^That's a great point. Any of the suggested camshafts would prefer the added compression, so if you're having the heads ported, might as well start with with the smaller chamber.

 

Thanks for getting back to me with more info. @68Formula is spot on as usual. I like the SUM-8707R1 here as well. It will have a nice steady lope but will be easy to tune and pretty easy to get along with. It'll have a wide powerband and pull strongly from 3,000 on out to 7,000+ with the same spring packs I mentioned previously. With the 3.07 gears, it might have a bit of character in parking lots or stop light to stop light traffic. However, your plan of 3.54 gears would cure that.

@Forcefed86 brings up some great points about going with 706 heads. Total Engine Airlfow (TEA) could optimize the 706 heads. They have a stage 1 and stage 2 option for the 706 heads. You would need to supply them with the cores.

This will be a fun and unique combo that will surprise some folks

 

Guess i should sell my die grinders and porting tools....... I usually do my own porting/bowl blending, chamber polishing on everything... except rotary motors..... I wont do that again. that is .020" from turning 280hp to 0 way too easily, especially with a can or two of liquid mechanic

I plan on running the stock 243/799 heads on the LS4 because they will have low miles (most LS4 motors are overlooked by RWD vehicle guys and have nearly no miles on them because the 4T65 transmission sucks and blows up and most people scrap the car with low miles) the heads may get titanium valves from the LS6 if I need to dive into them a bit more... the motor hasnt been purchased yet because I am waiting for one locally to drop in price from the current low price to an insanely low price. However will now dig into the 862/706 head rabbit hole. However from what I know (some of it from reading threads on this vary forum), the 706 heads help the smaller motors make more low end torque..... as in 4.8 and 5.3 liter motors in a truck. the 243 are generally better up top. now the slightly smaller chamber is good for a slight bump in compression. that alone is good for a few HP per most of the threads.

yes, porting the snot out of 706's can get them to flow almost as much as 243's then if you port the 243's you can get almost the same percentage of flow increase.

however since I am pushing about half the weight of a typical modified pickemup truck / chevelle / or 65% of the average mustang/camaro/corvette/etc and about 80% the weight of most RX7's do I really need to get 4cc less chamber just to get slightly smaller valves to help with low RPM torque? we are talking a car that originally zipped around the alps with only 35 cubic inch 4-cylinder at 16hp from the factory and will now have between 430hp and 470hp with only 400# more.

Not to mention the average price just for the CNC porting is more than I have in the car/trans/short shifter/suspension/wheels/carb/radiator/and pile of steel tubing for the frame

@Summitracing Joe, does this mean you are endorsing teh 8707 over the 8715? @68Formula again, thanks for the recommendation.

 

Nothing wrong with running a set of heads because they are in good shape and available. I’m only stating that economically keeping them doesn’t make sense to me. That’s only *IF* you have access to the cheaper heads and can sell the 243/799 for the typical going price of $400+. If you can’t, disregard.

As far as the low end vs high end TQ VS Compression… I don’t agree. More compression will basically take your same HP curve and move it up… across the entire curve. Similar to adding boost. Its def. not just for bottom end tq. And more compression will be better suited to a more race-oriented cam. (which will tend to neuter your power down low anyway) Which is what you want with a feather weight… ditch the low end power in favor of the upper RPM range. I’d run a big cam that bled off as much comp as possible, and run as much compression as I could on the fuel available.

I’m not suggesting you break the bank with CNC porting on a factory head. That’s counter-productive IMO. Milling them to hit your max compression is generally cheap. And a decent 3 angle valve job is also relatively cheap fo the power gained. CNC machining isn’t! For example: you should be able to mill .030 (or a bit more) and have them do a “race” 3 angle valve job for less than the $400 you sold the 243’s for. (that’s on factory valves, which are fine IMO). Then clean up the bowls yourself and do a mild port job. I’d bet you could pick up a good 40-50hp doing this depending on how good you are at porting, and how much you can mill on the fuel you plan on running. That should get you the best bang for your buck.

For example I just milled .100 off a stock 706 heads. I hand lapped the valves myself and fly cut my own OEM pistons. That’s it! Nice budget 13.25:1 5.3 with a bone stock bottom end and semi rowdy cam. (I run e85 ) No idea what it makes for power yet. But it happens to be in a 1st gen rx7 w a manual trans. So like you, I don’t think I’ll need a ton of power. But I wanted to maximize what I could get as cheaply as possible. I feel a buttload of compression and a big cam will net me more power per $ than a CNC head.

 

@Scott Danforth,

Don't go selling those die grinders and porting tools just yet. There are metal shavings that need to be flying around

I got a little overzealous thinking about the potential with the 706 heads and CNC machining. It comes down to your budget and the trajectory of the build. Truth is for what you're doing here along with your tools and skill set the 243's will work well. Do your own porting and bowl blending if that's something you're comfortable with. As @Forcefed86 referred to a good 3-angle valve job and head milling can go a long way and not be a killer on the budget. I also agree that added compression doesn't just add torque down low. You would see gains across the entire range in both horsepower and torque.

