long rod 400, 915 heads

This is a motor I've been thinking about for some time, already have most of the pieces.

A flat top piston would put the compression pretty close to 10:1, depending of course...….

So, for a 10:1 iron head motor with good quench (915 heads), how much cam duration would I need to
be able to run 91 pump gas ? Assuming decent cooling, not too lean, smooth out the sharp edges, etc.

Wont work down here in Southeast Texas, not on pump gas

I don't live in Texas, but in Missouri, I would plug all the engine info into my engine program, and input the octane fuel, and it would tell me exactly what would live. From my experience some where with 110 centerline and 230 or so duration should work just fine, built several like that for street cars. Just finished a 406 small block chevy, it has right at 10 to 1 pistons, it has a 110 centerline, advanced 4 degrees, 220 duration, with .500 lift approximately, it has around 140 psi cold cranking compression, and runs fine on pump gas. Dyno said it makes 357 HP @ 5,500 rpm and 457 ft. lbs of torque @ 4,000 rpm. from my memory. Went into an older corvette. Built several stroker 360 mopars with basically the same combo they all worked great as well.

If you mean a 440 rod in a 400, it wont fit, it's about .400" longer. I mentioned in another thread that a budget 400 can be built using a .040" over 72 style 440 piston making a .020" over 400 with the same deck height as a 68-9 383.

Diamond makes a piston for this combo.

Really? I must have missed it. What's the part number? What stroke?

A 1.48 CH 440 piston would do it. Would need some deck cutting to get quench, or just have the pin moved up 0.020" - 0.030"

440 rod and crank, mains cut down to 400 journals.

https://www.manciniracing.com/37strokcran4.html

383 crank but with 440 rods.

https://www.manciniracing.com/di94bo3st2.html

The first 400 block stroker motor I put together was with a 440 stock stroke forge steel OEM crank with the mains cut down and stock OEM 440 rods with flat top Ross pistons with valve reliefs for pump gas with stock type blue printed 906 heads.
I tried to get the customer to allow me to have it offset stroked to 3.91 and use a set of BB Chevy type long H beam rods but he said no
My first pump gas stroker motor I made for myself had a 4.25 stroke crank with a set of 6.800 long BB Chevy type rods with another custom made set of Ross pistons with 22 CC dish for CA 91 octane pump swill, that motor ran fine, it flat exceeded my wildest dreams

jwb123, Thanks much, very helpful.

The rest of the replies on this thread make it very difficult to remain polite.

Andy F posted a long rod 400 a while back that ran on pump gas and made good power. Maybe he'll chime in.

WOW !!! I still stand my ground, An IRON head 10-1 motor will be a PING monster in the heat down here, we are also at about sea level, I don't know what I posted that would be something to get upset about ?

We did build a long rod 400 street engine that worked pretty good but it was totally different than what the OP is talking about. We used ported Edelbrock heads for one thing and Hemi+0.100 rods with off the shelf stroker pistons. It pushed a street driver Duster to 10.90 times at the local track. Nice running combo but not really very economical to build. I don't see any point in building another one.

I’m not so sure a flat top 400 even with closed chambers is 10 to 1. More like 8.5 to 1

It all depends on the deck height, gasket and chamber size. A .035" over 400 with zero deck height, a steel shim gasket and 75 cc heads would have a compression of 11.39.

I ran a 11.5 iron head magnum 410 stroker, it ran fine with pump premium .030 quench and a 230@.050 cam 110LSA in a heavy 99 dakota RT. I did take many precautions to prevent detonation like true cold air intake, air gap intake, smoothed all the sharp edges on everything, EFI, routed fuel lines re-routed as far as possible from any heat source, 180 T-stat, ceramic coated headers to keep heat out of engine compartment, I opened up all the webbing in the accessoriy drive bracket to let air flow across the intake, big fan to keep air moving through engine bay... I did everything I could to nip it in the bud right from the git go and it worked great. I would think if you did everything right you would be fine. The one thing I would say is maybe get your quench just a hair bigger like .035 or so with the bigger bore.

Except you can’t have .020 quench.

A shorter rod would get the piston out of the head quicker, maybe less chance to detonate.

X2

Well, I will say thanks to everyone, I know folks are trying to be helpful.

I thought this would be a simple cam thread, then it shoots off into a piston and rod discussion.

Why do I want to build this ? The answer is not really relevant, but I will say that the combination
just intrigues me, it's just a big small block, big bore/short stroke/long rod deal. And I happen to have
most of the stuff already, including the 6.96 rods and the 1.320 Ross flattops (which they don't make anymore).
I want to make it run on pump gas, which OF COURSE will be possible, with the right cam. That is what I'm seeking.

To CSK, you seem to claim that NO CAM POSSIBLE will make this combo work in SE Texas. That rubbed me wrong.

I am grateful to read about 230-degree cams that the two guys had success with.

Thanks again.

I don't think your question makes any sense. The camshaft doesn't change the compression ratio. If you put a big cam in a high compression engine you can reduce cylinder filling at low speeds, but as soon as the engine comes up on the cam you have a high compression engine.

Be interesting to know what power it will make at rpm. One of the reasons for the long NASCAR rod in the hemi. Let us know how it works out.

Andy, you are right.

My understanding is that under conditions that marginally favor detonation, that detonation is more likely
at lower RPM. As RPM rises, even though you approach, and pass, the torque peak, the danger of detonation
goes down. This is likely due to increased mixture turbulence, and decreased time for bad flame front to propagate.

