340 with 302 cast head for pickup

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dartman340son

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Me and my dad are putting together a engine for his pickup truck because the original 318 overheated to the point of no return. We have a 10.5 flattop 340 ready to put together and he just had a set of the 318 lean burn heads casting 302 like what came on his truck rebuild like new from factory with a little stiffer springs. The engine will have a 318 performer intake manifold, headers into duels, with a 340 sixpack cam controlling the valves. For fuel management holly 750 double pump carb. The Pick up is 89 single cab long bed with factory gear in the rear 9.25 rear end.

I would like to know if anybody hear could give me a idea if we will run into any issues using these head with this bottomend. If not how much power do you think she will make. If need more info let me know.
 
If you are wanting to use as a daily driver on crap fuel I would look for a set of 915 J heads instead. You will have more compression than you want with the swirl port heads. Maybe somebody on here will swap you.
 
sounds like a bad combination for a pick up truck. Those closed chamber heads will up the compression over the 340 heads, which is exactly opposite of what you want.
 
Your going to have issues unless you have a tall block where the pistons stay below deck or you run a thick head gasket. The "10.5:1" pistons, if the deck is spec should be .018-.02" out of the hole. 750 Double Pump is far to large for the application as those small ports and that small of cam will give out long before you can use that much carb. What trans and gears?

If it were me, I'd either go back to a 318 and use the heads, intake and a 600cfm carb or find some 360 heads a 600cfm carb and your intake.
 
302' heads come from the factory with 1.78/1.50" valves.....and 318 spec light duty (wimpy) springs.

If guides are standard height..(not machined)...then Valve retainer to Valve seal clearance is still the same...around .490-.500

But you mention slightly stiffer springs....

I personally would recommend/use some 587' castings....or 915-J's....with 1.88/1.60" valves as a Minimum....if not 2.02/1.60 valves.....that have .550" single springs with dampners, and that have the tops of the valve guides machined down and race type valve seals installed....and eliminate the rotators from the exhaust valves....and let you slip just about any cam you would want in there...under .600" lift.

318 heads...although they WILL fit....are not Optimum in any situation...for a 340.

:farao:
 
I know about the crap gas and the high compression we had the same bottom end in our 68 dart with ported X heads milled 90 thao with a solid lift mopar performance cam and crane 1.7 roller rockers. It thundered and moved real good but a little to much for this truck. I told him about adding bigger valves to the 318 heads when we were having them done because that's what I was going to do with them and build a 318 and put them in my 88 dakoda. I was going to use a least the 360 valves 188 or 196 's I think but I got nowhere and he was paying.
It going to have built 904

It not going to be driven everyday but probably often. He not really worried about fuel milage because he has a bmw motorcycle that he rides almost every day.

Do you know what compression it would be I'm thinking like 11.5 to 1 I will post up more when I'm not on my phone
 
Need to know more about the pistons...are they proud of the deck or not? Any reliefs? How big? Head gasket dimensions?

And as said above, while they would physically bolt on, that doesn't mean they're a good fit. There's a set of ready to run 2.02/1.60 587 castings in the classifieds right now for $250...I'd rather run them than 302s that still need to be built on a 340, provided that you make sure the springs/guides will take the lift.
 
well I have done a ton of research now and found that the heads and his factory 10.5 to one 340 pistons wont work because it will make the compression ratio like 13.5 to one with a 54 tho head gasket way to high for pump so looks like the the x heads are going back on it along with the big mopar performance soild lift cam 528 lift 298 duration and his converter. the truck has 3.55 rear gear and a 31x10.50 tire. too much tire for the gear.
 
Going back to the 340/360 heads is a good idea. You could change the cam to something that will better match your Performer intake. What is the RPM range of that Mopar cam? You need parts that match. Is the truck a 4x4?
 
So do you have the exact model of piston? If flat-top as in the original post, your computed 13.5:1 static CR is way off; more like 10-10.5:1 with the stock 64 cc 302 head chamber, standard 340 pistons, .053 head gasket, and any sort of eyebrows in the pistons. It's hard to call this one without better piston info.....you need to help us to help you.

Are these some forged units or what? Domed or flat-top? Are they truly stock factory pistons? Speed Pro? Sealed Power? Original 10.5's weren't really 10.5 CR in the engine.....

That big cam is going to lower the DCR a lot. Agreed that it is not matched to the drive or manifolds.
 
