Whichever way you end up going, an update next fall would be nice to help others know about your experiences. Some may benefit from your experience, others will disregard it anyways
Even if you zero decked the block, you would still be at 45 thou. quench, using the comp gasket. Either way, zero or 5 thou. down, you still cant use the steel .016 gasket, right?? What is the 'ideal' quench distance, and the best way to get there?? If the block is decked after the boring and final honing is done, what consequences may happen? Also, what is the most dynamic compression one can use for 93 pump gas?
no that motor is 11-15 thousand in the hole. would give 26 thousand clearance. has 9.15 compression now
If he leaves the deck alone it will be .026-.030" (?) with the steel gasket and likely won't hit. If he decks the block, it can be set to any quench clearance. It doesn't have to be at blueprint 'zero'. The ideal quench distance is when the point of diminishing returns of the effect is reached. The increased compression of a similar chambered engine he has is showing signs of reaching that point. There isn't a ton of info shared about the two builds or his build strategies/calculations...so the only factor we are (I was) looking at is the total timing being shy from what's typically observed with these heads on one of his builds along with the static and dynamic compression ratios used in each. It has been shared here previously that Buick had observed counterproductive effects by running the quench tighter than .035(memory?) on Nails. Max dynamic for pump gas exceeds these examples by six or seven whole numbers...in a lab. The real world and each specific build paradigm having much more input to the octane tolerance package than just the engine's dynamic ratio, specifically THIS build...............{{seems to put the max dynamic ratio somewhere between the example that won't tolerate more than 28* and exactly where he would be if he just put it together with the thicker gaskets}} if all else is similar. It's been mentioned that there are various other ways of raising the engine's threshold to octane tolerance, but the lack of dialog suggests to me that it might be better to leave things conservative...because of the way running conditions (air temp, water temp, gas station or vehicle) would chip away at that safety margin. There might be an issue with incandescence... hot plug, hot exhaust valve, sharp edges on the piston or around the combustion chamber from machining. Temperature issues will quickly supercede pressures from dynamic compression ratios in the real world, so if one rides the edge...they are asking for trouble! The decision to NOT deck the block was claimed to have been largely based on the shop's workload and the desire to move forward on the assembly rather than what's being discussed in this thread, so I would guess that the benefits of decking the block were not considered terribly important at that time. I would feel more confident in the desire to deck the block if the OP had laid out strategies to manage heat in the chamber and raise the engine's threshold to octane tolerance as intended for the overall build plan. The effect of decking after boring wouldn't affect this build other than it would assemble more squarely, and have potentially more even compression from hole to hole(which is a questionable benefit being that they don't run the same temps). Being this is a 401 with a couple builds left in it, it 'could' goof things up for the next machinist depending on how things were located previously. Things are jacked around more for the first rebuild, esp. bore position (warpage, factory tolerances, etc.) There isn't necessarily a ton of time spent analyzing the block's deviation from blueprint when it's in the boring machine. Nobody is paying us hundreds per hour to CMM the block to assess it's closeness to perfection in order to save the owner some money It might just get honed...it might be bored with a following comment "it didn't clean up at .xxx, you'll have to get different pistons" (everybody LOVES that!) Either way it goes, I'm hoping the OP is more open to what other factors are at play and should be able to use his experiences to arrive at a decision. The books and experiences of nearly every engine builder say that almost universally it is better for the engine to have quench .035" than .055-.060", even with raising compression into a borderline range. The OP has other builds to base his data from. Some time down the road it would be a benefit to all here to learn from EXACTLY what went right or wrong as too often we read things long after the fact that obscure the root of the problem.
There are other factors as you near the tipping point of octane tolerance. Surface to volume ratio is different (same chamber, smaller volume cylinder). Rod angle and piston position per degree of rotation of each version and over stock, with affects on before and after ignition. Acceleration rate based on gears, weight, torque output... The need to run 28* timing might be from something right just as much as something wrong. We don't know much from this end of things.
what i dont understand on the big stroke 10.4 motor running best at 28* timing. why does everybody think is close to det and would run better with more timing then 28* if it could handle it. always been said the the nailhead likes 30-32 timing. now take a motor with longer rods needs less timing right? more compression needs less timing right?. I dont think 28* is off base. thats only 2-3 degree less then a normal nailhead. talked with guys racing normal nailheads saying that they ran best at 28* timing.
