I have been wanting to build a 'large' bore small block for a while now. Part of my concern is getting it through smog visually. I know I can transplant a newer motor and get it approved for smog, but what about an aftermarket block? Has anyone installed an aftermarket aluminum block and had any problems with the smog techs?
I believe that there was mention of a 406 recently on one groups with Allen's dyno runs. I am assuming that is a 4.155" bore with a 3.75" stroke. What block was this done on? I would not mind running a 400 sb, but the block is not the 'correct' period or later block. Plus, the aluminum block is a heck of alot stiffer then the 400 sb.
Many smog techs are clueless about what came on or didn't come on older cars. That 400 small block went to two different smog techs with 2 different fuel systems. The car it is in is a 1982 or 1983 model well before tpi, and it was smogged both times with no one noticing anything wrong! Paint your aluminum block, put all of the required smog stuff on it, and take it to smog as though it is stock. If you run into problems with the first smog tech, go to another one until you find one of the typical ignorant techs.
These guys are right on the money. After all the stuff I've done to my engine, the smog tech was most concerned because my spark plug wires look very thick!!
Some see mods and will not want to touch it or will ask for CARB numbers. You need to go somewhere else. As long as you are willing to go to a few different ones, especially if he gets to know you, all they care about is that it appears externally to have all the smog parts hooked up and working, and it passes out the pipe. I was told because of the current state of the CA treasury, they have not been running the "smog station sting" operations. Naturally, it can re-start at any time.
Many smog techs are clueless about what came on or didn't come on older cars. That 400 small block went to two different smog techs with 2 different fuel systems. The car it is in is a 1982 or 1983 model well before tpi, and it was smogged both times with no one noticing anything wrong! Paint your aluminum block, put all of the required smog stuff on it, and take it to smog as though it is stock. If you run into problems with the first smog tech, go to another one until you find one of the typical ignorant techs.
Ixnay on the orantignay This is a public forum.
Bill
Last edited by Burnout91 : 05-17-2008 at 01:12 PM.
Thanks guys. I think I will start planning my 377 build. At this point, the TPI will only be on for smog testing.
I'm getting a bit confused by the direction of this thread. A Dart iron block can go all the way to 440 ci. I don't know what the limits are for a Dart aluminum block. You may not want to take the block out to the max bore, but with aluminum there is no reason not to since it uses iron or steel sleeves and the sleeves can be replaced for a rebuild so you don't need to worry about leaving room to clean up the bore for future overhauls. The Dart block is already set up with clearance for the long stroke crank throw. I wouldn't worry about a long stroke limiting max revs. You are good for 6000-6500 rpm with the long stroke. If you build a motor to run more rpm than that, you will lose low end. You can have a usable rpm range of about 4000 rpm, where do you want it? You can build an engine that makes power all the way to 9000 rpm, but you will not have power below about 4500-5000 rpm. It won't pass smog, because the smog test on a stick shift requires the test to be run in 2nd gear and is typically run below 2500 rpm for the 15 mph and 25 mph test. The only way modern engines make power over a wider range than about 4000 rpm is with variable valve timing. They use a mechanical system that retards the cam at low rpm and advances the cam as the rpm's go up. I don't think anyone has developed anything like that for the sbc.
Another question, is the Dart aluminum block less expensive than the World Products Motown Light block? The Motown block can go to 454 ci in steel or 427 ci in aluminum.
o.k. here is my logic, flawed or not . Why the 377. Well, I like an engine that revs, and it does make good hp to boot. Now, let me explain or try to quantify that. We all know that a 383 is a 'quick' build for good hp and torque, and the tpi (as allen has shown) can support some good numbers.
Willing to trade off some low end torque for better high end. Would help acceleration, yes?
Want to look at a 5L50 trans. Closer gear ratios than the 700R or 4l60e. May have some problems shifting above 6500 rpms. Some upgrades will have to be done to the trans sooner or later. Would put in a 5 or 6 speed, but want it to be a close ratio gear box. Prefer the auto.
Have a individual throttle body manifold being design, cause three kids apparently don't take up enough of my time
The opening up of the bore really helps breathing. and a pair of AFR 195 comps, hollow stem ss valves, 1.7 rockers, and a solid roller somewhere in the neighborhood of 232 at 0.050". I'm not sure what the lobe separation will be yet. 112, 111?
Exhaust is an issue to figure out.
Desire extremely quick throttle response.
Sound of a V8 at 7k is beautiful
Want to keep the NA format.
So, the aftermarket block is not for the fullest cubes I could get, it is for the ease of getting the largest bore I can get. A 400 block would work, but getting a good one and second, the aftermarket blocks are so much stiffer around the cylinders.