...It's hard to call this one without better piston info.....you need to help us to help you.

Are these some forged units or what? Domed or flat-top? Are they truly stock factory pistons? Speed Pro? Sealed Power? Original 10.5's weren't really 10.5 CR in the engine.....
Click to expand...

^^Thank you...I guess when it was mentioned a couple times above, the point wasn't made clear.

http://torinocobra.com/Randys_tools.htm

use that calculator...you have to know the particulars, but it's a very useful tool
 
replicaracer43 said:
sounds like a bad combination for a pick up truck. Those closed chamber heads will up the compression over the 340 heads, which is exactly opposite of what you want.
Click to expand...
This sounds like a terrible combination for a truck. Probably'll be not quite fast enough without being able to run pump gas or tow either.

Is your 10.5:1 with 62cc- heads or not? When you get near 11.5:1 you won't be running pump gas at all. The bottom line comes down to on a truck, you should really be shooting for running cheap gas. If it never sees it a day in its life it will be much better assurance for driving under a load than if you cannot/barely can run pump premium. The cam's probably a reasonable choice for the rest of the build in the motor. You should not be attached to compression in a truck. If you're that worried about power, I'd run a large port intake over the Performer even if it's cast iron.

Sounds like it's not 4x4- but the tall tires in the combo don't make going all the way to the solid seem like a good idea.
 
The piston are TRW factory style cast 40 over pistons they are true flat tops not sure about valve reliefs. They stick .010 out of the hole. The intake will change as well to his port matched edlebrock torquer single plane. I mentioned the X heads that have been milled like 90 thou.

We had this same set up running in our 68 dart with same trans (built 904 with 3200 stall converter) 8 3/4 rear end with 3.91 gear and posi super stock springs car was fast but never took it to the track to see how fast.
My dad figured in the 450 to 500 hp range it would twist to 6500 and still be pulling. I will post a video of it running when I get home.

The truck is 89 two wheel drive no posi so one wheel peal but one project at time.

Thanks for all the feed back guys I try and keep you updated on any changes that might come into his mind.
 
X heads milled that much are probably going to be about as bad for the compression as the 302s. You really should be using large chamber heads for your truck and getting rid of some of your compression. I'd really go for something like the 308s- most of the later 360 heads had hardened seats and large chambers.
 
This is the video of the dart with the engine in it that we will be putting together to put in his truck. We hurt it a little bit in the tuning stages but got her dialed in now with the carb. We went from 68 jet in the front 78 rear (his old nitrus set up) to 80 or 82 all the way around. That is how much more fuel it needed just from the cam and roller rockers set up, also taking into account the new ethanol gas. It's been a while since he mess with the carb.

It still has a little chop at 1200 rpm idle.

[ame="https://youtu.be/qVxDp3tENN8"]https://youtu.be/qVxDp3tENN8[/ame]
 
While I'll give you that the engine does sound decent (audio cuts out past about 22 sec), the combo does sound like it would need some tweaking...but I still wouldn't use the 302 heads unless you absolutely needed it to run, like...today or tomorrow.

But, with that same calculator above, I used 4.08 bore, 3.31 bore, stock type felpro 0.053x4.18 gaskets (because if you use anything less, you'll be running a little too close on the piston to head clearance with your slugs out of the deck), 0.010 out of the hole, 6cc valve reliefs, .30" first piston ring, .0025" wall clearance, and 59cc combustion chambers (can be typical for 302 heads)...I still only came up with 10.4:1...totally livable on pump premium if your setup is done correctly.

You find any other heads yet?
 
Yea were not useing those heads now were useing the X heads he originally had on the engine there fully ported and port matched to his old edlebrock torquer intake mainfold.

I think that calculator is a little off I use this one http://www.zealautowerks.com/index.html or the advanced one if I can find all the necessary info to fill in all the blanks. Because how are you only getting 10.4 with the small heads when the big chamber heads are supposed to be that high with these pistons.
 
It takes all the info you put in, calculates it, and spits out an answer based on the input. If you have accurate data, it'll give a good answer.

I just used what I thought to be an accurate valve relief volume...if you have better numbers, please put them out.

EDIT: I think I see what's up with the calculator you're using...when it ask for valve reliefs, it expects you to put the valve reliefs as a negative number, but a dome is a positive number...the calculator I use is the reverse...so...
 