As an FYI the LS6 doesn't have titanium valves from the factory. They have 243 heads with steel hollow stem intake valves and steel sodium-filled exhaust valves. They used the same 243 heads as the LS4 just with different valves.

Regarding the cam. Yes, as you've described this build and your goals further I am leaning on the 8707R1 more so than the 8715R1. I originally recommended the 8715R1 because of your "no bucking" statement in post 1. Then as the discussion went on you adjusted that saying you're ok with "some un-refined manors" in post 27. That's when I felt the 8707R1 would be the best candidate. With the planned 3.54 gears, head work, and added compression this should be as fun to drive as it will look and sound

 

Hey @Summitracing ..... you went down the rabbit holes I sent you the links on didnt you..........:-D

 

Let me throw my monkey wrench in. I would bore the ,LS4 block out to 3.898(LS1 oem bore) port/cut the 243's and Summit 8710r1 cam. Power everywhere, tunes easy, would fast enough to scare the **** out of you in a ,2200 rear engine car. Look, a new rabbit hole...

 

Would require new sleeves in the block. Max bore on a LS4 would be 0.020 over or 3.800 bore unless you do custom sleves

 

Here is a rabbit hole of stock LS4 and cams only. https://ls1tech.com/forums/forced-in...ock-5-3-a.html

 

​​​​​​That's not right, you should be able to go 3.898/3.900 bote on that. The block is unique, but I do not think the sleeves are. Every other 5 3 alum block can go std LS1 bore, so why would this be different.

FYI, you cannot sleeve that block. The Gen 3 stuff is out as far sleeving these days as I believe they stopped making/doing the wet sleeves.

 

Unfortunately not on the LS4. Or the FWD / Fiero guys would have done it. Plenty of builds changed direction because you can not bore the LS4.

A cam and port job is all the motor is getting

​​​​

 

So I dumped all the cam specs into Dyno 2000 just to compare. (some of the comparisons match Richard Holdners vids)

This is using 243 head flow data off of a few builds on here.

based on this, I think the two choices are TSP MS3 and the comp XR281HR

The Summit 8707R1 falls off too quickly, the famed 54-459-11 cam that some have offered does have a peak in the 5-6k range.

 

Gut check says something is wrong with the 8707 data. Peaks @ only 6k in a 5.3? And then drops off faster than the 8715? Neither makes sense.

 

could be, however I cant find any actual dyno data on these cams anywhere like I can with the MS3, the BTR hotrod, etc. so I can only go off the simulation software. Keep in mind, the flow data is for stock 243 heads with bowl blending and a mild gasket matching.

 

Usually the sims will differ in terms of overall values from actual, but at least trend similar to real. For example, if you look at the Comp 275 to the 8715, I'd expect the results to compare the way they do. But the 8707 results don't fit at all. I think either an input was changed, or the cam data is not inputted correctly. I know some programs you can input both advertised and .050" cam specs and then select which one you want to use as the main basis; which can yield different results. Or maybe you were trying a different throttle body size or headers ,or compression, etc. and forgot to match the other cams when you selected the data for graphing, Or maybe something was fat-fingered.

Try making a copy of the 8715 file, input the 8707 data again independently (instead copying from the cam file you created) and see if the results change.

 

@Scott Danforth,

SUM-8715R1 and SUM-8707R1 share the same @.050" 43* intake closing and 55* exhaust opening. The only real difference between the two is -2* of overlap (8715R1) to 6* of overlap (8707R1). We base our rpm range on historical results. We're uncertain why a sim would lower the rpm range for a cam with more overlap. The only thing we could see would be if it factored in higher exhaust backpressure factors.

 

Not sure. even the 8709 tends to fall off quickly in the sim software.




yet, I am lightyears ahead of the LNF in the Solstice which weighs in at 3100.

Not sure I need to keep spelunking down the rabbit hole as sim software is just a guide. will review a few more of the holdener vids and compare those numbers next...... then attempt to iron out the whole balancer issue

 

Cam Motion finally came back with their Titan 3. However, it's only a 224/228 can. So I asked about the Titan 4....... Crickets so far

 

Contact Martin Smallwood and answer the 30 questions he go ask you. He will send you a custom cam on a cam motion core specificially for YOUR build.

 

You can easily do a whole lot worse than that one. Nice, upgraded heads, a compression bump, FAST intake mani, long tubes, and you have the makings for an extremely fun street ride. Absolutely, you can go bigger, but you lose power down low, street manners, and efficiency. Cam upgrades include all manner of compromises. Too big is bad on so many levels. Too small is a poor use of funds too. You need to find your own sweet spot.