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So if I don’t clip the heads at all I’m at ~11.8:1.
If I cut them to the maximum I might eek out 12.4:1 that’ll have been cut about .045” total.
Since 13.5:1 is out of reach do I just run it as is and save a few bucks and any potential headaches of extra tight PTV and intake fitment issues? 12.4:1 is in a weird grey zone for 91 where the performance gains aren’t huge but I’d still need boostane or E to keep from rattling it to death.
The heads would be more useful for me in the future with the larger chambers.
Would this thing suck at “only” 11.8:1 compression?
On 91, I would say less is more. What you really need to do is a good dynamic compression calculator and see where the total combo ends up. If it was mine, I would leave it alone for now and run it to how it tunes out. You can always cut the heads a little more later if you want the last squeeze.
So if I don’t clip the heads at all I’m at ~11.8:1.
If I cut them to the maximum I might eek out 12.4:1 that’ll have been cut about .045” total.
Since 13.5:1 is out of reach do I just run it as is and save a few bucks and any potential headaches of extra tight PTV and intake fitment issues? 12.4:1 is in a weird grey zone for 91 where the performance gains aren’t huge but I’d still need boostane or E to keep from rattling it to death.
The heads would be more useful for me in the future with the larger chambers.
Would this thing suck at “only” 11.8:1 compression?
I struggled with this myself a bit with my teardown, and I'll tell you where I ended up. Little known fact, but the combustion chamber is part of the intake tract. Preserving the larger chamber does have flow benefits. On mine, I decided to do the domed pistons in order to get the compression and not mill the heads down. My fear is this adds a bit of weight to the pistons, but at some point you gotta make a call, right?
Since you're stuck with 91, I think 11.8 will do fine. it might impact how your cam runs, as compression helps bigger cams. That said, when you do have fuel you can take advantage of, you can add timing. I have seen where sometimes you gain by reducing compression and pushing timing. I know 91 isn't that different from 93, but in your shoes, I think I would stay lower. I might do a 1 or 2 cc mill to get to 12:1, but you have to plan on the possibility of having to run on pure 91 octane, so I think that's your best bet.
Well this has been a long almost 6 year journey lol. A lot has happened since I bought the shortblock in 2018. There were also endless challenges and frustrations with this thing, especially in the block machining. Kind of just put it on ice for a while and ignored it as life got complicated and it really wasn't playing nice. The main motivation killer has been the extremely unfortunate event of California Speedway closing. We went from racing 20+ weekends a year to now only a few if we're lucky which all require significant travel. I always imagined the final landing place for this engine would be a super light tube chassis car and competing with it, but with nowhere local to play with either the rx7 or our drag race cars it is really looking bleak.
I'm shelving the idea of putting this engine in my rx7 for now. During this downtime I decided I missed having it as a street car and have built a separate hydraulic roller SBE ls7 with some minor upgrades. The street engine is in the car right now and I'm slowly finishing up putting it back together. Once I get the car back to where I want it with the mild combo I can decide which direction to take the build.
My dad was able to retire back in May and has put a ton of work in on the final assembly. Over the weekend we got the engine fully assembled and it is ready to head to the dyno which is tentatively scheduled for the first week of March, but we might pull it forward if we can. It is looking like it might go in our malibu wagon bracket car since it's engine is still in the machine shop, and we need to be racing mid March.
There have been a few tweaks to this thing since my first posts, but mostly the same. Biggest change is I decided to pull the plug on the external oil pump just due to complexity and the custom work that was needed. A Melling pump eliminated some serious work off the todo list. Also, a lot of debate went into if I should clip the heads or not, and if there was enough PTV clearance. I'm glad we decided to do it. Final compression is right at 12.5:1 which should benefit greatly from running E85, but not prevent me from driving it on 91 octane if needed. Our PTV estimations worked out well, and after cutting the heads with cold lash at .008" I have .071"/.088" clearance I/E.
Updated specs
429" LS7 build, 12.5:1 compression, wet sump conversion LS7 Block honed to 4.130" LS7 crank polished and checked Factory Ti rods in good condition and ARP bolts Mahle PowerPak flat top pistons
1/1/2 mm gas ported total seal rings. BES 285cc ported LS7 heads, new factory Ti valves and Ferrea stainless exhaust
Cometic 4.190x.051" head gaskets T&D steel pedestal mount adjustable roller tip 1.8 rockers
PAC 1237x solid roller valve spring kit, each one checked and shimmed to .085-100" clearance from bind
Comp Cams 258/272 .775/.756" lift 113 LSA +3* advance - their new low shock solid roller LGW/LGX lobes Manley 3/8 to 5/16" tapered 7.825" long pushrods, .145" wall.
