Realistic Octane Requirements

[pcnsd]

Going back to the original question. At 11:1 SCR, I think your realistic generic US fuel octane starting point will be ~95 (R+M)/2. I'll through in with F-bird' 88 that the suggested 91-93 pump blends are better suited for 10:1 in a street driven US V8.

[My427stang]

The engine if for a 1976 corvette that has a bone stock engine. This was my dream car as a kid so its been fun to own and work on over the last 10 years. I've done brakes, rear swingers, fan conversion, radiator, water pump, clutch etc etc. The last two pieces for the car are a front suspension overhaul and the engine.

The intent for the car is a Sunday driver that is reliable and a blast to drive. I want to be able to break the tires loose (something I cant do yet) but I don't plan on ever taking the car to the track or racing it. It has the stock 4 speed manual, 3.08 gears in the rear.

The 400 block was chosen over some other options to increase the cubic inches for torque. The goal was for a wide torque band without worrying about trying to reach a crazy peak HP. We found some used Vortec heads that we are reconditioning to match the 400. Vortecs were chosen as even stock Vortecs are a large upgrade to what was stock on the 400. A new rotating assembly for the 400 and new top end cam/lifters/etc was the plan without anything specific chosen yet. Since the plan was Vortec heads Ill eventually get a new intake manifold as well (this is slightly tricky with the low hood clearance of the 76 corvette). The end goal is to have a new exhaust as well, but the keeper of finances says engine first. So this will have the stock exhaust for a year or two till I can get headers and side exhaust.

At first, the cost was driving everything and even tried to hand hone the cylinders etc trying to just reuse as much as I could. I realized that it would be a better option to spend the time (and save up some money) to do it right. It would be cheaper to buy a crate motor but I've never built and engine before so I know Ill spend a bit more but Ill have a lot more fun and continue to learn even more.

You should have no issues with your goals.

- Vortec heads and a matching alum intake that fits the car
- Get that 400 to .040-.045 quench, bore it as little as possible to keep a good ring seal
- Shoot for about 9.5:1 compression
- Hyd roller would be convenient, but if you think you can break in a cam, a hyd flat tappet would work too
- I'd shoot for a cam 272-ish advertised with some split (more exhaust duration) and a 112 LSA to keep overlap in the mid-low 50s to keep power brakes happy
- As stated above, EFI would make it very happy, as would a tiny bit more converter, but if not a good Q-jet or 600-650 vac sec
- Recurve the distributor, not sure what Vortecs like, but with a tight quench it likely won't ened a lot of timing, but having a nice quick curve makes it snappy on the street

I also expect the headers will help significantly, especially if it currently has a single exhaust and cat on it.

Should be easy.

Some additional tips

- Autotec (Racetec) for relatively little money can make you whatever piston you want in 4032 and you don't have to settle
- Don't bore more than you absolutely need to, same with cutting the deck, just square deck it and bore it and get pistons to match. A stable bore is worth more than more inches
- Burn tires at will, but rememberthose Vette axles aren't cheap

[F-BIRD'88]

If you are using 6" connecting rods on his 400 build than the KB130 piston with its 18cc dish is right for this street motor.
If using 5.7" connecting rods use the KB147 piston.

Get Cam King to spec you a hyd roller for this car.
Something in the the 230 ish dur at .050"
If you must use a low riser intake like the Performer (Vortec) intake it will cost you a lil perf compared to the better RPM (vortec) intake
The RPM intake will fit under the stock Vette hood only if you use the correct 60's era GM air cleaner. Commonly known as the L-88 air cleaner or the L72 air cleaner from the 60's BBC muscle cars and vettes. You can buy these from resto parts supplies. You really only need the base.
use a 750 holley double pumper HP body style is best.
The Comp cams hyd flat tappet cam CS XE284H-10 or the slightly smaller CS XE274H-10 both will work very well if you go for a flat tappet cam.
If you are going to burp the wallet for a roller cam use a Comp extreme solid roller like XR-274R-10 cam and kit. Machine the vortec heads for these 1.46" springs in this K kit.

