Toyota Celica Supra Forum banner

Turbo prep for 5m

2498 Views 10 Replies 7 Participants Last post by  dohc82
Trolling for comments, suggestions, and any info I can get with regard to turbo addition to my 5mge. I am building this since I have 2 of them. Block is clean, on a stand, exterior painted. going to shop for mirror like finish/decking (Yes I have read reg reimers article on the mhg-and associated shop work)-same shop is doing the head. Aer there sodium filled valves available for this head? Ive heard that sod. valves can tolerate heat as well/better than 4 valves in 7m head? Yea/nay? Do I need to change (from stock) valve springs? Lifters? cams? Also does the compression ratio need to come down to go turbo? Shop guy said comp. lowering for these is usually done with new pistons. Lsat question is how far can one reasonably go WITHOUT the turbo (in terms of HP)?
Any answers or comments would greatly be appreciated.
1 - 11 of 11 Posts
I've read a few posts from members over the years who've tried Gude or other cams on the 5m and been disappointed. I spent a good bit talking to a cam expert long distance several calls discussing cams for my 6mgte. It was finally decided to leave cams stock. I was told changes in cam have a marginal improvement on a turbo motor but sacrifice a great deal in smoothness for your trouble. As for compression, many who are going for all out turbo power lower compression because the turbo is already superheating the intake charge before it gets to the cylinder and that extra 100 degrees or so can cause detonation. An alternative strategy, possibly more effective all around is to invest in a more efficient intercooler and fresh air intake to bring the intake charge temp back down as close to ambient as possible. Turbo is for doing what?.....artificially raising effective compression, right? Corky Bell says somewhere in his book there's no need to build a low compression sled. Now I'm going to contradict myself. The stock cast pistons are the second weakest link in the 5mgte after the stock headgasket which you've already got covered. I'd certainly at this point have some forged pistons made. As long as you are going to anyway, you might consider dropping to 8.8:1 like the 82-83 motor from 9.2:1 if yours is an 84+. Those turboing the earlier motors seem to be able to safely run a little higher boost even with a stock mk3 intercooler and its not enough that you lose alot in off-boost performance or that you can't compensate for in tuning. Thats my .02c on the subject. Good luck.

Phil D.
See less See more
Not to hijack the thread or anything, But your saying that the stock headgasket is the weakest link (which I do believe), what are some alternatives for us non-metal HG buying persons such as myself,
Can I get a stock 7M gasket with ARP studs and 80fbt (or whatever they torque them down to) ? Or is that basically the same as the stock 5M?
As others have mentioned in the past, the MHG's for the 7M will also work for the 5M or 6M. So basically, the stock 7M HG will work on the 5M, but why bother doing that, when a 5M HG is still good???

The general rule of thumb from MKIII owners on the SOGI list, is that the stock 7M headgasket (assuming you are still using a 7MGTE), is good up to about 12psi.. Beyond 12, plan on using a MHG.

On the 7M @ stock boost (around 6psi), the older HG's would still crap out, but the slightly redesigned ones that came out in 91 & 92 seem to behave much better. Assuming that you still plan to keep things under 12psi.
My headgasket is leaking oil (aswell as valvecover) so I will be replaceing it soon, like within the next week.
I did looks at some prices, and the 5M headgasket was cheaper then the 7M, so I was wondering if the 7M was made of beter meterals or what? (I want to fix this to where if I add a turbo or more motor add-ons in the future, I wont have to worry about it. As of right now I have oil leaking on the header so im really hoping I dont catch the car on fire for the next week, or atleast through the supra meet :-x
I put a 2.0mm TMS MHG from on my 5m. When I went to put the upper rear timming belt cover on I found that the MHG protruded out from under the head about 1-2mm. I had to take a dremel and make a 5" X 2mm notch in the timming cover.

I would go with the HKS or Greddy MHG. Skip the TMS.
Anyone know the answer to the sodium valve question? Aer they available? Are they worth the effort/expense? Does anyone have them? Still hoping for direction on the valve spring question. Can I go with stock replacements, or do I need beefed up? Howz about the forged pistons? Can I go with stock (size) forged pistons, keep compression ratio as-is (its a '85 motor), and keep the boost low? Im really a v-8 guy ('68 pontiac GTO-yes it runs, and yes its fast), and lowering compression is something I have never aspired to-its always been the other direction.
Ok, here is the run down of everything I am doing for my turbo conversion...

Used CT26/manifold/elbow
Am going to have a local shop crush bend a downpipe for now
2.0mm MHG
Cartech RRFPR
Bored .020 over (non-forged pistons so keeping boost low)
Balacned and blueprinted with clevite bearings
295cc injectors with the appropriate clips
Stock clutch (for now, dont think it will last long though)
3 way grind on valves (stock springs)
mechanical boost gauge and A/F meter in pillar pod from
stock fuel punp (for now, may put in walbro depending on what dyno says)
Rabid Chimp IC and piping (if it ever gets here)
Rabid Chimp Turbo oil lines
Greddy type S BOV
AEM adjustable cam gears
Possibly an apex-i Safc II if the dyno says I am way off
Possibly a boost controller
I will probably have to relocate the oil filter
Drilled out the fuel restrictor

I am probably forgetting a couple things and will edit this post if needed.

This setup would be good for 6-8 psi driving daily and maybe 10 psi on short bursts. I have heard some people go up to 12 without hurting stock internals of the 5m but I dont want to chance it. With all the engine work and parts I am looking at around $4500 (without SAFC) to complete the project.

My car already has 2.5" exhaust from the dual collectors back so exhaust should be ok.
See less See more
I know people are running boost without upgraded springs,
BUT if you plain on running some good boost I know there is a certin GM v8 valve springs that are a good upgrade (someone hop on and give which exact engine they are from!)
about the TMS headgasket... well with the 2.0mm gasket and the HKS gasket is the same identical thing for I have the HKS 2.0mm and it protudes to the timing belt casing like the stock ones... and i have to bring my timing belt casing to my buddy to have it grinded off straight
LegendOPower said:
I know people are running boost without upgraded springs,
BUT if you plain on running some good boost I know there is a certin GM v8 valve springs that are a good upgrade (someone hop on and give which exact engine they are from!)
Small block Chevy
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.