Isky Red Zone bushed solid lifters
Melling 10355 oil pump
Mains drilled for oil squirters
Improved Racing crank scraper, windage tray, and trap door baffle (fun fact, owner is also an LS RX7 guy)
Will dyno with a CID 4.5 and 1050 Dominator
The sweep pattern is really nice and very centered on both intake and exhaust.
Lash is .014/.016 hot. Will reset on the dyno, but guessing at .006/.008" cold.
We also have a CID LS3 4.0 and the core shift is horrendous. The LS7 4.5 fits beautifully. Very centered on the ports. Surprisingly, the runners are significantly smaller than the BES ports - like .200" narrower. Better than the other way around. We'll just be dynoing it like this. If the intake ever gets used for real we'll probably port match or run a program through it.
Overall very happy with the final assembly and really excited to see what it does. It'll be an interesting dyno day. Hoping it all plays nice together.
For power...if it doesn't make over 750 I think I'd be very disappointed. If it doesn't make at least 730, 1.7 hp/cube, I think something is wrong. We make 1.6 hp/cube on 91 octane hydraulic roller combos without much sweat. The cam I spec'ed hoping for 7300-7500 peak power rpm.
Beyond that, I'll leave the expectations low and hope it overachieves.
If you port the intake manifold I'm going to say 750hp flywheel! That is a healthy cam for sure.... Most ported LS7 heads flow around 390-400cfm
Are you going to dyno with the RX-7 headers also? I'm curious what difference they make....
You should clear 750 at the flywheel your TQ probably like 600-620. I had a 455 LS (4.19 x 4.125) motor with Brodix BR7 heads ported by Advance Induction cam was 246 / 258 on a 114 and only 650 lift hydraulic roller, Mamo MSD, 12 to 1 compression and it made 757 hp at 6,700 rpm and 660 tq at 5,000 rpm on a Superflow 902. Dyno headers nothing special something you would see on a Chevelle 1 7/8 inch. You have more cam and compression and better hi rpm induction than me but my engine is just a little bigger. When is dyno day?
I'll just be using the dyno headers at Westech which are typical 1 7/8" headers with 3" collectors. I don't have any 2" primaries, and my rx7 headers should be on the car by the time I'm at the dyno.
Nice 455! Great power for the cam size I bet it drives very nice.
Dyno is week of March 5th at the moment but we may move it forward.
Awesome thread and build. I say ~750hp at the flywheel too, sounds about right for the combo.
I hear you about your local track closing, California is TOUGH for that. California really did gut the racing world with their war on anything horsepower/racing over the last 20+ years it would seem. I lived in SoCal for almost a decade and can still remember being shocked that the closest 1/4 to SD was 2 hours away…and I had just sold my truck n trailer lmao. My old home track was 15 minutes on the dot from my front door.
California Speedway was purely business. During Covid they just got paid to store vehicles and tractor trailers and didn't have the liability of idiots going out every weekend trying to kill themselves. They sold it for $559 million just for the land, plus Nascar corporate kept enough to build themselves a new oval. Of course there's no accommodations for amateur racing of any kind..
Closest 1/4 mile track is Bakersfield and Vegas. This is Irwindale's last year as well so we even lose the 1/8 mile track.
LS7 build looks very nice! Just FYI, the T&D rockers have been known to **** the trunion needle bearings.. you can upgrade to bronze through T&D for pretty cheap. I had mine done and your engine still isn't in the car. You have more lift than me but our cam specs will be pretty similar after lash, will be interesting to see where you peak, even with the killer intake you have.
Thanks for the heads up. When I bought them there really wasn't much info floating around on them. I'm starting to see a few reports of that. At least it should show up in lash adjustments.
What's interesting is the T&D's on my dad's big block have pressurized oil feeding the rocker trunion through the pushrod cup. These don't have any oiling ports. I bet if it had better oiling the needle bearings would be fine.
On a big block chevy everything is just bigger from the trunions to the 7/16 stud. It is kind of like a Dana 60, the .903 chrysler lifter, 30 spline vs 35 spline axle that extra size just give it exponential strength which helps (though it may weigh a little more).
03-02-2020, 03:44 PM
