I have 3 sets of cams on the bench now; 260 schricks (11.2mm) unknown where the pulleys are set. 300 hyd pipers. Sure the pulleys are on right. I fitted/checked them it. Took ages. 300 mech kents. think the pulleys are on right. One of these three sets is going into a fully worked KR head. Std valve size (ex F1 prep guy) I have an adjustable inter cam pulley to be used, if needed. 45DCOE's 38 chokes Std 2L bottom. I have pocketted the pistons +1.5mm deep and 1mm on dia. 1st guess' . All built ready for a head dummy fit Going to be used for racing on grass MY QUESTION(s): I am on a budget (time/money) Will the slight loss in compression (pockets) make fitting 300 degree cams, over 260's a net loss? ie area under the torque curve 4-8000 This is my core question, brought about by all the knowlegdable discussion on here. (mr hill, mr toyota etc) Will there be a noticeable difference between 300 mech and hyds? ie I only have 8 mech followers 'in stock', so will have to buy more. Plus the time to get lashcaps measured/made. I have made some mini degree wheels for the cams. How do I easily zero them? How do people get an accurate dial gauge lift measurement when checking the no of cam degrees at full lift. I always struggle to get the dial gauge down the side of the cam onto the follower. Lastly, why do some pulleys have pointy teeth and some rounded, and does it matter which ones I use? ps: my last two race 16V engines have died in service, probably due to me not getting things spot on. Looking forward to comments
could you offset bush the rods and gain enough compression to make the 300 deg work? Steath used to do this to reduce compression in the old 16v turbo days
To answer your last question the pulleys teeth differ to reduce noise, the smaller teeth are the newer type. What compression and management will be used for the timing?
What's the chamber volume in the head? If you're on stock pistons you'd need to get it skimmed to the max to up the CR, for one of the 300* cam sets. I notice there are a set of Schrick 276s in the parts for sale section....
Offset bushes? Sounds possible, but I might worry who did it, and local machine shops vary around here. I wouldnt trust myself to do it, even though I have the gear. Chamber volume. I have measured it and written it down somewhere safe. Oh dear, I am going to have to do it again.. The heads had a couple of skims, but I do need to know the voliume. As its a nice head I am reluctant to skim it to within an inch of its life. No management, just a clockwork dizzy with luminition spark pack. Simple, cheap, and it isnt going to see much running below 4K. The core question remains. With say 10:1 and 260's am I going to get more area under the the torque curve between 4 and 8K, compared to 300's? Toothed wheel shape not important then.
Last two (dead) engines had the 300's, again both used std pistons. Just want to discuss options in light of all the excellent tech discussions on this site. Dont really want to buy more cams, got too many already.
With regard to the 300 deg cams. Are they actually a true 300 deg duration? Often the cams effective duration is not the same as they are named. Cams with 300deg duration require a much increased compression ratio to get the best out of them, and that CR gained by head skimming and block deck height reduction would be higher than the std oem pistons will cope with for a reasonable length of time at high revs.
solids are Kent 1605's and the hyds are Piper BP300. both 'off the peg' units. The reason I want to keep a std ABF bottom end is both cost and availability. I have two mint std bottom ends, and have had it from a trusted source that the std pistons are a good design. To go forged is 500 for pistons, 100 for a rebore : minimum. Usually plus, plus by the time you throw in new crank bearings, oil pump etc etc And then it takes time, there is a risk the machine shop will make a mess, small chance of swarf carry over, small risk of new rings not bedding in, running the engine in etc
That is my philosophy to, theres too much risk and too cost at my level. I'm trying to get a magic 100BHP/litre from minimal costs and standard bottom ends. I'm getting closer and will in the future be choosing cams to help me get closer to this so I'm interested in how the 300degs will perform. You may find the 260's you have are not as good as stock ABF/KR's, less lift etc..
I'd wager the 260's will give a wider spread of torque- but ultimately less peak & drop off sooner. 300's great from 5-5.5k upwards but flat below- especially if compression isn't bumped up. Guess it also depends if you have modified gearing to allow it to stay properly on the boil? As a possible reference my old ITBd 2L (stock 9A compression) peaked at 7300 & held it to 7700 with hyd 268/276 Schricks & DTA management
I thought stock figures were in the 230-240 degree range. Will have to check. Is the holy grail we are all seeking to have as flat and fat torque curve as possible over the intended speed range, so effectively it is maximising the area under it we are after. Original question, will the 260's give a better area than the 300's from 4-8000 on near std compression?
Something like that but there is a thread that has analysed ABF's against some 260's, think Nellis had big input into the thread.
My choice would be your combination + 288s or 276s. To really get the torque with revs you need compression though. I delivered a calibration map for a 9A engine with > 11.9 CR, bike ITBs, 276s and a 4-2-1 header. This was a road calibration. After the initial tune the rev limit had to be increased to 8000rpm as the car pulled fairly hard once it got to 4500rpm and slowly tapered off at 8000rpm. I am pulling this car in for some dyno development and will post up what it does when I get the det cans out and look at any fuel issues that was missed on the road. I will also link this result to maximum Gs in gear and correlate to other examples. 288s would have shifted the maximum torque to the right and may have had a plateau from 5000 to 6500rpm and a very slow drop off torque ramp allowing for a 8500rpm cut out. For stocker w/10.5:1 CR the cams will allow crap VEs at "low" engine speeds and end up being peaky as the engine attempts to fill to the maximum VE at high speed. Without CR increase this would compromise the whole idea.
You can also try what Glen ( Ess three) did with his combination of OE part and Shrick 268 job. Even sick this engine demonstrated a pattern as seen when it was tested years ago in the Maha unit. Pity all 4 did not play ball.
I'd think to make the 300s work you'd need a CR of around 11.25 or 11.5:1. It's going to be a big skim job to get there - either head or block I suppose. When you say it's a clockwork dizzy, are we talking modded Polo, Pug 205, or something else?
Need to read toyotec again tomorrow, clear in brain. The dizzy runs 8 degrees static, about 35 full advance. I bought it as a 'solution' (ie cheap, secondhand..) and its worked fine. Still , whats better from 4-8000, a set of 260's at 10:1 or 300's ?? To lay a few more cards on the table, I have a preference for 'big' cams. My 1st race 1600 8V ran a GS6, and I loved it. However, I am trying to learn from the experience of the brains on this forum. If necessary I will run both back to back, if a semi definitive answer is not available. I would prefer not to, as I havent an endless amount of seasons left in me.
- - duration at what lift? How is it possible to predict the effect of different cam durations on engine performance, without including the lobe to lifter clearance at which duration begins and ends? And what of the seldom mentioned lobe centres, also a major influence? We cannot rely on manufacturers singing to the same hymn sheet, as many publish "pub racing" specs for the crowd who "feel" higher numbers translate to higher performance and therefore pub cred - - 0.050" or 1.0mm is usually considered the lift at which meaningful gas flow begins and ends, and any credible manufacturer will state as much or provide a close alternative Not to throw cold water on these issues, but I'm reminded of a recent thread seeking to establish the mass of different hydraulic lifters whereby few were identified as being either dry or full of oil - - d'accord with BrianG on that one[:^(]
Slightly off top topic, but all good points. Piper and Kent quote similarly I believe. The ramp shape will be different between the 1605's and the BP300's. (mech-hyd). By the end of this week, I need to have made a decision. At the moment its the 1605's, lightweight buckets (cossy) and lash caps. Prob going to build it with the existing chain wheel on, and plasticine the inlet cutouts after checking the degrees at full lift on both cams. If necessary (> 2 degrees out) I will schrink on the adjustable chain wheel. And cc the chamber again.