[F-BIRD'88]

When you upgrade the vettes exhaust skip the side exhaust. You will grow to hate it. Just get good vette headers ( true 1-5/8 or 1-3/4") and custom build a true 2.5" dual exhaust using welded mandrel bent pipes exiting at the back in the stock position. There are MANY 2.5" in out vette type mufflers that are a upgrade to the OEM vette mufflers.. EG: Dyno MAX. EG Walker, EG: Magnaflow

Your initial cam choice is way too tiny for a high perf 400 in a vette
And your intial cr is way too high. Buy the engine components separate if you cannot get the right -18CC D dish KB pistons in a crank kit.
Do not build with a flat top piston and 64cc heads, the cr will be way too high.
it will need custom balancing anyway.
Intrnal balancing adds nothing to this street build.
A external balance 400 build is fine using a 400 balancer and flywheel with weight. A 5 speed trans would be a GREAT upgrade to modernize this vette with 3.08's and a cool high perf street 400 SBC.

[pdq67]

I seem to remember that Speedway Motors is selling something like .026" thick 400 SBC head gaskets. You might hunt them up!

OR

Read me again up above. --- Read me again. -- Read me again!!!

My 406 was POWERFUL, but not really a, "high rpm", engine even though I did wind it out to above 6500 a couple a times fine.

This is why to this day I love the 3" stroked engines because they will rpm to the moon!! Not as torquey, but they rpm forever! Run a solid flat tappet lifter cam in her and go have more fun than John Law will allow!

pdq67

[Littlekix]

The main difference I can tell between the KB 130 and KB 147 is wrist pin height. The 6.0 vs 5.7 makes some of the oil support disappear but with a street motor does that matter as much? From what I've read from piston manufacturers, they state that there is no difference in longevity if the wrist pin goes through part of the oil groove so long as the support ring is adequately installed. Seems odd, but then the kb147 has very little support in that area to begin with....

I've been poring over many of the rotating kits and it seems like for internal balance many kits are 6.0 inch rods but to get to 5.7 it jumps a lot in price due to only offering the forged crank which I think is a bit overkill for my street application.

Will I see a difference in performance or durability between the 5.7 or 6.0 combos? The cost seems to be significant (700$ extra approx).

From some of the reading on dynamic CR....it looks like I'll have iron vortex heads with 64cc chamber, 18cc dishes pistons, 45 squish, the static CR is about 9.8 however with some of the cams people are suggesting I have a dynamic CR of 8.0. This should allow 91 octane from some of the reading/graphs.

I'll keep playing with some of the cams but it looks like I am much more dialed in for the engine goals now, thanks for the help. If you have any other suggestions or comment keep em coming.

[F-BIRD'88]

Look for a cast steel scat crank kit with extrenal balance and for 5.7 rods. (Usually with kb 147 (-18cc) or kb 168 (-22cc) pistons.) . it should cost Less than a 6" rod kit.
The flat top piston kits are cheapest because the piston is WRONG for a pump gas 400 sbc w 64 cc heads.
If you cannot find a correct kit, buy the components separate. I recomend 5.7 rods, cast steel scat crank kb147 pistons. Get a cam that will make big street poeer and torq in your manual trans vette with the 3.08's.
Get off the fixation with dynamic calced cr BS.
10.1 cr is plenty. Cam it to go.

My street 5.7" rod 9.8 cr kb168 406 does wheelies (4.10… comp xe284h10 ported 2.02" 062 vortecs.. Runs high 11's. Drives great. Sounds boss.

You can build the same

If you are scared move to the next milder cam xe274H-10

Or go with the comp xr solid street roller cam and kit.
Xr280r-10 or XR274r-10. Buy the whole K kit.

[F-BIRD'88]

If you get the machine shop to deck the block for a measured true 0 deck, you can use either tge kb147 or the kb168 -22cc piston. (Both 5.7rod) there is no benefit to a 6" rod on this motor at this build level.
There is no benefit to a internal balance on this motor at this build level.
Note mine was built from separate components.
Not a off the shelf kit.

Some good engine kit suppliers builders, will create a engine kit for you with all the right parts.
Shop around. Work with your machibe shop and their suppliers.
The scat cast steel stroker cranks 3.75" are prefered and yours may well need custom balancing too....so.....

Get it right with the right parts rather than a kit that is not quite right.

The flat top piston 400 sbc kits are for a large chamber 72-76cc head or fir racing on race gas with 64cc heads.

[F-BIRD'88]

External balance 400. Your machine shop can inspect, reface your current 350 sbc manual flywheel and add the 400 weight to it for external balance or you can buy a new 400 ext balance manual flywheel.
Use a 400 balance w weight fir external balance.

Internal balance is not a must on this build.
I highly recomend the milder comp xr solid street roller cams over ANY hyd roller for you and this build.
Set the lash COLD, tightat .010"-.012". COLD.
It is as quiet or even quieter than a typical hyd roller and will out perform them.
These are designed and intended for street.

