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I am building a 347 stroker for my truck. I am using ford E7E heads that have larger vales 1.9 int, 1.6 ext, the intake and exhaust has been ported as well. I am using a HO 5.0 liter block and roller isky towing cam Part#: 371252/257 . I am not going to tow with this vehicle except for the occasional trip once or twice a year. My question is should I us a different piston since the current one Kieth Black (KB246) will bring up the compression ratio to 10:1 and I need to pass the dreaded smog test a couple of years from now. Please let me know your recommendations and I look forward to your response.<o></o>

 

well 10.1 should be ok with pump gas, just barly though. As for smog tests, the higher compression will burn more of the fuel in the cylender making the engine more efficent. If you have a visual inspection also, you will have to have the EGR system and the cat on there. You could probably just put on the EGR system and tack weld the flap shut. You will need vacume canisters also. Do not use platnum plugs, they tend to make you engine ping if you are barly getting by with pinging anyhow. Just out of curiosity, why didn't you just use a 351W block?

 

The reason was to give the impression (visual inspection) of a 5.0. This way I would not have to buy a new intake/Exhaust mods. Also I have never built a stroker before.

 

Is that cam listed with isky as a cam that will pass smog? I would check with isky to see if has a CARB exemtion number. It probably is Ok as most towing cams are fairly mild.

Listen to your engine carefully when towing, as this is when you will have the most load on your engine and could get some detonation, if you do experience detonation when towing,back off the throttle! You might have to use a octane booster in addition to premium fuel if you still have detonation.

 

I have a 302 with 289 HiPo heads that is rated at just over 10:1 with flat top pistons. I always have to run Premium fuel in it, and even then, sometimes it pings. It's very sensative to what brands of gas I use too. I don't care what it says on the pump for octane rating. Some company's gas is better then others. Retarding the timing will stop the ping, but then it won't pass your smog test most likely. One thing you could do, is sell the iron heads and buy an set of aluminum heads. They are less prone to detonation, and will handle a point higher in compression then iron heads. I have also heard of people using two head gaskets per cylinder to get their ratio down a little. I don't know about that "fix" though.

 

This would be a very important thing to keep in mind for building this engine at over 10:1, as stevef lives back east where the premium fuel is likely at 93 or 94 octane for premium. The highest octane premium avalible in California is 91. So, if he's having problems with higher octane at the same compression ratio, I would definiatly say drop your compression ratio down.

The other potential problem would be that a sroker motor has a higher actual compression that what the static compression ratio calculates to, due to the longer period of dwell by the pistons at TDC. I've been told this is another reason to keep your compression below 9.5 on stroker motors.

 

Very interesting. I didn't know that 93 isn't standard for the whole country. Good point about the actual c.r. vs. the static c.r. I forgot to mention that. Per original question, I would change those pistons out to a set of reverse dome, or dished. Whatever you want to call them. You'll have to do some research to determine what cc dish you need.

 

yeah, I dont know why we get crummy 91 octane premium out her and not 93, believe some of the north eastern states it is 94.

Any know why the octane goes down out west?


Hey stevef...I was reading in another post you run 383 stroker(s) in a boat? Twin screw? Sounds like fun...any experience with centrifical s/c's on boat motors?

 

I ran your numbers (assuming a 64cc chamber, zero deck, .040 total quench) and with that head/piston/cam combination came up with the following numbers

Static CR 9.89:1
Corrected 8.26:1 (taking into account the camshaft)

Considering a good rule of thumb to use is 8:1 max CR (corrected) for an Iron head w/Premium, I would look at possibly changing over to a different piston. Another option would be to change over to a 69cc chamber head, which would give you 9.37 static, 7.83 corrected, which should run fine on pump gas. Also, changing over to a cam with a later closing on the intake would also help to lower your CR. The cam you have closes the intake at 59degrees, changing it over to a cam that closed the intake at 64 degrees would get you down to 7.97:1 corrected which will run pump gas on an iron head. A comp cams 35-310-8 would work in that respect with a duration of 270/276 and a lift of 533/544, altho it would be a bit more "lumpy" than the cam you have chosen at 252/257 duration.
Also, DO NOT use the 2 head gaskets trick to try and lower your CR, doing so will ruin the quench effect in the cylinder and in turn make you more detonation prone, also, remember that your corrected compression will always be less than the "static" compression ratio. You can run Hi (static) CR's on the street, and on pump gas, regardless of whether the motor is a stroker or not. The trick is choosing the proper camshaft and careful engine bulding techniques.

