ls/vtec rev limits

ok ok ok, i’ve read through just about every thread there is in this forum about ls/vtec. on one hand, i hear that in order to do an ls/vtec conversion, you need to do some block work: shotpeen the rods, bore/hone/deck/balance, new bearing, new rod bolts, and better pistons/rods. By doing this, there’s nothing to worry about when revving at around 9 or 10k. Then on the other hand, I hear that it is possible to do a stock ls/vtec conv. without the block work, as long as you don’t rev past the Ls stock redline which I think is around 6500 rpm and will give you a considerable power gain. But then I read that it’s safe to rev up to about 7500 rpm with the stock ls/vtec minus the block work but the stock setup won’t actually produce a considerable amount of more power.
I’ve driven a few cars with vtec in them(ITR, CivicSi, and tricked out Civic EX) and at about 5500 rpm on all of them, the vtec kicks in. When driving each car, I wasn’t very knowledgable about vtec or about the redlines in each car so I would always shift at about 7000 - 7500 rpm anyways. I plan on doing the ls/vtec conv. and don’t really plan on pushin my car past 7500 when I do race. Since I plan on having the revs go no higher than that amount, is it ok that I don’t do the block work when I do the ls/vtec conv.? If so, why won’t this setup yield that much more power, I mean, I would think that having the vtec active for just about 1500 - 2000 rpm would be a lot better than having a regular b18a setup.
I’ve seen the dyno chart for a stock ls/vtec setup and it produced 155whp which is about 185hp at the flywheel, and the car had a timing problem and was backfiring during the dyno runs. I know that 7500 rpm doesn’t seem like much as compared to 9k and up, but it was between 7000 and 7500 that the most power was gained.


from what i know…VTEC heads breathe best at higher rpms, 7k+ and generate the most power at the higher rpms. in order to fully take advantage of the LS/VTEC setup you need to be able to rev high. now this isnt saying that you cant generate a good deal of power at slightly lower rpms, but it is not going to be at its full potential. VTEC heads are also designed to take higher compression as well and you are also cutting yourself short by not raising compression. stock b18 has 9.6:1 compression i think which is low compared to the VTECs. anyway a stock b18 has a redline of 6750 i think, but if your engine has relatively low miles im sure you could run it upto 7500 every once and while. if i were you i would plan on building the bottom end soon, just to avoid future problems. i had a post about my setup and i was told that even with shotpeening the stock rods and using ARP rod bolts its still not completely safe to rev past 7500 with out a block girdle.

hope this helps.


yes, you did help, and i appreciate it. i guess there’s no avoiding it, either way, block work is needed so i might as well have it done while the head is off. i got a setup off one of the threads and in it, it mentions gettin new bearings. is this really needed??? i mean, if i just shotpeen the rods, have them shaved to fit the different pistons, get rod bolts, and a block girdle, would this be enough as far as block work goes??? as for pistons, are b16a pistons ok as far as compression goes or are itr pistons a must??? since now i may as well do the block work, i guess it would be ok for me to rev up to about 8k when racing which is about as high as i’d go until i feel more comfortable with the car. i don’t really plan on racing much, just maybe a few times on the weekend, and as far as the little streetlight challenges go, i’d say no higher than about 7k, maybe 7500 if it was another vtec car.
i plan on workin on my car myself with a mechanic i know in order to save on labor and to get experience workin on my own car. i’m guessing that there’s no way around pullin the block out in order to get to the rods and pistons. i wish there was because it’d most likely save on time.


yes… put in new bearings…if you are going to build the block then you might as well do it right…along with that replace all the seals too. if you try to take shortcuts now you are going to pay later and if money is the problem just be patient and wait. but thats just my opinion, so take it how you want. i know i wouldnt be confident in the engine knowing that i could have went one step further and avoided a major problem

aiight, so i guess it’s all or nothing when going ls/vtec.
what about the pistons??? can i use b16a pistons or should i use itr pistons. from what i read, b16a pistons have like 11.something to 1 compression so i guessing that’s good.

im going to be using b16 pistons (usdm PR3). i believe that if you are using the stock rods then you would have to shave them slightly to accomodate ITR pistons. the b16 pistons on the other hand SHOULD be a direct replacement and you will not need to increase valve reliefs either. these pistons seem to be the best way to go if you are on a budget. ive heard anywhere from 11.1-11.7 compression with these.

damn you’re good

so with all this, i should be able to rev up almost as high as i want without any problems. along with the ls/vtec, i’m swapping out my auto for a 5-speed, and since i’m going vtec, i guess i need a gauge cluster that has about a 9k rpm limit. you’ve been more than helpful with all this, but i actually have one more question. where would i find a block girdle??? i’ve looked around online but i can’t seem to find one anywhere.

now dont go revving that high on those stock rods even if they are shotpeened…if you want to rev to 9k you are going to have to get some heavy duty rods b/c of the not so ideal r/s ratio (1.54). id say that 8k is safe with stock rods, ARP rod bolts, and new bearings. Eagle rods are good and about $350 a set. a GSR block girdle can be adapted to fit but requires some shaving because of clearance issues i believe. z10 engineering makes a direct fit block girdle but is pretty pricey .