Oh, I also looked at the "advanced" version...to be honest, the amount of material removed from the deck or from the heads is irrelevant once you input the piston to deck measurement, and combustion chamber volume. Also, the basic version on the link you provided does not include the head gasket diameter, piston to wall clearance, or first piston ring measurement...I suspect the calculator assumes gaskets the same or some "set" amount larger than bore diameter which is rarely the case, and possibly a theoretical zero for the other two measurements, which is also in error...both of those measurements will lower the number when compared to a zero measurement...
 
txstang84 said:
While I'll give you that the engine does sound decent (audio cuts out past about 22 sec), the combo does sound like it would need some tweaking...but I still wouldn't use the 302 heads unless you absolutely needed it to run, like...today or tomorrow.

But, with that same calculator above, I used 4.08 bore, 3.31 bore, stock type felpro 0.053x4.18 gaskets (because if you use anything less, you'll be running a little too close on the piston to head clearance with your slugs out of the deck), 0.010 out of the hole, 6cc valve reliefs, .30" first piston ring, .0025" wall clearance, and 59cc combustion chambers (can be typical for 302 heads)...I still only came up with 10.4:1...totally livable on pump premium if your setup is done correctly.
Click to expand...

I am running the same basic numbers and get 9.88:1 SCR. I used 64cc 302 combustion chamber sizes; I have not ever measured them but all the data I can find is that the 302's typically have 64 cc combustion chambers, stock and without being shaved. Anyone have better info on that? Easy enough for the OP to measure the 302's that he has. That combustion chamber actual size is the key parameter to know here. (And the piston eyebrows' cc's...)

I get 8.11 DCR with this cam; the cam has a lot of duration to lower DCR. Sounds doable to me...... and you'll have a decent quench gap to help. (But I have not thought out the tire size and vehicle weight however.)

As for the question on the original pistons and CR: The 'advertised' 10.5:1 SCR for the original engine was not really 10.5:1. More like 9.5:1 from all I can find. It computes to 9.7:1 with a .022" shim steel head gasket and 73 cc open combustion chambers.
 
nm9stheham said:
I am running the same basic numbers and get 9.88:1 SCR. I used 64cc 302 combustion chamber sizes; I have not ever measured them but all the data I can find is that the 302's typically have 64 cc combustion chambers, stock and without being shaved. Anyone have better info on that? Easy enough for the OP to measure the 302's that he has. That combustion chamber actual size is the key parameter to know here. (And the piston eyebrows' cc's...)

I get 8.11 DCR with this cam; the cam has a lot of duration to lower DCR. Sounds doable to me...... and you'll have a decent quench gap to help. (But I have not thought out the tire size and vehicle weight however.)

As for the question on the original pistons and CR: The 'advertised' 10.5:1 SCR for the original engine was not really 10.5:1. More like 9.5:1 from all I can find. It computes to 9.7:1 with a .022" shim steel head gasket and 73 cc open combustion chambers.
Click to expand...
They didn't usually have 73cc open chambers though. For stock heads that are totallly untouched I usually see what they're supposed to like 68cc for open Js and 62cc for Mags/318 heads. I would not count on deviations from the factory's rating lowering compression enough to nicely run pump gas- the results from those assumptions can be quite disappointing.
 
I never personally cc'd a set of 302s, but I've read at least three members on here that did theirs and came up with < 60cc...that's why I used it as the chamber size. If they're bigger, say closer to 64cc, all the better. But I personally wouldn't want to use them unported on anything other than a near stock build. IMHO, any set of stock 318 heads with as much cam as he's using and that single plane manifold is a poor match...but, hey, it's not mine so...I'll stop.
 
dartman340son said:
Me and my dad are putting together a engine for his pickup truck because the original 318 overheated to the point of no return. We have a 10.5 flattop 340 ready to put together and he just had a set of the 318 lean burn heads casting 302 like what came on his truck rebuild like new from factory with a little stiffer springs. The engine will have a 318 performer intake manifold, headers into duels, with a 340 sixpack cam controlling the valves. For fuel management holly 750 double pump carb. The Pick up is 89 single cab long bed with factory gear in the rear 9.25 rear end.

I would like to know if anybody hear could give me a idea if we will run into any issues using these head with this bottomend. If not how much power do you think she will make. If need more info let me know.
Click to expand...

If you have a 10.5-1 340 302 casting won't work period as 10.5-1 340 used positive deck height pistons and 302's are closed chamber heads. For a truck get some 360 heads.
 
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