[F-BIRD'88]

You could also build a 10:1 cr 383 usibg your 350 block.
It will also make a ton of street power and tirque with vortec heads.

[F-BIRD'88]

Cooling system mod for vortec heads on a 400.
If you buy a intake manifold (vortec) that do!s have the extra rear water ports near tge distributor. (Professional Products CROSSWIND dual plane high rise has these extra rear water ports) you can do a simple water hose relocate to improve coolibg and thermostat function.

Move tge heater hose from on thefront watervport near the thermostat, to the rear drivers side water port. By tge dizzy. Now you have improved coolibg and better thermostat action especially while the engine iscwarmibg up.. No more thermostat hunting.
No more overheat on 400' s. Also no real need to drill the face of the vortec heads for 400 block steam holes.
You still can if you want but with this simple water hose re route its just not needed.

Some intakes do not have the extra rear water ports.
The CROSSWIND VORTEC MANIFOLD DOES.
Use a 750 hp style holley double pumper and the correct aircleaner base. A holley carb with a choke horn will not work. A hp 750 works. A eddy 750 or 800 avs thunder carb works.
Don't bother with a vacuum seconday holley carb on this.

[F-BIRD'88]

Use the correct old gm air cleaner base so you can use a high rise dual plane manifold. None of the aftermarket bases are right or as good as this gm muscle car air cleaner base.

[F-BIRD'88]

Yiur machinist needs the pistons rods and crank in hand to cut the 400 block decks correctly.
.005" below deck is fine. (finished)
Plan on needing to balance the crank reguardlees of advertizing.... Internal balanced 400 builds often end up needing mallory. $$$$

[rebelrouser]

I am starting a new SBC 400 build and have some logistics questions.

The goal is to have a reliable and fun street motor that also teaches me a lot about building an engine. Its semi budget but more about learning how to build an engine, something I've never done before.

I just had the donor 400 CI block cleaned and checked for cracks etc and it looks like it will clean up nice at 0.020" over. The Machine shop is checking the line bore (machining if needed), decking and boring cylinders with plate. They are wanting me to mic the pistons to machine the bores to size. I am having some trouble identifying the correct combination such that I don't have to use race gas nor octane boosters.

The rotating kit I'm leaning towards is internally balanced, 4.145" Pistons, 5.7 Rods, Cast Crank from eagle (Kit B13470020 )

This kit, set at a deck height of 9.025", and assuming a head gasket at 0.043" Thick, with 64 cc Vortec heads equates to a CR of ~10.8 which is about what I was targeting.

A deck height of 9.025" and 0.043" Head gasket is a squish of 0.068" which from some of my reading seems to high? If I reduce this further with a smaller head gasket my CR goes to ~11 really quickly. Will this be too much for a street engine with 91-93 octane pump gas? Does anyone have any experience with something similar?

My second question comes in debating hydraulic roller vs flat tappet and cam specs. I am looking at Comp Cams K12-408-8 which is a milder roller cam. Since this will go with a Vortec head I am planning on having to cut the valve seats to allow for over a 0.420" lift.

With the faster closing exhaust will this act to artificially increase the compression ratio further, driving up the octane needs?

These may be myself thinking to much into these things, so please let me know some of your opinions. I've learned a lot reading at speed talk so all is appreciated.

Not an expert but I will tell you how I do it. I use performance trends engine software. Plug in all the parts I am going to use. Yes the program gives you projected HP and Torque, but it also calculates dynamic compression, and projects a advance curve to keep it from spark knocking. So I take the time to CC heads and get an actual static compression ratio, plug the numbers into the program with the octane fuel I want to use, generate the advance curve, put my distributor in the distributor machine and play with the springs until it matches what the program wants. It has never failed me yet. On my last EFI project, simply took the program advance curve and adjusted the timing maps to fit, worked like a charm.
This method may not be perfect, but it beats an educated guess. It also tells you what is possible long before you buy parts and melt pistons.

[Olds455]

Use the correct old gm air cleaner base so you can use a high rise dual plane manifold. None of the aftermarket bases are right or as good as this gm muscle car air cleaner base.

You mean a drop base air cleaner? I remember watching a video of some different filters and bases tested and the drop base showed a power loss over a standard base air cleaner. Whichever you use, fit the tallest air filter possible. I see a lot of C3 owners going with a 4" filter and a 2" drop base, it seems like.