I guess that I am looking to build a bit of a road racer. My other option is to bag it and buy a Cayman S and just make some payments. Thoughs?
Better acceleration? Better acceleration than what, and where? You will get better acceleration on a road race track, except the automatic will kill it unless it is extremely specialized in design. On a drag strip you will lose off the line unless you are running a high stall converter, but you may drive around people at the far end. On the street, I doubt if you will see any gains at legal speeds; and will probably see it going slower off the line.
An aluminum Motown block can be bored to 4.250 which gets you 396 ci with the stock stroke. I don't know what a Dart block can go to, but I thought it could go bigger than an iron 400 block. I think it can get close to 383 with the stock stroke, but I don't remember for sure.
You are building an engine that needs a close ration 5 or 6 speed tranny. I've never heard of a 5L50, is it a 5 speed auto? Your power characteristics with a 7000 rpm max will probably require more gears in an automatic, or else a final drive ration like a 1960's muscle car requiring about 4000 rpm at highway speeds.
Your basic problem is that you can make power over a range of 4000 rpm. If you build it to peak at 7000 rpm, it will be flat below 3000 rpm. I think it will be marginal at best for smog, because it has to lug for the 15 and 25 mph smog test on the rollers.
Finally, why would your option be a Porsche Cayman S? Unless I'm mistaken, the price of one of those is about the same as a Zo6 Vette, or for that money you could buy 2 Solstice GXP's or 2 Sky Redlines. Are you really debating whether to build a 3rd gen or buy a $70,000.00 car?
I don't want 500 ft-lbs of torque at 2k. It is hard to hook up on street tires massive amounts of torque and get good consistant acceleration. One of my buddies had a 396 Chevelle which was mildly built and you had to walk it out of the hole to keep from spinning through 1st and 2nd gears. I don't think I am giving up that much torque going to a 'large bore' sb vs a longer stroke.
As far as the bore size, I was originally just looking at the 4.125" bore. Yes, I should look at going to a 4.25 bore (397 cid or so), but when do I get into deminishing returns on the cylinder head with the bore being opened up(rotational weight trade off vs. flow)? The biggest thing about the large bore is its inhearent nature to be more tolerant to a fuel that has 'low' octane. I can build up the scr to 11:1, with a dynamic of 8.5 to 8.75:1 and not have run 91 all the time. Yes, there would be a performance difference, but if I'm just going to work and back (10 miles), cheaper gas the better and still have some fun.
There are some areas of cam that need to be worked out. I think if I can get peak hp to be around 6600 or 6800, that would be fine. That means that is should spin to 7k. I should be able to get it to pass smog. I'm not sure about it being 'flat' below 3k. Solid roller cam, high ratio rocker; they really want to help torque with the fast valve action.
5L50 is a 5 sp auto from GM, used in some Caddys (xlr). It is a 'close' ratio, maybe more of a 4 speed with an overdrive. Rear gears of 3.42 should be good. 1st is a 3.42 in the 5l50. That is a lot of torque multipulication.
There starts to be come a point (in my head) where spending 2 years to build and $^2 to boot, where buying something that already done and just making a payment can be more enjoyable. Don't get me wrong, I really like my GTA, that is why I have kept it for the last 7yrs sitting in the driveway. But it takes a lot of work as we all know to put together a good package. As far as the Porsche goes, vs the others, it's just choices and another thread for debate. Which is why I orginally started this thread. I wanted to get an idea of how much BS I had to go through at the smog shops if this was even worth it. Thanks for your comments. I do appreciate them.
The discplacement is not an issue for smog or low end torque. That is a cam issue based on your desire for a 7000 rpm motor. I don't know enough about the issues to be sure, but I think you might run into some real smog problems trying to build a 7000 rpm engine. I only mentioned the Zo6 because I think it's price is close to a Cayman S. The stock Vette with 430 hp would probably meet your performance requirements, and leave $20,000.00 on the table. A 377-396 small block with a cam design for 6000 rpm would do the job and meet smog without problems. It would be somewhat less expensive to build because it still uses the stock crank, but the cost of an aluminum block probably throws any thoughts of economy of build "out the window." I'm not familiar with the 5L50 at all, but I suspect it is like the 4L60E in that you need a computer to control the pressure to give it more pressure at the higher gear shifts, but less pressure for the 1-2 shift for smoothness? If that is the case, the obdII ecm is absolutely necessary unless GM performance is offering a stand alone computer to operate that trans. I also wonder why you would want to use that trans instead of just getting a 6 speed manual. I don't think it will cost you any less to convert to a 5L50 than it would to convert to a t-56. If the 5L50 is a Cadillac only trans, you would probably need to buy a new tranny, not used because they haven't been out that long. When you factor in the computer to run the tranny, it will probably not be cheap. The final question I would have on that trans is will it even bolt up to a Gen 1 sbc? I think the North Star series of motors has a different bell housing than the Gen 1 sbc.
