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northern member
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602 Posts
Discussion Starter #1
do any of you guys running pump gas have a hard time keeping the egt below 1500*. I always find that I need to jet way rich with pump 91 compared to race gas and today was no different , was tuning a new 516 bbc 10:1 compression afr 305 heads ,victor intake with 850 demon , comp xr292r , dry headers . to get egt below 1600* square jetted at 97's with no power valves ,timing set at 36*. it's in a 19.5 tunnel with B impeller @ 6200 and ran out of time with egt 1400* @ 4-4500 cruise 1550* @ wot. more jet , smaller air bleeds ? oh and no a/f meter but would like to get one . any suggestions thanks Rick .
 

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Highaboosta
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3,431 Posts
When I ran 850 holleys I ran # 80 jets with power valves.
If you dump too much fuel in it will still be burning coming out the pipes and your egts will be high. Is the motor sluggish with that much fuel ?

I would not tune by the EGTs.
I removed my EGT gauge and tune 100% from the O2 sensor.

36 degrees of timing might be high for pump gas.
 

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Cantard
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5,017 Posts
I would try the timming at 32 then try again. Pump gas is not what it used to be and when you buy 91 your lucky if your getting 89.
 

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Lurker
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1,417 Posts
We have found that going from race gas (leaded 110) to Unleaded race (I think it is 107) requires going up 3-5 jets. Going to Unleaded Pump Gas (93) needs between 5-7 jet sizes to stay at a baseline AFR.
 

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northern member
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602 Posts
Discussion Starter #5
the 850 Demon has annular boosters and was 80 pri. with a p.v. and 88 sec. out of the box ,with 30* timing the first time out saw over 1700* yikes. pulled the p.v. and jetted square with 92's and 32* timing better but still saw 1650* at wot.then it got 94's with 34* better but still around 1600*finally the 97's with the timing at 36*. runs nice but started to feel a little fat the last time on the bottom coming out of the hole if you just were rolling into it. what do you guys that use pyro get your egt at ? btw water temps steady at 160 * and the plugs show no signs of meltdown on them :D thanks Rick
 

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northern member
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602 Posts
Discussion Starter #6
what should max egt be

going to try this again on the weekend . engine builder says timing should be good at 36*. going to jet up to a couple sizes and try timing up and down a couple * and try to get pyro's to stay under 1500* anybody got egt # 's to share ? what are the bad ass 800hp pump gas guys running at ? this is just a 600 hp 516 :)sphss some leaded gas with some octane would do it but the owner wants to be able to run 91 unleaded:)st
 

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TEN THIRTY ONE
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1,293 Posts
On my deal we never measured EGT's on the dyno just AFR and re-jetted to get that correct. We ran 100 oct unleaded on our first hard pulls to be safe and found that the motor didn't like any more or any less than 33* of timing. We then tried the 91 oct pump gas and made the final tuning on that. If I remember correctly we did jet up a untill the HP started to fall off and then went back. Ended up with 907 on the final pull. However I don't trust the consistency of the 91 from pump to pump. My motor is right at the edge at 11.5 to 1 comp so I mix 1 part 111 race fuel with 4 parts pump gas to get 95 oct. Insurance!!! I wish we did measure EGT's but one day on the dyno is just not enough time.
 

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Banned
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1,263 Posts
Most AFR BBC's between 8.75:1-10:1 I've seen in boat application end up around 35º-36º, however these have less overlap cams for I/O wet exhausts.

Too much fuel can raise EGT's.
Less compression can have higher EGT's than more compression. Are we sure 10:1 ? Is this measured or guessed ?
Not enough timing can raise EGT's. Worth to try another few degrees for a run but be careful.

Also, do you have another 850+ carb to swap on and see how that works ?

EGT's can be nice but don't always tell you what to try next. I suggest to keep reading plugs especially with a light and magnifying glass to make sure there are no tiny and shiny aluminum specs (from your pistons!) showing up on it.

If anyone's interested in the cam specs to give an idea of this motor:
 

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Cantard
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5,017 Posts
I have found that mechanical advance is not my friend. Locked the distributor and set it at 32 (bbc 496) major difference. At anything below 33-3500.. well lets just say I didnt need to start the bbq. That carb needs to go. Jets that big are for alc. lol
 

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Cantard
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5,017 Posts
Not too many times I here someone sandbagging on a forum. Like your style.

Then again, are you running at higher elevation ? If so, what ?
I was kinda thinking that if it didnt make 675 ish it should be put on the bottom of the river with those parts.:D
 

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northern member
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602 Posts
Discussion Starter #12
Not too many times I here someone sandbagging on a forum. Like your style.

Then again, are you running at higher elevation ? If so, what ?
ya should of mentioned that were at 1800' , RCB19 907 on pump wow very nice! we get 91 from a bulk agent who gets it direct from the local refinery in town so far it's been reliable but other than that it's a gamble what your getting . cfm comp. calculated at 10.1:1 using specified comb. and dome volumes with measured quench clearance . thats the cam but it was ordered with a 112*LCA to flatten the torque curve . carb is new have had it apart and looks ok and the distribution is even but what warp said 3-5 sizes bigger on the jets for pump gas has always been enough . have a 1050 holley that we could try but that's not what the boat owner wants to hear. thanks for the feedback guys will update you after the next time out . Rick
 

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Cantard
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5,017 Posts
ya should of mentioned that were at 1800' , RCB19 907 on pump wow very nice! we get 91 from a bulk agent who gets it direct from the local refinery in town so far it's been reliable but other than that it's a gamble what your getting . cfm comp. calculated at 10.1:1 using specified comb. and dome volumes with measured quench clearance . thats the cam but it was ordered with a 112*LCA to flatten the torque curve . carb is new have had it apart and looks ok and the distribution is even but what warp said 3-5 sizes bigger on the jets for pump gas has always been enough . have a 1050 holley that we could try but that's not what the boat owner wants to hear. thanks for the feedback guys will update you after the next time out . Rick
Wasnt trying to be an ass, it just drives me crazy when using jets that big because it is normaly covering up a fuel issues or under carbed badly. One of my customers has almost a twin motor to yours and he was running an 850 race demon. I made him put on the dominator and car instantly picked up 1/2 a second and 8 mph. Went from 98 jets to 83. Runs much cleaner. By looking at were you are having trouble seems at lower rpm were it is prob real rich then at the top prob almost goin lean but just cant get enought out of the carb.
 

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northern member
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602 Posts
Discussion Starter #14
71hallett , no i didn't take you serious so it's all good . were actually happy with the power , on a dyno with a bigger carb it might pull 675 ? but i've found from tuning in a boat and looking at the impeller charts there not as generous , teaches you to build for torque . the guy has a history of flat footing everything to death so he bought the 850 thinking it would limit the top end while still making around 600 hp. btw advance is locked out . anymore ideas i'm all ears sounds like your doing a lot of similar stuff to what we are , how's your 8-71 coming along ?did the impeller and helped with the tune-up on one couple years back 433bbc A-B Aggressor impeller @ 6000 with 8lb's boost. be good to hear from more 500 to 700 hp guys must be a ton out there .
 

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Cantard
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5,017 Posts
I hope to be able to fire it up next weekend or begining of the following week. Waiting on a couple parts. (Rockers and mag) Was that 433 a destroked 454 or stroked 396?
 

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northern member
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602 Posts
Discussion Starter #16
71hallett ,it was a LS-6 that had the crank go bad and got a 427 crank and pistons.
 
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