Is this correct or old wives' tale ?

If I was targeting 12:1, I would have no chance, but at 10:1 I thought it would be managable with enough cam duration.
The other guys evidently had good luck at 230-degrees; I guessed that the long rod deal would require more duration
to stay out of detonation, maybe 240~250 min ?

Sorry but that answer makes no sence either....my 400 is a 12.5 pump gas motor.....cam shaft....316/340......682/687...with a lobe separation of 115....if the lobe separation was smaller the motor would never work with pump gas...So yes the cam shaft does have something to do with Compression....And i'm out....got no time to debate with garage racers or dyno people....have a good night

Sure you can put a big cam in it and kill off the low end torque but then you have a soggy bottom end that isn't any fun to drive on the street. If you are building a street car then cam it for the street and use premium fuel. If you can't afford premium fuel then lower the compression ratio to point that is safe to drive. A camshaft R&D project is really expensive and unless you have some decent test equipment you aren't going to know what is going on anyway. If you are planning on going EFI and have knock sensors on the engine then go for it. You can use the knock sensors to change the AFR or the timing. If you just have old school distributor and carb then how are you even going to know if you're on the ragged edge of detonation?

If you just have to build the combination that you're talking about then go ahead and build it but plan on starting off with higher octane fuel and then gradually trying different mixtures of fuel until you find out what it will run on. If it was my car I'd use a Sniper and a Hyperspark distributor so I at least had control over the AFR and timing. A knock sensor would also make sense.

I was wondering how long till the EFI sales pitch showed up. Don't forget to mention TrickFlow heads too.

his idea of 10-1 with pump gas will work just fine with his thoughts on cam timing and a little slower distributor advance springs. I didn't see it mentioned, but the weight of the vehicle it's going in will also have some bearing.....detonation is load dependent to some degree. I have a 4100 lb. pickup with 906 heads a little over 10-1 and with the little bit of ethanol (5%) now in our pump gas, it's detonation free at 38* total timing...in the heat of summer 85-90*

My opinion is that it will run on pump fuel just fine. If it pings just back off timing a bit, but I doubt it will.
Although every combo is different. I ran a 12.7 to 1 383 on pump gas for over a year and didn’t have a problem. That happened because I didn’t know what was in the motor when I bought the car. But it also had a 5200 stall and 590 cam, 4.56 gears and 2800 pound car.
When I tore the motor down I found it had 20+cc domes and 915 heads.
Seems to me you should be able to make it work. You haven’t mentioned the rest of your combo.

I learned long ago that the spark plug heat range has a lot to do with any pump gas motor pinging or not

Just because you don't hear it pinging doesn't mean it isn't detonating.

Kevin

He is absolutely correct on this, there is pinging(audible is bad ) and preignition, which you don't hear

THIS ^^^^^^ & thats a fact when the rod bearings fall out of the rods when you pull a rod cap off . but it ran great .

I have a 400 with a 4.375 bore, stock stroke 383 crank, 6.800 Compstar rods and Icon 1.475 CH pistons, for zero deck at 9.965 deck height. I'm using a .045 MLS gasket and mildly ported 452 heads(245cfm @ .550), cam is a hydraulic roller 230/238 Erson, and it hasn't been dynoed yet. Compression is 9.2:1. The plan is pump swill. We'll see what happens. S/F....Ken M

While not the same engine family, a 408 i built had somewhat similar specs. Iron EQ heads, 10.1/1 compression, 235/249/107 cam in at 105. Made max torque at 4600 max hp at 5700. It ran well on pump 93 e10. My opinion on why it ran well is the three way combo of cam, converter and timing curve. With that cam it didn't have very high cylinder pressure till 3000 plus rpm, the converter was loose enough the motor never saw less than 4000 rpm at full load. The timing curve was conservative with 14 initial and 30 total in at 4000 rpm. It also had vacuum advance working. 30 total was the best timing on the dyno with a mix of 2gal 100 +3gal 93 pump. The motor never pinged on straight 93e10 driving. So the final combo means a lot to me.
A buddy built a 451 with 906 heads, kb reverse dome pistons with tight quench, heads were from Herb McCandless; plunge cut in the bowls, .030 shaved to make them flat. The dyno operater was afraid it would not do well with over 10 compression but it ran excellent on 93! So i like the idea of picking the cam you want to run, be conservative on timing curve and total, and some kind of knock sensor for tuning since detonation isn't heard until it is past the point it can start to do damage. Good water flow through the motor cold air intake are also important.

If you want to run pump gas on a performance engine, My experience is don't forget the advance curve. You have a hard time trying to do it with springs and weights, but it is easy with a computer. They make boxes just to run a distributor with, or an aftermarket injection system with timing control. You can even on some systems install a knock sensor. It's not rocket science OEM's been doing it for decades. I have used one like this, with a procharger on a blow thru carb, but you could do the same with just a carb. Basically the unit can retard timing so you set the maxium advance, and it will retard as programmed. Lots of options to do this. And to get started, there are engine software programs that will calculate an advance curve to get in the ball park. So buying a control box and engine software is about a $400.00 investment, pretty small compared to what an engine costs today.

https://www.cbperformance.com/CB-s-Black-Box-Programmable-Timing-Control-Module-p/2013.htm