam and especially with a high speed header is superior, but I felt like the one Engine master episode just stared with a way, WAY too small intake port for the CID and RPM and worked their way through a WAY too small head, then a smallish head and a too big head.

SBC head lines also tend to get more expensive as you go up in port size and often the bigger heads flow more per inch of cross-sectional area - so you’re testing a VERY good big head against a pretty decent small head and that helps make the case for buying the big head but isn’t really a valid way to test for only differences in intake port volume on a given CID engine at a particular RPM.


Adam

 

I just told AFR I wanted 56cc chambers. They missed slightly. By the time I polished the chambers it probably was 56 cc. It required angle milling. I don’t recall how much material. No problems with intake gasket or intake geometry at all. The intake just sat closer to the china wall. Very close. That may be the limitation ultimately without doing some milling work.

I also used “the right stuff” on the intake just in case. Hasn’t failed me yet.