Only thing I can add is that WHEN dyno time was paid for the results that were achieved. A 401 bored .030 over. 13 1/2 -1, 6.535" Chevy rods. Heavy forged pistons. A prototype set of MY ROCKERS. Ported heads by Steve Magnotti. The engine responded better at 36* to a certain RPM & then fell off sooner & DIDN'T make the same amount of HP as at 28*. So this means the advanced timing was better for a heavier car (or a 2 speed auto) to get it moving. At 28* it DIDN'T fall off as soon, made more HP & revved to 7100 & we NEVER did find the fall-off point. We didn't want to go any higher RPM wise as each hole the weight was ALMOST one pound heavier than stock because of the extra weight of the piston & rod assembly. From the high point of previous RPM's of approx. 5900-6000 to the 7100 we stopped at wasn't 30 HP. So all this is telling us, in my mind anyway, I WANT MORE AIR. I know on my '64 Riv. that the car ALWAYS ran it's best when the timing was at 36* & retarded 4* above 3800 RPM's. In my mind this has something to do with the combustion chamber design of the "Nail" along with it's ability to have VERY HIGH SWIRL RPM's to help fill the cylinders. When my engine was assembled in the early 70's I & many others were not as knowledgeable & had the available parts & formulas we have today at our finger tips. Going back, since day one, my cranking compression was only 135-145. Meaning my REAL compression ratio is probably somewhere around 8.2-1. Today the cranking compression is closer to 120-130 so it's getting tired with more than 200K on it. Just my thoughts on the matter at hand. Tom T.
(responding to post #46) Because nobody knows all the relevant specs of your builds, and combustion problems are silent until extreme and severe. I'm not confident based on how this thread reads that the plugs would be read with enough of a discerning eye to catch early signs of troubles. (No offense intended! ) I'm saying that unless you know the why and what...it's safe to give some cushion instead of pushing more cylinder pressure. Everyone wants to make 10 more hp, nobody wants to make an indestructable fool proof engine. My direction is coming from being able to find 40hp an easier and safer way than pushing compression and with the desire to run inconsistent pump gas. Example.. now that your heads, induction and cam work better, are you going to see more cylinder pressure from a VE increase or did the porting slow down some of the port's mixture motion (swirl) hence, flame speed? Both? How are you determining if that timing figure is showing the net effects of faster burn rate or that the engine is happier? What is your AF ratio throughout the rpm range and how are you incorporating that into timing requirements as you make changes? 28* 'might' be showing you signs of trouble...you would have to determine that yourself. You are at the point in which it would be wise to set aside the tribal knowledge aspects like, "They say that Nails like..." or "Long rods like..." and see the where it steers you. Keep them in mind though! You are running with changes outside the norm of most of the nailheads usually discussed in several aspects. I've done some extremely high compression engines, so I know what factors to push and when as well as taken the surprise beating to my pocket book when an unexpected variable shows up. With machinery and processes I like to incorporate a little poka-yoke (fool proof or "inadvertent error prevention") into things. Why let the gas station's decision to use a different refinery delivery that particular day destroy your engine? It doesn't matter to me what your engine build strategy is, I was only opening up dialogue related to your post. I like the stroked Nail builds and creativity involved here, as well as appreciate the need to push things further. I wouldn't be offended if you went the opposite direction from my opinion.
General comment to the 36* scenario on Tom's... It makes sense that with assuming lower dynamic compression that the lower rpm ranges would need more timing because the lower pressure charge has a slower burn rate (bottom end of cam's power range). That's normal. At high rpms, the need for less timing coincides with a faster burn rate and there would be negative torque to fight with 36*. The longer rod engine would also be sensitive to too much timing at high rpm due to the piston's position in the cylinder and the effects of negative torque. There's a sharper rise in pressure to fight. That's how I'd explain the slower rate of power loss with those timing changes. The nail is starved anyways. Higher swirl serves to speed up burn and reduce timing, to a point.
i guess it all makes sense. like Tom said more timing down low then less at higher rpms. dont forget this is stroked with 446 ci and mega low end, torque converter flashes in the low 3000 rpms so am not needing the low end extra timing, but helping my mid and top end with the low total timing. i do use a lead octane boost which gives an extra 3 point octane boost. the only other thing is to run some race gas and try more timing. but then again race gas needs more timing anyways
You mean .3 octane boost? Are you seeing any difference in timing without your fuel additive and does it do anything to the burn rate (forget octane boost for the moment)? Which race fuel? I'm assuming it's to test the pump gas/compression theory? Don't need the extra bottom end or "won't take the timing"? Otherwise... Why would you 'try' race fuel on a low compression engine? (That makes little sense to me.) If you have to add a little high test to keep your engine safe or if you show a power increase from timing as a result it is absolutely telling you it isn't fully safe for pump gas and the 12 hp you seek is at great risk. If you don't mind race gas, then built it as high compression as you can and enjoy using it. I haven't forgotten which engine is which. You would still see a benefit of timing slightly above 3000 if it needed it slightly below, that's what 'might' be an indicator of whether or not more compression would be a good move. I'm basing much of my complete guess on the use of fairly small cams here.