Building 377 as a means to get an engine that revs is silly. Its the cam, not the cubic inches. You can build a 400 to rev to the same rpm as a 377, and it will make more power. If all you want is a 'high rpm' '377' then build a 350 with an appropriate choice of cam and you will have less headache and less low end torque.
I will agree with you and some more homework needs to be done for a 7k smog legal motor (at the tail pipe) can be done. The trans is electric and I am willing to bet it will have some mounting issues that will need to be addressed. OBDII is what it is looking like for control of things. I don't want a t56. Not that there bad trannys, just have never like the gear ratios. Richmond overdrive 6 spd is a better choice, IMO. Closer ratios, and not just two ODs. I really want to try for the auto if I can, otherwise my next choice would be a sequential. Now there is an impractical everyday trans! I think the trade study still is in progress and I need to determine how much effort I want to put in.
Max, you are right. While the cam controls most of that power range, the development of the cubic inches helps determine how that cam is going to act. And how it affects drevs/dt. And cubic inches (what ever it will work out to be) is the second issue with the first being the larger bore to increase insensitivity to fuel octane and still make 'good' power. An extremely tight quench with good rods is just going to help.
I will agree with you and some more homework needs to be done for a 7k smog legal motor (at the tail pipe) can be done. The trans is electric and I am willing to bet it will have some mounting issues that will need to be addressed. OBDII is what it is looking like for control of things. I don't want a t56. Not that there bad trannys, just have never like the gear ratios. Richmond overdrive 6 spd is a better choice, IMO. Closer ratios, and not just two ODs. I really want to try for the auto if I can, otherwise my next choice would be a sequential. Now there is an impractical everyday trans! I think the trade study still is in progress and I need to determine how much effort I want to put in.
Max, you are right. While the cam controls most of that power range, the development of the cubic inches helps determine how that cam is going to act. And how it affects drevs/dt. And cubic inches (what ever it will work out to be) is the second issue with the first being the larger bore to increase insensitivity to fuel octane and still make 'good' power. An extremely tight quench with good rods is just going to help.
You didn't open a "can of worms" with this response, it is a "55 gallon drum of worms!"
You cannot run an obdII ecm with an obdI ecm, it has to be one or the other. You cannot run an obdII ecm with an engine that did not come from the factory with an obdII ecm. You cannot run an obdI ecm with an engine that originally came from the factory with an obdII ecm or vice versa. If the 5L50 trans is operated by the ecm, the only way you can use it in a 3rd gen, with a 1st gen sbc, is if GM or the after market offers a stand alone computer to operate that trans in another application. You can't run a 1st gen sbc with obdII, it won't pass visual on smog even if you could get it to work.
Regarding the choice available on stick shift trannys. Have you looked at the after market t-56? I have the 1le version of the t-5 in my T/A. My rpms drop 1000 between each gear from 1st to 5th. I originally had the standard t-5 and the rpms dropped 1000 between 1-4 with a 2000 rpm drop in 5th. Kevin has a t-56 out of a 4th gen in his car with a 3.7x rear end ratio and 6th is not particularly useful below 80 mph because the stock ratios are so high. Don has the after market t-56 in his car, and his 5th is pretty close to 5th in my car and 6th is close to the 5th gear in a standard t-5. The Richmond offers 5 gears in the same space as the 4 gear in a t-5 with 6th being an overdrive. Do you need the gear ratios closer than 1000 rpm apart? The price for the Richmond in Summit is about $500.00 higher than the prices I have heard quoted for the Tremec t-56, but I don't know the current price of the t-56. You definately want the after market Tremec t-56 as opposed to a used t-56 from a 4th gen because you can't use the 4th gen speedo drive in a 3rd gen. To put a 3rd gen speedo drive in the 4th gen tranny requires a new tail housing ($500.00), or cutting out the old speedo drive and installing a new adapter kit with epoxy.
To me its just a bunch of extra work making specific cubic inch engines that on a 'street' car wont make any difference. The 5 or so HP you may possibly gain by larger bores or modified dwell times just isnt worth looking into. Build the cheapest setup you can, without some special crank to fit 400 mains or special pistons to fit your stroke and rods, and you'll get much more for your money.