 

Breeze- Spoken like a true scholar. Now find an equation that includes the effects of aluminum heads on acceptable compression ratio verses iron heads. There IS a difference, due to the better inherent cooling properties of aluminum. <p>
94F150-408- Yeah, the boat is a 28' Chris Craft Stinger. It was fun with the stock 260 horse 350's, but even more so now that I went from 520 hp total to almost 750 with the 383's. Because of the marine spec cams, I couldn't get any more out of them. I considered putting the right parts together to supercharge them, but decided not to because of the cost involved. I'm running Alpha One outdrives, and they're not supposed to spin any faster then 4,800 rpm's. I'm turning them at 5,100 as it is. Sure I could change props, but I'm pushing the envelope as is with the hp I'm running through the Alpha. Swapping over to Bravo drives and superchargers would cost about a years pay for me. Now if I win the lottery.........

 

Maximum cr without pinging is something that is attributed to more than engine charecteristics.....

Alttitude where you live is another factor...Dennis (mil1ion) lives in Alberta, and he has a stock 429 tjet...(11:1 CR) he gets by on premium canadian gas (not sure if canadian makes a difference)

I also have read differing opinons on what you will get by with....some say 10:1 some say you can squeeze by with 11:1

you could also mix a few gallons of Avgas with your premium to make it work octane numbers in fuel are averagable, and it does work that way

from the owner of a truck with a 429 tjet that doesnt have it running yet, and has put a lot of research on this board into getting ready for it....good luck

 

The difference between the aluminum head and the iron head is, as mentioned, due to the better cooling with the aluminum head, as a rule of thumb, an aluminum head is good for .5 increase (sometimes more) in CR over an iron head, not to mention the better flow characteristics (as cast) over a stock iron head, weight savings, etc. KB Silvolite has finally gotten there website back online a while back, and they have some very handy calcualtors on line to figure your CR, etc http://kb-silvolite.com/calc.php along with some very handy articles on compression ratios and such by John Erb the chief engineer at KB

 

Good link Breeze, another one to take a look at for information regarding octane requuirements and the factors affecting it is this one, look towards the end of the article for the information on octane.

cheveron.com/prodserv/fuels/bulletin/motorgas/ch5.shtml

stevef...sounds like a fun boat, I've got a 21' Chapparal with a Magnum 350, 300 hp at the prop, Bravo 3 outdrive. Top speed now on GPS is 68, I would like to get this up to closer to 80, not sure what I should tackle first to get the HP needed, suggestions?

 

Thanks Breeze

I think the cam would work best for me, but will the Truck pass smog? I have a MAF conversion kit in already installed and i will use 24lb injectors too. Also I was thinking of smoothing out the combustion chambers to help the detonation problem and I can find 92 octane out here in southern california. Let me know your feedback and thanks for everyones help. I need it

 

Whether or not the truck will pass smog depends alot on how detailed a inspection it is... if it is a basic "lift the hood and look" with a sniffer, you would probably get by... if its a more detailed "poke and prod" under the hood where they look at actual part/numbers/etc then it can become a bit more tricky. The one nice thing about running a higher CR is it will take a bit more cam with going into the total rump rump rump sound of cars with big cams and lower CR's. Polishing the combustion chambers would be a big help. With the truck having the MAF conversion on it, it makes cam selection a bit easier, however, radical cams are still problematic due to the eratic vacuum signals the computer gets at idle. I would call Comp Cams (1-800-999-0853) and talk to their tech guys, as they have all the numbers on their cams at their finger tips. Tell them what youre building, etc, and that you are looking for a reasonably computer friendly cam with an intake closing of around 64 degrees