Also note that the factory crank is probably only balanced to 8k and if you want to go higher you are going to need the whole rotating assembly balanced. you should probably do this anyway to be on the safe side.

im sorry to keep tellin you more and more stuff to do…but it sounds like you want to rev HIGH. and you cannot take shortcuts when you are up that high. but if you are looking for a reliable, fairly revable motor, you can easily get that with a modest budget.

thank you again for you input. I don’t really plan on revving any higher than about 7500 and that’s only when weekend racing. when you say that i can build a fairly reliable and revable car on a modest budget, what do you mean? yea, i pretty much am on a budget, and the more i’d have to do, the longer i’d have to wait. if i can get away with goin no higher than about 7K, maybe 7500 if i mis-shift and not have to do as much to the car, i’d rather do that. i would think that at least having the vtec kick in for only about 1500rpm is better than running with a regular b18a setup.

I don’t really plan on going rev happy with the car, it’s just i want something that i can at least keep up with people i know. my girlfriends brother is in a racing crew and all except for one guy, they all have really nice cars. the only one who doesn’t, his car really isn’t bad, just slow. he has a ford probe gt and it’s all tricked out, but it’s auto but even he’s gonna change it to a stick. they all want me to start racing with them, but my car’s stock and worse than that, it’s an automatic.

well id say you have 2 budget options:

a: more expensive but more powerful

-shotpeen rods
-new bearings and seals
-PR3 pistons
-ARP rod bolts and head studs
-balance crank

with this you will be safe to rev 8k…and generate a very respectable amount of power. you could even get VTEC to kick in lower (say 4200-4500) b/c you be creating a lot more lower end power with the raised compression.

id say you’ll be around 175-180 whp

b:run a stock bottom end and slap on the VTEC head, rev to 7000 for a while and build up later if you want

you’ll probably baseline around 150-155 whp with this setup

some people would argue everything i have said…but from everything ive read and been told… this seems pretty factual

alright, you’ve convinced me. i’ll just be as patient as i can and do things right the first time. i may as well do all that and look into some better rods. i 'm guessing that you’re numbers are coming off of a built block and stock b16a vtec head. what if i want to swap cams from a gsr or even itr into the head, the block should be able to handle that right? well, most likely i won’t go that far unless i find a good deal. the stock head, no block work seems like it would be good enough to take on the newer gsr’s. i dunno, most likely i’ll wait and do everything all at once, but if i can find a few good deals to do just the stock setup, i may do that. well, thank you for all of your help again and being patient with me.

oh sorry, one more thing. one of my friends is supposed to be a really smart engineer and seems to think he has all the answers when it comes to cars. he told me that by advancing the vtec, you take away from the powerband and end up losing perfomance. according to him, retarding the vtec is better than advancing it. i dunno how this is suppose to work but that’s what he said.

glad i could help…
i cant tell you what to do but i gave you the info you need to make your decision. ive seen dynos of cars with built bottom ends and ITR cams putting down 220whp, so anything is possible. as for setting the VTEC for higher or lower rpms, it all depends on how your engine is set up and what fuel curves you are running. the Mugen program kicks in at 4400 i believe and is supposed to be a really good program, but does guzzle gas. i dont really have an answer for you though…opinions vary on that topic.


Stock rods that have been shotpeened will get you to 8000 RPM and that’s it. Even then, they’re not going to be very happy.

The best VTEC switchover point is determined mainly by which cams you have. There is no cam that makes the most power all the way across the board. Each profile has a specific range where it makes the most power. In a VTEC engine, there is a point where the torque curves for the low- and high-RPM cam profiles intersect. This is where you want to engage VTEC.

When you guys are talking about b16a pr3 (usdm) pistons, would pistons from a JDM b16a work with eagle rods? Im getting a b16a swap also, and running the b16a engine while i do the bottom end work and rebuild on my b18 block, and i was hoping to use the pistons and head and transmission from my b16a swap in the ls/vtec setup, About how much would the required machine shop work cost (balance rotating assy, make the modifications to the head, and possible hone my block) is there anything else that needs to be done?

from what i’ve been hearing just about all over this message board is that yes, eagle rods will work with your b16a pistons. in fact, gettin eagle rods is more recommended over just shot-peening your original rods cus they’re stronger and will be able to handle more stress. i’ve noticed that when people talk about just shot-peening they’re rods, someone comes back with a reply that just shot-peening is not enough, a block girdle is gonna be needed as well. but when people mention getting eagle rods, getting a block girdle doesn’t seem to get mentioned. maybe i’m wrong cus i’m not real experienced but i’m getting this from what i have read from other members.

Eagle rods and a block girdle suer wouldnt hurt either, i mean as long as your going to have the bottom end apart bulletproofing it, you may as well go all the way.

yup, that’s my way of thinking too. there’s no use in doing a few things now, then later on have to take out the block and take it apart again because not everything was done the first time.