Also funny is that I take things literally and can't always tell if people are playing with me Winter threads and boredom are coming, lol.
Excerpt from chamber coating company... "It should be noted that the faster the engine is turning, the shorter the time for the crankshaft angle to reach that 16 degrees ATDC position (PCP). The burn time of the gas is controlled by the chemical makeup of the fuel itself, the temperature of the fuel, and how well it is mixed with the required oxygen. Octane additives do not change the burn rate of the gas. Racing engine fuel has a different chemical design so that it will burn faster to keep up with high RPM engines. Octane rating is NOT involved in this fuel burn time, regardless of what rumors you may have heard or may have said yourself. "
you lost me again f85. 10.4 is not low compression . the 12 hp gain would be for 9.15 compression motor. its a lead additive with gives 3 points octane not .3 points. anyways my thread was is 26 thousand clearance alright and seems like i should be ok. i shouldnt have mixed up the thread with two different builts.
Didn't mean to confuse you! I'm still aware of which is which I'm using the example of one engine to illustrate how you have the ability to utilize it towards determining the other build's direction. 10.4 isn't high or low, it's the edge of pump gas with a fairly small cam and relatively heavy car. It might be showing you signs you could use towards the other one. It appears to me that you are contemplating another "edge of pump gas" build, that's all. My comment on 3 points of octane is coming from a long history of cans of octane boost suggesting 3 points and misleading the public to believe that 95 will become 98 octane where in fact it will only become 95.3. (Disclaimer being that I've read recently claims that there is some kind of new additive that does increase octane ratings rather well but I suspect it is either not largely known or also as history has shown...untrue) I don't believe that if this engine ends up a little tricky with pump gas that you can magically solve that with a miracle can or that it's a wise strategy to dump some race fuel into it or that if you have to dial back timing too much that you are going to see your 12 hp that was eluded to. Use whatever gasket you want to and enjoy your car
Edited post........... Okay, I believe these are my final numbers. 409.82 CID 4.210" bore 3.68" stroke : crank offset ground .050", resulting in .40" added stroke. 6.8" BBC Eagle CRS H beam rods Heads mildly ported, and combustion chambers polished. Stainless valves, heads resurfaced and cc'd 125cc Heads, intake(Docs mod done), and exhaust manifolds gasket matched. 2.5" stainless mandrel bent free flowing exhaust w/x pipe. TA 25 cam 800 cfm Edelbrock 1965 Skylark 2 door post car 1966 ST400 trans. variable pitch convertor 255/60R-15 Radials on back, 27.1" diameter 3.08:1 rear end ratio. I want to drive to BCA events next summer. 30 degrees timing in (12 initial and 18 mechanical) on pump gas, 93 octane. Will try 100 LL. I'm going to put the pistons .020" in the hole, 40cc piston dome, for 9.88:1 static compression with .016" steel gasket. Compression height 1.34" theoretical. Actual to be determined after square decking block. Dynamic compression 7.76:1 with cam installed 4 degrees advanced. 7.49:1 straight up. I appreciate any and all comments. Sincerely, David
dlmwtvl, looks like a great built. 2 things, will the 6.8 rods clear everything ? and who makes a .040 head gasket ?
plus your pin height will be about 1.33 will that be into your rings ? if it works your have some very light pistons.
Taking the rod journal down from 2.250" to 2.200" will only add .050" of stroke. The centerline will only be moved .025" with .050" taken off the back side or bottom side of the rod journal before the top side cleans up and the journal is a circle again. Usually the crank shop will want an extra .010" for indexing to make sure all the journals clean up, so you'll only have an extra .040" of stroke.(.020" more going down passed the centerline to bottom dead center and .020" more going back up passed the centerline to the top dead center) Unless you have .010" of undersize ground in the crank to get all of the .050" more stroke, you'll only get an extra .040" more. With only an extra .040" more stroke means when you calculate the pistons compression distance it will be half the stroke; Deck height - half the stroke - rod length = piston's compression distance or compression height whichever one you want to call it. Cool build though! If in you wanted even more stroke you could go with a Nissan rod with a 2.086" rod journal OR if you want to get greedy with stroke you can get basically the same Nissan rods that have a 1.850" rod journal size! The length of both of the mentioned rods are 6.495" long and are both wide enough to be able to narrow them to fit the Nailhead like BBC rods can be. So the stroke can only be increased as much as the diameter is decreased minus the sacrificial .010" for indexing and to ensure 100% cleanup of all journals. For the good Nailhead pistons, contact Tom Telesco(Telriv) here on v8. GL
