3G Go Kart Project , Cylinder Head

[FyreDaug]

Where can I get some head parts to get 7500 safely?


Im just working on the assumption that the rest of the motor is good for up to 7500 and I wont spin bearings, and that the majority of the higher revving issues on this car is valve float, so correct me if im wrong.
Im gonna be picking up a stage 2 tri-flow cam for this kart project, and they claim 3500-7500rpm, and there may be a few times where id like to hit that high, 6000 is the most I really ever see out of these motors, its carb so I could technically go higher, but if it is a valve float issue above 6300 or so, then id like to get some tighter springs and some other minor head work to get 7500.
Is there any bottom end stuff needed? Are the main bearings good for that kinda speed?

[B16KILLA]

Im just working on the assumption that the rest of the motor is good for up to 7500 and I wont spin bearings, and that the majority of the higher revving issues on this car is valve float, so correct me if im wrong.
Im gonna be picking up a stage 2 tri-flow cam for this kart project, and they claim 3500-7500rpm, and there may be a few times where id like to hit that high, 6000 is the most I really ever see out of these motors, its carb so I could technically go higher, but if it is a valve float issue above 6300 or so, then id like to get some tighter springs and some other minor head work to get 7500.
Is there any bottom end stuff needed? Are the main bearings good for that kinda speed?

To get there safely, I say knife edge the crank,balance to whole bottom end to the down to the gram,maybe a custom piston head that would still maintain the compression you want and not hit the valves at high rpm's,stonger intake and exhaust valve springs, you'll also need a tighter timing belt tensioner.Theres alot to consider when doing something like this . Plus you also have to think about accidently over revving a time or to ( it happens to everyone) no matter if you miss a gear or what.I dont think that the main bearings would take that.

[bobafett]

if you plan to sustain a lot of high rpm driving i would look at new oem honda bearings or some nice king bearing or something of the sort. also if you want to run 7500 a lot then some lighter bottom end parts couldnt hurt your cause.

lighter rods, pistons, crank, etc, maybe a flywheel could all help the efficiency and longevity of a high rpm motor. just make sure its all properly balanced, thats probably the biggest thing.

if you are prepared to spend a bit of money, the a20 head pretty well sucks at high rpm efficiency, so some headwork will make that high rpm time a lot more enjoyable. i would get ahold of someone at www.sivalves.com and see if they can build any custom springs for your application. i know they do carry a decent setup for valves. but ur getting into some serious money at this point.

if you ARE worried about over revving, an EFI setup could take out some of the worry. and if you are running this in a kart, then maybe some megasquirt efi conversion might be ideal for your setup.

[Justin86]

valve float is your first problem which is around 6800. The cheapest way would be to shave some weight off the valve stem, and retainers. Also to go cheap is to put a small spacer (.1") under the valve spring to load it.

Then for the botttom end at the minimal have it balanced.

Now this is the cheap and minimal to get by. The proper and long lasting way is listed in above post.

[FyreDaug]

bleh screw it, I was hoping it was simply some head work, because I was going to do it anyways. Ill probably just throw some better springs on there anyways when I do some mild porting.

[A20A1]

I thought the thread title had an odd ring to it.

I used to rev like that, my bottom end gave out before the head did... I don't think the head even gave out but it probably would have.

[snoopyloopy]

I thought the thread title had an odd ring to it.

I used to rev like that, my bottom end gave out before the head did... I don't think the head even gave out but it probably would have.

i dare say this post perpetuates the odd ring from the title...

[FyreDaug]

So pretty much the amount of work needed to get to 7500 is pretty much an engine rebuild anyways. Ill do it down the road if I feel like it or, if the motor(s) give out

[bobafett]

rofl more like an engine build to make it last.

[rjudgey]

Revving at 7500rpm
Well most my engines rev to thats as a minimum normally pull 8k.
The best thing you can do is get a set of ET/A18 Prelude head springs and retainers there good for high rpm use.
The weakest point are the stock Honda bearings as they are poo for high revs, i would get ACL/King/Toga tri metal that will sort out any issues with throwing bearings but obviously you need to make sure that everything is balanced, the cranks straight etc. don't knife edge the crank as theres not much of it to knife edge leave it be just double check the balance when you ahve the flywheel lightened witht eh pressure plate and bolts attached too.
Cast pistons are fine upto 7500rpm but you need to give them a little extra room to breathe 0.05mm so obviously you'll need bigger rings to cover the extra gap so get a oversize set and gap them by hand for best compression. Also for high Revs you'll be needing a good carb at least a Weber DGV 38/38 or better would be a pair of DCOE 45's but then your talking some money. Bottom line is if you rev a worn stock block to that extreme you'll wear out the bearings very quickly and when that happens it will ruin the crank and rods.

[FyreDaug]

What do you mean by ET/A18? Is the ET something more specific than a regular 2nd gen lude?

[gfrg88]

What do you mean by ET/A18? Is the ET something more specific than a regular 2nd gen lude?

et/a18 is like bs(or bt?)/a20

basically the head off of a 2g lude with dual carbs....

[TheWatcher]

i dare say this post perpetuates the odd ring from the title...

I was gonna tell him to go find a tranny.

Peace.

[A20A1]

I edited the tile btw.. so don't rag on him too much.

[rjudgey]

The timing belt tensioner's are fine still using ones that have 100k plus miles on them, i just take them off every now and then and clean it up adn let it soak in some quality oil and clean it off and put it back on. You could replace every 60k to be safe but there solid anyway just tighten them up to 30-35lb ft to make sure they don't move. Valve train is excellent at high revs only problem is on the head bearings can wear on the cam pulley side and the next two along as this is where the most pressure is from the cam and the belt so you need to keep and eye on it and strip and re-polish every 15-20k miles to keep tip top using quality oil and uprated toga oil pump will help more. Water pumps seems okay and could be replaced by electric ones to stop cavatation in coolant. Also worth looking at a larger pulley for the alternator or smaller one on the crank to drive it as i'vechewed through quite a few sets of bushes and regulators tend to blow up after 10-15k miles too for some reason but i've only ever replaced with secondhand units so maybe they don't last because of this not sure. Other than that should be fine oh forged rods and ARP bolts might be a good idea.

[FyreDaug]

Seems like quite a bit of work like I said, its obviously no easy journey. So this is what I plan to do, drive 1 motor until either it dies or the second one is ready (if it dies, ill speed up the progress on the 2nd one). The second one will probably be a full build, both motors have betwqeen 200-300k on them

EDIT: oh and I havent seen any ludes with dual carbs around here... yet anyways. I assume they arent the same in the regular ludes then?

[rjudgey]

Yeah the carbed lude seems to have really strong springs for some strange reason ET/A18 are very similar ET had slightly earlier block A18 same as yours but 1.8 litre bore size. Another consideration is a ET1 or ES from a carbed 2G accord sometimes they come with double springs as well.

[FyreDaug]

sounds good, ill check em out. If I grab them and test them, what should the lb/inch or whatever it is (sorry cant remember) for proper pressure... Since they are 20 some years old I wanna make sure they are still up to spec

[rjudgey]

sorry don't have the specs on the springs just feel by hand which are stronger, the exhaust springs on the ET/A18 seem overkill but could be used on anything 290 degrees or more, the inlet springs although singles are actually really hard as well good for at least 8000rpm. The doubles on the ET1 are not too bad but need shimming up to get the best out of them or if you were to convert your exhaust valves to inlet valves you can use the double valve springs on the exhaust valves instead which are pretty good at high revs too, i actually used A20 exhaust valve springs and retainers on the inlet side of the head worked really well.

[FyreDaug]

Ok maybe I can do that, just something to stiffen up the head. If I do build it, I doubt ill go over 7200rpm, which isnt much more than stock, but just so I have a little more room to pull, and to err on the safe side incase of a mis-shift at high rpms (these synchros arent exactly the best, and higher rpm is worse.... tranny rebuild eventually... oh well itll be fun)

EDIT: Because its still carbed, this weber will be good to bring it to 10krpm no problem, esp with a lighter flywheel, im kinda scared for the bottom end.... Stock shifts for now I guess, thanks for the input

[rjudgey]

It will never rev to 10k unless your going down a very very long extremely steep hill. The most i've ever managed to rev an ET to was 8k with a 285 degree camshaft with two pairs of Weber DCOE 45's heavily moddified even with a 300 degree camshaft an A20 head very well modified and some seriously light rods i think it might just be possible.

[FyreDaug]

Either way its not gonna be good for the motor if I mis-shift, and to try to reduce valve float may be a good idea if the head is getting rebuilt anyways.

Is there any other potential gains from springs? (doubt it) like because it closes faster you get more torque?

[A20A1]

A heavier spring follows the cam lobe more accurately. also it assures you that the valve will close when it's supposed to. It will close earlier than maybe a lighter spring but not any earlier then the cam lobe dictates.

[rjudgey]

If the springs are too stiff it will cause unwanted friction and you'll loose power.

[FyreDaug]

If the springs are too stiff it will cause unwanted friction and you'll loose power.

Yeah thats what I was thinking after I posted that